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diff --git a/doc/src/sgml/html/warm-standby-failover.html b/doc/src/sgml/html/warm-standby-failover.html new file mode 100644 index 0000000..f3c1002 --- /dev/null +++ b/doc/src/sgml/html/warm-standby-failover.html @@ -0,0 +1,65 @@ +<?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>27.3. Failover</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="warm-standby.html" title="27.2. Log-Shipping Standby Servers" /><link rel="next" href="hot-standby.html" title="27.4. Hot Standby" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">27.3. Failover</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="warm-standby.html" title="27.2. Log-Shipping Standby Servers">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="high-availability.html" title="Chapter 27. High Availability, Load Balancing, and Replication">Up</a></td><th width="60%" align="center">Chapter 27. High Availability, Load Balancing, and Replication</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="hot-standby.html" title="27.4. Hot Standby">Next</a></td></tr></table><hr /></div><div class="sect1" id="WARM-STANDBY-FAILOVER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">27.3. Failover</h2></div></div></div><p> + If the primary server fails then the standby server should begin + failover procedures. + </p><p> + If the standby server fails then no failover need take place. If the + standby server can be restarted, even some time later, then the recovery + process can also be restarted immediately, taking advantage of + restartable recovery. If the standby server cannot be restarted, then a + full new standby server instance should be created. + </p><p> + If the primary server fails and the standby server becomes the + new primary, and then the old primary restarts, you must have + a mechanism for informing the old primary that it is no longer the primary. This is + sometimes known as <acronym class="acronym">STONITH</acronym> (Shoot The Other Node In The Head), which is + necessary to avoid situations where both systems think they are the + primary, which will lead to confusion and ultimately data loss. + </p><p> + Many failover systems use just two systems, the primary and the standby, + connected by some kind of heartbeat mechanism to continually verify the + connectivity between the two and the viability of the primary. It is + also possible to use a third system (called a witness server) to prevent + some cases of inappropriate failover, but the additional complexity + might not be worthwhile unless it is set up with sufficient care and + rigorous testing. + </p><p> + <span class="productname">PostgreSQL</span> does not provide the system + software required to identify a failure on the primary and notify + the standby database server. Many such tools exist and are well + integrated with the operating system facilities required for + successful failover, such as IP address migration. + </p><p> + Once failover to the standby occurs, there is only a + single server in operation. This is known as a degenerate state. + The former standby is now the primary, but the former primary is down + and might stay down. To return to normal operation, a standby server + must be recreated, + either on the former primary system when it comes up, or on a third, + possibly new, system. The <a class="xref" href="app-pgrewind.html" title="pg_rewind"><span class="refentrytitle"><span class="application">pg_rewind</span></span></a> utility can be + used to speed up this process on large clusters. + Once complete, the primary and standby can be + considered to have switched roles. Some people choose to use a third + server to provide backup for the new primary until the new standby + server is recreated, + though clearly this complicates the system configuration and + operational processes. + </p><p> + So, switching from primary to standby server can be fast but requires + some time to re-prepare the failover cluster. Regular switching from + primary to standby is useful, since it allows regular downtime on + each system for maintenance. This also serves as a test of the + failover mechanism to ensure that it will really work when you need it. + Written administration procedures are advised. + </p><p> + To trigger failover of a log-shipping standby server, run + <code class="command">pg_ctl promote</code>, call <code class="function">pg_promote()</code>, + or create a trigger file with the file name and path specified by the + <code class="varname">promote_trigger_file</code>. If you're planning to use + <code class="command">pg_ctl promote</code> or to call + <code class="function">pg_promote()</code> to fail over, + <code class="varname">promote_trigger_file</code> is not required. If you're + setting up the reporting servers that are only used to offload read-only + queries from the primary, not for high availability purposes, you don't + need to promote it. + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="warm-standby.html" title="27.2. Log-Shipping Standby Servers">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="high-availability.html" title="Chapter 27. High Availability, Load Balancing, and Replication">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="hot-standby.html" title="27.4. Hot Standby">Next</a></td></tr><tr><td width="40%" align="left" valign="top">27.2. Log-Shipping Standby Servers </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 27.4. Hot Standby</td></tr></table></div></body></html>
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