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<!--$Id: intro.html,v 1.1.1.1 2003/11/20 22:14:20 toshok Exp $-->
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<title>Berkeley DB Reference Guide: Introduction</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<table width="100%"><tr valign=top>
<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Berkeley DB Replication</dl></h3></td>
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<p>
<h1 align=center>Introduction</h1>
<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.  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>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clients to be out of date for an application-controlled amount of time.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>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>
<!--$Id: intro.html,v 1.1.1.1 2003/11/20 22:14:20 toshok Exp $-->
<p><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-&gt;set_rep_transport</a></td><td>Configure replication transport</td></tr>
<tr><td><a href="../../api_c/rep_elect.html">DB_ENV-&gt;rep_elect</a></td><td>Hold a replication election</td></tr>
<tr><td><a href="../../api_c/rep_limit.html">DB_ENV-&gt;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-&gt;rep_process_message</a></td><td>Process a replication message</td></tr>
<tr><td><a href="../../api_c/rep_start.html">DB_ENV-&gt;rep_start</a></td><td>Configure an environment for replication</td></tr>
<tr><td><a href="../../api_c/rep_stat.html">DB_ENV-&gt;rep_stat</a></td><td>Replication statistics</td></tr>
</table>
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