diff options
Diffstat (limited to 'lib/stdlib/doc/src/ets.xml')
| -rw-r--r-- | lib/stdlib/doc/src/ets.xml | 186 |
1 files changed, 157 insertions, 29 deletions
diff --git a/lib/stdlib/doc/src/ets.xml b/lib/stdlib/doc/src/ets.xml index 7b9f0e7772..746f94d3f4 100644 --- a/lib/stdlib/doc/src/ets.xml +++ b/lib/stdlib/doc/src/ets.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>1996</year><year>2009</year> + <year>1996</year><year>2010</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -13,12 +13,12 @@ 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/. - + 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. - + </legalnotice> <title>ets</title> @@ -56,8 +56,8 @@ Even if there are no references to a table from any process, it will not automatically be destroyed unless the owner process terminates. It can be destroyed explicitly by using - <c>delete/1</c>.</p> - <p>Since R13B01, table ownership can be transferred at process termination + <c>delete/1</c>. The default owner is the process that created the + table. Table ownership can be transferred at process termination by using the <seealso marker="#heir">heir</seealso> option or explicitly by calling <seealso marker="#give_away/3">give_away/3</seealso>.</p> <p>Some implementation details:</p> @@ -82,11 +82,15 @@ <c>float()</c> that extends to the same value, hence the key <c>1</c> and the key <c>1.0</c> are regarded as equal in an <c>ordered_set</c> table.</p> - <p>In general, the functions below will exit with reason - <c>badarg</c> if any argument is of the wrong format, or if the - table identifier is invalid.</p> </description> - + <section> + <title>Failure</title> + <p>In general, the functions below will exit with reason + <c>badarg</c> if any argument is of the wrong format, if the + table identifier is invalid or if the operation is denied due to + table access rights (<seealso marker="#protected">protected</seealso> + or <seealso marker="#private">private</seealso>).</p> + </section> <section><marker id="concurrency"></marker> <title>Concurrency</title> <p>This module provides some limited support for concurrent access. @@ -481,6 +485,9 @@ Error: fun containing local Erlang function calls <item><c>Item=protection, Value=public|protected|private</c> <br></br> The table access rights.</item> + <item><c>Item=compressed, Value=true|false</c> <br></br> + + Indicates if the table is compressed or not.</item> </list> </desc> </func> @@ -947,9 +954,10 @@ ets:select(Table,MatchSpec),</code> <type> <v>Name = atom()</v> <v>Options = [Option]</v> - <v> Option = Type | Access | named_table | {keypos,Pos} | {heir,pid(),HeirData} | {heir,none} | {write_concurrency,bool()}</v> + <v> Option = Type | Access | named_table | {keypos,Pos} | {heir,pid(),HeirData} | {heir,none} | Tweaks</v> <v> Type = set | ordered_set | bag | duplicate_bag</v> <v> Access = public | protected | private</v> + <v> Tweaks = {write_concurrency,bool()} | {read_concurrency,bool()} | compressed</v> <v> Pos = int()</v> <v> HeirData = term()</v> </type> @@ -963,7 +971,7 @@ ets:select(Table,MatchSpec),</code> table is named or not. If one or more options are left out, the default values are used. This means that not specifying any options (<c>[]</c>) is the same as specifying - <c>[set,protected,{keypos,1},{heir,none},{write_concurrency,false}]</c>.</p> + <c>[set,protected,{keypos,1},{heir,none},{write_concurrency,false},{read_concurrency,false}]</c>.</p> <list type="bulleted"> <item> <p><c>set</c> @@ -1002,12 +1010,14 @@ ets:select(Table,MatchSpec),</code> Any process may read or write to the table.</p> </item> <item> + <marker id="protected"></marker> <p><c>protected</c> The owner process can read and write to the table. Other processes can only read the table. This is the default setting for the access rights.</p> </item> <item> + <marker id="private"></marker> <p><c>private</c> Only the owner process can read or write to the table.</p> </item> @@ -1039,15 +1049,22 @@ ets:select(Table,MatchSpec),</code> the owner terminates.</p> </item> <item> + <marker id="new_2_write_concurrency"></marker> <p><c>{write_concurrency,bool()}</c> - Performance tuning. Default is <c>false</c>, which means that the table - is optimized towards concurrent read access. An operation that + Performance tuning. Default is <c>false</c>, in which case an operation that mutates (writes to) the table will obtain exclusive access, blocking any concurrent access of the same table until finished. If set to <c>true</c>, the table is optimized towards concurrent write access. Different objects of the same table can be mutated (and read) by concurrent processes. This is achieved to some degree - at the expense of single access and concurrent reader performance. + at the expense of sequential access and concurrent reader performance. + The <c>write_concurrency</c> option can be combined with the + <seealso marker="#new_2_read_concurrency">read_concurrency</seealso> + option. You typically want to combine these when large concurrent + read bursts and large concurrent write bursts are common (see the + documentation of the + <seealso marker="#new_2_read_concurrency">read_concurrency</seealso> + option for more information). Note that this option does not change any guarantees about <seealso marker="#concurrency">atomicy and isolation</seealso>. Functions that makes such promises over several objects (like @@ -1055,6 +1072,38 @@ ets:select(Table,MatchSpec),</code> <p>Table type <c>ordered_set</c> is not affected by this option in current implementation.</p> </item> + <item> + <marker id="new_2_read_concurrency"></marker> + <p><c>{read_concurrency,bool()}</c> + Performance tuning. Default is <c>false</c>. When set to + <c>true</c>, the table is optimized for concurrent read + operations. When this option is enabled on a runtime system with + SMP support, read operations become much cheaper; especially on + systems with multiple physical processors. However, switching + between read and write operations becomes more expensive. You + typically want to enable this option when concurrent read + operations are much more frequent than write operations, or when + concurrent reads and writes comes in large read and write + bursts (i.e., lots of reads not interrupted by writes, and lots + of writes not interrupted by reads). You typically do + <em>not</em> want to enable this option when the common access + pattern is a few read operations interleaved with a few write + operations repeatedly. In this case you will get a performance + degradation by enabling this option. The <c>read_concurrency</c> + option can be combined with the + <seealso marker="#new_2_write_concurrency">write_concurrency</seealso> + option. You typically want to combine these when large concurrent + read bursts and large concurrent write bursts are common.</p> + </item> + <item> + <marker id="new_2_compressed"></marker> + <p><c>compressed</c> + If this option is present, the table data will be stored in a more compact format to + consume less memory. The downside is that it will make table operations slower. + Especially operations that need to inspect entire objects, + such as <c>match</c> and <c>select</c>, will get much slower. The key element + is not compressed in current implementation.</p> + </item> </list> </desc> </func> @@ -1355,6 +1404,28 @@ is_integer(X), is_integer(Y), X + Y < 4711]]></code> </desc> </func> <func> + <name>select_count(Tab, MatchSpec) -> NumMatched</name> + <fsummary>Match the objects in an ETS table against a match_spec and returns the number of objects for which the match_spec returned 'true'</fsummary> + <type> + <v>Tab = tid() | atom()</v> + <v>Object = tuple()</v> + <v>MatchSpec = match_spec()</v> + <v>NumMatched = integer()</v> + </type> + <desc> + <p>Matches the objects in the table <c>Tab</c> using a + <seealso marker="#match_spec">match_spec</seealso>. If the + match_spec returns <c>true</c> for an object, that object + considered a match and is counted. For any other result from + the match_spec the object is not considered a match and is + therefore not counted.</p> + <p>The function could be described as a <c>match_delete/2</c> + that does not actually delete any elements, but only counts + them.</p> + <p>The function returns the number of objects matched.</p> + </desc> + </func> + <func> <name>select_delete(Tab, MatchSpec) -> NumDeleted</name> <fsummary>Match the objects in an ETS table against a match_spec and deletes objects where the match_spec returns 'true'</fsummary> <type> @@ -1381,25 +1452,82 @@ is_integer(X), is_integer(Y), X + Y < 4711]]></code> </desc> </func> <func> - <name>select_count(Tab, MatchSpec) -> NumMatched</name> - <fsummary>Match the objects in an ETS table against a match_spec and returns the number of objects for which the match_spec returned 'true'</fsummary> + <name>select_reverse(Tab, MatchSpec) -> [Match]</name> + <fsummary>Match the objects in an ETS table against a match_spec.</fsummary> <type> <v>Tab = tid() | atom()</v> - <v>Object = tuple()</v> + <v>Match = term()</v> <v>MatchSpec = match_spec()</v> - <v>NumMatched = integer()</v> </type> <desc> - <p>Matches the objects in the table <c>Tab</c> using a - <seealso marker="#match_spec">match_spec</seealso>. If the - match_spec returns <c>true</c> for an object, that object - considered a match and is counted. For any other result from - the match_spec the object is not considered a match and is - therefore not counted.</p> - <p>The function could be described as a <c>match_delete/2</c> - that does not actually delete any elements, but only counts - them.</p> - <p>The function returns the number of objects matched.</p> + + <p>Works like <c>select/2</c>, but returns the list in reverse + order for the <c>ordered_set</c> table type. For all other table + types, the return value is identical to that of <c>select/2</c>.</p> + + </desc> + </func> + <func> + <name>select_reverse(Tab, MatchSpec, Limit) -> {[Match],Continuation} | '$end_of_table'</name> + <fsummary>Match the objects in an ETS table against a match_spec and returns part of the answers.</fsummary> + <type> + <v>Tab = tid() | atom()</v> + <v>Match = term()</v> + <v>MatchSpec = match_spec()</v> + <v>Continuation = term()</v> + </type> + <desc> + + <p>Works like <c>select/3</c>, but for the <c>ordered_set</c> + table type, traversing is done starting at the last object in + Erlang term order and moves towards the first. For all other + table types, the return value is identical to that of + <c>select/3</c>.</p> + + <p>Note that this is <em>not</em> equivalent to + reversing the result list of a <c>select/3</c> call, as the result list + is not only reversed, but also contains the last <c>Limit</c> + matching objects in the table, not the first.</p> + + </desc> + </func> + <func> + <name>select_reverse(Continuation) -> {[Match],Continuation} | '$end_of_table'</name> + <fsummary>Continue matching objects in an ETS table.</fsummary> + <type> + <v>Match = term()</v> + <v>Continuation = term()</v> + </type> + <desc> + + <p>Continues a match started with + <c>ets:select_reverse/3</c>. If the table is an + <c>ordered_set</c>, the traversal of the table will continue + towards objects with keys earlier in the Erlang term order. The + returned list will also contain objects with keys in reverse + order.</p> + + <p>For all other table types, the behaviour is exatly that of <c>select/1</c>.</p> + <p>Example:</p> + <code> +1> T = ets:new(x,[ordered_set]). +2> [ ets:insert(T,{N}) || N <- lists:seq(1,10) ]. +... +3> {R0,C0} = ets:select_reverse(T,[{'_',[],['$_']}],4). +... +4> R0. +[{10},{9},{8},{7}] +5> {R1,C1} = ets:select_reverse(C0). +... +6> R1. +[{6},{5},{4},{3}] +7> {R2,C2} = ets:select_reverse(C1). +... +8> R2. +[{2},{1}] +9> '$end_of_table' = ets:select_reverse(C2). +... + </code> </desc> </func> <func> @@ -1686,7 +1814,7 @@ true</pre> </desc> </func> <func> - <name>to_dets(Tab, DetsTab) -> Tab</name> + <name>to_dets(Tab, DetsTab) -> DetsTab</name> <fsummary>Fill a Dets table with objects from an ETS table.</fsummary> <type> <v>Tab = tid() | atom()</v> |