<!--$Id: intro.so,v 1.8 2003/04/16 20:28:05 margo Exp $--> <!--Copyright 1997-2003 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB Reference Guide: Introduction</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <a name="2"><!--meow--></a> <table width="100%"><tr valign=top> <td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Berkeley DB Replication</dl></h3></td> <td align=right><a href="../transapp/faq.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../rep/id.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p> <h3 align=center>Introduction</h3> <p>Berkeley DB includes support for building highly available applications based on replication. Berkeley DB replication groups consist of some number of independently configured database environments. There is a single <i>master</i> database environment and one or more <i>client</i> database environments. Master environments support both database reads and writes; client environments support only database reads. If the master environment fails, applications may upgrade a client to be the new master. The database environments might be on separate computers, on separate hardware partitions in a non-uniform memory access (NUMA) system, or on separate disks in a single server. The only constraint is that all the participants in a replication group all be on machines of the same endianness. (We expect this constraint to be removed in a future release.) As always with Berkeley DB environments, any number of concurrent processes or threads may access a database environment. In the case of a master environment, any number of threads of control may read and write the environment, and in the case of a client environment, any number of threads of control may read the environment.</p> <p>Applications may be written to provide various degrees of consistency between the master and clients. The system can be run synchronously such that replicas are guaranteed to be up-to-date with all committed transactions, but doing so may incur a significant performance penalty. Higher performance solutions sacrifice total consistency, allowing the clients to be out of date for an application-controlled amount of time.</p> <p>While Berkeley DB includes the database infrastructure necessary to construct highly available database environments, applications must still provide some critical components:</p> <ol> <p><li>The application is responsible for providing the communication infrastructure. Applications may use whatever wire protocol is appropriate for their application (for example, RPC, TCP/IP, UDP, VI or message-passing over the backplane). <p><li>The application is responsible for naming. Berkeley DB refers to the members of a replication group using an application-provided ID, and applications must map that ID to a particular database environment or communication channel. <p><li>The application is responsible for monitoring the status of the master and clients, and identifying any unavailable database environments. <p><li>The application must provide whatever security policies are needed. For example, the application may choose to encrypt data, use a secure socket layer, or do nothing at all. The level of security is left to the sole discretion of the application. </ol> <p>Finally, the Berkeley DB replication implementation has one other additional feature to increase application reliability. Replication in Berkeley DB is implemented to perform database updates using a different code path than the standard ones. This means operations that manage to crash the replication master due to a software bug will not necessarily also crash replication clients.</p> <!--$Id: m4.methods,v 1.1 2002/08/30 20:02:36 bostic Exp $--> <table border=1 align=center> <tr><th>Replication and Related Methods</th><th>Description</th></tr> <tr><td><a href="../../api_c/rep_transport.html">DB_ENV->set_rep_transport</a></td><td>Configure replication transport</td></tr> <tr><td><a href="../../api_c/rep_elect.html">DB_ENV->rep_elect</a></td><td>Hold a replication election</td></tr> <tr><td><a href="../../api_c/rep_limit.html">DB_ENV->set_rep_limit</a></td><td>Limit data sent in response to a single message</td></tr> <tr><td><a href="../../api_c/rep_message.html">DB_ENV->rep_process_message</a></td><td>Process a replication message</td></tr> <tr><td><a href="../../api_c/rep_start.html">DB_ENV->rep_start</a></td><td>Configure an environment for replication</td></tr> <tr><td><a href="../../api_c/rep_stat.html">DB_ENV->rep_stat</a></td><td>Replication statistics</td></tr> </table> <table width="100%"><tr><td><br></td><td align=right><a href="../transapp/faq.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../rep/id.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p><font size=1><a href="../../sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font> </body> </html>
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