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diff --git a/lib/mnesia/doc/src/mnesia.xml b/lib/mnesia/doc/src/mnesia.xml index ed5b879f7f..f441ba4c63 100644 --- a/lib/mnesia/doc/src/mnesia.xml +++ b/lib/mnesia/doc/src/mnesia.xml @@ -8,16 +8,17 @@ <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> - The contents of this file are subject to the Erlang Public License, - Version 1.1, (the "License"); you may not use this file except in - compliance with the License. You should have received a copy of the - Erlang Public License along with this software. If not, it can be - retrieved online at http://www.erlang.org/. + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 - Software distributed under the License is distributed on an "AS IS" - basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See - the License for the specific language governing rights and limitations - under the License. + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. </legalnotice> @@ -32,291 +33,254 @@ <file></file> </header> <module>mnesia</module> - <modulesummary>A Distributed Telecommunications DBMS </modulesummary> + <modulesummary>A distributed telecommunications DBMS</modulesummary> <description> - <p><c>Mnesia</c> is a distributed DataBase Management System (DBMS), - appropriate for telecommunications applications and other Erlang - applications which require continuous operation and exhibit soft - real-time properties. - </p> - <p>Listed below are some of the most important and attractive capabilities, Mnesia provides: - </p> + + <p>The following are some of the most important and attractive + capabilities provided by <c>Mnesia</c>:</p> <list type="bulleted"> - <item> - <p>A relational/object hybrid data model which is - suitable for telecommunications applications. - </p> + <item>A relational/object hybrid data model that is suitable + for telecommunications applications. </item> - <item> - <p>A specifically designed DBMS query language, QLC (as an add-on library). - </p> + <item>A DBMS query language, Query List Comprehension (QLC) as + an add-on library. </item> - <item> - <p>Persistence. Tables may be coherently kept on disc as - well as in main memory. - </p> + <item>Persistence. Tables can be coherently kept on disc and + in the main memory. </item> - <item> - <p>Replication. Tables may be replicated at several nodes. - </p> + <item>Replication. Tables can be replicated at several nodes. </item> - <item> - <p>Atomic transactions. A series of table manipulation - operations can be grouped into a single atomic - transaction. - </p> + <item>Atomic transactions. A series of table manipulation + operations can be grouped into a single atomic transaction. </item> - <item> - <p>Location transparency. Programs can be written without - knowledge of the actual location of data. - </p> + <item>Location transparency. Programs can be written without + knowledge of the actual data location. </item> - <item> - <p>Extremely fast real time data searches. - </p> + <item>Extremely fast real-time data searches. </item> - <item> - <p>Schema manipulation routines. It is possible to - reconfigure the DBMS at runtime without stopping the - system. - </p> + <item>Schema manipulation routines. The DBMS can be + reconfigured at runtime without stopping the system. </item> </list> - <p>This Reference Manual describes the Mnesia API. This includes - functions used to define and manipulate Mnesia tables. - </p> - <p>All functions documented in these pages can be used in any - combination with queries using the list comprehension notation. The - query notation is described in the QLC's man page. - </p> - <p>Data in Mnesia is organized as a set of tables. Each table - has a name which must be an atom. Each table is made up of - Erlang records. The user is responsible for the record - definitions. Each table also has a set of properties. Below - are some of the properties that are associated with each - table: - </p> + <p>This Reference Manual describes the <c>Mnesia</c> API. This + includes functions that define and manipulate <c>Mnesia</c> + tables.</p> + <p>All functions in this Reference Manual can be used in any + combination with queries using the list comprehension notation. + For information about the query notation, see the + <seealso marker="stdlib:qlc">qlc</seealso> + manual page in <c>STDLIB</c>.</p> + <p>Data in <c>Mnesia</c> is organized as a set of tables. Each table + has a name that must be an atom. Each table is made up of + Erlang records. The user is responsible for the record + definitions. Each table also has a set of properties. The + following are some of the properties that are associated with each + table:</p> <list type="bulleted"> <item> - <p><c>type</c>. Each table can either have 'set', - 'ordered_set' or 'bag' semantics. Note: currently 'ordered_set' - is not supported for 'disc_only_copies'. If a table is of type - 'set' it means that each key leads to either one or zero - records. <br></br> -If a new item is inserted with the same key as - an existing record, the old record is overwritten. On the - other hand, if a table is of type 'bag', each key can map to - several records. However, all records in type bag tables are - unique, only the keys may be duplicated. - </p> + <p><c>type</c>. Each table can have <c>set</c>, + <c>ordered_set</c>, or <c>bag</c> semantics. Notice that + currently <c>ordered_set</c> is not supported for + <c>disc_only_copies</c>.</p> + <p>If a table is of type <c>set</c>, each key leads to + either one or zero records.</p> + <p>If a new item is inserted with the same key as an + existing record, the old record is overwritten. However, + if a table is of type <c>bag</c>, each key can map to + several records. All records in type <c>bag</c> tables are + unique, only the keys can be duplicated.</p> </item> <item> <p><c>record_name</c>. All records stored in a table must - have the same name. You may say that the records must be - instances of the same record type. - </p> + have the same name. The records must be instances of the + same record type.</p> </item> <item> - <p><c>ram_copies</c> A table can be replicated on a number - of Erlang nodes. The <c>ram_copies</c> property specifies a - list of Erlang nodes where RAM copies are kept. These - copies can be dumped to disc at regular intervals. However, + <p><c>ram_copies</c>. A table can be replicated on a number + of Erlang nodes. Property <c>ram_copies</c> specifies a + list of Erlang nodes where RAM copies are kept. These + copies can be dumped to disc at regular intervals. However, updates to these copies are not written to disc on a - transaction basis. - </p> + transaction basis.</p> </item> <item> - <p><c>disc_copies</c> The <c>disc_copies</c> property + <p><c>disc_copies</c>. This property specifies a list of Erlang nodes where the table is kept in - RAM as well as on disc. All updates of the table are - performed on the actual table and are also logged to disc. + RAM and on disc. All updates of the table are + performed in the actual table and are also logged to disc. If a table is of type <c>disc_copies</c> at a certain node, - it means that the entire table is resident in RAM memory as - well as on disc. Each transaction performed on the table is - appended to a LOG file as well as written into the RAM - table. - </p> + the entire table is resident in RAM memory and on disc. + Each transaction performed on the table is appended to a + <c>LOG</c> file and written into the RAM table.</p> </item> <item> - <p><c>disc_only_copies</c> Some, or all, table replicas + <p><c>disc_only_copies</c>. Some, or all, table replicas can be kept on disc only. These replicas are considerably - slower than the RAM based replicas. - </p> + slower than the RAM-based replicas.</p> </item> <item> - <p><c>index</c> This is a list of attribute names, or + <p><c>index</c>. This is a list of attribute names, or integers, which specify the tuple positions on which - Mnesia shall build and maintain an extra index table. - </p> + <c>Mnesia</c> is to build and maintain an extra index + table.</p> </item> <item> - <p><c>local_content</c> When an application requires + <p><c>local_content</c>. When an application requires tables whose contents are local to each node, - <c>local_content</c> tables may be used. The name of the - table is known to all Mnesia nodes, but its contents are + <c>local_content</c> tables can be used. The table name + is known to all <c>Mnesia</c> nodes, but its content is unique on each node. This means that access to such a table - must be done locally. Set the <c>local_content</c> field to - <c>true</c> if you want to enable the <c>local_content</c> - behavior. The default is <c>false</c>. - </p> + must be done locally. Set field <c>local_content</c> to + <c>true</c> to enable the <c>local_content</c> + behavior. Default is <c>false</c>.</p> </item> <item> - <p><c>majority</c> This attribute can be either <c>true</c> or - <c>false</c> (default is <c>false</c>). When <c>true</c>, a majority - of the table replicas must be available for an update to succeed. - Majority checking can be enabled on tables with mission-critical data, - where it is vital to avoid inconsistencies due to network splits. - </p> + <p><c>majority</c>. This attribute is <c>true</c> or + <c>false</c>; default is <c>false</c>. When <c>true</c>, + a majority of the table replicas must be available for an + update to succeed. Majority checking can be enabled on + tables with mission-critical data, where it is vital to + avoid inconsistencies because of network splits.</p> </item> <item> - <p><c>snmp</c> Each (set based) Mnesia table can be - automatically turned into an SNMP ordered table as well. - This property specifies the types of the SNMP keys. - </p> + <p><c>snmp</c>. Each (set-based) <c>Mnesia</c> table can be + automatically turned into a Simple Network Management + Protocol (SNMP) ordered table as well. + This property specifies the types of the SNMP keys.</p> </item> <item> <p><c>attributes</c>. The names of the attributes for the - records that are inserted in the table. - </p> + records that are inserted in the table.</p> </item> </list> - <p>See <c>mnesia:create_table/2</c> about the complete set of - table properties and their details. - </p> - <p>This document uses a table of persons to illustrate various - examples. The following record definition is assumed: - </p> + <p>For information about the complete set of table properties + and their details, see <c>mnesia:create_table/2</c>.</p> + <p>This Reference Manual uses a table of persons to illustrate + various examples. The following record definition is assumed:</p> <code type="none"> -record(person, {name, age = 0, address = unknown, salary = 0, - children = []}), - </code> - <p>The first attribute of the record is the primary key, or key - for short. - </p> - <p>The function descriptions are sorted in alphabetic order. <em>Hint:</em> - start to read about <c>mnesia:create_table/2</c>, - <c>mnesia:lock/2</c> and <c>mnesia:activity/4</c> before you continue on - and learn about the rest. - </p> - <p>Writing or deleting in transaction context creates a local copy - of each modified record during the transaction. During iteration, - i.e. <c>mnesia:fold[lr]/4</c> <c>mnesia:next/2</c> <c>mnesia:prev/2</c> - <c>mnesia:snmp_get_next_index/2</c>, mnesia will compensate for - every written or deleted record, which may reduce the - performance. If possible avoid writing or deleting records in - the same transaction before iterating over the table. - </p> + children = []}),</code> + <p>The first record attribute is the primary key, or key + for short.</p> + <p>The function descriptions are sorted in alphabetical order. + It is recommended to start to read about + <c>mnesia:create_table/2</c>, <c>mnesia:lock/2</c>, and + <c>mnesia:activity/4</c> before you continue and learn + about the rest.</p> + <p>Writing or deleting in transaction-context creates a local + copy of each modified record during the transaction. During + iteration, that is, <c>mnesia:fold[lr]/4</c>, + <c>mnesia:next/2</c>, <c>mnesia:prev/2</c>, and + <c>mnesia:snmp_get_next_index/2</c>, <c>Mnesia</c> + compensates for every written or deleted record, which can + reduce the performance.</p> + <p>If possible, avoid writing or deleting records in the same + transaction before iterating over the table.</p> </description> + <funcs> <func> - <name>abort(Reason) -> transaction abort </name> - <fsummary>Abort the current transaction.</fsummary> + <name>abort(Reason) -> transaction abort</name> + <fsummary>Terminates the current transaction.</fsummary> <desc> - <p>Makes the transaction silently + <p>Makes the transaction silently return the tuple <c>{aborted, Reason}</c>. - The abortion of a Mnesia transaction means that - an exception will be thrown to an enclosing <c>catch</c>. + Termination of a <c>Mnesia</c> transaction means that + an exception is thrown to an enclosing <c>catch</c>. Thus, the expression <c>catch mnesia:abort(x)</c> does - not abort the transaction. </p> + not terminate the transaction.</p> </desc> </func> <func> <name>activate_checkpoint(Args) -> {ok,Name,Nodes} | {error,Reason}</name> - <fsummary>Activate a checkpoint.</fsummary> + <fsummary>Activates a checkpoint.</fsummary> <desc> - <p>A checkpoint is a consistent view of the system. + <marker id="activate_checkpoint"></marker> + <p>A checkpoint is a consistent view of the system. A checkpoint can be activated on a set of tables. - This checkpoint can then be traversed and will - present a view of the system as it existed at the time when - the checkpoint was activated, even if the tables are being or have been - manipulated. - </p> - <p><c>Args</c> is a list of the following tuples: - </p> + This checkpoint can then be traversed and + presents a view of the system as it existed at the time when + the checkpoint was activated, even if the tables are + being or have been manipulated.</p> + <p><c>Args</c> is a list of the following tuples:</p> <list type="bulleted"> <item> - <p><c>{name,Name}</c>. <c>Name</c> of checkpoint. Each - checkpoint must have a name which is unique to the + <p><c>{name,Name}</c>. <c>Name</c> is the checkpoint name. + Each checkpoint must have a name that is unique to the associated nodes. The name can be reused only once the checkpoint has been deactivated. By default, a name - which is probably unique is generated. - </p> + that is probably unique is generated.</p> </item> <item> <p><c>{max,MaxTabs}</c>. <c>MaxTabs</c> is a list of - tables that should be included in the checkpoint. The - default is []. For these tables, the redundancy will be - maximized and checkpoint information will be retained together + tables that are to be included in the checkpoint. + Default is <c>[]</c>. For these tables, the redundancy is + maximized and checkpoint information is retained together with all replicas. The checkpoint becomes more fault tolerant if the tables have several replicas. When a new - replica is added by means of the schema manipulation - function <c>mnesia:add_table_copy/3</c>, a retainer will - also be attached automatically. - </p> + replica is added by the schema manipulation + function <c>mnesia:add_table_copy/3</c>, a retainer is + also attached automatically.</p> </item> <item> <p><c>{min,MinTabs}</c>. <c>MinTabs</c> is a list of - tables that should be included in the checkpoint. The - default is []. For these tables, the redundancy will be - minimized and the checkpoint information will only be retained - with one replica, preferably on the local node. - </p> + tables that are to be included in the checkpoint. + Default is []. For these tables, the redundancy is + minimized and the checkpoint information is only retained + with one replica, preferably on the local node.</p> </item> <item> <p><c>{allow_remote,Bool}</c>. <c>false</c> means that all retainers must be local. The checkpoint cannot be activated if a table does not reside locally. <c>true</c> allows retainers to be allocated on any - node. Default is set to <c>true</c>. - </p> + node. Default is <c>true</c>.</p> </item> <item> <p><c>{ram_overrides_dump,Bool}</c>. Only applicable - for <c>ram_copies</c>. <c>Bool</c> allows you to choose - to backup the table state as it is in RAM, or as it is on - disc. <c>true</c> means that the latest committed - records in RAM should be included in the checkpoint. - These are the records that the application accesses. - <c>false</c> means that the records dumped to DAT files - should be included in the checkpoint. These are the - records that will be loaded at startup. Default is - <c>false</c>. - </p> + for <c>ram_copies</c>. <c>Bool</c> allows you to choose + to back up the table state as it is in RAM, or as it is + on disc. <c>true</c> means that the latest committed + records in RAM are to be included in the checkpoint. + These are the records that the application accesses. + <c>false</c> means that the records dumped to <c>DAT</c> + files are to be included in the checkpoint. These + records are loaded at startup. Default is <c>false</c>.</p> </item> </list> <p>Returns <c>{ok,Name,Nodes}</c> or <c>{error,Reason}</c>. - <c>Name</c> is the (possibly generated) name of the - checkpoint. <c>Nodes</c> are the nodes that + <c>Name</c> is the (possibly generated) checkpoint name. + <c>Nodes</c> are the nodes that are involved in the checkpoint. Only nodes that keep a - checkpoint retainer know about the checkpoint. - </p> + checkpoint retainer know about the checkpoint.</p> </desc> </func> <func> <name>activity(AccessContext, Fun [, Args]) -> ResultOfFun | exit(Reason)</name> - <fsummary>Execute <c>Fun</c>in <c>AccessContext</c>.</fsummary> + <fsummary>Executes <c>Fun</c> in <c>AccessContext</c>.</fsummary> <desc> - <p>Invokes <c>mnesia:activity(AccessContext, Fun, Args, AccessMod)</c> where <c>AccessMod</c> is the default + <marker id="activity_2_3"></marker> + <p>Calls <c>mnesia:activity(AccessContext, Fun, Args, + AccessMod)</c>, where <c>AccessMod</c> is the default access callback module obtained by <c>mnesia:system_info(access_module)</c>. <c>Args</c> - defaults to the empty list <c>[]</c>.</p> + defaults to <c>[]</c> (empty list).</p> </desc> </func> <func> <name>activity(AccessContext, Fun, Args, AccessMod) -> ResultOfFun | exit(Reason)</name> - <fsummary>Execute <c>Fun</c>in <c>AccessContext</c>.</fsummary> - <desc> - <p>This function executes the functional object <c>Fun</c> - with the arguments <c>Args</c>. - </p> - <p>The code which executes inside the activity can - consist of a series of table manipulation functions, which is - performed in a <c>AccessContext</c>. Currently, the following - access contexts are supported: - </p> + <fsummary>Executes <c>Fun</c> in <c>AccessContext</c>.</fsummary> + <desc> + <marker id="activity_4"></marker> + <p>Executes the functional object <c>Fun</c> + with argument <c>Args</c>.</p> + <p>The code that executes inside the activity can + consist of a series of table manipulation functions, which are + performed in an <c>AccessContext</c>. Currently, the following + access contexts are supported:</p> <taglist> <tag><c>transaction</c></tag> <item> @@ -324,10 +288,10 @@ If a new item is inserted with the same key as </item> <tag><c>{transaction, Retries}</c></tag> <item> - <p>Invokes <c>mnesia:transaction(Fun, Args, Retries)</c>. Note that the result from the <c>Fun</c> is - returned if the transaction was successful (atomic), - otherwise the function exits with an abort reason. - </p> + <p>Calls <c>mnesia:transaction(Fun, Args, Retries)</c>. + Notice that the result from <c>Fun</c> is + returned if the transaction is successful (atomic), + otherwise the function exits with an abort reason.</p> </item> <tag><c>sync_transaction</c></tag> <item> @@ -335,540 +299,499 @@ If a new item is inserted with the same key as </item> <tag><c>{sync_transaction, Retries}</c></tag> <item> - <p>Invokes <c>mnesia:sync_transaction(Fun, Args, Retries)</c>. Note that the result from the <c>Fun</c> is - returned if the transaction was successful (atomic), - otherwise the function exits with an abort reason. - </p> + <p>Calls <c>mnesia:sync_transaction(Fun, Args, Retries)</c>. + Notice that the result from <c>Fun</c> is + returned if the transaction is successful (atomic), + otherwise the function exits with an abort reason.</p> </item> <tag><c>async_dirty</c></tag> <item> - <p>Invokes <c>mnesia:async_dirty(Fun, Args)</c>. - </p> + <p>Calls <c>mnesia:async_dirty(Fun, Args)</c>.</p> </item> <tag><c>sync_dirty</c></tag> <item> - <p>Invokes <c>mnesia:sync_dirty(Fun, Args)</c>. - </p> + <p>Calls <c>mnesia:sync_dirty(Fun, Args)</c>.</p> </item> <tag><c>ets</c></tag> <item> - <p>Invokes <c>mnesia:ets(Fun, Args)</c>. - </p> + <p>Calls <c>mnesia:ets(Fun, Args)</c>.</p> </item> </taglist> <p>This function (<c>mnesia:activity/4</c>) differs in an - important aspect from the <c>mnesia:transaction</c>, + important way from the functions <c>mnesia:transaction</c>, <c>mnesia:sync_transaction</c>, - <c>mnesia:async_dirty</c>, <c>mnesia:sync_dirty</c> and - <c>mnesia:ets</c> functions. The <c>AccessMod</c> argument - is the name of a callback module which implements the - <c>mnesia_access</c> behavior. - </p> - <p>Mnesia will forward calls to the following functions: - </p> + <c>mnesia:async_dirty</c>, <c>mnesia:sync_dirty</c>, and + <c>mnesia:ets</c>. Argument <c>AccessMod</c> + is the name of a callback module, which implements the + <c>mnesia_access</c> behavior.</p> + <p><c>Mnesia</c> forwards calls to the following functions:</p> <list type="bulleted"> - <item> - <p>mnesia:lock/2 (read_lock_table/1, write_lock_table/1)</p> + <item>mnesia:lock/2 (read_lock_table/1, write_lock_table/1) </item> - <item> - <p>mnesia:write/3 (write/1, s_write/1)</p> + <item>mnesia:write/3 (write/1, s_write/1) </item> - <item> - <p>mnesia:delete/3 (delete/1, s_delete/1)</p> + <item>mnesia:delete/3 (delete/1, s_delete/1) </item> - <item> - <p>mnesia:delete_object/3 (delete_object/1, s_delete_object/1)</p> + <item>mnesia:delete_object/3 (delete_object/1, s_delete_object/1) </item> - <item> - <p>mnesia:read/3 (read/1, wread/1)</p> + <item>mnesia:read/3 (read/1, wread/1) </item> - <item> - <p>mnesia:match_object/3 (match_object/1)</p> + <item>mnesia:match_object/3 (match_object/1) </item> - <item> - <p>mnesia:all_keys/1</p> + <item>mnesia:all_keys/1 </item> - <item> - <p>mnesia:first/1</p> + <item>mnesia:first/1 </item> - <item> - <p>mnesia:last/1</p> + <item>mnesia:last/1 </item> - <item> - <p>mnesia:prev/2</p> + <item>mnesia:prev/2 </item> - <item> - <p>mnesia:next/2</p> + <item>mnesia:next/2 </item> - <item> - <p>mnesia:index_match_object/4 (index_match_object/2)</p> + <item>mnesia:index_match_object/4 (index_match_object/2) </item> - <item> - <p>mnesia:index_read/3</p> + <item>mnesia:index_read/3 </item> - <item> - <p>mnesia:table_info/2</p> + <item>mnesia:table_info/2 </item> </list> - <p>to the corresponding: - </p> + <p>to the corresponding:</p> <list type="bulleted"> - <item> - <p>AccessMod:lock(ActivityId, Opaque, LockItem, LockKind)</p> + <item>AccessMod:lock(ActivityId, Opaque, LockItem, LockKind) </item> - <item> - <p>AccessMod:write(ActivityId, Opaque, Tab, Rec, LockKind)</p> + <item>AccessMod:write(ActivityId, Opaque, Tab, Rec, LockKind) </item> - <item> - <p>AccessMod:delete(ActivityId, Opaque, Tab, Key, LockKind)</p> + <item>AccessMod:delete(ActivityId, Opaque, Tab, Key, LockKind) </item> - <item> - <p>AccessMod:delete_object(ActivityId, Opaque, Tab, RecXS, LockKind)</p> + <item>AccessMod:delete_object(ActivityId, Opaque, Tab, RecXS, + LockKind) </item> - <item> - <p>AccessMod:read(ActivityId, Opaque, Tab, Key, LockKind)</p> + <item>AccessMod:read(ActivityId, Opaque, Tab, Key, LockKind) </item> - <item> - <p>AccessMod:match_object(ActivityId, Opaque, Tab, Pattern, LockKind)</p> + <item>AccessMod:match_object(ActivityId, Opaque, Tab, Pattern, + LockKind) </item> - <item> - <p>AccessMod:all_keys(ActivityId, Opaque, Tab, LockKind)</p> + <item>AccessMod:all_keys(ActivityId, Opaque, Tab, LockKind) </item> - <item> - <p>AccessMod:first(ActivityId, Opaque, Tab)</p> + <item>AccessMod:first(ActivityId, Opaque, Tab) </item> - <item> - <p>AccessMod:last(ActivityId, Opaque, Tab)</p> + <item>AccessMod:last(ActivityId, Opaque, Tab) </item> - <item> - <p>AccessMod:prev(ActivityId, Opaque, Tab, Key)</p> + <item>AccessMod:prev(ActivityId, Opaque, Tab, Key) </item> - <item> - <p>AccessMod:next(ActivityId, Opaque, Tab, Key)</p> + <item>AccessMod:next(ActivityId, Opaque, Tab, Key) </item> - <item> - <p>AccessMod:index_match_object(ActivityId, Opaque, Tab, Pattern, Attr, LockKind)</p> + <item>AccessMod:index_match_object(ActivityId, Opaque, Tab, + Pattern, Attr, LockKind) </item> - <item> - <p>AccessMod:index_read(ActivityId, Opaque, Tab, SecondaryKey, Attr, LockKind)</p> + <item>AccessMod:index_read(ActivityId, Opaque, Tab, + SecondaryKey, Attr, LockKind) </item> - <item> - <p>AccessMod:table_info(ActivityId, Opaque, Tab, InfoItem)</p> + <item>AccessMod:table_info(ActivityId, Opaque, Tab, InfoItem) </item> </list> - <p>where <c>ActivityId</c> is a record which represents the - identity of the enclosing Mnesia activity. The first field - (obtained with <c>element(1, ActivityId)</c> contains an - atom which may be interpreted as the type of the activity: - <c>'ets'</c>, <c>'async_dirty'</c>, <c>'sync_dirty'</c> or - <c>'tid'</c>. <c>'tid'</c> means that the activity is a + <p><c>ActivityId</c> is a record that represents the identity + of the enclosing <c>Mnesia</c> activity. The first field + (obtained with <c>element(1, ActivityId)</c>) contains an + atom, which can be interpreted as the activity type: + <c>ets</c>, <c>async_dirty</c>, <c>sync_dirty</c>, or + <c>tid</c>. <c>tid</c> means that the activity is a transaction. The structure of the rest of the identity - record is internal to Mnesia. - </p> - <p><c>Opaque</c> is an opaque data structure which is internal - to Mnesia.</p> + record is internal to <c>Mnesia</c>.</p> + <p><c>Opaque</c> is an opaque data structure that is internal + to <c>Mnesia</c>.</p> </desc> </func> <func> <name>add_table_copy(Tab, Node, Type) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Copy a table to a remote node.</fsummary> + <fsummary>Copies a table to a remote node.</fsummary> <desc> - <p>This function makes another copy of a table at the - node <c>Node</c>. The <c>Type</c> argument must be - either of the atoms <c>ram_copies</c>, <c>disc_copies</c>, - or + <marker id="add_table_copy"></marker> + <p>Makes another copy of a table at the node <c>Node</c>. + Argument <c>Type</c> must be either of the atoms + <c>ram_copies</c>, <c>disc_copies</c>, or <c>disc_only_copies</c>. For example, the following call - ensures that a disc replica of the <c>person</c> table also - exists at node <c>Node</c>.</p> + ensures that a disc replica of the <c>person</c> table also + exists at node <c>Node</c>:</p> <code type="none"> -mnesia:add_table_copy(person, Node, disc_copies) - </code> +mnesia:add_table_copy(person, Node, disc_copies)</code> <p>This function can also be used to add a replica of the table named <c>schema</c>.</p> </desc> </func> <func> <name>add_table_index(Tab, AttrName) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Create an index for a table. </fsummary> - <desc> - <p>Table indices can and should be used whenever the user - wants to frequently use some other field than the key field - to look up records. If this other field has an index - associated with it, these lookups can occur in constant time - and space. For example, if our application wishes to use - the age field of persons to efficiently find all person with - a specific age, it might be a good idea to have an index on - the age field. This can be accomplished with the following + <fsummary>Creates an index for a table.</fsummary> + <desc> + <marker id="add_table_index"></marker> + <p>Table indexes can be used whenever the user + wants to use frequently some other field than the key field + to look up records. If this other field has an associated + index, these lookups can occur in constant time + and space. For example, if your application wishes to use + field <c>age</c> to find efficiently all persons with + a specific age, it can be a good idea to have an index on + field <c>age</c>. This can be done with the following call:</p> <code type="none"> -mnesia:add_table_index(person, age) - </code> - <p>Indices do not come free, they occupy space which is - proportional to the size of the table. They also cause insertions - into the table to execute slightly slower. </p> +mnesia:add_table_index(person, age)</code> + <p>Indexes do not come for free. They occupy space that is + proportional to the table size, and they cause insertions + into the table to execute slightly slower.</p> </desc> </func> <func> <name>all_keys(Tab) -> KeyList | transaction abort</name> - <fsummary>Return all keys in a table.</fsummary> + <fsummary>Returns all keys in a table.</fsummary> <desc> - <p>This function returns a list of all keys in the table - named <c>Tab</c>. The semantics of this function is context - sensitive. See <c>mnesia:activity/4</c> for more information. In - transaction context it acquires a read lock on the entire + <marker id="all_keys"></marker> + <p>Returns a list of all keys in the table named <c>Tab</c>. + The semantics of this function is context-sensitive. + For more information, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a read lock on the entire table.</p> </desc> </func> <func> - <name>async_dirty(Fun, [, Args]) -> ResultOfFun | exit(Reason)</name> - <fsummary>Call the Fun in a context which is not protected by a transaction.</fsummary> + <name>async_dirty(Fun, [, Args]) -> ResultOfFun | exit(Reason)</name> + <fsummary>Calls the <c>Fun</c> in a context that is not protected by a transaction.</fsummary> <desc> - <p>Call the <c>Fun</c> in a context which is not protected - by a transaction. The Mnesia function calls performed in the - <c>Fun</c> are mapped to the corresponding dirty - functions. This still involves logging, replication and + <marker id="async_dirty"></marker> + <p>Calls the <c>Fun</c> in a context that is not protected by + a transaction. The <c>Mnesia</c> function calls performed in + the <c>Fun</c> are mapped to the corresponding dirty + functions. This still involves logging, replication, and subscriptions, but there is no locking, local transaction storage, or commit protocols involved. Checkpoint retainers - and indices are updated, but they will be updated dirty. As - for normal mnesia:dirty_* operations, the operations are - performed semi-asynchronously. See - <c>mnesia:activity/4</c> and the Mnesia User's Guide for - more details. - </p> - <p>It is possible to manipulate the Mnesia tables without + and indexes are updated, but they are updated dirty. As + for normal <c>mnesia:dirty_*</c> operations, the operations + are performed semi-asynchronously. For details, see + <c>mnesia:activity/4</c> and the User's Guide.</p> + <p>The <c>Mnesia</c> tables can be manipulated without using transactions. This has some serious disadvantages, but - is considerably faster since the transaction manager is not + is considerably faster, as the transaction manager is not involved and no locks are set. A dirty operation does, - however, guarantee a certain level of consistency and it is - not possible for the dirty operations to return garbled - records. All dirty operations provide location transparency - to the programmer and a program does not have to be aware of - the whereabouts of a certain table in order to function. - </p> - <p><em>Note:</em>It is more than 10 times more efficient to read records dirty - than within a transaction. - </p> - <p>Depending on the application, it may be a good idea to use + however, guarantee a certain level of consistency, and + the dirty operations cannot return garbled records. + All dirty operations provide location transparency + to the programmer, and a program does not have to be aware + of the whereabouts of a certain table to function.</p> + <p>Notice that it is more than ten times more efficient to + read records dirty than within a transaction.</p> + <p>Depending on the application, it can be a good idea to use the dirty functions for certain operations. Almost all - Mnesia functions which can be called within transactions - have a dirty equivalent which is much more - efficient. However, it must be noted that it is possible for - the database to be left in an inconsistent state if dirty - operations are used to update it. Dirty operations should - only be used for performance reasons when it is absolutely - necessary. </p> - <p><em>Note:</em> Calling (nesting) a <c>mnesia:[a]sync_dirty</c> - inside a transaction context will inherit the transaction semantics. - </p> + <c>Mnesia</c> functions that can be called within + transactions have a dirty equivalent, which is much more + efficient.</p> + <p>However, notice that there is a risk that the database can + be left in an inconsistent state if dirty operations are + used to update it. Dirty operations are only to be used + for performance reasons when it is absolutely necessary.</p> + <p>Notice that calling (nesting) <c>mnesia:[a]sync_dirty</c> + inside a transaction-context inherits the transaction + semantics.</p> </desc> </func> <func> <name>backup(Opaque [, BackupMod]) -> ok | {error,Reason}</name> - <fsummary>Back up all tables in the database.</fsummary> + <fsummary>Backs up all tables in the database.</fsummary> <desc> - <p>Activates a new checkpoint covering all Mnesia tables, - including the schema, with maximum degree of redundancy and - performs a backup using <c>backup_checkpoint/2/3</c>. The + <marker id="backup"></marker> + <p>Activates a new checkpoint covering all <c>Mnesia</c> tables, + including the schema, with maximum degree of redundancy, and + performs a backup using <c>backup_checkpoint/2/3</c>. The default value of the backup callback module <c>BackupMod</c> is obtained by <c>mnesia:system_info(backup_module)</c>.</p> </desc> </func> <func> - <name>backup_checkpoint(Name, Opaque [, BackupMod]) -> ok | {error,Reason}</name> - <fsummary>Back up all tables in a checkpoint.</fsummary> + <name>backup_checkpoint(Name, Opaque [, BackupMod]) -> ok | {error,Reason}</name> + <fsummary>Backs up all tables in a checkpoint.</fsummary> <desc> - <p>The tables are backed up to external media using the backup + <marker id="backup_checkpoint"></marker> + <p>The tables are backed up to external media using backup module <c>BackupMod</c>. Tables with the local contents property are backed up as they exist on the current - node. <c>BackupMod</c> is the default backup callback + node. <c>BackupMod</c> is the default backup callback module obtained by - <c>mnesia:system_info(backup_module)</c>. See the User's - Guide about the exact callback interface (the - <c>mnesia_backup behavior</c>).</p> + <c>mnesia:system_info(backup_module)</c>. For information + about the exact callback interface (the + <c>mnesia_backup behavior</c>), see the User's Guide.</p> </desc> </func> <func> <name>change_config(Config, Value) -> {error, Reason} | {ok, ReturnValue}</name> - <fsummary>Change a configuration parameter.</fsummary> + <fsummary>Changes a configuration parameter.</fsummary> <desc> - <p>The <c>Config</c> should be an atom of the following - configuration parameters: </p> + <marker id="change_config"></marker> + <p><c>Config</c> is to be an atom of the following + configuration parameters:</p> <taglist> <tag><c>extra_db_nodes</c></tag> <item> - <p><c>Value</c> is a list of nodes which Mnesia should try to connect to. - The <c>ReturnValue</c> will be those nodes in - <c>Value</c> that Mnesia are connected to. - <br></br> -Note: This function shall only be used to connect to newly started ram nodes - (N.D.R.S.N.) with an empty schema. If for example it is used after the network - have been partitioned it may lead to inconsistent tables. - <br></br> -Note: Mnesia may be connected to other nodes than those - returned in <c>ReturnValue</c>.</p> + <p><c>Value</c> is a list of nodes that <c>Mnesia</c> + is to try to connect to. <c>ReturnValue</c> is those + nodes in <c>Value</c> that <c>Mnesia</c> is connected + to.</p> + <p>Notice that this function must only be used to connect + to newly started RAM nodes (N.D.R.S.N.) with an empty + schema. If, for example, this function is used after + the network has been partitioned, it can lead to + inconsistent tables.</p> + <p>Notice that <c>Mnesia</c> can be connected to other + nodes than those returned in <c>ReturnValue</c>.</p> </item> <tag><c>dc_dump_limit</c></tag> <item> - <p><c>Value</c> is a number. See description in - <c>Configuration Parameters</c> below. - The <c>ReturnValue</c> is the new value. Note this configuration parameter - is not persistent, it will be lost when mnesia stopped.</p> + <p><c>Value</c> is a number. See the description in + <seealso marker="#configuration_parameters">Section + Configuration Parameters</seealso>. <c>ReturnValue</c> + is the new value. Notice that this configuration + parameter is not persistent. It is lost when + <c>Mnesia</c> has stopped.</p> </item> </taglist> </desc> </func> <func> <name>change_table_access_mode(Tab, AccessMode) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Change the access mode for the table.</fsummary> - <desc> - <p>The <c>AcccessMode</c> is by default the atom - <c>read_write</c> but it may also be set to the atom - <c>read_only</c>. If the <c>AccessMode</c> is set to - <c>read_only</c>, it means that it is not possible to perform - updates to the table. At startup Mnesia always loads + <fsummary>Changes the access mode for the table.</fsummary> + <desc> + <marker id="change_table_access_mode"></marker> + <p><c>AcccessMode</c> is by default the atom + <c>read_write</c> but it can also be set to the atom + <c>read_only</c>. If <c>AccessMode</c> is set to + <c>read_only</c>, updates to the table cannot be + performed. At startup, <c>Mnesia</c> always loads <c>read_only</c> tables locally regardless of when and if - Mnesia was terminated on other nodes.</p> + <c>Mnesia</c> is terminated on other nodes.</p> </desc> </func> <func> <name>change_table_copy_type(Tab, Node, To) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Change the storage type of a table.</fsummary> + <fsummary>Changes the storage type of a table.</fsummary> <desc> + <marker id="change_table_copy_type"></marker> <p>For example:</p> <code type="none"> -mnesia:change_table_copy_type(person, node(), disc_copies) - </code> - <p>Transforms our <c>person</c> table from a RAM table into - a disc based table at <c>Node</c>. - </p> - <p>This function can also be used to change the storage type of - the table named <c>schema</c>. The schema table can only - have <c>ram_copies</c> or <c>disc_copies</c> as the storage type. If the - storage type of the schema is <c>ram_copies</c>, no other table - can be disc resident on that node.</p> +mnesia:change_table_copy_type(person, node(), disc_copies)</code> + <p>Transforms the <c>person</c> table from a RAM table into + a disc-based table at <c>Node</c>.</p> + <p>This function can also be used to change the storage type + of the table named <c>schema</c>. The schema table can only + have <c>ram_copies</c> or <c>disc_copies</c> as the storage + type. If the storage type of the schema is <c>ram_copies</c>, + no other table can be disc-resident on that node.</p> </desc> </func> <func> <name>change_table_load_order(Tab, LoadOrder) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Change the load order priority for the table.</fsummary> + <fsummary>Changes the load order priority for the table.</fsummary> <desc> + <marker id="change_table_load_order"></marker> <p>The <c>LoadOrder</c> priority is by default <c>0</c> (zero) - but may be set to any integer. The tables with the highest - <c>LoadOrder</c> priority will be loaded first at startup.</p> + but can be set to any integer. The tables with the highest + <c>LoadOrder</c> priority are loaded first at startup.</p> </desc> </func> <func> <name>change_table_majority(Tab, Majority) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Change the majority check setting for the table.</fsummary> + <fsummary>Changes the majority check setting for the table.</fsummary> <desc> - <p><c>Majority</c> must be a boolean; the default is <c>false</c>. - When <c>true</c>, a majority of the table's replicas must be available - for an update to succeed. When used on fragmented tables, <c>Tab</c> - must be the name base table. Directly changing the majority setting on - individual fragments is not allowed.</p> + <p><c>Majority</c> must be a boolean. Default is <c>false</c>. + When <c>true</c>, a majority of the table replicas must be + available for an update to succeed. When used on fragmented + tables, <c>Tab</c> must be the base table name. Directly + changing the majority setting on individual fragments is + not allowed.</p> </desc> </func> <func> <name>clear_table(Tab) -> {aborted, R} | {atomic, ok}</name> <fsummary>Deletes all entries in a table.</fsummary> <desc> + <marker id="clear_table"></marker> <p>Deletes all entries in the table <c>Tab</c>.</p> </desc> </func> <func> <name>create_schema(DiscNodes) -> ok | {error,Reason}</name> - <fsummary>Create a brand new schema on the specified nodes.</fsummary> + <fsummary>Creates a new schema on the specified nodes.</fsummary> <desc> + <marker id="create_schema"></marker> <p>Creates a new database on disc. Various files are - created in the local Mnesia directory of each node. Note - that the directory must be unique for each node. Two nodes - may never share the same directory. If possible, use a local - disc device in order to improve performance.</p> + created in the local <c>Mnesia</c> directory of each node. + Notice that the directory must be unique for each node. + Two nodes must never share the same directory. If possible, + use a local disc device to improve performance.</p> <p><c>mnesia:create_schema/1</c> fails if any of the Erlang nodes given as <c>DiscNodes</c> are not alive, if - Mnesia is running on anyone of the nodes, or if anyone of - the nodes already has a schema. Use + <c>Mnesia</c> is running on any of the nodes, or if any + of the nodes already have a schema. Use <c>mnesia:delete_schema/1</c> to get rid of old faulty - schemas. - </p> - <p><em>Note:</em> Only nodes with disc should be - included in <c>DiscNodes</c>. Disc-less nodes, that is nodes - where all tables including the schema only resides in RAM, - may not be included.</p> + schemas.</p> + <p>Notice that only nodes with disc are to be included in + <c>DiscNodes</c>. Disc-less nodes, that is, nodes where + all tables including the schema only resides in RAM, + must not be included.</p> </desc> </func> <func> <name>create_table(Name, TabDef) -> {atomic, ok} | {aborted, Reason}</name> - <fsummary>Create a Mnesia table called <c>Name</c>with properties as described by the argument <c>TabDef</c>.</fsummary> + <fsummary>Creates a <c>Mnesia</c> table called <c>Name</c>with properties as described by argument <c>TabDef</c>.</fsummary> <desc> - <p>This function creates a Mnesia table called <c>Name</c> - according to the - argument <c>TabDef</c>. This list must be a list of - <c>{Item, Value}</c> tuples, where the following values are - allowed:</p> + <marker id="create_table"></marker> + <p>Creates a <c>Mnesia</c> table called + <c>Name</c> according to argument <c>TabDef</c>. This + list must be a list of <c>{Item, Value}</c> tuples, + where the following values are allowed:</p> <list type="bulleted"> <item> - <p><c>{access_mode, Atom}</c>. The access mode is by - default the atom <c>read_write</c> but it may also be - set to the atom <c>read_only</c>. If the - <c>AccessMode</c> is set to <c>read_only</c>, it means - that it is not possible to perform updates to the table. - </p> - <p>At startup Mnesia always loads <c>read_only</c> tables - locally regardless of when and if Mnesia was terminated - on other nodes. This argument returns the access mode of - the table. The access mode may either be read_only or - read_write. - </p> - </item> - <item> - <p><c>{attributes, AtomList}</c> a list of the + <p><c>{access_mode, Atom}</c>. The access mode is by + default the atom <c>read_write</c> but it can also be + set to the atom <c>read_only</c>. If <c>AccessMode</c> + is set to <c>read_only</c>, updates to the table + cannot be performed.</p> + <p>At startup, <c>Mnesia</c> always loads <c>read_only</c> + table locally regardless of when and if <c>Mnesia</c> is + terminated on other nodes. This argument returns the + access mode of the table. The access mode can be + <c>read_only</c> or <c>read_write</c>.</p> + </item> + <item> + <p><c>{attributes, AtomList}</c> is a list of the attribute names for the records that are supposed to - populate the table. The default value is <c>[key, val]</c>. The table must have at least one extra - attribute in addition to the key. - </p> - <p>When accessing single attributes in a record, it is not - necessary, or even recommended, to hard code any - attribute names as atoms. Use the construct - <c>record_info(fields, RecordName)</c> instead. It can be - used for records of type <c>RecordName</c></p> + populate the table. Default is <c>[key, val]</c>. + The table must at least have one extra attribute in + addition to the key.</p> + <p>When accessing single attributes in a record, it is + not necessary, or even recommended, to hard code any + attribute names as atoms. Use construct + <c>record_info(fields, RecordName)</c> instead. It can + be used for records of type <c>RecordName</c>.</p> </item> <item> <p><c>{disc_copies, Nodelist}</c>, where <c>Nodelist</c> is a list of the nodes where this table - is supposed to have disc copies. If a table replica is + is supposed to have disc copies. If a table replica is of type <c>disc_copies</c>, all write operations on this - particular replica of the table are written to disc as - well as to the RAM copy of the table. - </p> - <p>It is possible - to have a replicated table of type <c>disc_copies</c> - on one node, and another type on another node. The - default value is <c>[]</c></p> + particular replica of the table are written to disc and + to the RAM copy of the table.</p> + <p>It is possible to have a replicated table of type + <c>disc_copies</c> on one node and another type on + another node. Default is <c>[]</c>.</p> </item> <item> <p><c>{disc_only_copies, Nodelist}</c>, where <c>Nodelist</c> is a list of the nodes where this table - is supposed to have <c>disc_only_copies</c>. A disc only - table replica is kept on disc only and unlike the other - replica types, the contents of the replica will not + is supposed to have <c>disc_only_copies</c>. A disc only + table replica is kept on disc only and unlike the other + replica types, the contents of the replica do not reside in RAM. These replicas are considerably slower - than replicas held in RAM. - </p> + than replicas held in RAM.</p> </item> <item> <p><c>{index, Intlist}</c>, where <c>Intlist</c> is a list of attribute names (atoms) or - record fields for which Mnesia shall build and maintain - an extra index table. The <c>qlc</c> query compiler may - or may not utilize any additional indices while - processing queries on a table. - </p> + record fields for which <c>Mnesia</c> is to build and + maintain an extra index table. The <c>qlc</c> query + compiler <em>may</em> be able to optimize queries + if there are indexes available.</p> </item> <item> <p><c>{load_order, Integer}</c>. The load order - priority is by default <c>0</c> (zero) but may be set to - any integer. The tables with the highest load order - priority will be loaded first at startup. - </p> - </item> - <item> - <p><c>{majority, Flag}</c>, where <c>Flag</c> must be a boolean. - If <c>true</c>, any (non-dirty) update to the table will abort unless - a majority of the table's replicas are available for the commit. - When used on a fragmented table, all fragments will be given - the same majority setting. - </p> - </item> + priority is by default <c>0</c> (zero) but can be set + to any integer. The tables with the highest load order + priority are loaded first at startup.</p> + </item> + <item> + <p><c>{majority, Flag}</c>, where <c>Flag</c> must be a + boolean. If <c>true</c>, any (non-dirty) update to the + table is aborted, unless a majority of the table + replicas are available for the commit. When used on a + fragmented table, all fragments are given the same + the same majority setting.</p> + </item> <item> <p><c>{ram_copies, Nodelist}</c>, where <c>Nodelist</c> is a list of the nodes where this table - is supposed to have RAM copies. A table replica of type - <c>ram_copies</c> is obviously not written to disc on a - per transaction basis. It is possible to dump - <c>ram_copies</c> replicas to disc with the function - <c>mnesia:dump_tables(Tabs)</c>. The default value for - this attribute is <c>[node()]</c>. - </p> + is supposed to have RAM copies. A table replica of type + <c>ram_copies</c> is not written to disc on a per + transaction basis. <c>ram_copies</c> replicas can be + dumped to disc with the function + <c>mnesia:dump_tables(Tabs)</c>. Default value for + this attribute is <c>[node()]</c>.</p> </item> <item> <p><c>{record_name, Name}</c>, where <c>Name</c> must - be an atom. All records, stored in the table, must have + be an atom. All records stored in the table must have this name as the first element. It defaults to the same - name as the name of the table. - </p> - </item> - <item> - <p><c>{snmp, SnmpStruct}</c>. See - <c>mnesia:snmp_open_table/2</c> for a description of - <c>SnmpStruct</c>. If this attribute is present in the - <c>ArgList</c> to <c>mnesia:create_table/2</c>, the - table is immediately accessible by means of the Simple - Network Management Protocol (SNMP). This means that - applications which use SNMP to manipulate and control - the system can be designed easily, since Mnesia provides - a direct mapping between the logical tables that make up - an SNMP control application and the physical data which - makes up a Mnesia table. - </p> - </item> - <item> - <p><c>{storage_properties, [{Backend, Properties}]</c>. - Forwards additional properties to the backend storage. - <c>Backend</c> can currently be <c>ets</c> or <c>dets</c> and - <c>Properties</c> is a list of options sent to the backend storage - during table creation. <c>Properties</c> may not contain properties - already used by mnesia such as <c>type</c> or <c>named_table</c>. - </p> - <p>For example:</p> - <code type="none"> + name as the table name.</p> + </item> + <item> + <p><c>{snmp, SnmpStruct}</c>. For a description of + <c>SnmpStruct</c>, see <c>mnesia:snmp_open_table/2</c>. + If this attribute is present in <c>ArgList</c> to + <c>mnesia:create_table/2</c>, the table is immediately + accessible by SNMP. Therefore applications that use + SNMP to manipulate and control the system can be + designed easily, since <c>Mnesia</c> provides a + direct mapping between the logical tables that make up + an SNMP control application and the physical data that + makes up a <c>Mnesia</c> table.</p> + </item> + <item> + <p><c>{storage_properties, [{Backend, Properties}]</c> + forwards more properties to the back end storage. + <c>Backend</c> can currently be <c>ets</c> or <c>dets</c>. + <c>Properties</c> is a list of options sent to the + back end storage during table creation. <c>Properties</c> + cannot contain properties already used by <c>Mnesia</c>, + such as <c>type</c> or <c>named_table</c>.</p> + <p>For example:</p> + <code type="none"> mnesia:create_table(table, [{ram_copies, [node()]}, {disc_only_copies, nodes()}, - {storage_properties, - [{ets, [compressed]}, {dets, [{auto_save, 5000}]} ]}]) - </code> + {storage_properties, + [{ets, [compressed]}, {dets, [{auto_save, 5000}]} ]}])</code> </item> <item> <p><c>{type, Type}</c>, where <c>Type</c> must be - either of the atoms <c>set</c>, <c>ordered_set</c> or - <c>bag</c>. The default value is <c>set</c>. In a - <c>set</c> all records have unique keys and in a - <c>bag</c> several records may have the same key, but + either of the atoms <c>set</c>, <c>ordered_set</c>, or + <c>bag</c>. Default is <c>set</c>. In a + <c>set</c>, all records have unique keys. In a + <c>bag</c>, several records can have the same key, but the record content is unique. If a non-unique record is - stored the old, conflicting record(s) will simply be - overwritten. Note: currently 'ordered_set' - is not supported for 'disc_only_copies'. - </p> + stored, the old conflicting records are overwritten.</p> + <p>Notice that currently <c>ordered_set</c> is not + supported for <c>disc_only_copies</c>.</p> </item> <item> - <p><c>{local_content, Bool}</c>, where <c>Bool</c> must be - either <c>true</c> or <c>false</c>. The default value is <c>false</c>.</p> + <p><c>{local_content, Bool}</c>, where <c>Bool</c> is + <c>true</c> or <c>false</c>. Default is <c>false</c>.</p> </item> </list> - <p>For example, the following call creates the <c>person</c> table - previously defined and replicates it on 2 nodes: - </p> + <p>For example, the following call creates the <c>person</c> + table (defined earlier) and replicates it on two nodes:</p> <code type="none"> -mnesia:create_table(person, +mnesia:create_table(person, [{ram_copies, [N1, N2]}, - {attributes, record_info(fields,person)}]). - </code> - <p>If it was required that Mnesia build and maintain an extra index - table on the <c>address</c> attribute of all the <c>person</c> - records that are inserted in the table, the following code would be issued: - </p> + {attributes, record_info(fields, person)}]).</code> + <p>If it is required that <c>Mnesia</c> must build and + maintain an extra index table on attribute <c>address</c> + of all the <c>person</c> records that are inserted in the + table, the following code would be issued:</p> <code type="none"> mnesia:create_table(person, [{ram_copies, [N1, N2]}, {index, [address]}, - {attributes, record_info(fields,person)}]). - </code> - <p>The specification of <c>index</c> and <c>attributes</c> may be - hard coded as <c>{index, [4]}</c> and - <c>{attributes, [name, age, address, salary, children]}</c> - respectively. - </p> + {attributes, record_info(fields, person)}]). + </code> + <p>The specification of <c>index</c> and <c>attributes</c> + can be hard-coded as <c>{index, [2]}</c> and + <c>{attributes, [name, age, address, salary, children]}</c>, + respectively.</p> <p><c>mnesia:create_table/2</c> writes records into the - <c>schema</c> table. This function, as well as all other + table <c>schema</c>. This function, and all other schema manipulation functions, are implemented with the normal transaction management system. This guarantees that schema updates are performed on all nodes in an atomic @@ -877,163 +800,169 @@ mnesia:create_table(person, </func> <func> <name>deactivate_checkpoint(Name) -> ok | {error, Reason}</name> - <fsummary>Deactivate a checkpoint.</fsummary> + <fsummary>Deactivates a checkpoint.</fsummary> <desc> + <marker id="deactivate_checkpoint"></marker> <p>The checkpoint is automatically deactivated when some of - the tables involved have no retainer attached to them. This may - happen when nodes go down or when a replica is deleted. - Checkpoints will also be deactivated with this function. + the tables involved have no retainer attached to them. This + can occur when nodes go down or when a replica is deleted. + Checkpoints are also deactivated with this function. <c>Name</c> is the name of an active checkpoint.</p> </desc> </func> <func> <name>del_table_copy(Tab, Node) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Delete the replica of table <c>Tab</c>at node <c>Node</c>.</fsummary> + <fsummary>Deletes the replica of table <c>Tab</c> at node <c>Node</c>.</fsummary> <desc> + <marker id="del_table_copy"></marker> <p>Deletes the replica of table <c>Tab</c> at node <c>Node</c>. When the last replica is deleted with this - function, the table disappears entirely. - </p> - <p>This function may also be used to delete a replica of - the table named <c>schema</c>. Then the mnesia node will be removed. - Note: Mnesia must be stopped on the node first.</p> + function, the table disappears entirely.</p> + <p>This function can also be used to delete a replica of + the table named <c>schema</c>. The <c>Mnesia</c> node is + then removed. Notice that <c>Mnesia</c> must be + stopped on the node first.</p> </desc> </func> <func> <name>del_table_index(Tab, AttrName) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Delete an index in a table. </fsummary> + <fsummary>Deletes an index in a table.</fsummary> <desc> - <p>This function deletes the index on attribute with name + <marker id="del_table_index"></marker> + <p>Deletes the index on attribute with name <c>AttrName</c> in a table.</p> </desc> </func> <func> - <name>delete({Tab, Key}) -> transaction abort | ok </name> - <fsummary>Delete all records in table <c>Tab</c>with the key <c>Key</c>.</fsummary> + <name>delete({Tab, Key}) -> transaction abort | ok</name> + <fsummary>Deletes all records in table <c>Tab</c> with the key <c>Key</c>.</fsummary> <desc> - <p>Invokes <c>mnesia:delete(Tab, Key, write)</c></p> + <marker id="delete_2"></marker> + <p>Calls <c>mnesia:delete(Tab, Key, write)</c>.</p> </desc> </func> <func> - <name>delete(Tab, Key, LockKind) -> transaction abort | ok </name> - <fsummary>Delete all records in table <c>Tab</c>with the key <c>Key</c>.</fsummary> + <name>delete(Tab, Key, LockKind) -> transaction abort | ok</name> + <fsummary>Deletes all records in table <c>Tab</c>with the key <c>Key</c>.</fsummary> <desc> + <marker id="delete_3"></marker> <p>Deletes all records in table <c>Tab</c> with the key - <c>Key</c>. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a lock of type <c>LockKind</c> in the - record. Currently the lock types <c>write</c> and + <c>Key</c>.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a lock of type + <c>LockKind</c> in the record. + Currently, the lock types <c>write</c> and <c>sticky_write</c> are supported.</p> </desc> </func> <func> - <name>delete_object(Record) -> transaction abort | ok </name> - <fsummary>Delete a record</fsummary> + <name>delete_object(Record) -> transaction abort | ok</name> + <fsummary>Delete a record.</fsummary> <desc> - <p>Invokes <c>mnesia:delete_object(Tab, Record, write)</c> where + <marker id="delete_object_1"></marker> + <p>Calls <c>mnesia:delete_object(Tab, Record, write)</c>, where <c>Tab</c> is <c>element(1, Record)</c>.</p> </desc> </func> <func> - <name>delete_object(Tab, Record, LockKind) -> transaction abort | ok </name> - <fsummary>Delete a record</fsummary> + <name>delete_object(Tab, Record, LockKind) -> transaction abort | ok</name> + <fsummary>Deletes a record.</fsummary> <desc> - <p>If a table is of type <c>bag</c>, we may sometimes - want to delete only some of the records with a certain - key. This can be done with the <c>delete_object/3</c> - function. A complete record must be supplied to this - function. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a lock of type <c>LockKind</c> on the - record. Currently the lock types <c>write</c> and + <marker id="delete_object_3"></marker> + <p>If a table is of type <c>bag</c>, it can sometimes be + needed to delete only some of the records with a certain + key. This can be done with the function <c>delete_object/3</c>. + A complete record must be supplied to this function.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a lock of type + <c>LockKind</c> on the record. + Currently, the lock types <c>write</c> and <c>sticky_write</c> are supported.</p> </desc> </func> <func> <name>delete_schema(DiscNodes) -> ok | {error,Reason}</name> - <fsummary>Delete the schema on the given nodes</fsummary> + <fsummary>Deletes the schema on the given nodes.</fsummary> <desc> + <marker id="delete_schema"></marker> <p>Deletes a database created with <c>mnesia:create_schema/1</c>. <c>mnesia:delete_schema/1</c> fails if any of the Erlang - nodes given as <c>DiscNodes</c> is not alive, or if Mnesia - is running on any of the nodes. - </p> - <p>After the database has been deleted, it may still be - possible to start Mnesia as a disc-less node. This depends on - how the configuration parameter <c>schema_location</c> is set. - </p> + nodes given as <c>DiscNodes</c> are not alive, or if + <c>Mnesia</c> is running on any of the nodes.</p> + <p>After the database is deleted, it can still be possible + to start <c>Mnesia</c> as a disc-less node. This depends + on how configuration parameter <c>schema_location</c> is + set.</p> <warning> - <p>This function must be used with extreme - caution since it makes existing persistent data - obsolete. Think twice before using it. </p> + <p>Use this function with extreme caution, as it makes + existing persistent data obsolete. Think twice before + using it.</p> </warning> </desc> </func> <func> - <name>delete_table(Tab) -> {aborted, Reason} | {atomic, ok} </name> - <fsummary>Delete permanently all replicas of table <c>Tab</c>.</fsummary> + <name>delete_table(Tab) -> {aborted, Reason} | {atomic, ok}</name> + <fsummary>Deletes permanently all replicas of table <c>Tab</c>.</fsummary> <desc> + <marker id="delete_table"></marker> <p>Permanently deletes all replicas of table <c>Tab</c>.</p> </desc> </func> <func> - <name>dirty_all_keys(Tab) -> KeyList | exit({aborted, Reason}).</name> + <name>dirty_all_keys(Tab) -> KeyList | exit({aborted, Reason})</name> <fsummary>Dirty search for all record keys in table.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:all_keys/1</c> function.</p> + <marker id="delete_all_keys"></marker> + <p>Dirty equivalent of the function <c>mnesia:all_keys/1</c>.</p> </desc> </func> <func> - <name>dirty_delete({Tab, Key}) -> ok | exit({aborted, Reason}) </name> + <name>dirty_delete({Tab, Key}) -> ok | exit({aborted, Reason})</name> <fsummary>Dirty delete of a record.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_delete(Tab, Key)</c>.</p> + <marker id="dirty_delete"></marker> + <p>Calls <c>mnesia:dirty_delete(Tab, Key)</c>.</p> </desc> </func> <func> - <name>dirty_delete(Tab, Key) -> ok | exit({aborted, Reason}) </name> - <fsummary>Dirty delete of a record. </fsummary> + <name>dirty_delete(Tab, Key) -> ok | exit({aborted, Reason})</name> + <fsummary>Dirty delete of a record.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:delete/3</c> function.</p> + <p>Dirty equivalent of the function <c>mnesia:delete/3</c>.</p> </desc> </func> <func> - <name>dirty_delete_object(Record) </name> + <name>dirty_delete_object(Record)</name> <fsummary>Dirty delete of a record.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_delete_object(Tab, Record)</c> + <marker id="dirty_delete_object_1"></marker> + <p>Calls <c>mnesia:dirty_delete_object(Tab, Record)</c>, where <c>Tab</c> is <c>element(1, Record)</c>.</p> </desc> </func> <func> - <name>dirty_delete_object(Tab, Record) </name> - <fsummary>Dirty delete of a record. </fsummary> + <name>dirty_delete_object(Tab, Record)</name> + <fsummary>Dirty delete of a record.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:delete_object/3</c> function.</p> + <p>Dirty equivalent of the function <c>mnesia:delete_object/3</c>.</p> </desc> </func> <func> - <name>dirty_first(Tab) -> Key | exit({aborted, Reason}) </name> - <fsummary>Return the key for the first record in a table.</fsummary> + <name>dirty_first(Tab) -> Key | exit({aborted, Reason})</name> + <fsummary>Returns the key for the first record in a table.</fsummary> <desc> + <marker id="dirty_first"></marker> <p>Records in <c>set</c> or <c>bag</c> tables are not ordered. - However, there - is an ordering of the records which is not known - to the user. Accordingly, it is possible to traverse a table by means - of this function in conjunction with the <c>mnesia:dirty_next/2</c> - function. + However, there is an ordering of the records that is unknown + to the user. Therefore, a table can be traversed by this + function with the function <c>mnesia:dirty_next/2</c>. </p> - <p>If there are no records at all in the table, this function - returns the atom <c>'$end_of_table'</c>. For this reason, it - is highly undesirable, but not disallowed, to use this atom + <p>If there are no records in the table, this function + returns the atom <c>'$end_of_table'</c>. It is therefore + highly undesirable, but not disallowed, to use this atom as the key for any user records.</p> </desc> </func> @@ -1041,74 +970,82 @@ mnesia:create_table(person, <name>dirty_index_match_object(Pattern, Pos)</name> <fsummary>Dirty pattern match using index.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_index_match_object(Tab, Pattern, Pos)</c> where <c>Tab</c> is <c>element(1, Pattern)</c>.</p> + <marker id="dirty_index_match_object_2"></marker> + <p>Starts + <c>mnesia:dirty_index_match_object(Tab, Pattern, Pos)</c>, + where <c>Tab</c> is <c>element(1, Pattern)</c>.</p> </desc> </func> <func> <name>dirty_index_match_object(Tab, Pattern, Pos)</name> <fsummary>Dirty pattern match using index.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:index_match_object/4</c> function.</p> + <p>Dirty equivalent of the function + <c>mnesia:index_match_object/4</c>.</p> </desc> </func> <func> <name>dirty_index_read(Tab, SecondaryKey, Pos)</name> <fsummary>Dirty read using index.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:index_read/3</c> function.</p> + <marker id="dirty_index_read"></marker> + <p>Dirty equivalent of the function + <c>mnesia:index_read/3</c>.</p> </desc> </func> <func> - <name>dirty_last(Tab) -> Key | exit({aborted, Reason}) </name> - <fsummary>Return the key for the last record in a table.</fsummary> + <name>dirty_last(Tab) -> Key | exit({aborted, Reason})</name> + <fsummary>Returns the key for the last record in a table.</fsummary> <desc> - <p>This function works exactly like - <c>mnesia:dirty_first/1</c> but returns the last object in - Erlang term order for the <c>ordered_set</c> table type. For - all other table types, <c>mnesia:dirty_first/1</c> and + <marker id="dirty_last"></marker> + <p>Works exactly like <c>mnesia:dirty_first/1</c> but returns + the last object in Erlang term order for the <c>ordered_set</c> + table type. For all other table types, + <c>mnesia:dirty_first/1</c> and <c>mnesia:dirty_last/1</c> are synonyms.</p> </desc> </func> <func> - <name>dirty_match_object(Pattern) -> RecordList | exit({aborted, Reason}).</name> + <name>dirty_match_object(Pattern) -> RecordList | exit({aborted, Reason})</name> <fsummary>Dirty pattern match pattern.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_match_object(Tab, Pattern)</c> + <marker id="dirty_match_object_1"></marker> + <p>Calls <c>mnesia:dirty_match_object(Tab, Pattern)</c>, where <c>Tab</c> is <c>element(1, Pattern)</c>.</p> </desc> </func> <func> - <name>dirty_match_object(Tab, Pattern) -> RecordList | exit({aborted, Reason}).</name> + <name>dirty_match_object(Tab, Pattern) -> RecordList | exit({aborted, Reason})</name> <fsummary>Dirty pattern match pattern.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:match_object/3</c> function.</p> + <p>Dirty equivalent of the function + <c>mnesia:match_object/3</c>.</p> </desc> </func> <func> - <name>dirty_next(Tab, Key) -> Key | exit({aborted, Reason}) </name> - <fsummary>Return the next key in a table. </fsummary> + <name>dirty_next(Tab, Key) -> Key | exit({aborted, Reason})</name> + <fsummary>Return the next key in a table.</fsummary> <desc> - <p>This function makes it possible to traverse a table - and perform operations on all records in the table. When - the end of the table is reached, the special key + <marker id="dirty_next"></marker> + <p>Traverses a table and + performs operations on all records in the table. + When the end of the table is reached, the special key <c>'$end_of_table'</c> is returned. Otherwise, the function - returns a key which can be used to read the actual record.The + returns a key that can be used to read the actual record. The behavior is undefined if another Erlang process performs write operations on the table while it is being traversed with the - <c>mnesia:dirty_next/2</c> function.</p> + function <c>mnesia:dirty_next/2</c>.</p> </desc> </func> <func> - <name>dirty_prev(Tab, Key) -> Key | exit({aborted, Reason}) </name> - <fsummary>Return the previous key in a table. </fsummary> + <name>dirty_prev(Tab, Key) -> Key | exit({aborted, Reason})</name> + <fsummary>Returns the previous key in a table.</fsummary> <desc> - <p>This function works exactly like - <c>mnesia:dirty_next/2</c> but returns the previous object in - Erlang term order for the ordered_set table type. For - all other table types, <c>mnesia:dirty_next/2</c> and + <marker id="dirty_prev"></marker> + <p>Works exactly like <c>mnesia:dirty_next/2</c> but returns + the previous object in Erlang term order for the + <c>ordered_set</c> table type. For all other table types, + <c>mnesia:dirty_next/2</c> and <c>mnesia:dirty_prev/2</c> are synonyms.</p> </desc> </func> @@ -1116,33 +1053,34 @@ mnesia:create_table(person, <name>dirty_read({Tab, Key}) -> ValueList | exit({aborted, Reason}</name> <fsummary>Dirty read of records.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_read(Tab, Key)</c>.</p> + <marker id="dirty_read"></marker> + <p>Calls <c>mnesia:dirty_read(Tab, Key)</c>.</p> </desc> </func> <func> <name>dirty_read(Tab, Key) -> ValueList | exit({aborted, Reason}</name> <fsummary>Dirty read of records.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:read/3</c> function.</p> + <p>Dirty equivalent of the function <c>mnesia:read/3</c>.</p> </desc> </func> <func> <name>dirty_select(Tab, MatchSpec) -> ValueList | exit({aborted, Reason}</name> - <fsummary>Dirty match the objects in <c>Tab</c>against <c>MatchSpec</c>.</fsummary> + <fsummary>Dirty matches the objects in <c>Tab</c> against <c>MatchSpec</c>.</fsummary> <desc> - <p>This is the dirty equivalent of the - <c>mnesia:select/2</c> function.</p> + <marker id="dirty_select"></marker> + <p>Dirty equivalent of the function <c>mnesia:select/2</c>.</p> </desc> </func> <func> <name>dirty_slot(Tab, Slot) -> RecordList | exit({aborted, Reason})</name> - <fsummary>Return the list of records that are associated with Slot in a table.</fsummary> + <fsummary>Returns the list of records that are associated with <c>Slot</c> in a table.</fsummary> <desc> - <p>This function can be used to traverse a table in a - manner similar to the <c>mnesia:dirty_next/2</c> function. - A table has a number of slots which range from 0 (zero) to some - unknown upper bound. The function + <marker id="dirty_slot"></marker> + <p>Traverses a table in a + manner similar to the function <c>mnesia:dirty_next/2</c>. + A table has a number of slots that range from 0 (zero) to + an unknown upper bound. The function <c>mnesia:dirty_slot/2</c> returns the special atom <c>'$end_of_table'</c> when the end of the table is reached. The behavior of this function is undefined if a write @@ -1154,40 +1092,45 @@ mnesia:create_table(person, <name>dirty_update_counter({Tab, Key}, Incr) -> NewVal | exit({aborted, Reason})</name> <fsummary>Dirty update of a counter record.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_update_counter(Tab, Key, Incr)</c>.</p> + <marker id="dirty_update_counter"></marker> + <p>Calls <c>mnesia:dirty_update_counter(Tab, Key, Incr)</c>.</p> </desc> </func> <func> <name>dirty_update_counter(Tab, Key, Incr) -> NewVal | exit({aborted, Reason})</name> <fsummary>Dirty update of a counter record.</fsummary> <desc> - <p>There are no special counter records in Mnesia. However, + <p><c>Mnesia</c> has no special counter records. However, records of the form <c>{Tab, Key, Integer}</c> can be used - as (possibly disc resident) counters, when <c>Tab</c> is a - <c>set</c>. This function updates a counter with a - positive or negative number. However, counters can never become less + as (possibly disc-resident) counters when <c>Tab</c> is a + <c>set</c>. This function updates a counter with a positive + or negative number. However, counters can never become less than zero. There are two significant differences between this function and the action of first reading the record, performing the arithmetics, and then writing the record:</p> <list type="bulleted"> - <item>It is much more efficient</item> - <item><c>mnesia:dirty_update_counter/3</c> is - performed as an atomic operation despite the fact that it is not - protected by a transaction.</item> + <item>It is much more efficient. + </item> + <item><c>mnesia:dirty_update_counter/3</c> is performed + as an atomic operation although it is not protected + by a transaction. + </item> </list> <p>If two processes perform <c>mnesia:dirty_update_counter/3</c> - simultaneously, both updates will take effect without the + simultaneously, both updates take effect without the risk of losing one of the updates. The new value <c>NewVal</c> of the counter is returned.</p> - <p>If <c>Key</c> don't exits, a new record is created with the value - <c>Incr</c> if it is larger than 0, otherwise it is set to 0.</p> + <p>If <c>Key</c> do not exists, a new record is created with + value <c>Incr</c> if it is larger than 0, otherwise it is + set to 0.</p> </desc> </func> <func> <name>dirty_write(Record) -> ok | exit({aborted, Reason})</name> <fsummary>Dirty write of a record.</fsummary> <desc> - <p>Invokes <c>mnesia:dirty_write(Tab, Record)</c> + <marker id="dirty_write_1"></marker> + <p>Calls <c>mnesia:dirty_write(Tab, Record)</c>, where <c>Tab</c> is <c>element(1, Record)</c>.</p> </desc> </func> @@ -1195,623 +1138,607 @@ mnesia:create_table(person, <name>dirty_write(Tab, Record) -> ok | exit({aborted, Reason})</name> <fsummary>Dirty write of a record.</fsummary> <desc> - <p>This is the dirty equivalent of <c>mnesia:write/3</c>.</p> + <p>Dirty equivalent of the function <c>mnesia:write/3</c>.</p> </desc> </func> <func> <name>dump_log() -> dumped</name> - <fsummary>Perform a user initiated dump of the local log file.</fsummary> + <fsummary>Performs a user-initiated dump of the local log file.</fsummary> <desc> - <p>Performs a user initiated dump of the local log file. - This is usually not necessary since Mnesia, by default, - manages this automatically. - See configuration parameters - <seealso marker="#dump_log_time_threshold">dump_log_time_threshold</seealso> and - <seealso marker="#dump_log_write_threshold">dump_log_write_threshold</seealso>. - </p> + <marker id="dump_log"></marker> + <p>Performs a user-initiated dump of the local log file. + This is usually not necessary, as <c>Mnesia</c> by default + manages this automatically. See configuration parameters + <seealso marker="#dump_log_time_threshold">dump_log_time_threshold</seealso> + and + <seealso marker="#dump_log_write_threshold">dump_log_write_threshold</seealso>. + </p> </desc> </func> <func> <name>dump_tables(TabList) -> {atomic, ok} | {aborted, Reason}</name> - <fsummary>Dump all RAM tables to disc.</fsummary> + <fsummary>Dumps all RAM tables to disc.</fsummary> <desc> - <p>This function dumps a set of <c>ram_copies</c> tables + <marker id="dump_tables"></marker> + <p>Dumps a set of <c>ram_copies</c> tables to disc. The next time the system is started, these tables are initiated with the data found in the files that are the - result of this dump. None of the tables may have disc - resident replicas.</p> + result of this dump. None of the tables can have + disc-resident replicas.</p> </desc> </func> <func> - <name>dump_to_textfile(Filename) </name> - <fsummary>Dump local tables into a text file.</fsummary> + <name>dump_to_textfile(Filename)</name> + <fsummary>Dumps local tables into a text file.</fsummary> <desc> - <p>Dumps all local tables of a mnesia system into a text file - which can then be edited (by means of a normal text editor) - and then later be reloaded with + <marker id="dump_to_textfile"></marker> + <p>Dumps all local tables of a <c>Mnesia</c> system into a + text file, which can be edited (by a normal text editor) + and then be reloaded with <c>mnesia:load_textfile/1</c>. Only use this function for educational purposes. Use other functions to deal with real backups.</p> </desc> </func> <func> - <name>error_description(Error) -> String </name> - <fsummary>Return a string describing a particular Mnesia error.</fsummary> + <name>error_description(Error) -> String</name> + <fsummary>Returns a string describing a particular <c>Mnesia</c> error.</fsummary> <desc> - <p>All Mnesia transactions, including all the schema - update functions, either return the value <c>{atomic, Val}</c> or the tuple <c>{aborted, Reason}</c>. The - <c>Reason</c> can be either of the following atoms. The - <c>error_description/1</c> function returns a descriptive - string which describes the error. - </p> + <marker id="error_description"></marker> + <p>All <c>Mnesia</c> transactions, including all the schema + update functions, either return value <c>{atomic, Val}</c> + or the tuple <c>{aborted, Reason}</c>. <c>Reason</c> can + be either of the atoms in the following list. The + function <c>error_description/1</c> returns a descriptive + string that describes the error.</p> <list type="bulleted"> - <item> - <p><c>nested_transaction</c>. Nested transactions are - not allowed in this context. - </p> + <item><c>nested_transaction</c>. Nested transactions are + not allowed in this context. </item> - <item> - <p><c>badarg</c>. Bad or invalid argument, possibly - bad type. - </p> + <item><c>badarg</c>. Bad or invalid argument, possibly + bad type. </item> - <item> - <p><c>no_transaction</c>. Operation not allowed - outside transactions. - </p> + <item><c>no_transaction</c>. Operation not allowed + outside transactions. </item> - <item> - <p><c>combine_error</c>. Table options were illegally - combined. - </p> + <item><c>combine_error</c>. Table options illegally + combined. </item> - <item> - <p><c>bad_index</c>. Index already exists or was out - of bounds. - </p> + <item><c>bad_index</c>. Index already exists, or was out + of bounds. </item> - <item> - <p><c>already_exists</c>. Schema option is already set. - </p> + <item><c>already_exists</c>. Schema option to be activated + is already on. </item> - <item> - <p><c>index_exists</c>. Some operations cannot be performed on - tabs with index. - </p> + <item><c>index_exists</c>. Some operations cannot be + performed on tables with an index. </item> - <item> - <p><c>no_exists</c>. Tried to perform operation on - non-existing, or not alive, item. - </p> + <item><c>no_exists</c>. Tried to perform operation on + non-existing (not-alive) item. </item> - <item> - <p><c>system_limit</c>. Some system_limit was exhausted. - </p> + <item><c>system_limit</c>. A system limit was exhausted. </item> - <item> - <p><c>mnesia_down</c>. A transaction involving - records at some remote node which died while - transaction was executing. Record(s) are no longer - available elsewhere in the network. - </p> + <item><c>mnesia_down</c>. A transaction involves records + on a remote node, which became unavailable before the + transaction was completed. Records are no longer + available elsewhere in the network. </item> - <item> - <p><c>not_a_db_node</c>. A node which does not exist - in the schema was mentioned. - </p> + <item><c>not_a_db_node</c>. A node was mentioned that does + not exist in the schema. </item> - <item> - <p><c>bad_type</c>. Bad type on some arguments. - </p> + <item><c>bad_type</c>. Bad type specified in argument. </item> - <item> - <p><c>node_not_running</c>. Node not running. - </p> + <item><c>node_not_running</c>. Node is not running. </item> - <item> - <p><c>truncated_binary_file</c>. Truncated binary in file. - </p> + <item><c>truncated_binary_file</c>. Truncated binary in file. </item> - <item> - <p><c>active</c>. Some delete operations require that - all active records are removed. - </p> + <item><c>active</c>. Some delete operations require that + all active records are removed. </item> - <item> - <p><c>illegal</c>. Operation not supported on record. - </p> + <item><c>illegal</c>. Operation not supported on this + record. </item> </list> - <p>The <c>Error</c> may be <c>Reason</c>, - <c>{error, Reason}</c>, or <c>{aborted, Reason}</c>. The - <c>Reason</c> may be an atom or a tuple with <c>Reason</c> + <p><c>Error</c> can be <c>Reason</c>, + <c>{error, Reason}</c>, or <c>{aborted, Reason}</c>. + <c>Reason</c> can be an atom or a tuple with <c>Reason</c> as an atom in the first field.</p> + <p>The following examples illustrate a function that returns an error, + and the method to retrieve more detailed error information:</p> + <list type="bulleted"> + <item>The function + <seealso marker="#create_table/2">mnesia:create_table(bar, [{attributes, 3.14}])</seealso> + returns the tuple <c>{aborted,Reason}</c>, where <c>Reason</c> is + the tuple <c>{bad_type,bar,3.14000}</c>.</item> + <item>The function + <seealso marker="#error_description/1">mnesia:error_description(Reason)</seealso> + returns the term <c>{"Bad type on some provided + arguments",bar,3.14000}</c>, which is an error description + suitable for display.</item> + </list> </desc> </func> <func> <name>ets(Fun, [, Args]) -> ResultOfFun | exit(Reason)</name> - <fsummary>Call the Fun in a raw context which is not protected by a transaction.</fsummary> + <fsummary>Calls the <c>Fun</c> in a raw context that is not protected by a transaction.</fsummary> <desc> - <p>Call the <c>Fun</c> in a raw context which is not protected by - a transaction. The Mnesia function call is performed in the - <c>Fun</c> are performed directly on the local <c>ets</c> tables on - the assumption that the local storage type is + <marker id="ets"></marker> + <p>Calls the <c>Fun</c> in a raw context that is not protected by + a transaction. The <c>Mnesia</c> function call is performed in + the <c>Fun</c> and performed directly on the local <c>ets</c> + tables on the assumption that the local storage type is <c>ram_copies</c> and the tables are not replicated to other nodes. Subscriptions are not triggered and checkpoints are - not updated, but it is extremely fast. This function can + not updated, but it is extremely fast. This function can also be applied to <c>disc_copies</c> tables if all - operations are read only. See <c>mnesia:activity/4</c> - and the Mnesia User's Guide for more details.</p> - <p><em>Note:</em> Calling (nesting) a <c>mnesia:ets</c> - inside a transaction context will inherit the transaction semantics.</p> + operations are read only. For details, see + <c>mnesia:activity/4</c> and the User's Guide.</p> + <p>Notice that calling (nesting) a <c>mnesia:ets</c> inside a + transaction-context inherits the transaction semantics.</p> </desc> </func> <func> - <name>first(Tab) -> Key | transaction abort </name> - <fsummary>Return the key for the first record in a table.</fsummary> + <name>first(Tab) -> Key | transaction abort</name> + <fsummary>Returns the key for the first record in a table.</fsummary> <desc> - <p>Records in <c>set</c> or <c>bag</c> tables are not ordered. - However, there - is an ordering of the records which is not known - to the user. Accordingly, it is possible to traverse a table by means - of this function in conjunction with the <c>mnesia:next/2</c> - function. - </p> - <p>If there are no records at all in the table, this function - returns the atom <c>'$end_of_table'</c>. For this reason, it - is highly undesirable, but not disallowed, to use this atom + <marker id="first"></marker> + <p>Records in <c>set</c> or <c>bag</c> tables are not ordered. + However, there is an ordering of the records that is unknown + to the user. A table can therefore be traversed by this + function with the function <c>mnesia:next/2</c>.</p> + <p>If there are no records in the table, this function + returns the atom <c>'$end_of_table'</c>. It is therefore + highly undesirable, but not disallowed, to use this atom as the key for any user records.</p> </desc> </func> <func> - <name>foldl(Function, Acc, Table) -> NewAcc | transaction abort </name> - <fsummary>Call Function for each record in Table </fsummary> + <name>foldl(Function, Acc, Table) -> NewAcc | transaction abort</name> + <fsummary>Calls <c>Function</c> for each record in <c>Table</c>.</fsummary> <desc> - <p>Iterates over the table <c>Table</c> and calls - <c>Function(Record, NewAcc)</c> for each <c>Record</c> in the table. - The term returned from <c>Function</c> will be used as the second - argument in the next call to the <c>Function</c>. - </p> - <p><c>foldl</c> returns the same term as the last call to + <marker id="foldl"></marker> + <p>Iterates over the table <c>Table</c> and calls + <c>Function(Record, NewAcc)</c> for each <c>Record</c> in + the table. The term returned from <c>Function</c> is used + as the second argument in the next call to <c>Function</c>.</p> + <p><c>foldl</c> returns the same term as the last call to <c>Function</c> returned.</p> </desc> </func> <func> - <name>foldr(Function, Acc, Table) -> NewAcc | transaction abort </name> - <fsummary>Call Function for each record in Table </fsummary> + <name>foldr(Function, Acc, Table) -> NewAcc | transaction abort</name> + <fsummary>Calls <c>Function</c> for each record in <c>Table</c>.</fsummary> <desc> - <p>This function works exactly like - <c>foldl/3</c> but iterates the table in the opposite order - for the <c>ordered_set</c> table type. For - all other table types, <c>foldr/3</c> and + <marker id="foldr"></marker> + <p>Works exactly like <c>foldl/3</c> but iterates the table + in the opposite order for the <c>ordered_set</c> table type. + For all other table types, <c>foldr/3</c> and <c>foldl/3</c> are synonyms.</p> </desc> </func> <func> - <name>force_load_table(Tab) -> yes | ErrorDescription </name> - <fsummary>Force a table to be loaded into the system </fsummary> + <name>force_load_table(Tab) -> yes | ErrorDescription</name> + <fsummary>Forces a table to be loaded into the system.</fsummary> <desc> - <p>The Mnesia algorithm for table load might lead to a + <marker id="force_load_table"></marker> + <p>The <c>Mnesia</c> algorithm for table load can lead to a situation where a table cannot be loaded. This situation - occurs when a node is started and Mnesia concludes, or + occurs when a node is started and <c>Mnesia</c> concludes, or suspects, that another copy of the table was active after - this local copy became inactive due to a system crash. - </p> + this local copy became inactive because of a system crash.</p> <p>If this situation is not acceptable, this function can be - used to override the strategy of the Mnesia table load - algorithm. This could lead to a situation where some - transaction effects are lost with a inconsistent database as + used to override the strategy of the <c>Mnesia</c> table + load algorithm. This can lead to a situation where some + transaction effects are lost with an inconsistent database as result, but for some applications high availability is more important than consistent data.</p> </desc> </func> <func> <name>index_match_object(Pattern, Pos) -> transaction abort | ObjList</name> - <fsummary>Match records and utilizes index information.</fsummary> + <fsummary>Matches records and uses index information.</fsummary> <desc> - <p>Invokes <c>mnesia:index_match_object(Tab, Pattern, Pos, read)</c> where <c>Tab</c> is <c>element(1, Pattern)</c>.</p> + <marker id="index_match_object_2"></marker> + <p>Starts + <c>mnesia:index_match_object(Tab, Pattern, Pos, read)</c>, + where <c>Tab</c> is <c>element(1, Pattern)</c>.</p> </desc> </func> <func> <name>index_match_object(Tab, Pattern, Pos, LockKind) -> transaction abort | ObjList</name> - <fsummary>Match records and utilizes index information.</fsummary> - <desc> - <p>In a manner similar to the <c>mnesia:index_read/3</c> - function, we can also utilize any index information when we - try to match records. This function takes a pattern which - obeys the same rules as the <c>mnesia:match_object/3</c> - function with the exception that this function requires the - following conditions: - </p> + <fsummary>Matches records and uses index information.</fsummary> + <desc> + <marker id="index_match_object_4"></marker> + <p>In a manner similar to the function <c>mnesia:index_read/3</c>, + any index information can be used when trying to match records. + This function takes a pattern that obeys the same rules as the + function <c>mnesia:match_object/3</c>, except that this function + requires the following conditions:</p> <list type="bulleted"> <item> <p>The table <c>Tab</c> must have an index on - position <c>Pos</c>. - </p> + position <c>Pos</c>.</p> </item> <item> <p>The element in position <c>Pos</c> in - <c>Pattern</c> must be bound. <c>Pos</c> may either be - an integer (#record.Field), or an attribute name.</p> + <c>Pattern</c> must be bound. <c>Pos</c> is + an integer (<c>#record.Field</c>) or an attribute name.</p> </item> </list> <p>The two index search functions described here are - automatically invoked when searching tables with <c>qlc</c> - list comprehensions and also when using the low level - <c>mnesia:[dirty_]match_object</c> functions. - </p> - <p></p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a lock of type <c>LockKind</c> on the - entire table or on a single record. Currently, the lock type - <c>read</c> is supported. - </p> + automatically started when searching tables with <c>qlc</c> + list comprehensions and also when using the low-level + <c>mnesia:[dirty_]match_object</c> functions.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a lock of type + <c>LockKind</c> on the entire table or on a single record. + Currently, the lock type <c>read</c> is supported.</p> </desc> </func> <func> - <name>index_read(Tab, SecondaryKey, Pos) -> transaction abort | RecordList </name> - <fsummary>Read records via index table. </fsummary> + <name>index_read(Tab, SecondaryKey, Pos) -> transaction abort | RecordList</name> + <fsummary>Reads records through index table.</fsummary> <desc> - <p>Assume there is an index on position <c>Pos</c> for a + <marker id="index_read"></marker> + <p>Assume that there is an index on position <c>Pos</c> for a certain record type. This function can be used to read the records without knowing the actual key for the record. For - example, with an index in position 1 of the <c>person</c> - table, the call <c>mnesia:index_read(person, 36, #person.age)</c> returns a list of all persons with age - equal to 36. <c>Pos</c> may also be an attribute name - (atom), but if the notation <c>mnesia:index_read(person, 36, age)</c> is used, the field position will be searched for in - runtime, for each call. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a read lock on the entire table.</p> + example, with an index in position 1 of table <c>person</c>, + the call <c>mnesia:index_read(person, 36, #person.age)</c> + returns a list of all persons with age 36. <c>Pos</c> can + also be an attribute name (atom), but if the notation + <c>mnesia:index_read(person, 36, age)</c> is used, the + field position is searched for in runtime, for each call.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a read lock on the entire + table.</p> </desc> </func> <func> - <name>info() -> ok </name> - <fsummary>Print some information about the system on the tty.</fsummary> + <name>info() -> ok</name> + <fsummary>Prints system information on the terminal.</fsummary> <desc> - <p>Prints some information about the system on the tty. - This function may be used even if Mnesia is not started. - However, more information will be displayed if Mnesia is - started.</p> + <marker id="info"></marker> + <p>Prints system information on the terminal. + This function can be used even if <c>Mnesia</c> is not + started. However, more information is displayed if + <c>Mnesia</c> is started.</p> </desc> </func> <func> <name>install_fallback(Opaque) -> ok | {error,Reason}</name> - <fsummary>Install a backup as fallback.</fsummary> + <fsummary>Installs a backup as fallback.</fsummary> <desc> - <p>Invokes <c>mnesia:install_fallback(Opaque, Args)</c> where + <marker id="install_fallback_1"></marker> + <p>Calls <c>mnesia:install_fallback(Opaque, Args)</c>, where <c>Args</c> is <c>[{scope, global}]</c>.</p> </desc> </func> <func> <name>install_fallback(Opaque), BackupMod) -> ok | {error,Reason}</name> - <fsummary>Install a backup as fallback.</fsummary> + <fsummary>Installs a backup as fallback.</fsummary> <desc> - <p>Invokes <c>mnesia:install_fallback(Opaque, Args)</c> where + <p>Calls <c>mnesia:install_fallback(Opaque, Args)</c>, where <c>Args</c> is <c>[{scope, global}, {module, BackupMod}]</c>.</p> </desc> </func> <func> <name>install_fallback(Opaque, Args) -> ok | {error,Reason}</name> - <fsummary>Install a backup as fallback.</fsummary> - <desc> - <p>This function is used to install a backup as fallback. The - fallback will be used to restore the database at the next - start-up. Installation of fallbacks requires Erlang to be up - and running on all the involved nodes, but it does not - matter if Mnesia is running or not. The installation of the - fallback will fail if the local node is not one of the disc - resident nodes in the backup. - </p> - <p><c>Args</c> is a list of the following tuples: - </p> + <fsummary>Installs a backup as fallback.</fsummary> + <desc> + <p>Installs a backup as fallback. The fallback is used to + restore the database at the next startup. Installation of + fallbacks requires Erlang to be operational on all the + involved nodes, but it does not matter if <c>Mnesia</c> + is running or not. The installation of the fallback fails + if the local node is not one of the disc-resident nodes + in the backup.</p> + <p><c>Args</c> is a list of the following tuples:</p> <list type="bulleted"> <item> - <p><c>{module, BackupMod}</c>. - All accesses of the backup media is performed via a - callback module named <c>BackupMod</c>. The - <c>Opaque</c> argument is forwarded to the callback - module which may interpret it as it wish. The default + <p><c>{module, BackupMod}</c>. + All accesses of the backup media are performed through + a callback module named <c>BackupMod</c>. Argument + <c>Opaque</c> is forwarded to the callback module, + which can interpret it as it wishes. The default callback module is called <c>mnesia_backup</c> and it - interprets the <c>Opaque</c> argument as a local + interprets argument <c>Opaque</c> as a local filename. The default for this module is also - configurable via the <c>-mnesia mnesia_backup</c> - configuration parameter. </p> + configurable through configuration parameter + <c>-mnesia mnesia_backup</c>.</p> </item> <item> - <p><c>{scope, Scope}</c> - The <c>Scope</c> of a fallback may either be + <p><c>{scope, Scope}</c>. + The <c>Scope</c> of a fallback is either <c>global</c> for the entire database or <c>local</c> for one node. By default, the installation of a fallback - is a global operation which either is performed all - nodes with disc resident schema or none. Which nodes - that are disc resident or not, is determined from the - schema info in the backup.</p> - <p>If the <c>Scope</c> of the operation is <c>local</c> - the fallback will only be installed on the local node.</p> + is a global operation, which either is performed on all + nodes with a disc-resident schema or none. Which nodes + that are disc-resident is determined from the + schema information in the backup.</p> + <p>If <c>Scope</c> of the operation is <c>local</c>, + the fallback is only installed on the local node.</p> </item> <item> - <p><c>{mnesia_dir, AlternateDir}</c> + <p><c>{mnesia_dir, AlternateDir}</c>. This argument is only valid if the scope of the installation is <c>local</c>. Normally the installation - of a fallback is targeted towards the Mnesia directory - as configured with the <c>-mnesia dir</c> configuration - parameter. But by explicitly supplying an - <c>AlternateDir</c> the fallback will be installed there - regardless of the Mnesia directory configuration + of a fallback is targeted to the <c>Mnesia</c> directory, + as configured with configuration parameter + <c>-mnesia dir</c>. But by explicitly supplying an + <c>AlternateDir</c>, the fallback is installed there + regardless of the <c>Mnesia</c> directory configuration parameter setting. After installation of a fallback on - an alternate Mnesia directory that directory is fully - prepared for usage as an active Mnesia directory. - </p> - <p>This is a somewhat dangerous feature which must be - used with care. By unintentional mixing of directories - you may easily end up with a inconsistent database, if + an alternative <c>Mnesia</c> directory, that directory + is fully prepared for use as an active <c>Mnesia</c> + directory.</p> + <p>This is a dangerous feature that must be + used with care. By unintentional mixing of directories, + you can easily end up with an inconsistent database, if the same backup is installed on more than one directory.</p> </item> </list> </desc> </func> <func> - <name>is_transaction() -> boolean </name> - <fsummary>Check if code is running in a transaction.</fsummary> + <name>is_transaction() -> boolean</name> + <fsummary>Checks if code is running in a transaction.</fsummary> <desc> - <p>When this function is executed inside a transaction context + <marker id="is_transaction"></marker> + <p>When this function is executed inside a transaction-context, it returns <c>true</c>, otherwise <c>false</c>.</p> </desc> </func> <func> - <name>last(Tab) -> Key | transaction abort </name> - <fsummary>Return the key for the last record in a table.</fsummary> + <name>last(Tab) -> Key | transaction abort</name> + <fsummary>Returns the key for the last record in a table.</fsummary> <desc> - <p>This function works exactly like - <c>mnesia:first/1</c> but returns the last object in - Erlang term order for the <c>ordered_set</c> table type. For - all other table types, <c>mnesia:first/1</c> and + <p>Works exactly like + <c>mnesia:first/1</c>, but returns the last object in + Erlang term order for the <c>ordered_set</c> table type. + For all other table types, <c>mnesia:first/1</c> and <c>mnesia:last/1</c> are synonyms.</p> </desc> </func> <func> <name>load_textfile(Filename)</name> - <fsummary>Load tables from a text file.</fsummary> + <fsummary>Loads tables from a text file.</fsummary> <desc> + <marker id="load_textfile"></marker> <p>Loads a series of definitions and data found in the text file (generated with <c>mnesia:dump_to_textfile/1</c>) - into Mnesia. This function also starts Mnesia and possibly - creates a new schema. This function is intended for - educational purposes only and using other functions to deal - with real backups, is recommended.</p> + into <c>Mnesia</c>. This function also starts <c>Mnesia</c> + and possibly creates a new schema. This function is + intended for educational purposes only. It is recommended + to use other functions to deal with real backups.</p> </desc> </func> <func> <name>lock(LockItem, LockKind) -> Nodes | ok | transaction abort</name> <fsummary>Explicit grab lock.</fsummary> <desc> + <marker id="lock"></marker> <p>Write locks are normally acquired on all nodes where a - replica of the table resides (and is active). Read locks are - acquired on one node (the local node if a local - replica exists). Most of the context sensitive access functions - acquire an implicit lock if they are invoked in a - transaction context. The granularity of a lock may either - be a single record or an entire table. - </p> - <p>The normal usage is to call the function without checking - the return value since it exits if it fails and the - transaction is restarted by the transaction manager. It - returns all the locked nodes if a write lock is acquired, and - <c>ok</c> if it was a read lock. - </p> - <p>This function <c>mnesia:lock/2</c> is intended to support - explicit locking on tables but also intended for situations - when locks need to be acquired regardless of how tables are - replicated. Currently, two <c>LockKind</c>'s are supported: - </p> + replica of the table resides (and is active). Read locks + are acquired on one node (the local node if a local + replica exists). Most of the context-sensitive access + functions acquire an implicit lock if they are started in a + transaction-context. The granularity of a lock can either + be a single record or an entire table.</p> + <p>The normal use is to call the function without checking + the return value, as it exits if it fails and the + transaction is restarted by the transaction manager. It + returns all the locked nodes if a write lock is acquired + and <c>ok</c> if it was a read lock.</p> + <p>The function <c>mnesia:lock/2</c> is intended to support + explicit locking on tables, but is also intended for + situations when locks need to be acquired regardless of + how tables are replicated. Currently, two kinds of + <c>LockKind</c> are supported:</p> <taglist> <tag><c>write</c></tag> <item> - <p>Write locks are exclusive, which means that if one + <p>Write locks are exclusive. This means that if one transaction manages to acquire a write lock on an item, - no other transaction may acquire any kind of lock on the - same item. - </p> + no other transaction can acquire any kind of lock on + the same item.</p> </item> <tag><c>read</c></tag> <item> - <p>Read locks may be shared, which means that if one + <p>Read locks can be shared. This means that if one transaction manages to acquire a read lock on an item, - other transactions may also acquire a read lock on the - same item. However, if someone has a read lock no one can - acquire a write lock at the same item. If some one has a - write lock no one can acquire a read lock nor - a write lock at the same item.</p> + other transactions can also acquire a read lock on the + same item. However, if someone has a read lock, no one + can acquire a write lock at the same item. If someone + has a write lock, no one can acquire either a read lock + or a write lock at the same item.</p> </item> </taglist> <p>Conflicting lock requests are automatically queued if there is no risk of a deadlock. Otherwise the transaction must be - aborted and executed again. Mnesia does this automatically - as long as the upper limit of maximum <c>retries</c> is not - reached. See <c>mnesia:transaction/3</c> for the details. - </p> - <p>For the sake of completeness sticky write locks will also - be described here even if a sticky write lock is not - supported by this particular function: - </p> + terminated and executed again. <c>Mnesia</c> does this + automatically as long as the upper limit of the maximum + <c>retries</c> is not reached. For details, see + <c>mnesia:transaction/3</c>.</p> + <p>For the sake of completeness, sticky write locks are also + described here even if a sticky write lock is not + supported by this function:</p> <taglist> <tag><c>sticky_write</c></tag> <item> - <p>Sticky write locks are a mechanism which can be used + <p>Sticky write locks are a mechanism that can be used to optimize write lock acquisition. If your application uses replicated tables mainly for fault tolerance (as opposed to read access optimization purpose), sticky - locks may be the best option available. - </p> - <p>When a sticky write lock is acquired, all nodes will be - informed which node is locked. Subsequently, - sticky lock requests from the same node will be - performed as a local operation without any + locks can be the best option available.</p> + <p>When a sticky write lock is acquired, all nodes are + informed which node is locked. Then, + sticky lock requests from the same node are + performed as a local operation without any communication with other nodes. The sticky lock - lingers on the node even after the transaction has - ended. See the Mnesia User's Guide for more information.</p> + lingers on the node even after the transaction + ends. For details, see the User's Guide.</p> </item> </taglist> - <p>Currently, two kinds of <c>LockItem</c>'s are supported by - this function: - </p> + <p>Currently, this function supports two kinds of + <c>LockItem</c>:</p> <taglist> <tag><c>{table, Tab}</c></tag> <item> <p>This acquires a lock of type <c>LockKind</c> on the - entire table <c>Tab</c>. - </p> + entire table <c>Tab</c>.</p> </item> <tag><c>{global, GlobalKey, Nodes}</c></tag> <item> <p>This acquires a lock of type <c>LockKind</c> on the global resource <c>GlobalKey</c>. The lock is acquired - on all active nodes in the <c>Nodes</c> list. </p> + on all active nodes in the <c>Nodes</c> list.</p> </item> </taglist> - <p>Locks are released when the outermost transaction ends. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires locks otherwise it just ignores the - request.</p> + <p>Locks are released when the outermost transaction ends.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires locks, otherwise it + ignores the request.</p> </desc> </func> <func> - <name>match_object(Pattern) ->transaction abort | RecList </name> - <fsummary>Match <c>Pattern</c>for records. </fsummary> + <name>match_object(Pattern) -> transaction abort | RecList</name> + <fsummary>Matches <c>Pattern</c> for records.</fsummary> <desc> - <p>Invokes <c>mnesia:match_object(Tab, Pattern, read)</c> where + <marker id="match_object_1"></marker> + <p>Calls <c>mnesia:match_object(Tab, Pattern, read)</c>, where <c>Tab</c> is <c>element(1, Pattern)</c>.</p> </desc> </func> <func> - <name>match_object(Tab, Pattern, LockKind) ->transaction abort | RecList </name> - <fsummary>Match <c>Pattern</c>for records. </fsummary> + <name>match_object(Tab, Pattern, LockKind) -> transaction abort | RecList</name> + <fsummary>Matches <c>Pattern</c> for records.</fsummary> <desc> - <p>This function takes a pattern with 'don't care' variables - denoted as a '_' parameter. This function returns a list of - records which matched the pattern. Since the second element + <marker id="match_object_3"></marker> + <p>Takes a pattern with "don't care" variables + denoted as a <c>'_'</c> parameter. This function returns + a list of records that matched the pattern. + Since the second element of a record in a table is considered to be the key for the record, the performance of this function depends on whether - this key is bound or not. - </p> - <p>For example, the call <c>mnesia:match_object(person, {person, '_', 36, '_', '_'}, read)</c> returns a list of all person records with an - age field of thirty-six (36). - </p> + this key is bound or not.</p> + <p>For example, the call <c>mnesia:match_object(person, + {person, '_', 36, '_', '_'}, read)</c> returns a list of + all person records with an <c>age</c> field of 36.</p> <p>The function <c>mnesia:match_object/3</c> - automatically uses indices if these exist. However, no - heuristics are performed in order to select the best - index. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a lock of type <c>LockKind</c> on the - entire table or a single record. Currently, the lock type - <c>read</c> is supported.</p> + automatically uses indexes if these exist. However, no + heuristics are performed to select the best index.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a lock of type + <c>LockKind</c> on the entire table or a single record. + Currently, the lock type <c>read</c> is supported.</p> </desc> </func> <func> <name>move_table_copy(Tab, From, To) -> {aborted, Reason} | {atomic, ok}</name> - <fsummary>Move the copy of table <c>Tab</c>from node<c>From</c>to node <c>To</c>.</fsummary> + <fsummary>Moves the copy of table <c>Tab</c> from node <c>From</c> to node <c>To</c>.</fsummary> <desc> + <marker id="move_table_copy"></marker> <p>Moves the copy of table <c>Tab</c> from node - <c>From</c> to node <c>To</c>. - </p> + <c>From</c> to node <c>To</c>.</p> <p>The storage type is preserved. For example, a RAM table - moved from one node remains a RAM on the new node. It is - still possible for other transactions to read and write in - the table while it is being moved. - </p> + moved from one node remains a RAM on the new node. Other + transactions can still read and write in + the table while it is being moved.</p> <p>This function cannot be used on <c>local_content</c> tables.</p> </desc> </func> <func> - <name>next(Tab, Key) -> Key | transaction abort </name> - <fsummary>Return the next key in a table. </fsummary> + <name>next(Tab, Key) -> Key | transaction abort</name> + <fsummary>Returns the next key in a table.</fsummary> <desc> - <p>This function makes it possible to traverse a table - and perform operations on all records in the table. When + <marker id="next"></marker> + <p>Traverses a table and + performs operations on all records in the table. When the end of the table is reached, the special key - <c>'$end_of_table'</c> is returned. Otherwise, the function - returns a key which can be used to read the actual record.</p> + <c>'$end_of_table'</c> is returned. Otherwise the function + returns a key that can be used to read the actual record.</p> </desc> </func> <func> - <name>prev(Tab, Key) -> Key | transaction abort </name> - <fsummary>Return the previous key in a table. </fsummary> + <name>prev(Tab, Key) -> Key | transaction abort</name> + <fsummary>Returns the previous key in a table.</fsummary> <desc> - <p>This function works exactly like - <c>mnesia:next/2</c> but returns the previous object in - Erlang term order for the ordered_set table type. For - all other table types, <c>mnesia:next/2</c> and + <p>Works exactly like + <c>mnesia:next/2</c>, but returns the previous object in + Erlang term order for the <c>ordered_set</c> table type. + For all other table types, <c>mnesia:next/2</c> and <c>mnesia:prev/2</c> are synonyms.</p> </desc> </func> <func> - <name>read({Tab, Key}) -> transaction abort | RecordList </name> - <fsummary>Read records(s) with a given key. </fsummary> + <name>read({Tab, Key}) -> transaction abort | RecordList</name> + <fsummary>Reads records(s) with a given key.</fsummary> <desc> - <p>Invokes <c>mnesia:read(Tab, Key, read)</c>.</p> + <marker id="read_2"></marker> + <p>Calls function <c>mnesia:read(Tab, Key, read)</c>.</p> </desc> </func> <func> - <name>read(Tab, Key) -> transaction abort | RecordList </name> - <fsummary>Read records(s) with a given key. </fsummary> + <name>read(Tab, Key) -> transaction abort | RecordList</name> + <fsummary>Reads records(s) with a given key.</fsummary> <desc> - <p>Invokes <c>mnesia:read(Tab, Key, read)</c>.</p> + <p>Calls function <c>mnesia:read(Tab, Key, read)</c>.</p> </desc> </func> <func> - <name>read(Tab, Key, LockKind) -> transaction abort | RecordList </name> - <fsummary>Read records(s) with a given key. </fsummary> + <name>read(Tab, Key, LockKind) -> transaction abort | RecordList</name> + <fsummary>Reads records(s) with a given key.</fsummary> <desc> - <p>This function reads all records from table <c>Tab</c> with + <marker id="read_3"></marker> + <p>Reads all records from table <c>Tab</c> with key <c>Key</c>. This function has the same semantics regardless of the location of <c>Tab</c>. If the table is - of type <c>bag</c>, the <c>mnesia:read(Tab, Key)</c> can + of type <c>bag</c>, the function + <c>mnesia:read(Tab, Key)</c> can return an arbitrarily long list. If the table is of type - <c>set</c>, the list is either of length 1, or <c>[]</c>. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a lock of type + <c>set</c>, the list is either of length 1, or <c>[]</c>.</p> + <p>The semantics of this function is context-sensitive. + For details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a lock of type <c>LockKind</c>. Currently, the lock types <c>read</c>, - <c>write</c> and <c>sticky_write</c> are supported. - </p> - <p>If the user wants to update the record it is more efficient to - use <c>write/sticky_write</c> as the LockKind. If majority checking - is active on the table, it will be checked as soon as a write lock is - attempted. This can be used to quickly abort if the majority condition - isn't met. - </p> + <c>write</c>, and <c>sticky_write</c> are supported.</p> + <p>If the user wants to update the record, it is more + efficient to use <c>write/sticky_write</c> as the + <c>LockKind</c>. If majority checking is active on the + table, it is checked as soon as a write lock is + attempted. This can be used to end quickly if the + majority condition is not met.</p> </desc> </func> <func> <name>read_lock_table(Tab) -> ok | transaction abort</name> - <fsummary>Set a read lock on an entire table.</fsummary> + <fsummary>Sets a read lock on an entire table.</fsummary> <desc> - <p>Invokes <c>mnesia:lock({table, Tab}, read)</c>.</p> + <marker id="read_lock_table"></marker> + <p>Calls the function + <c>mnesia:lock({table, Tab}, read)</c>.</p> </desc> </func> <func> <name>report_event(Event) -> ok</name> - <fsummary>Report a user event to Mnesia's event handler.</fsummary> + <fsummary>Reports a user event to the <c>Mnesia</c> event handler.</fsummary> <desc> - <p>When tracing a system of Mnesia applications it is useful - to be able to interleave Mnesia's own events with - application related events that give information about the - application context. - </p> + <marker id="report_event"></marker> + <p>When tracing a system of <c>Mnesia</c> applications it is + useful to be able to interleave <c>Mnesia</c> own events with + application-related events that give information about the + application context.</p> <p>Whenever the application begins a - new and demanding Mnesia task, or if it is entering a new - interesting phase in its execution, it may be a good idea to - use <c>mnesia:report_event/1</c>. The <c>Event</c> may be + new and demanding <c>Mnesia</c> task, or if it enters a new + interesting phase in its execution, it can be a good idea to + use <c>mnesia:report_event/1</c>. <c>Event</c> can be any term and generates a <c>{mnesia_user, Event}</c> event - for any processes that subscribe to Mnesia system + for any processes that subscribe to <c>Mnesia</c> system events.</p> </desc> </func> @@ -1819,221 +1746,237 @@ mnesia:create_table(person, <name>restore(Opaque, Args) -> {atomic, RestoredTabs} |{aborted, Reason}</name> <fsummary>Online restore of backup.</fsummary> <desc> - <p>With this function, tables may be restored online from a - backup without restarting Mnesia. <c>Opaque</c> is forwarded - to the backup module. <c>Args</c> is a list of the following - tuples: - </p> + <marker id="restore"></marker> + <p>With this function, tables can be restored online from a + backup without restarting <c>Mnesia</c>. + <c>Opaque</c> is forwarded to the backup module. + <c>Args</c> is a list of the following tuples:</p> <list type="bulleted"> <item> - <p><c>{module,BackupMod}</c> The backup module - <c>BackupMod</c> will be used to access the backup - media. If omitted, the default backup module will be - used. - </p> + <c>{module,BackupMod}</c>. The backup module + <c>BackupMod</c> is used to access the backup media. + If omitted, the default backup module is used. </item> - <item><c>{skip_tables, TabList}</c> Where <c>TabList</c> - is a list of tables which should not be read from the + <item><c>{skip_tables, TabList}</c>, where <c>TabList</c> + is a list of tables that is not to be read from the backup. </item> - <item><c>{clear_tables, TabList}</c> Where - <c>TabList</c> is a list of tables which should be - cleared, before the records from the backup are inserted, - ie. all records in the tables are deleted before the - tables are restored. Schema information about the tables - is not cleared or read from backup. - </item> - <item><c>{keep_tables, TabList}</c> Where <c>TabList</c> - is a list of tables which should be not be cleared, before - the records from the backup are inserted, i.e. the records - in the backup will be added to the records in the table. + <item><c>{clear_tables, TabList}</c>, where + <c>TabList</c> is a list of tables that is to be + cleared before the records from the backup are inserted. + That is, all records in the tables are deleted before the + tables are restored. Schema information about the tables + is not cleared or read from the backup. + </item> + <item><c>{keep_tables, TabList}</c>, where <c>TabList</c> + is a list of tables that is not to be cleared before the + records from the backup are inserted. That is, the records + in the backup are added to the records in the table. Schema information about the tables is not cleared or read - from backup. - </item> - <item><c>{recreate_tables, TabList}</c> Where - <c>TabList</c> is a list of tables which should be - re-created, before the records from the backup are - inserted. The tables are first deleted and then created with - the schema information from the backup. All the nodes in the - backup needs to be up and running. - </item> - <item><c>{default_op, Operation}</c> Where <c>Operation</c> is - one of the following operations <c>skip_tables</c>, - <c>clear_tables</c>, <c>keep_tables</c> or - <c>recreate_tables</c>. The default operation specifies - which operation should be used on tables from the backup - which are not specified in any of the lists above. If - omitted, the operation <c>clear_tables</c> will be used. + from the backup. + </item> + <item><c>{recreate_tables, TabList}</c>, where + <c>TabList</c> is a list of tables that is to be + recreated before the records from the backup are inserted. + The tables are first deleted and then created with the + schema information from the backup. All the nodes in the + backup need to be operational. + </item> + <item><c>{default_op, Operation}</c>, where <c>Operation</c> + is either of the operations <c>skip_tables</c>, + <c>clear_tables</c>, <c>keep_tables</c>, or + <c>recreate_tables</c>. The default operation specifies + which operation that is to be used on tables from the backup + that is not specified in any of the mentioned lists. If + omitted, operation <c>clear_tables</c> is used. </item> </list> - <p>The affected tables are write locked during the - restoration, but regardless of the lock conflicts caused by - this, the applications can continue to do their work while + <p>The affected tables are write-locked during the + restoration. However, regardless of the lock conflicts caused + by this, the applications can continue to do their work while the restoration is being performed. The restoration is - performed as one single transaction. - </p> - <p>If the database is - huge, it may not be possible to restore it online. In such - cases, the old database must be restored by installing a + performed as one single transaction.</p> + <p>If the database is huge, + it it not always possible to restore it online. In such + cases, restore the old database by installing a fallback and then restart.</p> </desc> </func> <func> - <name>s_delete({Tab, Key}) -> ok | transaction abort </name> - <fsummary>Set sticky lock and delete records.</fsummary> + <name>s_delete({Tab, Key}) -> ok | transaction abort</name> + <fsummary>Sets sticky lock and delete records.</fsummary> <desc> - <p>Invokes <c>mnesia:delete(Tab, Key, sticky_write)</c></p> + <marker id="s_delete"></marker> + <p>Calls the function + <c>mnesia:delete(Tab, Key, sticky_write)</c></p> </desc> </func> <func> - <name>s_delete_object(Record) -> ok | transaction abort </name> - <fsummary>Set sticky lock and delete record.</fsummary> + <name>s_delete_object(Record) -> ok | transaction abort</name> + <fsummary>Sets sticky lock and delete record.</fsummary> <desc> - <p>Invokes <c>mnesia:delete_object(Tab, Record, sticky_write)</c> where <c>Tab</c> is <c>element(1, Record)</c>.</p> + <marker id="s_delete_object"></marker> + <p>Calls the function + <c>mnesia:delete_object(Tab, Record, sticky_write)</c>, + where <c>Tab</c> is <c>element(1, Record)</c>.</p> </desc> </func> <func> - <name>s_write(Record) -> ok | transaction abort </name> - <fsummary>Write <c>Record</c>and sets stick lock.</fsummary> + <name>s_write(Record) -> ok | transaction abort</name> + <fsummary>Writes <c>Record</c> and sets sticky lock.</fsummary> <desc> - <p>Invokes <c>mnesia:write(Tab, Record, sticky_write)</c> + <marker id="s_write"></marker> + <p>Calls the function + <c>mnesia:write(Tab, Record, sticky_write)</c>, where <c>Tab</c> is <c>element(1, Record)</c>.</p> </desc> </func> <func> - <name>schema() -> ok </name> - <fsummary>Print information about all table definitions on the tty. </fsummary> + <name>schema() -> ok</name> + <fsummary>Prints information about all table definitions on the terminal.</fsummary> <desc> - <p>Prints information about all table definitions on the tty.</p> + <p>Prints information about all table definitions on the terminal.</p> </desc> </func> <func> - <name>schema(Tab) -> ok </name> - <fsummary>Print information about one table definition on the tty.</fsummary> + <name>schema(Tab) -> ok</name> + <fsummary>Prints information about one table definition on the terminal.</fsummary> <desc> - <p>Prints information about one table definition on the tty.</p> + <p>Prints information about one table definition on the terminal.</p> </desc> </func> <func> - <name>select(Tab, MatchSpec [, Lock]) -> transaction abort | [Object] </name> - <fsummary>Match the objects in <c>Tab</c>against <c>MatchSpec</c>.</fsummary> + <name>select(Tab, MatchSpec [, Lock]) -> transaction abort | [Object]</name> + <fsummary>Matches the objects in <c>Tab</c> against <c>MatchSpec</c>.</fsummary> <desc> - <p>Matches the objects in the table <c>Tab</c> using a - match_spec as described in the ERTS Users Guide. Optionally a lock + <marker id="select_2_3"></marker> + <p>Matches the objects in table <c>Tab</c> using a + <c>match_spec</c> as described in the + <seealso marker="stdlib:ets#select/3">ets:select/3</seealso>. + Optionally a lock <c>read</c> or <c>write</c> can be given as the third - argument, default is <c>read</c>. The return value depends - on the <c>MatchSpec</c>.</p> - <p><em>Note:</em> for best performance <c>select</c> should - be used before any modifying operations are done on that table - in the same transaction, i.e. don't use <c>write</c> or <c>delete</c> - before a <c>select</c>.</p> - <p>In its simplest forms the match_spec's look like this:</p> + argument. Default is <c>read</c>. The return value depends + on <c>MatchSpec</c>.</p> + <p>Notice that for best performance, <c>select</c> is to be + used before any modifying operations are done on that table + in the same transaction. That is, do not use <c>write</c> + or <c>delete</c> before a <c>select</c>.</p> + <p>In its simplest forms, the <c>match_spec</c> look as + follows:</p> <list type="bulleted"> - <item>MatchSpec = [MatchFunction]</item> - <item>MatchFunction = {MatchHead, [Guard], [Result]}</item> - <item>MatchHead = tuple() | record()</item> - <item>Guard = {"Guardtest name", ...}</item> - <item>Result = "Term construct"</item> + <item><c>MatchSpec = [MatchFunction]</c></item> + <item><c>MatchFunction = {MatchHead, [Guard], [Result]}</c></item> + <item><c>MatchHead = tuple() | record()</c></item> + <item><c>Guard = {"Guardtest name", ...}</c></item> + <item><c>Result = "Term construct"</c></item> </list> - <p>See the ERTS Users Guide and <c>ets</c> documentation for a - complete description of the select.</p> - <p>For example to find the names of all male persons with an age over 30 in table - Tab do:</p> + <p>For a complete description of <c>select</c>, see the + <seealso marker="erts:index">ERTS</seealso> User's Guide and the + <seealso marker="stdlib:ets">ets</seealso> manual page in + <c>STDLIB</c>.</p> + <p>For example, to find the names of all male persons older + than 30 in table <c>Tab</c>:</p> <code type="none"> MatchHead = #person{name='$1', sex=male, age='$2', _='_'}, Guard = {'>', '$2', 30}, Result = '$1', -mnesia:select(Tab,[{MatchHead, [Guard], [Result]}]), - </code> +mnesia:select(Tab,[{MatchHead, [Guard], [Result]}]),</code> </desc> </func> <func> - <name>select(Tab, MatchSpec, NObjects, Lock) -> transaction abort | {[Object],Cont} | '$end_of_table'</name> - <fsummary>Match the objects in <c>Tab</c>against <c>MatchSpec</c>.</fsummary> + <name>select(Tab, MatchSpec, NObjects, Lock) -> transaction abort | {[Object],Cont} | '$end_of_table'</name> + <fsummary>Matches the objects in <c>Tab</c> against <c>MatchSpec</c>.</fsummary> <desc> - <p>Matches the objects in the table <c>Tab</c> using a - match_spec as described in ERTS users guide, and returns - a chunk of terms and a continuation, the wanted number - of returned terms is specified by the <c>NObjects</c> argument. - The lock argument can be <c>read</c> or <c>write</c>. - The continuation should be used as argument to <c>mnesia:select/1</c>, + <marker id="select_4"></marker> + <p>Matches the objects in table <c>Tab</c> using a + <c>match_spec</c> as described in the + <seealso marker="erts:index">ERTS</seealso> User's Guide, + and returns a chunk of terms and a continuation. + The wanted number of returned terms is specified by + argument <c>NObjects</c>. The lock argument can be + <c>read</c> or <c>write</c>. The continuation is to be + used as argument to <c>mnesia:select/1</c>, if more or all answers are needed.</p> - <p><em>Note:</em> for best performance <c>select</c> should - be used before any modifying operations are done on that - table in the same transaction, i.e. don't use + <p>Notice that for best performance, <c>select</c> is to be + used before any modifying operations are done on that table + in the same transaction. That is, do not use <c>mnesia:write</c> or <c>mnesia:delete</c> before a - <c>mnesia:select</c>. For efficiency the <c>NObjects</c> is - a recommendation only and the result may contain anything - from an empty list to all available results. </p> + <c>mnesia:select</c>. For efficiency, <c>NObjects</c> is + a recommendation only and the result can contain anything + from an empty list to all available results.</p> </desc> </func> <func> - <name>select(Cont) -> transaction abort | {[Object],Cont} | '$end_of_table'</name> - <fsummary>Continues selecting objects. </fsummary> + <name>select(Cont) -> transaction abort | {[Object],Cont} | '$end_of_table'</name> + <fsummary>Continues selecting objects.</fsummary> <desc> <p>Selects more objects with the match specification initiated - by <c>mnesia:select/4</c>. - </p> - <p><em>Note:</em> Any modifying operations, i.e. <c>mnesia:write</c> - or <c>mnesia:delete</c>, that are done between the <c>mnesia:select/4</c> - and <c>mnesia:select/1</c> calls will not be visible in the result.</p> + by <c>mnesia:select/4</c>.</p> + <p>Notice that any modifying operations, that is, + <c>mnesia:write</c> or <c>mnesia:delete</c>, that are done + between the <c>mnesia:select/4</c> and <c>mnesia:select/1</c> + calls are not visible in the result.</p> </desc> </func> <func> <name>set_debug_level(Level) -> OldLevel</name> - <fsummary>Change the internal debug level of Mnesia</fsummary> + <fsummary>Changes the internal debug level of <c>Mnesia</c>.</fsummary> <desc> - <p>Changes the internal debug level of Mnesia. See the - chapter about configuration parameters for details.</p> + <marker id="set_debug_level"></marker> + <p>Changes the internal debug level of <c>Mnesia</c>. + For details, see + <seealso marker="#configuration_parameters">Section + Configuration Parameters</seealso>.</p> </desc> </func> <func> - <name>set_master_nodes(MasterNodes) -> ok | {error, Reason} </name> - <fsummary>Set the master nodes for all tables</fsummary> + <name>set_master_nodes(MasterNodes) -> ok | {error, Reason}</name> + <fsummary>Sets the master nodes for all tables.</fsummary> <desc> - <p>For each table Mnesia will determine its replica nodes - (<c>TabNodes</c>) and invoke <c>mnesia:set_master_nodes(Tab, TabMasterNodes)</c> where <c>TabMasterNodes</c> is the - intersection of <c>MasterNodes</c> and <c>TabNodes</c>. See - <c>mnesia:set_master_nodes/2</c> about the semantics.</p> + <marker id="set_master_nodes_1"></marker> + <p>For each table <c>Mnesia</c> determines its replica nodes + (<c>TabNodes</c>) and starts + <c>mnesia:set_master_nodes(Tab, TabMasterNodes)</c>. where + <c>TabMasterNodes</c> is the intersection of + <c>MasterNodes</c> and <c>TabNodes</c>. For semantics, see + <c>mnesia:set_master_nodes/2</c>.</p> </desc> </func> <func> - <name>set_master_nodes(Tab, MasterNodes) -> ok | {error, Reason} </name> - <fsummary>Set the master nodes for a table</fsummary> + <name>set_master_nodes(Tab, MasterNodes) -> ok | {error, Reason}</name> + <fsummary>Sets the master nodes for a table.</fsummary> <desc> - <p>If the application detects that there has been a - communication failure (in a potentially partitioned network) which - may have caused an inconsistent database, it may use the + <marker id="set_master_nodes_2"></marker> + <p>If the application detects a + communication failure (in a potentially partitioned network) + that can have caused an inconsistent database, it can use the function <c>mnesia:set_master_nodes(Tab, MasterNodes)</c> to - define from which nodes each table will be loaded. - At startup Mnesia's normal table load algorithm will be - bypassed and the table will be loaded from one of the master - nodes defined for the table, regardless of when and if Mnesia - was terminated on other nodes. The <c>MasterNodes</c> may only - contain nodes where the table has a replica and if the + define from which nodes each table is to be loaded. + At startup, the <c>Mnesia</c> normal table load algorithm is + bypassed and the table is loaded from one of the master nodes + defined for the table, regardless of when and if <c>Mnesia</c> + terminated on other nodes. <c>MasterNodes</c> can only + contain nodes where the table has a replica. If the <c>MasterNodes</c> list is empty, the master node recovery - mechanism for the particular table will be reset and the - normal load mechanism will be used at next restart. - </p> - <p>The master node setting is always local and it may be - changed regardless of whether Mnesia is started or not. - </p> - <p>The database may also become inconsistent if the - <c>max_wait_for_decision</c> configuration parameter is used + mechanism for the particular table is reset, and the + normal load mechanism is used at the next restart.</p> + <p>The master node setting is always local. It can be + changed regardless if <c>Mnesia</c> is started or not.</p> + <p>The database can also become inconsistent if + configuration parameter <c>max_wait_for_decision</c> is used or if <c>mnesia:force_load_table/1</c> is used.</p> </desc> </func> <func> <name>snmp_close_table(Tab) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Remove the possibility for SNMP to manipulate the table.</fsummary> + <fsummary>Removes the possibility for SNMP to manipulate the table.</fsummary> <desc> - <p>Removes the possibility for SNMP to manipulate the - table.</p> + <p>Removes the possibility for SNMP to manipulate the table.</p> </desc> </func> <func> <name>snmp_get_mnesia_key(Tab, RowIndex) -> {ok, Key} | undefined</name> - <fsummary>Get the corresponding Mnesia key from an SNMP index.</fsummary> + <fsummary>Gets the corresponding <c>Mnesia</c> key from an SNMP index.</fsummary> <type> <v>Tab ::= atom()</v> <v>RowIndex ::= [integer()]</v> @@ -2041,44 +1984,43 @@ mnesia:select(Tab,[{MatchHead, [Guard], [Result]}]), <v>key() ::= integer() | string() | [integer()]</v> </type> <desc> - <p>Transforms an SNMP index to the corresponding Mnesia key. - If the SNMP table has multiple keys, the key is a tuple of - the key columns.</p> + <p>Transforms an SNMP index to the corresponding <c>Mnesia</c> + key. If the SNMP table has multiple keys, the key is a tuple + of the key columns.</p> </desc> </func> <func> <name>snmp_get_next_index(Tab, RowIndex) -> {ok, NextIndex} | endOfTable</name> - <fsummary>Get the index of the next lexicographical row.</fsummary> + <fsummary>Gets the index of the next lexicographical row.</fsummary> <type> <v>Tab ::= atom()</v> <v>RowIndex ::= [integer()]</v> <v>NextIndex ::= [integer()]</v> </type> <desc> - <p>The <c>RowIndex</c> may specify a non-existing row. - Specifically, it might be the empty list. Returns the index + <p><c>RowIndex</c> can specify a non-existing row. + Specifically, it can be the empty list. Returns the index of the next lexicographical row. If <c>RowIndex</c> is the - empty list, this function will return the index of the first row + empty list, this function returns the index of the first row in the table.</p> </desc> </func> <func> <name>snmp_get_row(Tab, RowIndex) -> {ok, Row} | undefined</name> - <fsummary>Retrieve a row indexed by an SNMP index.</fsummary> + <fsummary>Retrieves a row indexed by an SNMP index.</fsummary> <type> <v>Tab ::= atom()</v> <v>RowIndex ::= [integer()]</v> <v>Row ::= record(Tab)</v> </type> <desc> - <p>Makes it possible to read a row by its SNMP index. This - index is specified as an SNMP OBJECT IDENTIFIER, a list of - integers.</p> + <p>Reads a row by its SNMP index. This index is specified as + an SNMP Object Identifier, a list of integers.</p> </desc> </func> <func> <name>snmp_open_table(Tab, SnmpStruct) -> {aborted, R} | {atomic, ok}</name> - <fsummary>Organize a Mnesia table as an SNMP table.</fsummary> + <fsummary>Organizes a <c>Mnesia</c> table as an SNMP table.</fsummary> <type> <v>Tab ::= atom()</v> <v>SnmpStruct ::= [{key, type()}]</v> @@ -2086,624 +2028,558 @@ mnesia:select(Tab,[{MatchHead, [Guard], [Result]}]), <v>type_spec() ::= fix_string | string | integer</v> </type> <desc> - <p>It is possible to establish a direct one to one mapping - between Mnesia tables and SNMP tables. Many - telecommunication applications are controlled and monitored - by the SNMP protocol. This connection between Mnesia and - SNMP makes it simple and convenient to achieve this. - </p> - <p>The <c>SnmpStruct</c> argument is a list of SNMP + <p>A direct one-to-one mapping can be established between + <c>Mnesia</c> tables and SNMP tables. Many telecommunication + applications are controlled and monitored by the SNMP + protocol. This connection between <c>Mnesia</c> and SNMP + makes it simple and convenient to achieve this mapping.</p> + <p>Argument <c>SnmpStruct</c> is a list of SNMP information. Currently, the only information needed is - information about the key types in the table. It is not - possible to handle multiple keys in Mnesia, but many SNMP + information about the key types in the table. Multiple + keys cannot be handled in <c>Mnesia</c>, but many SNMP tables have multiple keys. Therefore, the following convention is used: if a table has multiple keys, these must - always be stored as a tuple of the keys. Information about + always be stored as a tuple of the keys. Information about the key types is specified as a tuple of atoms describing - the types. The only significant type is - <c>fix_string</c>. This means that a string has fixed - size. For example: - </p> + the types. The only significant type is <c>fix_string</c>. + This means that a string has a fixed size.</p> + <p>For example, the following causes table <c>person</c> + to be ordered as an SNMP table:</p> <code type="none"> -mnesia:snmp_open_table(person, [{key, string}]) - </code> - <p>causes the <c>person</c> table to be ordered as an SNMP - table. - </p> +mnesia:snmp_open_table(person, [{key, string}])</code> <p>Consider the following schema for a table of company employees. Each employee is identified by department number - and name. The other table column stores the telephone number: - </p> + and name. The other table column stores the telephone + number:</p> <code type="none"> mnesia:create_table(employee, [{snmp, [{key, {integer, string}}]}, - {attributes, record_info(fields, employees)}]), - </code> - <p>The corresponding SNMP table would have three columns; - <c>department</c>, <c>name</c> and <c>telno</c>. - </p> - <p>It is possible to have table columns that are not visible + {attributes, record_info(fields, employees)}]),</code> + <p>The corresponding SNMP table would have three columns: + <c>department</c>, <c>name</c>, and <c>telno</c>.</p> + <p>An option is to have table columns that are not visible through the SNMP protocol. These columns must be the last columns of the table. In the previous example, the SNMP table could have columns <c>department</c> and <c>name</c> - only. The application could then use the <c>telno</c> column + only. The application could then use column <c>telno</c> internally, but it would not be visible to the SNMP - managers. - </p> + managers.</p> <p>In a table monitored by SNMP, all elements must be - integers, strings, or lists of integers. - </p> + integers, strings, or lists of integers.</p> <p>When a table is SNMP ordered, modifications are more - expensive than usual, O(logN). And more memory is used. - </p> - <p><em>Note:</em>Only the lexicographical SNMP ordering is - implemented in Mnesia, not the actual SNMP monitoring.</p> + expensive than usual, O(logN). Also, more memory is used.</p> + <p>Notice that only the lexicographical SNMP ordering is + implemented in <c>Mnesia</c>, not the actual SNMP monitoring.</p> </desc> </func> <func> - <name>start() -> ok | {error, Reason} </name> - <fsummary>Start a local Mnesia system.</fsummary> + <name>start() -> ok | {error, Reason}</name> + <fsummary>Starts a local <c>Mnesia</c> system.</fsummary> <desc> - <p>The start-up procedure for a set of Mnesia nodes is a - fairly complicated operation. A Mnesia system consists of a set - of nodes, with Mnesia started locally on all + <marker id="start"></marker> + <p>The startup procedure for a set of <c>Mnesia</c> nodes is a + fairly complicated operation. A <c>Mnesia</c> system consists + of a set of nodes, with <c>Mnesia</c> started locally on all participating nodes. Normally, each node has a directory where - all the Mnesia files are written. This directory will be - referred to as the Mnesia directory. Mnesia may also be - started on disc-less nodes. See <c>mnesia:create_schema/1</c> - and the Mnesia User's Guide for more information about disc-less - nodes. - </p> - <p>The set of nodes which makes up a Mnesia system is kept in - a schema and it is possible to add and remove Mnesia nodes + all the <c>Mnesia</c> files are written. This directory is + referred to as the <c>Mnesia</c> directory. <c>Mnesia</c> can + also be started on disc-less nodes. For more information + about disc-less nodes, see <c>mnesia:create_schema/1</c> + and the User's Guide.</p> + <p>The set of nodes that makes up a <c>Mnesia</c> system is kept + in a schema. <c>Mnesia</c> nodes can be added to or removed from the schema. The initial schema is normally created on disc with the function <c>mnesia:create_schema/1</c>. On disc-less nodes, a tiny default schema is generated each time - Mnesia is started. During the start-up procedure, Mnesia - will exchange schema information between the nodes in order - to verify that the table definitions are compatible. - </p> - <p>Each schema has a unique cookie which may be regarded as a + <c>Mnesia</c> is started. During the startup procedure, + <c>Mnesia</c> exchanges schema information between the nodes + to verify that the table definitions are compatible.</p> + <p>Each schema has a unique cookie, which can be regarded as a unique schema identifier. The cookie must be the same on all - nodes where Mnesia is supposed to run. See the Mnesia - User's Guide for more information about these details. - </p> - <p>The schema file, as well as all other files which Mnesia - needs, are kept in the Mnesia directory. The command line - option <c>-mnesia dir Dir</c> can be used to specify the - location of this directory to the Mnesia system. If no such - command line option is found, the name of the directory - defaults to <c>Mnesia.Node</c>. - </p> - <p><c>application:start(mnesia)</c> may also be used.</p> + nodes where <c>Mnesia</c> is supposed to run. For details, + see the User's Guide.</p> + <p>The schema file and all other files that <c>Mnesia</c> + needs are kept in the <c>Mnesia</c> directory. The + command-line option <c>-mnesia dir Dir</c> can be used to + specify the location of this directory to the <c>Mnesia</c> + system. If no such command-line option is found, the name + of the directory defaults to <c>Mnesia.Node</c>.</p> + <p><c>application:start(mnesia)</c> can also be used.</p> </desc> </func> <func> - <name>stop() -> stopped </name> - <fsummary>Stop Mnesia locally.</fsummary> + <name>stop() -> stopped</name> + <fsummary>Stops <c>Mnesia</c> locally.</fsummary> <desc> - <p>Stops Mnesia locally on the current node. - </p> - <p><c>application:stop(mnesia)</c> may also be used.</p> + <marker id="stop"></marker> + <p>Stops <c>Mnesia</c> locally on the current node.</p> + <p><c>application:stop(mnesia)</c> can also be used.</p> </desc> </func> <func> - <name>subscribe(EventCategory) -> {ok, Node} | {error, Reason} </name> - <fsummary>Subscribe to events of type <c>EventCategory</c>.</fsummary> + <name>subscribe(EventCategory) -> {ok, Node} | {error, Reason}</name> + <fsummary>Subscribes to events of type <c>EventCategory</c>.</fsummary> <desc> + <marker id="subscribe"></marker> <p>Ensures that a copy of all events of type - <c>EventCategory</c> are sent to the caller. The event - types available are described in the Mnesia User's Guide at <seealso marker="Mnesia_chap5#event_handling">Mnesia Event Handling</seealso>.</p> - <p><c>Node</c> is the local node. For table events to be subscribed, mnesia must have a readable local copy of the table on the node.</p> + <c>EventCategory</c> is sent to the caller. The available + event types are described in the <seealso marker="Mnesia_chap5#event_handling">User's Guide</seealso>.</p> </desc> </func> <func> - <name>sync_dirty(Fun, [, Args]) -> ResultOfFun | exit(Reason) </name> - <fsummary>Call the Fun in a context which is not protected by a transaction.</fsummary> + <name>sync_dirty(Fun, [, Args]) -> ResultOfFun | exit(Reason)</name> + <fsummary>Calls the <c>Fun</c> in a context that is not protected by a transaction.</fsummary> <desc> - <p>Call the <c>Fun</c> in a context which is not protected - by a transaction. The Mnesia function calls performed in the - <c>Fun</c> are mapped to the corresponding dirty functions. + <marker id="sync_dirty"></marker> + <p>Calls the <c>Fun</c> in a context that is not protected by + a transaction. The <c>Mnesia</c> function calls performed in + the <c>Fun</c> are mapped to the corresponding dirty functions. It is performed in almost the same context as <c>mnesia:async_dirty/1,2</c>. The difference is that the operations are performed synchronously. The caller waits for the updates to be performed on all active replicas before - the <c>Fun</c> returns. See <c>mnesia:activity/4</c> and the - Mnesia User's Guide for more details.</p> + the <c>Fun</c> returns. For details, see + <c>mnesia:activity/4</c> and the User's Guide.</p> </desc> </func> <func> - <name>sync_log() -> ok | {error, Reason} </name> - <fsummary>Perform a file sync of the local log file.</fsummary> + <name>sync_log() -> ok | {error, Reason}</name> + <fsummary>Performs a file sync of the local log file.</fsummary> <desc> <p>Ensures that the local transaction log file is synced to disk. - On a single node system data written to disk tables, since the last dump, - can be lost in case of a power outage. - See <seealso marker="#dump_log/0">dump_log/0</seealso>. - </p> + On a single node system, data written to disk tables since the + last dump can be lost if there is a power outage. + See <seealso marker="#dump_log/0">dump_log/0</seealso>.</p> </desc> </func> - <func> - <name>sync_transaction(Fun, [[, Args], Retries]) -> {aborted, Reason} | {atomic, ResultOfFun} </name> - <fsummary>Synchronously execute a transaction.</fsummary> + <name>sync_transaction(Fun, [[, Args], Retries]) -> {aborted, Reason} | {atomic, ResultOfFun}</name> + <fsummary>Synchronously executes a transaction.</fsummary> <desc> - <p>This function waits until data have been committed and + <marker id="sync_transaction"></marker> + <p>Waits until data have been committed and logged to disk (if disk is used) on every involved node before - it returns, otherwise it behaves as + it returns, otherwise it behaves as <c>mnesia:transaction/[1,2,3]</c>.</p> - <p>This functionality can be used to avoid that one process may overload - a database on another node.</p> + <p>This functionality can be used to avoid that one process + overloads a database on another node.</p> </desc> </func> <func> <name>system_info(InfoKey) -> Info | exit({aborted, Reason})</name> - <fsummary>Return information about the Mnesia system</fsummary> + <fsummary>Returns information about the <c>Mnesia</c> system.</fsummary> <desc> - <p>Returns information about the Mnesia system, such as - transaction statistics, db_nodes, and configuration parameters. - Valid keys are:</p> + <marker id="system_info"></marker> + <p>Returns information about the <c>Mnesia</c> system, such as + transaction statistics, <c>db_nodes</c>, and configuration + parameters. The valid keys are as follows:</p> <list type="bulleted"> <item> - <p><c>all</c>. This argument returns a list of all - local system information. Each element is a - <c>{InfoKey, InfoVal}</c> tuples.<em>Note:</em> New <c>InfoKey</c>'s may - be added and old undocumented <c>InfoKey</c>'s may be removed without + <p><c>all</c>. Returns a list of all local system + information. Each element is a <c>{InfoKey, InfoVal}</c> + tuple.</p> + <p>New <c>InfoKey</c>s can be added and old + undocumented <c>InfoKey</c>s can be removed without notice.</p> </item> <item> - <p><c>access_module</c>. This argument returns the name of - the module which is configured to be the activity access - callback module. - </p> + <p><c>access_module</c>. Returns the name of module that is + configured to be the activity access callback module.</p> </item> <item> - <p><c>auto_repair</c>. This argument returns - <c>true</c> or <c>false</c> to indicate if Mnesia is - configured to invoke the auto repair facility on corrupted - disc files. - </p> + <p><c>auto_repair</c>. Returns <c>true</c> or <c>false</c> + to indicate if <c>Mnesia</c> is configured to start the + auto-repair facility on corrupted disc files.</p> </item> <item> - <p><c>backup_module</c>. This argument returns the name of - the module which is configured to be the backup - callback module. - </p> + <p><c>backup_module</c>. Returns the name of the module + that is configured to be the backup callback module.</p> </item> <item> - <p><c>checkpoints</c>. This argument - returns a list of the names of the - checkpoints currently active on this node. - </p> + <p><c>checkpoints</c>. Returns a list of the names of the + checkpoints currently active on this node.</p> </item> <item> - <p><c>event_module</c>. This argument returns the name of - the module which is the event handler callback module. - </p> + <p><c>event_module</c>. Returns the name of the module + that is the event handler callback module.</p> </item> <item> - <p><c>db_nodes</c>. This argument returns - the nodes which make up the persistent database. Disc - less nodes will only be included in the list of nodes if - they explicitly has been added to the schema, e.g. with + <p><c>db_nodes</c>. Returns the nodes that make up the + persistent database. Disc-less nodes are only included + in the list of nodes if they explicitly have been added + to the schema, for example, with <c>mnesia:add_table_copy/3</c>. The function can be - invoked even if Mnesia is not yet running. - </p> + started even if <c>Mnesia</c> is not yet running.</p> </item> <item> - <p><c>debug</c>. This argument returns the current - debug level of Mnesia. - </p> + <p><c>debug</c>. Returns the current debug level of + <c>Mnesia</c>.</p> </item> <item> - <p><c>directory</c>. This argument returns the name of - the Mnesia directory. It can be invoked even if Mnesia is - not yet running. - </p> + <p><c>directory</c>. Returns the name of the <c>Mnesia</c> + directory. It can be called even if <c>Mnesia</c> is + not yet running.</p> </item> <item> - <p><c>dump_log_load_regulation</c>. This argument - returns a boolean which tells whether Mnesia is - configured to load regulate the dumper process or not. - This feature is temporary and will disappear in future - releases. - </p> + <p><c>dump_log_load_regulation</c>. Returns a boolean that + tells if <c>Mnesia</c> is configured to regulate the + dumper process load.</p> + <p>This feature is temporary and will be removed in future + releases.</p> </item> <item> - <p><c>dump_log_time_threshold</c>. This argument - returns the time threshold for transaction log dumps in - milliseconds. - </p> + <p><c>dump_log_time_threshold</c>. Returns the time + threshold for transaction log dumps in milliseconds.</p> </item> <item> - <p><c>dump_log_update_in_place</c>. This argument - returns a boolean which tells whether Mnesia is - configured to perform the updates in the dets files - directly or if the updates should be performed in a copy - of the dets files. - </p> + <p><c>dump_log_update_in_place</c>. Returns a boolean that + tells if <c>Mnesia</c> is configured to perform the + updates in the <c>dets</c> files directly, or if the + updates are to be performed in a copy of the <c>dets</c> + files.</p> </item> <item> - <p><c>dump_log_write_threshold</c>. This argument - returns the write threshold for transaction log dumps as - the number of writes to the transaction log. - </p> + <p><c>dump_log_write_threshold</c>. + Returns the write threshold for transaction log dumps as + the number of writes to the transaction log.</p> </item> <item> - <p><c>extra_db_nodes</c>. This argument returns a list - of extra db_nodes to be contacted at start-up. - </p> + <p><c>extra_db_nodes</c>. Returns a list + of extra <c>db_nodes</c> to be contacted at startup.</p> </item> <item> - <p><c>fallback_activated</c>. This argument returns - true if a fallback is activated, otherwise false. - </p> + <p><c>fallback_activated</c>. Returns <c>true</c> + if a fallback is activated, otherwise <c>false</c>.</p> </item> <item> - <p><c>held_locks</c>. This argument returns a list of - all locks held by the local Mnesia lock manager. - </p> + <p><c>held_locks</c>. Returns a list of all + locks held by the local <c>Mnesia</c> lock manager.</p> </item> <item> - <p><c>is_running</c>. This argument returns <c>yes</c> - or <c>no</c> to indicate if Mnesia is running. It may - also return <c>starting</c> or <c>stopping</c>. Can be - invoked even if Mnesia is not yet running. - </p> + <p><c>is_running</c>. Returns <c>yes</c> or <c>no</c> to + indicate if <c>Mnesia</c> is running. It can + also return <c>starting</c> or <c>stopping</c>. Can be + called even if <c>Mnesia</c> is not yet running.</p> </item> <item> - <p><c>local_tables</c>. This argument returns a list - of all tables which are configured to reside locally. - </p> + <p><c>local_tables</c>. Returns a list + of all tables that are configured to reside locally.</p> </item> <item> - <p><c>lock_queue</c>. This argument returns a list of + <p><c>lock_queue</c>. Returns a list of all transactions that are queued for execution by the - local lock manager. - </p> + local lock manager.</p> </item> <item> - <p><c>log_version</c>. This argument returns the - version number of the Mnesia transaction log format. - </p> + <p><c>log_version</c>. Returns the version + number of the <c>Mnesia</c> transaction log format.</p> </item> <item> - <p><c>master_node_tables</c>. This argument returns a - list of all tables with at least one master node. - </p> + <p><c>master_node_tables</c>. Returns a + list of all tables with at least one master node.</p> </item> <item> - <p><c>protocol_version</c>. This argument - returns the version number - of the Mnesia inter-process communication protocol. - </p> + <p><c>protocol_version</c>. Returns the version number of + the <c>Mnesia</c> inter-process communication protocol.</p> </item> <item> - <p><c>running_db_nodes</c>. This argument returns a - list of nodes where Mnesia currently is running. This - function can be invoked even if Mnesia is not yet - running, but it will then have slightly different - semantics. If Mnesia is down on the local node, the - function will return those other <c>db_nodes</c> and - <c>extra_db_nodes</c> that for the moment are up and - running. If Mnesia is started, the function will return - those nodes that Mnesia on the local node is fully - connected to. Only those nodes that Mnesia has exchanged - schema information with are included as + <p><c>running_db_nodes</c>. Returns a list of nodes where + <c>Mnesia</c> currently is running. This function can be + called even if <c>Mnesia</c> is not yet running, but it + then has slightly different semantics.</p> + <p>If <c>Mnesia</c> is down on the local node, the function + returns those other <c>db_nodes</c> and + <c>extra_db_nodes</c> that for the moment are + operational.</p> + <p>If <c>Mnesia</c> is started, the function returns + those nodes that <c>Mnesia</c> on the local node is fully + connected to. Only those nodes that <c>Mnesia</c> has + exchanged schema information with are included as <c>running_db_nodes</c>. After the merge of schemas, the - local Mnesia system is fully operable and applications - may perform access of remote replicas. Before the schema - merge Mnesia will only operate locally. Sometimes there - may be more nodes included in the + local <c>Mnesia</c> system is fully operable and + applications can perform access of remote replicas. + Before the schema merge, <c>Mnesia</c> only operates + locally. Sometimes there are more nodes included in the <c>running_db_nodes</c> list than all <c>db_nodes</c> - and <c>extra_db_nodes</c> together. - </p> + and <c>extra_db_nodes</c> together.</p> </item> <item> - <p><c>schema_location</c>. This argument returns the - initial schema location. - </p> + <p><c>schema_location</c>. Returns the + initial schema location.</p> </item> <item> - <p><c>subscribers</c>. This argument returns a list of - local processes currently subscribing to system events. - </p> + <p><c>subscribers</c>. Returns a list of + local processes currently subscribing to system events.</p> </item> <item> - <p><c>tables</c>. This argument returns a list of all - locally known tables. - </p> + <p><c>tables</c>. Returns a list of all + locally known tables.</p> </item> <item> - <p><c>transactions</c>. This argument returns a list - of all currently active local transactions. - </p> + <p><c>transactions</c>. Returns a list + of all currently active local transactions.</p> </item> <item> - <p><c>transaction_failures</c>. This argument returns - a number which indicates how many transactions have - failed since Mnesia was started. - </p> + <p><c>transaction_failures</c>. Returns a + number that indicates how many transactions have + failed since <c>Mnesia</c> was started.</p> </item> <item> - <p><c>transaction_commits</c>. This argument returns a - number which indicates how many transactions have - terminated successfully since Mnesia was started. - </p> + <p><c>transaction_commits</c>. Returns a + number that indicates how many transactions have + terminated successfully since <c>Mnesia</c> was started.</p> </item> <item> - <p><c>transaction_restarts</c>. This argument returns - a number which indicates how many transactions have been - restarted since Mnesia was started. - </p> + <p><c>transaction_restarts</c>. Returns a + number that indicates how many transactions have been + restarted since <c>Mnesia</c> was started.</p> </item> <item> - <p><c>transaction_log_writes</c>. This argument - returns a number which indicates the number of write - operation that have been performed to the transaction - log since start-up. - </p> + <p><c>transaction_log_writes</c>. + Returns a number that indicates how many write + operations that have been performed to the transaction + log since startup.</p> </item> <item> - <p><c>use_dir</c>. This argument returns a boolean - which indicates whether the Mnesia directory is used or - not. Can be invoked even if Mnesia is not yet running. - </p> + <p><c>use_dir</c>. Returns a boolean that indicates if + the <c>Mnesia</c> directory is used or not. Can be + started even if <c>Mnesia</c> is not yet running.</p> </item> <item> - <p><c>version</c>. This argument returns the current - version number of Mnesia. - </p> + <p><c>version</c>. Returns the current + version number of <c>Mnesia</c>.</p> </item> </list> </desc> </func> <func> - <name>table(Tab [,[Option]]) -> QueryHandle </name> + <name>table(Tab [,[Option]]) -> QueryHandle</name> <fsummary>Return a QLC query handle.</fsummary> <desc> - <p><marker id="qlc_table"></marker> -Returns a QLC (Query List Comprehension) query handle, see - <seealso marker="stdlib:qlc">qlc(3)</seealso>.The module <c>qlc</c> implements a query language, it - can use mnesia tables as sources of data. Calling - <c>mnesia:table/1,2</c> is the means to make the <c>mnesia</c> - table <c>Tab</c> usable to QLC.</p> - <p>The list of Options may contain mnesia options or QLC - options, the following options are recognized by Mnesia: - <c>{traverse, SelectMethod},{lock, Lock},{n_objects,Number}</c>, any other option is forwarded - to QLC. The <c>lock</c> option may be <c>read</c> or - <c>write</c>, default is <c>read</c>. The option - <c>n_objects</c> specifies (roughly) the number of objects - returned from mnesia to QLC. Queries to remote tables may - need a larger chunks to reduce network overhead, default - <c>100</c> objects at a time are returned. The option - <c>traverse</c> determines the method to traverse the whole - table (if needed), the default method is <c>select</c>:</p> + <marker id="qlc_table"></marker> + <marker id="table"></marker> + <p>Returns a Query List Comprehension (QLC) query handle, + see the <seealso marker="stdlib:qlc">qlc(3)</seealso> + manual page in <c>STDLIB</c>. The module <c>qlc</c> + implements a query language that can use <c>Mnesia</c> + tables as sources of data. Calling + <c>mnesia:table/1,2</c> is the means to make the + <c>mnesia</c> table <c>Tab</c> usable to QLC.</p> + <p><c>Option</c> can contain <c>Mnesia</c> + options or QLC options. <c>Mnesia</c> recognizes the + following options (any other option is forwarded to + QLC).</p> + <list type="bulleted"> + <item><c>{lock, Lock}</c>, where <c>lock</c> can be + <c>read</c> or <c>write</c>. Default is <c>read</c>. + </item> + <item><c>{n_objects,Number}</c>, where <c>n_objects</c> + specifies (roughly) the number of objects returned + from <c>Mnesia</c> to QLC. Queries to remote tables + can need a larger chunk to reduce network overhead. + By default, <c>100</c> objects at a time are returned. + </item> + <item><c>{traverse, SelectMethod}</c>, where + <c>traverse</c> determines the method to traverse + the whole table (if needed). The default method is + <c>select</c>. + </item> + </list> + <p>There are two alternatives for <c>select</c>:</p> <list type="bulleted"> <item> <p><c>select</c>. The table is traversed by calling - <c>mnesia:select/4</c> and <c>mnesia:select/1</c>. The - match specification (the second argument of <c>select/3</c>) - is assembled by QLC: simple filters are - translated into equivalent match specifications while - more complicated filters have to be applied to all + <c>mnesia:select/4</c> and <c>mnesia:select/1</c>. + The match specification (the second argument of + <c>select/3</c>) is assembled by QLC: simple filters + are translated into equivalent match specifications. + More complicated filters need to be applied to all objects returned by <c>select/3</c> given a match specification that matches all objects.</p> </item> <item> - <p><c>{select, MatchSpec}</c>. As for <c>select</c> - the table is traversed by calling <c>mnesia:select/3</c> and - <c>mnesia:select/1</c>. The difference is that the match - specification is explicitly given. This is how to state - match specifications that cannot easily be expressed - within the syntax provided by QLC.</p> + <p><c>{select, MatchSpec}</c>. As for <c>select</c>, + the table is traversed by calling <c>mnesia:select/3</c> + and <c>mnesia:select/1</c>. The difference is that the + match specification is explicitly given. This is how to + state match specifications that cannot easily be + expressed within the syntax provided by QLC.</p> </item> </list> </desc> </func> <func> <name>table_info(Tab, InfoKey) -> Info | exit({aborted, Reason})</name> - <fsummary>Return local information about table.</fsummary> + <fsummary>Returns local information about table.</fsummary> <desc> + <marker id="table_info"></marker> <p>The <c>table_info/2</c> function takes two arguments. - The first is the name of a Mnesia table, the second is one of - the following keys: - </p> + The first is the name of a <c>Mnesia</c> table. + The second is one of the following keys:</p> <list type="bulleted"> <item> - <p><c>all</c>. This argument returns a list of all - local table information. Each element is a <c>{InfoKey, ItemVal}</c> tuples. <em>Note:</em> New <c>InfoItem</c>'s may be - added and old undocumented <c>InfoItem</c>'s may be removed without - notice.</p> + <p><c>all</c>. Returns a list of all local table + information. Each element is a + <c>{InfoKey, ItemVal}</c> tuple.</p> + <p>New <c>InfoItem</c>s can be added and old undocumented + <c>InfoItem</c>s can be removed without notice.</p> </item> <item> - <p><c>access_mode</c>. This argument returns the - access mode of the table. The access mode may either be - read_only or read_write. - </p> + <p><c>access_mode</c>. Returns the + access mode of the table. The access mode can be + <c>read_only</c> or <c>read_write</c>.</p> </item> <item> - <p><c>arity</c>. This argument returns the arity of - records in the table as specified in the schema. - </p> + <p><c>arity</c>. Returns the arity of + records in the table as specified in the schema.</p> </item> <item> - <p><c>attributes</c>. This argument returns the table - attribute names which are specified in the schema. - </p> + <p><c>attributes</c>. Returns the table + attribute names that are specified in the schema.</p> </item> <item> - <p><c>checkpoints</c>. This argument returns the names - of the currently active checkpoints which involves this - table on this node. - </p> + <p><c>checkpoints</c>. Returns the names + of the currently active checkpoints, which involve this + table on this node.</p> </item> <item> - <p><c>cookie</c>. This argument returns a table cookie - which is a unique system generated identifier for the + <p><c>cookie</c>. Returns a table cookie, + which is a unique system-generated identifier for the table. The cookie is used internally to ensure that two different table definitions using the same table name cannot accidentally be intermixed. The cookie is - generated when the table is initially created. - </p> + generated when the table is created initially.</p> </item> <item> - <p><c>disc_copies</c>. This argument returns the nodes - where a disc_copy of the table resides according to the - schema. - </p> + <p><c>disc_copies</c>. Returns the nodes where a + <c>disc_copy</c> of the table resides according to the + schema.</p> </item> <item> - <p><c>disc_only_copies </c>. This argument returns the - nodes where a disc_only_copy of the table resides - according to the schema. - </p> + <p><c>disc_only_copies</c>. Returns the nodes where a + <c>disc_only_copy</c> of the table resides + according to the schema.</p> </item> <item> - <p><c>index</c>. This argument returns the list of - index position integers for the table. - </p> + <p><c>index</c>. Returns the list of + index position integers for the table.</p> </item> <item> - <p><c>load_node</c>. This argument returns the name of - the node that Mnesia loaded the table from. The - structure of the returned value is unspecified but may - be useful for debugging purposes. - </p> + <p><c>load_node</c>. Returns the name of + the node that <c>Mnesia</c> loaded the table from. The + structure of the returned value is unspecified, but + can be useful for debugging purposes.</p> </item> <item> - <p><c>load_order</c>. This argument returns the load + <p><c>load_order</c>. Returns the load order priority of the table. It is an integer and - defaults to <c>0</c> (zero). - </p> + defaults to <c>0</c> (zero).</p> </item> <item> - <p><c>load_reason</c>. This argument returns the - reason of why Mnesia decided to load the table. The - structure of the returned value is unspecified but may - be useful for debugging purposes. - </p> + <p><c>load_reason</c>. Returns the + reason of why <c>Mnesia</c> decided to load the table. + The structure of the returned value is unspecified, but + can be useful for debugging purposes.</p> </item> <item> - <p><c>local_content</c>. This argument returns - <c>true</c> or <c>false</c> to indicate whether the - table is configured to have locally unique content on - each node. - </p> + <p><c>local_content</c>. Returns <c>true</c> or + <c>false</c> to indicate if the table is configured to + have locally unique content on each node.</p> </item> <item> - <p><c>master_nodes</c>. This argument returns the - master nodes of a table. - </p> + <p><c>master_nodes</c>. Returns the master nodes of a + table.</p> </item> <item> - <p><c>memory</c>. This argument returns the number of - words allocated to the table on this node. - </p> + <p><c>memory</c>. Returns the number of + words allocated to the table on this node.</p> </item> <item> - <p><c>ram_copies</c>. This argument returns the nodes - where a ram_copy of the table resides according to the - schema. - </p> + <p><c>ram_copies</c>. Returns the nodes where a + <c>ram_copy</c> of the table resides according to the + schema.</p> </item> <item> - <p><c>record_name</c>. This argument returns the - record name, common for all records in the table - </p> + <p><c>record_name</c>. Returns the + record name, common for all records in the table.</p> </item> <item> - <p><c>size</c>. This argument returns the number of - records inserted in the table. - </p> + <p><c>size</c>. Returns the number of + records inserted in the table.</p> </item> <item> - <p><c>snmp</c>. This argument returns the SNMP struct. - <c>[]</c>meaning that the table currently has no SNMP - properties. - </p> + <p><c>snmp</c>. Returns the SNMP struct. <c>[]</c> means + that the table currently has no SNMP properties.</p> </item> <item> - <p><c>storage_type</c>.This argument returns the local + <p><c>storage_type</c>. Returns the local storage type of the table. It can be <c>disc_copies</c>, <c>ram_copies</c>, <c>disc_only_copies</c>, or the atom <c>unknown</c>. <c>unknown</c> is returned for all - tables which only reside remotely. - </p> + tables that only reside remotely.</p> </item> <item> - <p><c>subscribers</c>. This argument returns a list + <p><c>subscribers</c>. Returns a list of local processes currently subscribing to local table - events which involve this table on this node. - </p> + events that involve this table on this node.</p> </item> <item> - <p><c>type</c>. This argument returns the table type, - which is either <c>bag</c>, <c>set</c> or <c>ordered_set</c>.. - </p> + <p><c>type</c>. Returns the table type, which is + <c>bag</c>, <c>set</c>, or <c>ordered_set</c>.</p> </item> <item> - <p><c>user_properties</c>. This argument returns the - user associated table properties of the table. It is a - list of the stored property records. - </p> + <p><c>user_properties</c>. Returns the + user-associated table properties of the table. It is a + list of the stored property records.</p> </item> <item> - <p><c>version</c>. This argument returns the current + <p><c>version</c>. Returns the current version of the table definition. The table version is incremented when the table definition is changed. The - table definition may be incremented directly when the - table definition has been changed in a schema - transaction, or when a committed table definition is - merged with table definitions from other nodes during - start-up. - </p> + table definition can be incremented directly when it + has been changed in a schema transaction, or + when a committed table definition is merged with + table definitions from other nodes during startup.</p> </item> <item> - <p><c>where_to_read</c>.This argument returns the node - where the table can be read. If the value <c>nowhere</c> - is returned, the table is not loaded, or it resides at a - remote node which is not running. - </p> + <p><c>where_to_read</c>. Returns the node + where the table can be read. If value <c>nowhere</c> + is returned, either the table is not loaded or it + resides at a remote node that is not running.</p> </item> <item> - <p><c>where_to_write</c>. This argument returns a list - of the nodes that currently hold an active replica of - the table. - </p> + <p><c>where_to_write</c>. Returns a list of the nodes + that currently hold an active replica of the table.</p> </item> <item> - <p><c>wild_pattern</c>. This argument returns a - structure which can be given to the various match - functions for a certain table. A record tuple is where all - record fields have the value <c>'_'</c>. - </p> + <p><c>wild_pattern</c>. Returns a + structure that can be given to the various match + functions for a certain table. A record tuple is where + all record fields have value <c>'_'</c>.</p> </item> </list> </desc> </func> <func> <name>transaction(Fun [[, Args], Retries]) -> {aborted, Reason} | {atomic, ResultOfFun}</name> - <fsummary>Execute a transaction.</fsummary> + <fsummary>Executes a transaction.</fsummary> <desc> - <p>This function executes the functional object <c>Fun</c> - with arguments <c>Args</c> as a transaction. - </p> - <p>The code which executes inside the transaction + <marker id="transaction"></marker> + <p>Executes the functional object <c>Fun</c> + with arguments <c>Args</c> as a transaction.</p> + <p>The code that executes inside the transaction can consist of a series of table manipulation functions. - If something goes wrong inside the transaction as a result of a - user error or a certain table not being available, the - entire transaction is aborted and the function - <c>transaction/1</c> returns the tuple - <c>{aborted, Reason}</c>. - </p> - <p>If all is well, <c>{atomic, ResultOfFun}</c> is returned where - <c>ResultOfFun</c> is the value of the last expression in - <c>Fun</c>. - </p> - <p>A function which adds a family to the database can be - written as follows if we have a structure <c>{family, Father, Mother, ChildrenList}</c>: - </p> + If something goes wrong inside the transaction as a result + of a user error or a certain table not being available, the + entire transaction is terminated and the function + <c>transaction/1</c> returns the tuple + <c>{aborted, Reason}</c>.</p> + <p>If all is going well, <c>{atomic, ResultOfFun}</c> is + returned, where <c>ResultOfFun</c> is the value of the + last expression in <c>Fun</c>.</p> + <p>A function that adds a family to the database can be + written as follows if there is a structure + <c>{family, Father, Mother, ChildrenList}</c>:</p> <code type="none"> add_family({family, F, M, Children}) -> ChildOids = lists:map(fun oid/1, Children), @@ -2715,23 +2591,20 @@ add_family({family, F, M, Children}) -> end, mnesia:transaction(Trans). -oid(Rec) -> {element(1, Rec), element(2, Rec)}. - </code> - <p>This code adds a set of people to the database. Running this code - within one transaction will ensure that either the whole - family is added to the database, or the whole transaction - aborts. For example, if the last child is badly formatted, - or the executing process terminates due to an +oid(Rec) -> {element(1, Rec), element(2, Rec)}.</code> + <p>This code adds a set of people to the database. Running + this code within one transaction ensures that either the whole + family is added to the database, or the whole transaction + terminates. For example, if the last child is badly formatted, + or the executing process terminates because of an <c>'EXIT'</c> signal while executing the family code, the - transaction aborts. Accordingly, the situation where half a - family is added can never occur. - </p> + transaction terminates. Thus, the situation where half a + family is added can never occur.</p> <p>It is also useful to update the database within a transaction if several processes concurrently update the same records. - For example, the function <c>raise(Name, Amount)</c>, which - adds <c>Amount</c> to the salary field of a person, should - be implemented as follows: - </p> + For example, the function <c>raise(Name, Amount)</c>, which + adds <c>Amount</c> to the salary field of a person, is to + be implemented as follows:</p> <code type="none"> raise(Name, Amount) -> mnesia:transaction(fun() -> @@ -2743,71 +2616,68 @@ raise(Name, Amount) -> _ -> mnesia:abort("No such person") end - end). - </code> - <p>When this function executes within a transaction, + end).</code> + <p>When this function executes within a transaction, several processes running on different nodes can concurrently - execute the <c>raise/2</c> function without interfering - with each other. - </p> - <p>Since Mnesia detects deadlocks, a transaction can be - restarted any number of times. This function will attempt a restart as specified in - <c>Retries</c>. <c>Retries</c> must - be an integer greater than 0 or the atom <c>infinity</c>. Default is - <c>infinity</c>.</p> + execute the function <c>raise/2</c> without interfering + with each other.</p> + <p>Since <c>Mnesia</c> detects deadlocks, a transaction can be + restarted any number of times. This function attempts a + restart as specified in <c>Retries</c>. <c>Retries</c> must + be an integer greater than 0 or the atom <c>infinity</c>. + Default is <c>infinity</c>.</p> </desc> </func> <func> - <name>transform_table(Tab, Fun, NewAttributeList, NewRecordName) -> {aborted, R} | {atomic, ok} </name> - <fsummary>Change format on all records in table. <c>Tab</c></fsummary> + <name>transform_table(Tab, Fun, NewAttributeList, NewRecordName) -> {aborted, R} | {atomic, ok}</name> + <fsummary>Changes format on all records in table <c>Tab</c>.</fsummary> <desc> - <p>This function applies the argument <c>Fun</c> to all - records in the table. <c>Fun</c> is a function which takes a - record of the old type and returns a transformed record of the - new type. The <c>Fun</c> argument can also be the atom - <c>ignore</c>, it indicates that only the meta data about the table will - be updated. Usage of <c>ignore</c> is not recommended but included - as a possibility for the user to do his own transform. - <c>NewAttributeList</c> and <c>NewRecordName</c> - specifies the attributes and the new record type of converted - table. Table name will always remain unchanged, if the - record_name is changed only the mnesia functions which - uses table identifiers will work, e.g. <c>mnesia:write/3</c> - will work but <c>mnesia:write/1</c> will not.</p> + <marker id="transform_table_4"></marker> + <p>Applies argument <c>Fun</c> to all + records in the table. <c>Fun</c> is a function that takes a + record of the old type and returns a transformed record of + the new type. Argument <c>Fun</c> can also be the atom + <c>ignore</c>, which indicates that only the metadata + about the table is updated. Use of + <c>ignore</c> is not recommended, but included + as a possibility for the user do to an own transformation.</p> + <p><c>NewAttributeList</c> and <c>NewRecordName</c> + specify the attributes and the new record type of the + converted table. Table name always remains unchanged. If + <c>record_name</c> is changed, only the <c>Mnesia</c> + functions that use table identifiers work, for example, + <c>mnesia:write/3</c> works, but not <c>mnesia:write/1</c>.</p> </desc> </func> <func> - <name>transform_table(Tab, Fun, NewAttributeList) -> {aborted, R} | {atomic, ok} </name> - <fsummary>Change format on all records in table. <c>Tab</c></fsummary> + <name>transform_table(Tab, Fun, NewAttributeList) -> {aborted, R} | {atomic, ok}</name> + <fsummary>Changes format on all records in table <c>Tab</c>.</fsummary> <desc> - <p>Invokes <c>mnesia:transform_table(Tab, Fun, NewAttributeList, RecName)</c> - where <c>RecName</c> is <c>mnesia:table_info(Tab, record_name)</c>.</p> + <p>Calls <c>mnesia:transform_table(Tab, Fun, + NewAttributeList, RecName)</c>, where <c>RecName</c> is + <c>mnesia:table_info(Tab, record_name)</c>.</p> </desc> </func> <func> <name>traverse_backup(Source, [SourceMod,] Target, [TargetMod,] Fun, Acc) -> {ok, LastAcc} | {error, Reason}</name> <fsummary>Traversal of a backup.</fsummary> <desc> - <p>With this function it is possible to iterate over a backup, - either for the purpose of transforming it into a new backup, - or just reading it. The arguments are explained briefly - below. See the Mnesia User's Guide for additional - details. - </p> + <marker id="traverse_backup"></marker> + <p>Iterates over a backup, either to transform it into a + new backup, or read it. The arguments are explained briefly + here. For details, see the User's Guide.</p> <list type="bulleted"> <item><c>SourceMod</c> and <c>TargetMod</c> are the names of - the modules which actually access the backup - media. + the modules that actually access the backup media. </item> <item><c>Source</c> and <c>Target</c> are opaque data used - exclusively by the modules <c>SourceMod</c> and - <c>TargetMod</c> for the purpose of initializing the - backup media. + exclusively by modules <c>SourceMod</c> and <c>TargetMod</c> + to initialize the backup media. </item> <item><c>Acc</c> is an initial accumulator value. </item> <item><c>Fun(BackupItems, Acc)</c> is applied to each item in - the backup. The Fun must return a tuple + the backup. The <c>Fun</c> must return a tuple <c>{BackupItems,NewAcc}</c>, where <c>BackupItems</c> is a list of valid backup items, and <c>NewAcc</c> is a new accumulator value. The returned backup items are written @@ -2821,355 +2691,341 @@ raise(Name, Amount) -> </func> <func> <name>uninstall_fallback() -> ok | {error,Reason}</name> - <fsummary>Uninstall a fallback.</fsummary> + <fsummary>Uninstalls a fallback.</fsummary> <desc> - <p>Invokes <c>mnesia:uninstall_fallback([{scope, global}])</c>.</p> + <marker id="uninstall_fallback_0"></marker> + <p>Calls the function + <c>mnesia:uninstall_fallback([{scope, global}])</c>.</p> </desc> </func> <func> <name>uninstall_fallback(Args) -> ok | {error,Reason}</name> - <fsummary>Uninstall a fallback.</fsummary> + <fsummary>Uninstalls a fallback.</fsummary> <desc> - <p>This function is used to de-install a fallback before it + <p>Deinstalls a fallback before it has been used to restore the database. This is normally a distributed operation that is either performed on all - nodes with disc resident schema or none. Uninstallation of - fallbacks requires Erlang to be up and running on all - involved nodes, but it does not matter if Mnesia is running - or not. Which nodes that are considered as disc-resident - nodes is determined from the schema info in the local - fallback. - </p> - <p><c>Args</c> is a list of the following tuples: - </p> + nodes with disc resident schema, or none. Uninstallation of + fallbacks requires Erlang to be operational on all + involved nodes, but it does not matter if <c>Mnesia</c> is + running or not. Which nodes that are considered as + disc-resident nodes is determined from the schema + information in the local fallback.</p> + <p><c>Args</c> is a list of the following tuples:</p> <list type="bulleted"> - <item> - <p><c>{module, BackupMod}</c>. - See <c>mnesia:install_fallback/2</c> about the - semantics.</p> + <item><c>{module, BackupMod}</c>. For semantics, + see <c>mnesia:install_fallback/2</c>. </item> - <item> - <p><c>{scope, Scope}</c> - See <c>mnesia:install_fallback/2</c> about the - semantics.</p> + <item><c>{scope, Scope}</c>. For semantics, + see <c>mnesia:install_fallback/2</c>. </item> - <item> - <p><c>{mnesia_dir, AlternateDir}</c> - See <c>mnesia:install_fallback/2</c> about the - semantics.</p> + <item><c>{mnesia_dir, AlternateDir}</c>. For semantics, + see <c>mnesia:install_fallback/2</c>. </item> </list> </desc> </func> <func> - <name>unsubscribe(EventCategory) -> {ok, Node} | {error, Reason} </name> - <fsummary>Subscribe to events of type <c>EventCategory</c>.</fsummary> + <name>unsubscribe(EventCategory) -> {ok, Node} | {error, Reason}</name> + <fsummary>Subscribes to events of type <c>EventCategory</c>.</fsummary> <desc> + <marker id="unsubscribe"></marker> <p>Stops sending events of type <c>EventCategory</c> to the caller.</p> <p><c>Node</c> is the local node.</p> </desc> </func> <func> - <name>wait_for_tables(TabList,Timeout) -> ok | {timeout, BadTabList} | {error, Reason} </name> - <fsummary>Wait for tables to be accessible.</fsummary> + <name>wait_for_tables(TabList, Timeout) -> ok | {timeout, BadTabList} | {error, Reason}</name> + <fsummary>Waits for tables to be accessible.</fsummary> <desc> - <p>Some applications need to wait for certain tables to - be accessible in order to do useful work. - <c>mnesia:wait_for_tables/2</c> hangs until all tables in the - <c>TabList</c> are accessible, or until <c>timeout</c> is - reached.</p> + <marker id="wait_for_tables"></marker> + <p>Some applications need to wait for certain tables to be + accessible to do useful work. <c>mnesia:wait_for_tables/2</c> + either hangs until all tables in <c>TabList</c> are accessible, + or until <c>timeout</c> is reached.</p> </desc> </func> <func> - <name>wread({Tab, Key}) -> transaction abort | RecordList </name> - <fsummary>Read records with given key.</fsummary> + <name>wread({Tab, Key}) -> transaction abort | RecordList</name> + <fsummary>Reads records with given key.</fsummary> <desc> - <p>Invoke <c>mnesia:read(Tab, Key, write)</c>.</p> + <marker id="wread"></marker> + <p>Calls the function <c>mnesia:read(Tab, Key, write)</c>.</p> </desc> </func> <func> - <name>write(Record) -> transaction abort | ok </name> + <name>write(Record) -> transaction abort | ok</name> <fsummary>Writes a record into the database.</fsummary> <desc> - <p>Invoke <c>mnesia:write(Tab, Record, write)</c> where - <c>Tab</c> is <c>element(1, Record)</c>.</p> + <marker id="write_1"></marker> + <p>Calls the function <c>mnesia:write(Tab, Record, write)</c>, + where <c>Tab</c> is <c>element(1, Record)</c>.</p> </desc> </func> <func> - <name>write(Tab, Record, LockKind) -> transaction abort | ok </name> - <fsummary>Write a record into the database.</fsummary> + <name>write(Tab, Record, LockKind) -> transaction abort | ok</name> + <fsummary>Writes a record into the database.</fsummary> <desc> - <p>Writes the record <c>Record</c> to the table <c>Tab</c>. - </p> - <p>The function returns <c>ok</c>, or aborts if an error - occurs. For example, the transaction aborts if no - <c>person</c> table exists. - </p> - <p>The semantics of this function is context sensitive. See - <c>mnesia:activity/4</c> for more information. In transaction - context it acquires a lock of type <c>LockKind</c>. The - following lock types are supported: <c>write</c> and - <c>sticky_write</c>.</p> + <marker id="write_3"></marker> + <p>Writes record <c>Record</c> to table <c>Tab</c>.</p> + <p>The function returns <c>ok</c>, or terminates if an error + occurs. For example, the transaction terminates if no + <c>person</c> table exists.</p> + <p>The semantics of this function is context-sensitive. For + details, see <c>mnesia:activity/4</c>. In + transaction-context, it acquires a lock of type + <c>LockKind</c>. The lock types <c>write</c> and + <c>sticky_write</c> are supported.</p> </desc> </func> <func> <name>write_lock_table(Tab) -> ok | transaction abort</name> - <fsummary>Set write lock on an entire table.</fsummary> + <fsummary>Sets write lock on an entire table.</fsummary> <desc> - <p>Invokes <c>mnesia:lock({table, Tab}, write)</c>.</p> + <marker id="write_lock_table"></marker> + <p>Calls the function + <c>mnesia:lock({table, Tab}, write)</c>.</p> </desc> </func> </funcs> <section> <title>Configuration Parameters</title> - <p>Mnesia reads the following application configuration + <marker id="configuration_parameters"></marker> + <p><c>Mnesia</c> reads the following application configuration parameters:</p> <list type="bulleted"> <item> - <p><c>-mnesia access_module Module</c>. The - name of the Mnesia activity access callback module. The default is - <c>mnesia</c>. - </p> + <p><c>-mnesia access_module Module</c>. The name of the + <c>Mnesia</c> activity access callback module. Default is + <c>mnesia</c>.</p> </item> <item> - <p><c>-mnesia auto_repair true | false</c>. This flag controls - whether Mnesia will try to automatically repair - files that have not been properly closed. The default is - <c>true</c>. - </p> + <p><c>-mnesia auto_repair true | false</c>. This flag + controls if <c>Mnesia</c> automatically tries to repair + files that have not been properly closed. Default is + <c>true</c>.</p> </item> <item> - <p><c>-mnesia backup_module Module</c>. The - name of the Mnesia backup callback module. The default is - <c>mnesia_backup</c>. - </p> + <p><c>-mnesia backup_module Module</c>. The name of the + <c>Mnesia</c> backup callback module. Default is + <c>mnesia_backup</c>.</p> </item> <item> - <p><c>-mnesia debug Level</c> - Controls the debug level of Mnesia. - Possible values are:</p> + <p><c>-mnesia debug Level</c>. Controls the debug level + of <c>Mnesia</c>. The possible values are as follows:</p> <taglist> <tag><c>none</c></tag> <item> - <p>No trace outputs at all. This is the default setting. - </p> + <p>No trace outputs. This is the default.</p> </item> <tag><c>verbose</c></tag> <item> <p>Activates tracing of important debug events. These - debug events generate <c>{mnesia_info, Format, Args}</c> - system events. Processes may subscribe to these events with - <c>mnesia:subscribe/1</c>. The events are always sent to Mnesia's - event handler. - </p> + events generate <c>{mnesia_info, Format, Args}</c> + system events. Processes can subscribe to these events with + <c>mnesia:subscribe/1</c>. The events are always sent to + the <c>Mnesia</c> event handler.</p> </item> <tag><c>debug</c></tag> <item> <p>Activates all events at the verbose level plus full trace of all debug events. These debug events generate - <c>{mnesia_info, Format, Args}</c> system events. Processes may - subscribe to these events with <c>mnesia:subscribe/1</c>. The - events are always sent to the Mnesia event handler. On this - debug level, the Mnesia event handler starts subscribing to - updates in the schema table. - </p> + <c>{mnesia_info, Format, Args}</c> system events. + Processes can subscribe to these events with + <c>mnesia:subscribe/1</c>. The events are always sent to + the <c>Mnesia</c> event handler. On this debug level, + the <c>Mnesia</c> event handler starts subscribing to + updates in the schema table.</p> </item> <tag><c>trace</c></tag> <item> - <p>Activates all events at the level debug. On this - debug level, the Mnesia event handler starts subscribing to - updates on all Mnesia tables. This level is only intended - for debugging small toy systems since many large - events may be generated. - </p> + <p>Activates all events at the debug level. On this + level, the <c>Mnesia</c> event handler starts subscribing + to updates on all <c>Mnesia</c> tables. This level is + intended only for debugging small toy systems, as many + large events can be generated.</p> </item> <tag><c>false</c></tag> - <item> - <p>An alias for none. - </p> + <item>An alias for none. </item> <tag><c>true</c></tag> - <item> - <p>An alias for debug. - </p> + <item>An alias for debug. </item> </taglist> </item> <item> <p><c>-mnesia core_dir Directory</c>. The name of the - directory where Mnesia core files is stored or - false. Setting it implies that also ram only nodes, will - generate a core file if a crash occurs. </p> + directory where <c>Mnesia</c> core files is stored, or + false. Setting it implies that also RAM-only nodes + generate a core file if a crash occurs.</p> </item> <item> - <p><c>-mnesia dc_dump_limit Number</c>. - Controls how often <c>disc_copies</c> tables are dumped from memory. + <p><c>-mnesia dc_dump_limit Number</c>. Controls how often + <c>disc_copies</c> tables are dumped from memory. Tables are dumped when <c>filesize(Log) > (filesize(Tab)/Dc_dump_limit)</c>. - Lower values reduces cpu overhead but increases disk space and - startup times. The default is 4.</p> + Lower values reduce CPU overhead but increase disk space + and startup times. Default is 4.</p> </item> <item> <p><c>-mnesia dir Directory</c>. The name of the directory - where all Mnesia data is stored. The name of the directory must - be unique for the current node. Two nodes may, under no - circumstances, share the same Mnesia directory. The results are - totally unpredictable.</p> + where all <c>Mnesia</c> data is stored. The directory name + must be unique for the current node. Two nodes must never + share the the same <c>Mnesia</c> directory. The results + are unpredictable.</p> + </item> + <item> + <p><c>-mnesia dump_disc_copies_at_startup true | false</c>. + If set to false, this disables the dumping of <c>disc_copies</c> + tables during startup while tables are being loaded. The default + is true.</p> </item> <item> <p><c>-mnesia dump_log_load_regulation true | false</c>. - Controls if the log dumps should be performed as fast as - possible or if the dumper should do its own load - regulation. This feature is temporary and will disappear in a - future release. The default is <c>false</c>. - </p> + Controls if log dumps are to be performed as fast as + possible, or if the dumper is to do its own load + regulation. Default is <c>false</c>.</p> + <p>This feature is temporary and will be removed in a + future release</p> </item> <item> <p><c>-mnesia dump_log_update_in_place true | false</c>. - Controls if log dumps are performed on a copy of - the original data file, or if the log dump is - performed on the original data file. The default is <c>true</c></p> + Controls if log dumps are performed on a copy of the + original data file, or if the log dump is performed + on the original data file. Default is <c>true</c></p> </item> <item> - <marker id=" dump_log_write_threshold"></marker> - <p><c>-mnesia dump_log_write_threshold Max</c>, where - <c>Max</c> is an integer which specifies the maximum number of writes - allowed to the transaction log before a new dump of the log - is performed. It defaults to 100 log writes. - </p> + <marker id=" dump_log_write_threshold"></marker> + <p><c>-mnesia dump_log_write_threshold Max</c>. + <c>Max</c> is an integer that specifies the maximum + number of writes allowed to the transaction log before + a new dump of the log is performed. Default is <c>100</c> + log writes.</p> </item> <item> - <marker id=" dump_log_time_threshold"></marker> - <p><c>-mnesia dump_log_time_threshold Max</c>, - where <c>Max</c> is an integer which - specifies the dump log interval in milliseconds. It defaults - to 3 minutes. If a dump has not been performed within - <c>dump_log_time_threshold</c> milliseconds, then a new dump is - performed regardless of how many writes have been - performed. - </p> + <marker id=" dump_log_time_threshold"></marker> + <p><c>-mnesia dump_log_time_threshold Max</c>. + <c>Max</c> is an integer that specifies the dump log + interval in milliseconds. Default is 3 minutes. If a + dump has not been performed within + <c>dump_log_time_threshold</c> milliseconds, a new dump + is performed regardless of the number of writes + performed.</p> </item> <item> - <p><c>-mnesia event_module Module</c>. The - name of the Mnesia event handler callback module. The default is - <c>mnesia_event</c>. - </p> + <p><c>-mnesia event_module Module</c>. The name of the + <c>Mnesia</c> event handler callback module. Default is + <c>mnesia_event</c>.</p> </item> <item> <p><c>-mnesia extra_db_nodes Nodes</c> specifies a list of - nodes, in addition to the ones found in the schema, with which - Mnesia should also establish contact. The default value - is the empty list <c>[]</c>. - </p> + nodes, in addition to the ones found in the schema, with + which <c>Mnesia</c> is also to establish contact. Default + is <c>[]</c> (empty list).</p> </item> <item> - <p><c>-mnesia fallback_error_function {UserModule, UserFunc}</c> - specifies a user supplied callback function - which will be called if a fallback is installed and mnesia - goes down on another node. Mnesia will call the function - with one argument the name of the dying node, e.g. - <c>UserModule:UserFunc(DyingNode)</c>. - Mnesia should be restarted or else - the database could be inconsistent. - The default behaviour is to terminate mnesia. - </p> + <p><c>-mnesia fallback_error_function {UserModule, UserFunc}</c>. + Specifies a user-supplied callback function, which is + called if a fallback is installed and <c>Mnesia</c> goes + down on another node. <c>Mnesia</c> calls the function + with one argument, the name of the dying node, for example, + <c>UserModule:UserFunc(DyingNode)</c>. <c>Mnesia</c> must + be restarted, otherwise the database can be inconsistent. + The default behavior is to terminate <c>Mnesia</c>.</p> </item> <item> <p><c>-mnesia max_wait_for_decision Timeout</c>. Specifies - how long Mnesia will wait for other nodes to share their - knowledge regarding the outcome of an unclear transaction. By - default the <c>Timeout</c> is set to the atom - <c>infinity</c>, which implies that if Mnesia upon startup - encounters a "heavyweight transaction" whose outcome is - unclear, the local Mnesia will wait until Mnesia is started - on some (in worst cases all) of the other nodes that were - involved in the interrupted transaction. This is a very rare - situation, but when/if it happens, Mnesia does not guess if - the transaction on the other nodes was committed or aborted. - Mnesia will wait until it knows the outcome and then act - accordingly. - </p> + how long <c>Mnesia</c> waits for other nodes to share their + knowledge about the outcome of an unclear transaction. By + default, <c>Timeout</c> is set to the atom <c>infinity</c>. + This implies that if <c>Mnesia</c> upon startup detects + a "heavyweight transaction" whose outcome is unclear, the + local <c>Mnesia</c> waits until <c>Mnesia</c> is started + on some (in the worst case all) of the other nodes that were + involved in the interrupted transaction. This is a rare + situation, but if it occurs, <c>Mnesia</c> does not guess if + the transaction on the other nodes was committed or + terminated. <c>Mnesia</c> waits until it knows the outcome + and then acts accordingly.</p> <p>If <c>Timeout</c> is set to an integer value in - milliseconds, Mnesia will force "heavyweight transactions" + milliseconds, <c>Mnesia</c> forces "heavyweight transactions" to be finished, even if the outcome of the transaction for the moment is unclear. After <c>Timeout</c> milliseconds, - Mnesia will commit/abort the transaction and continue with - the startup. This may lead to a situation where the - transaction is committed on some nodes and aborted on other - nodes. If the transaction was a schema transaction, the - inconsistency may be fatal. - </p> + <c>Mnesia</c> commits or terminates the transaction and + continues with the startup. This can lead to a situation + where the transaction is committed on some nodes and + terminated on other nodes. If the transaction is a + schema transaction, the inconsistency can be fatal.</p> </item> <item> - <p><c>-mnesia no_table_loaders NUMBER</c> specifies the number of - parallel table loaders during start. More loaders can be good if the - network latency is high or if many tables contains few records. - The default value is <c>2</c>. - </p> + <p><c>-mnesia no_table_loaders NUMBER</c>. Specifies the number + of parallel table loaders during start. More loaders can be + good if the network latency is high or if many tables + contain few records. Default is <c>2</c>.</p> </item> <item> - <p><c>-mnesia send_compressed Level</c> specifies the level of - compression to be used when copying a table from the local node to - another one. The default level is 0. - </p> - <p><c>Level</c> must be an integer in the interval [0, 9], with 0 - representing no compression and 9 representing maximum compression. - Before setting it to a non-zero value, make sure the remote nodes - understand this configuration. - </p> + <p><c>-mnesia send_compressed Level</c>. Specifies the level of + compression to be used when copying a table from the local + node to another one. Default is <c>0</c>.</p> + <p><c>Level</c> must be an integer in the interval + <c>[0, 9]</c>, where <c>0</c> means no compression and + <c>9</c> means maximum compression. Before setting it to a + non-zero value, ensure that the remote nodes + understand this configuration.</p> </item> <item> - <p><c>-mnesia schema_location Loc</c> controls where - Mnesia will look for its schema. The parameter - <c>Loc</c> may be one of the following atoms: </p> + <p><c>-mnesia schema_location Loc</c>. Controls where + <c>Mnesia</c> looks for its schema. Parameter + <c>Loc</c> can be one of the following atoms:</p> <taglist> <tag><c>disc</c></tag> <item> <p>Mandatory disc. The schema is assumed to be located - in the Mnesia directory. If the schema cannot be found, - Mnesia refuses to start. This is the old behavior. - </p> + in the <c>Mnesia</c> directory. If the schema cannot + be found, <c>Mnesia</c> refuses to start. This is the + old behavior.</p> </item> <tag><c>ram</c></tag> <item> <p>Mandatory RAM. The schema resides in RAM - only. At start-up, a tiny new schema is generated. This - default schema just contains the definition of the schema - table and only resides on the local node. Since no other - nodes are found in the default schema, the configuration - parameter <c>extra_db_nodes</c> must be used in - order to let the - node share its table definitions with other nodes. (The - <c>extra_db_nodes</c> parameter may also be used on disc based nodes.) - </p> + only. At startup, a tiny new schema is generated. This + default schema only contains the definition of the schema + table and only resides on the local node. Since no other + nodes are found in the default schema, configuration + parameter <c>extra_db_nodes</c> must be used to let the + node share its table definitions with other nodes.</p> + <p>Parameter <c>extra_db_nodes</c> can also be + used on disc based nodes.</p> </item> <tag><c>opt_disc</c></tag> <item> - <p>Optional disc. The schema may reside either on disc - or in RAM. If the schema is found on disc, Mnesia starts as a - disc based node and the storage type of the schema table is - <c>disc_copies</c>. If no schema is found on disc, Mnesia starts - as a disc-less node and the storage type of the schema table is - <c>ram_copies</c>. The default value for the application parameter - is <c>opt_disc</c>. - </p> + <p>Optional disc. The schema can reside on disc or in + RAM. If the schema is found on disc, <c>Mnesia</c> + starts as a disc-based node and the storage type of + the schema table is <c>disc_copies</c>. If no schema is + found on disc, <c>Mnesia</c> starts as a disc-less node + and the storage type of the schema table is + <c>ram_copies</c>. Default value for the application + parameter is <c>opt_disc</c>.</p> </item> </taglist> </item> </list> - <p>First the SASL application parameters are checked, then - the command line flags are checked, and finally, the default - value is chosen. - </p> + <p>First, the <c>SASL</c> application parameters are checked, + then the command-line flags are checked, and finally, the + default value is chosen.</p> </section> <section> <title>See Also</title> - <p>mnesia_registry(3), mnesia_session(3), qlc(3), - dets(3), ets(3), disk_log(3), application(3) - </p> + <p><seealso marker="kernel:application">application(3)</seealso>, + <seealso marker="stdlib:dets">dets(3)</seealso>, + <seealso marker="kernel:disk_log">disk_log(3)</seealso>, + <seealso marker="stdlib:ets">ets(3)</seealso>, + <seealso marker="mnesia:mnesia_registry">mnesia_registry(3)</seealso>, + <seealso marker="stdlib:qlc">qlc(3)</seealso></p> </section> </erlref> |