codekingpro/portable-devtools

1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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>Chapter 50. Replication Progress Tracking</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="logicaldecoding-two-phase-commits.html" title="49.10. Two-phase Commit Support for Logical Decoding" /><link rel="next" href="archive-modules.html" title="Chapter 51. Archive Modules" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">Chapter 50. Replication Progress Tracking</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="logicaldecoding-two-phase-commits.html" title="49.10. Two-phase Commit Support for Logical Decoding">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="server-programming.html" title="Part V. Server Programming">Up</a></td><th width="60%" align="center">Part V. Server Programming</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="archive-modules.html" title="Chapter 51. Archive Modules">Next</a></td></tr></table><hr /></div><div class="chapter" id="REPLICATION-ORIGINS"><div class="titlepage"><div><div><h2 class="title">Chapter 50. Replication Progress Tracking</h2></div></div></div><a id="id-1.8.15.2" class="indexterm"></a><a id="id-1.8.15.3" class="indexterm"></a><p>3  Replication origins are intended to make it easier to implement4  logical replication solutions on top5  of <a class="link" href="logicaldecoding.html" title="Chapter 49. Logical Decoding">logical decoding</a>.6  They provide a solution to two common problems:7  </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>How to safely keep track of replication progress</p></li><li class="listitem"><p>How to change replication behavior based on the8     origin of a row; for example, to prevent loops in bi-directional9     replication setups</p></li></ul></div><p>10 </p><p>11  Replication origins have just two properties, a name and an ID. The name,12  which is what should be used to refer to the origin across systems, is13  free-form <code class="type">text</code>. It should be used in a way that makes conflicts14  between replication origins created by different replication solutions15  unlikely; e.g., by prefixing the replication solution's name to it.16  The ID is used only to avoid having to store the long version17  in situations where space efficiency is important. It should never be shared18  across systems.19 </p><p>20  Replication origins can be created using the function21  <a class="link" href="functions-admin.html#PG-REPLICATION-ORIGIN-CREATE"><code class="function">pg_replication_origin_create()</code></a>;22  dropped using23  <a class="link" href="functions-admin.html#PG-REPLICATION-ORIGIN-DROP"><code class="function">pg_replication_origin_drop()</code></a>;24  and seen in the25  <a class="link" href="catalog-pg-replication-origin.html" title="53.44. pg_replication_origin"><code class="structname">pg_replication_origin</code></a>26  system catalog.27 </p><p>28  One nontrivial part of building a replication solution is to keep track of29  replay progress in a safe manner. When the applying process, or the whole30  cluster, dies, it needs to be possible to find out up to where data has31  successfully been replicated. Naive solutions to this, such as updating a32  row in a table for every replayed transaction, have problems like run-time33  overhead and database bloat.34 </p><p>35  Using the replication origin infrastructure a session can be36  marked as replaying from a remote node (using the37  <a class="link" href="functions-admin.html#PG-REPLICATION-ORIGIN-SESSION-SETUP"><code class="function">pg_replication_origin_session_setup()</code></a>38  function). Additionally the <acronym class="acronym">LSN</acronym> and commit39  time stamp of every source transaction can be configured on a per40  transaction basis using41  <a class="link" href="functions-admin.html#PG-REPLICATION-ORIGIN-XACT-SETUP"><code class="function">pg_replication_origin_xact_setup()</code></a>.42  If that's done replication progress will persist in a crash safe43  manner. Replay progress for all replication origins can be seen in the44  <a class="link" href="view-pg-replication-origin-status.html" title="54.18. pg_replication_origin_status">45   <code class="structname">pg_replication_origin_status</code>46  </a> view. An individual origin's progress, e.g., when resuming47  replication, can be acquired using48  <a class="link" href="functions-admin.html#PG-REPLICATION-ORIGIN-PROGRESS"><code class="function">pg_replication_origin_progress()</code></a>49  for any origin or50  <a class="link" href="functions-admin.html#PG-REPLICATION-ORIGIN-SESSION-PROGRESS"><code class="function">pg_replication_origin_session_progress()</code></a>51  for the origin configured in the current session.52 </p><p>53  In replication topologies more complex than replication from exactly one54  system to one other system, another problem can be that it is hard to avoid55  replicating replayed rows again. That can lead both to cycles in the56  replication and inefficiencies. Replication origins provide an optional57  mechanism to recognize and prevent that. When configured using the functions58  referenced in the previous paragraph, every change and transaction passed to59  output plugin callbacks (see <a class="xref" href="logicaldecoding-output-plugin.html" title="49.6. Logical Decoding Output Plugins">Section 49.6</a>)60  generated by the session is tagged with the replication origin of the61  generating session.  This allows treating them differently in the output62  plugin, e.g., ignoring all but locally-originating rows.  Additionally63  the <a class="link" href="logicaldecoding-output-plugin.html#LOGICALDECODING-OUTPUT-PLUGIN-FILTER-ORIGIN" title="49.6.4.7. Origin Filter Callback">64  <code class="function">filter_by_origin_cb</code></a> callback can be used65  to filter the logical decoding change stream based on the66  source. While less flexible, filtering via that callback is67  considerably more efficient than doing it in the output plugin.68 </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="logicaldecoding-two-phase-commits.html" title="49.10. Two-phase Commit Support for Logical Decoding">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="server-programming.html" title="Part V. Server Programming">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="archive-modules.html" title="Chapter 51. Archive Modules">Next</a></td></tr><tr><td width="40%" align="left" valign="top">49.10. Two-phase Commit Support for Logical Decoding </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 51. Archive Modules</td></tr></table></div></body></html>