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diff --git a/docs/programmer_reference/rep_partview.html b/docs/programmer_reference/rep_partview.html new file mode 100644 index 00000000..8da359a7 --- /dev/null +++ b/docs/programmer_reference/rep_partview.html @@ -0,0 +1,169 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <title>Replication views</title> + <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> + <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> + <link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" /> + <link rel="up" href="rep.html" title="Chapter 12. Berkeley DB Replication" /> + <link rel="prev" href="group_membership.html" title="Managing Replication Manager group membership" /> + <link rel="next" href="rep_filename.html" title="Managing replication directories and files" /> + </head> + <body> + <div xmlns="" class="navheader"> + <div class="libver"> + <p>Library Version 12.1.6.1</p> + </div> + <table width="100%" summary="Navigation header"> + <tr> + <th colspan="3" align="center">Replication views</th> + </tr> + <tr> + <td width="20%" align="left"><a accesskey="p" href="group_membership.html">Prev</a> </td> + <th width="60%" align="center">Chapter 12. Berkeley DB Replication </th> + <td width="20%" align="right"> <a accesskey="n" href="rep_filename.html">Next</a></td> + </tr> + </table> + <hr /> + </div> + <div class="sect1" lang="en" xml:lang="en"> + <div class="titlepage"> + <div> + <div> + <h2 class="title" style="clear: both"><a id="rep_partview"></a>Replication views</h2> + </div> + </div> + </div> + <p> + A <span class="bold"><strong>view</strong></span> is a replication + site that maintains a copy of the replication group's data + without incurring other overhead from participating in the + replication group. Views are useful for applications that + require read scalability, are geographically distributed, have + slow network connections to some sites, or require only a + subset of replicated databases at some sites. + </p> + <p> + A client is a <span class="bold"><strong>participant</strong></span> + in the replication group because it helps to determine the + master and contributes to transaction durability. A view + receives its copy of the replicated data without participating + in the replication group in these other ways. Specifically, a + view cannot ever become master, a view does not vote in + elections, and a view does not contribute to transaction + durability. A view is similar to an unelectable client because + neither can become master. They differ because an unelectable + client participates in the replication group by voting and + contributing to transaction durability. + </p> + <p> + A <span class="bold"><strong>full view</strong></span> contains a + copy of all replicated databases. You define a full view by + calling the <a href="../api_reference/C/repset_view.html" class="olink">DB_ENV->rep_set_view()</a> method before opening the + environment and supplying a NULL value for the <span class="bold"><strong>partial_func</strong></span> parameter. You can + then complete any other environment configuration, open the + environment, and eventually start replication using the + <a href="../api_reference/C/repmgrstart.html#repmgrstart_DB_REP_CLIENT" class="olink">DB_REP_CLIENT</a> flags value. + </p> + <p> + A <span class="bold"><strong>partial view</strong></span> contains a + subset of the replicated databases. You define a partial view + using the same steps used to define a full view, except that + you supply a <span class="bold"><strong>partial_func</strong></span> + callback to the <a href="../api_reference/C/repset_view.html" class="olink">DB_ENV->rep_set_view()</a> method. The partial function + uses application-specific logic to determine the names of the + database files to replicate. The partial function should set + its <span class="bold"><strong>result</strong></span> output parameter + to 0 to reject a database file or to a non-zero value to + replicate it. Note that named in-memory databases are always + replicated to partial views regardless of partial function + logic. + </p> + <p> + The decision about whether to replicate a particular + database file to a partial view is made at the time the + database file is first created. It is possible to change the + partial function to replicate a different set of database + files. However, any database file that was already being + replicated will continue to be replicated regardless of the + new partial function logic because it already exists at that + site. + </p> + <p> + Recovery on a partial view should always be performed using + the <a href="../api_reference/C/envopen.html#envopen_DB_RECOVER" class="olink">DB_RECOVER</a> flag to the <a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> method after calling + the <a href="../api_reference/C/repset_view.html" class="olink">DB_ENV->rep_set_view()</a> method to supply the partial function. You + should not use the <a href="../api_reference/C/db_recover.html" class="olink">db_recover</a> utility to recover a partial view + because it cannot use a partial function. + </p> + <p> + Defining a site as a view is a permanent decision; once a + site is defined as a view it can never be transformed into a + participant. This means that on a view site, the <a href="../api_reference/C/repset_view.html" class="olink">DB_ENV->rep_set_view()</a> + method must always be called before opening the environment. + </p> + <p> + An existing participant can be permanently demoted to a + view at any time by calling the <a href="../api_reference/C/repset_view.html" class="olink">DB_ENV->rep_set_view()</a> method before + opening its environment and starting replication. Demoting a + participant to a view can fail when starting replication and + return <code class="literal">DB_REP_UNAVAIL</code> if the master is + unavailable or there are insufficient participants to + acknowledge this operation. You can pause and retry starting + replication until it succeeds. + </p> + <p> + A view cannot become master and does not vote in elections, + but elections among the participant sites need to know the + number of participants in the replication group. Replication + Manager automatically manages elections and tracks the number + of participants. In Base API applications, the number of sites + in the replication group set by the <a href="../api_reference/C/repnsites.html" class="olink">DB_ENV->rep_set_nsites()</a> method should + only count participant sites. Similarly, when a participant + site calls the <a href="../api_reference/C/repelect.html" class="olink">DB_ENV->rep_elect()</a> method, the <span class="bold"><strong>nsites</strong></span> + value should only count participant + sites. A view should never call the <a href="../api_reference/C/repelect.html" class="olink">DB_ENV->rep_elect()</a> method. + </p> + <p> + A transaction's durability within a replication group is + based on its replication to other sites that can potentially + take over as master if the current master fails. A view cannot + become master, so it cannot contribute to transaction + durabilty. As a result, Replication Manager views do not send + acknowledgements. Base API applications should not count + messages returning <a href="../api_reference/C/repmessage.html#repmsg_DB_REP_ISPERM" class="olink">DB_REP_ISPERM</a> from a view as contributing + to transaction durability. + </p> + <p> + Replication Manager views participate in replication + group-aware log archiving. A view can also be configured as a + client-to-client peer of another site in the replication + group. If a partial view does not contain the information + requested, Replication Manager will redirect the request to + the master. + </p> + </div> + <div class="navfooter"> + <hr /> + <table width="100%" summary="Navigation footer"> + <tr> + <td width="40%" align="left"><a accesskey="p" href="group_membership.html">Prev</a> </td> + <td width="20%" align="center"> + <a accesskey="u" href="rep.html">Up</a> + </td> + <td width="40%" align="right"> <a accesskey="n" href="rep_filename.html">Next</a></td> + </tr> + <tr> + <td width="40%" align="left" valign="top">Managing Replication Manager + group membership </td> + <td width="20%" align="center"> + <a accesskey="h" href="index.html">Home</a> + </td> + <td width="40%" align="right" valign="top"> Managing replication directories and files</td> + </tr> + </table> + </div> + </body> +</html> |