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diff --git a/lib/mnesia/doc/src/Mnesia_chap1.xml b/lib/mnesia/doc/src/Mnesia_chap1.xml new file mode 100644 index 0000000000..9af81c85cb --- /dev/null +++ b/lib/mnesia/doc/src/Mnesia_chap1.xml @@ -0,0 +1,265 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE chapter SYSTEM "chapter.dtd"> + +<chapter> + <header> + <copyright> + <year>1997</year><year>2009</year> + <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/. + + 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>Introduction</title> + <prepared>Claes Wikström, Hans Nilsson and Håkan Mattsson</prepared> + <responsible>Bjarne Däcker</responsible> + <docno></docno> + <approved>Bjarne Däcker</approved> + <checked>Bjarne Däcker</checked> + <date></date> + <rev>C</rev> + <file>Mnesia_chap1.xml</file> + </header> + <p>This book describes the Mnesia DataBase Management + System (DBMS). <em>Mnesia</em> is a distributed Database Management + System, appropriate for telecommunications applications and other + Erlang applications which require continuous operation and soft + real-time properties. It is one section of the Open Telecom Platform + (OTP), which is a control system platform for building + telecommunications applications.</p> + + <section> + <title>About Mnesia</title> + <p>The management of data in telecommunications system has many + aspects whereof some, but not all, are addressed by traditional + commercial DBMSs (Data Base Management Systems). In particular the + very high level of fault tolerance which is required in many nonstop + systems, combined with requirements on the DBMS to run in the same + address space as the application, have led us to implement a brand new + DBMS. called Mnesia. Mnesia is implemented in, and very tightly + connected to, the programming language Erlang and it provides the + functionality that is necessary for the implementation of fault + tolerant telecommunications systems. Mnesia is a multiuser Distributed + DBMS specially made for industrial telecommunications applications + written in the symbolic programming language Erlang, which is also + the intended target language. Mnesia tries to address all of the data + management issues required for typical telecommunications systems and + it has a number of features that are not normally found in traditional + databases. <br></br> + + In telecommunications applications there are different needs + from the features provided by traditional DBMSs. The applications now + implemented in the Erlang language need a mixture of a broad range + of features, which generally are not satisfied by traditional DBMSs. + Mnesia is designed with requirements like the following in mind:</p> + <list type="ordered"> + <item>Fast real-time key/value lookup</item> + <item>Complicated non real-time queries mainly for + operation and maintenance</item> + <item>Distributed data due to distributed + applications</item> + <item>High fault tolerance</item> + <item>Dynamic re-configuration</item> + <item>Complex objects</item> + </list> + <p>What + sets Mnesia apart from most other DBMSs is that it is designed with + the typical data management problems of telecommunications applications + in mind. Hence Mnesia combines many concepts found in traditional + databases, such as transactions and queries with concepts found in data + management systems for telecommunications applications, such as very + fast real-time operations, configurable degree of fault tolerance (by + means of replication) and the ability to reconfigure the system without + stopping or suspending it. Mnesia is also interesting due to its tight + coupling to the programming language Erlang, thus almost turning Erlang + into a database programming language. This has many benefits, the + foremost is that + the impedance mismatch between data format used by the + DBMS and data format used by the programming language, which is used + to manipulate the data, completely disappears. <br></br> +</p> + </section> + + <section> + <title>The Mnesia DataBase Management System (DBMS)</title> + <p></p> + + <section> + <title>Features</title> + <p>Mnesia contains the following features which combine to produce a fault-tolerant, + distributed database management system written in Erlang: + </p> + <list type="bulleted"> + <item>Database schema can be dynamically reconfigured at runtime. + </item> + <item>Tables can be declared to have properties such as location, + replication, and persistence. + </item> + <item>Tables can be moved or replicated to several nodes to improve + fault tolerance. The rest of the system can still access the tables + to read, write, and delete records. + </item> + <item>Table locations are transparent to the programmer. + Programs address table names and the system itself keeps track of + table locations. + </item> + <item>Database transactions can be distributed, and a large number of + functions can be called within one transaction. + </item> + <item>Several transactions can run concurrently, and their execution is + fully synchronized by the database management system. + Mnesia ensures that no two processes manipulate data simultaneously. + </item> + <item>Transactions can be assigned the property of being executed on + all nodes in the system, or on none. Transactions can also be bypassed + in favor of running so called "dirty operations", which reduce + overheads and run very fast. + </item> + </list> + <p>Details of these features are described in the following sections.</p> + </section> + <p></p> + + <section> + <title>Add-on Applications</title> + <p>QLC and Mnesia Session can be used in conjunction with Mnesia to produce + specialized functions which enhance the operational ability of Mnesia. + Both Mnesia Session and QLC have their own documentation as part + of the OTP documentation set. Below are the main features of Mnesia Session + and QLC when used in conjunction with Mnesia:</p> + <list type="bulleted"> + <item><em>QLC</em> has the ability to optimize the query + compiler for the Mnesia Database Management System, essentially making + the DBMS more efficient.</item> + <item><em>QLC</em>, can be used as a database programming + language for Mnesia. It includes a notation called "list + comprehensions" and can be used to make complex database + queries over a set of tables.</item> + <item><em>Mnesia Session</em> is an interface for the Mnesia Database + Management System</item> + <item><em>Mnesia Session</em> enables access to the + Mnesia DBMS from foreign programming languages (i.e. other + languages than Erlang).</item> + </list> + <p></p> + + <section> + <title>When to Use Mnesia</title> + <p>Use Mnesia with the following types of applications: + </p> + <list type="bulleted"> + <item>Applications that need to replicate data. + </item> + <item>Applications that perform complicated searches on data. + </item> + <item>Applications that need to use atomic transactions to + update several records simultaneously. + </item> + <item>Applications that use soft real-time characteristics. + </item> + </list> + <p>On the other hand, Mnesia may not be appropriate with the + following types of applications: + </p> + <list type="bulleted"> + <item>Programs that process plain text or binary data files + </item> + <item>Applications that merely need a look-up dictionary + which can be stored to disc can utilize the standard + library module <c>dets</c>, which is a disc based version + of the module <c>ets</c>. + </item> + <item>Applications which need disc logging facilities can + utilize the module <c>disc_log</c> by preference. + </item> + <item>Not suitable for hard real time systems. + </item> + </list> + </section> + </section> + + <section> + <title>Scope and Purpose</title> + <p>This manual is included in the OTP document set. It describes + how to build Mnesia database applications, and how to integrate + and utilize the Mnesia database management system with + OTP. Programming constructs are described, and numerous + programming examples are included to illustrate the use of + Mnesia. + </p> + </section> + + <section> + <title>Prerequisites</title> + <p>Readers of this manual are assumed to be familiar with system + development principles and database management systems. Readers + are also assumed to be familiar with the Erlang programming + language.</p> + </section> + + <section> + <title>About This Book</title> + <p>This book contains the following chapters: + </p> + <list type="bulleted"> + <item>Chapter 2, "Getting Started with Mnesia", introduces + Mnesia with an example database. Examples are shown of how to + start an Erlang session, specify a Mnesia database directory, + initialize a database schema, start Mnesia, and create + tables. Initial prototyping of record definitions is also + discussed. + </item> + <item>Chapter 3, "Building a Mnesia Database", more formally + describes the steps introduced in Chapter 2, namely the Mnesia + functions which define a database schema, start Mnesia, and + create the required tables. + </item> + <item>Chapter 4, "Transactions and other access contexts", + describes the transactions properties which make Mnesia into a + fault tolerant, real-time distributed database management + system. This chapter also describes the concept of locking in + order to ensure consistency in tables, and so called "dirty + operations", or short cuts which bypass the transaction system + to improve speed and reduce overheads. + </item> + <item>Chapter 5, "Miscellaneous Mnesia Features", describes + features which enable the construction of more complex + database applications. These features includes indexing, + checkpoints, distribution and fault tolerance, disc-less + nodes, replication manipulation, local content tables, concurrency, + and object based programming in Mnesia. + </item> + <item>Chapter 6, "Mnesia System Information", describes the + files contained in the Mnesia database directory, database + configuration data, core and table dumps, as well as the + important subject of backup, fall-back, and disaster recovery + principles. + </item> + <item>Chapter 7, "Combining Mnesia with SNMP", is a short + chapter which outlines Mnesia integrated with SNMP. + </item> + <item>Appendix A, "Mnesia Errors Messages", lists Mnesia error + messages and their meanings. + </item> + <item>Appendix B, "The Backup Call Back Interface", is a + program listing of the default implementation of this facility. + </item> + <item>Appendix C, "The Activity Access Call Back Interface", + is a program outlining of one possible implementations of this facility. + </item> + </list> + </section> + </section> +</chapter> + |