diff options
Diffstat (limited to 'doc/src/sgml/html/auto-explain.html')
| -rw-r--r-- | doc/src/sgml/html/auto-explain.html | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/doc/src/sgml/html/auto-explain.html b/doc/src/sgml/html/auto-explain.html new file mode 100644 index 0000000..8527d17 --- /dev/null +++ b/doc/src/sgml/html/auto-explain.html @@ -0,0 +1,189 @@ +<?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>F.4. auto_explain</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="auth-delay.html" title="F.3. auth_delay" /><link rel="next" href="basebackup-to-shell.html" title="F.5. basebackup_to_shell" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.4. auto_explain</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="auth-delay.html" title="F.3. auth_delay">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="basebackup-to-shell.html" title="F.5. basebackup_to_shell">Next</a></td></tr></table><hr /></div><div class="sect1" id="AUTO-EXPLAIN"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.4. auto_explain</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="auto-explain.html#id-1.11.7.13.5">F.4.1. Configuration Parameters</a></span></dt><dt><span class="sect2"><a href="auto-explain.html#id-1.11.7.13.6">F.4.2. Example</a></span></dt><dt><span class="sect2"><a href="auto-explain.html#id-1.11.7.13.7">F.4.3. Author</a></span></dt></dl></div><a id="id-1.11.7.13.2" class="indexterm"></a><p> + The <code class="filename">auto_explain</code> module provides a means for + logging execution plans of slow statements automatically, without + having to run <a class="xref" href="sql-explain.html" title="EXPLAIN"><span class="refentrytitle">EXPLAIN</span></a> + by hand. This is especially helpful for tracking down un-optimized queries + in large applications. + </p><p> + The module provides no SQL-accessible functions. To use it, simply + load it into the server. You can load it into an individual session: + +</p><pre class="programlisting"> +LOAD 'auto_explain'; +</pre><p> + + (You must be superuser to do that.) More typical usage is to preload + it into some or all sessions by including <code class="literal">auto_explain</code> in + <a class="xref" href="runtime-config-client.html#GUC-SESSION-PRELOAD-LIBRARIES">session_preload_libraries</a> or + <a class="xref" href="runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">shared_preload_libraries</a> in + <code class="filename">postgresql.conf</code>. Then you can track unexpectedly slow queries + no matter when they happen. Of course there is a price in overhead for + that. + </p><div class="sect2" id="id-1.11.7.13.5"><div class="titlepage"><div><div><h3 class="title">F.4.1. Configuration Parameters</h3></div></div></div><p> + There are several configuration parameters that control the behavior of + <code class="filename">auto_explain</code>. Note that the default behavior is + to do nothing, so you must set at least + <code class="varname">auto_explain.log_min_duration</code> if you want any results. + </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"> + <code class="varname">auto_explain.log_min_duration</code> (<code class="type">integer</code>) + <a id="id-1.11.7.13.5.3.1.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_min_duration</code> is the minimum statement + execution time, in milliseconds, that will cause the statement's plan to + be logged. Setting this to <code class="literal">0</code> logs all plans. + <code class="literal">-1</code> (the default) disables logging of plans. For + example, if you set it to <code class="literal">250ms</code> then all statements + that run 250ms or longer will be logged. Only superusers can change this + setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_analyze</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.2.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_analyze</code> causes <code class="command">EXPLAIN ANALYZE</code> + output, rather than just <code class="command">EXPLAIN</code> output, to be printed + when an execution plan is logged. This parameter is off by default. + Only superusers can change this setting. + </p><div class="note"><h3 class="title">Note</h3><p> + When this parameter is on, per-plan-node timing occurs for all + statements executed, whether or not they run long enough to actually + get logged. This can have an extremely negative impact on performance. + Turning off <code class="varname">auto_explain.log_timing</code> ameliorates the + performance cost, at the price of obtaining less information. + </p></div></dd><dt><span class="term"> + <code class="varname">auto_explain.log_buffers</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.3.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_buffers</code> controls whether buffer + usage statistics are printed when an execution plan is logged; it's + equivalent to the <code class="literal">BUFFERS</code> option of <code class="command">EXPLAIN</code>. + This parameter has no effect + unless <code class="varname">auto_explain.log_analyze</code> is enabled. + This parameter is off by default. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_wal</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.4.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_wal</code> controls whether WAL + usage statistics are printed when an execution plan is logged; it's + equivalent to the <code class="literal">WAL</code> option of <code class="command">EXPLAIN</code>. + This parameter has no effect + unless <code class="varname">auto_explain.log_analyze</code> is enabled. + This parameter is off by default. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_timing</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.5.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_timing</code> controls whether per-node + timing information is printed when an execution plan is logged; it's + equivalent to the <code class="literal">TIMING</code> option of <code class="command">EXPLAIN</code>. + The overhead of repeatedly reading the system clock can slow down + queries significantly on some systems, so it may be useful to set this + parameter to off when only actual row counts, and not exact times, are + needed. + This parameter has no effect + unless <code class="varname">auto_explain.log_analyze</code> is enabled. + This parameter is on by default. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_triggers</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.6.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_triggers</code> causes trigger + execution statistics to be included when an execution plan is logged. + This parameter has no effect + unless <code class="varname">auto_explain.log_analyze</code> is enabled. + This parameter is off by default. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_verbose</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.7.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_verbose</code> controls whether verbose + details are printed when an execution plan is logged; it's + equivalent to the <code class="literal">VERBOSE</code> option of <code class="command">EXPLAIN</code>. + This parameter is off by default. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_settings</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.8.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_settings</code> controls whether information + about modified configuration options is printed when an execution plan is logged. + Only options affecting query planning with value different from the built-in + default value are included in the output. This parameter is off by default. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_format</code> (<code class="type">enum</code>) + <a id="id-1.11.7.13.5.3.9.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_format</code> selects the + <code class="command">EXPLAIN</code> output format to be used. + The allowed values are <code class="literal">text</code>, <code class="literal">xml</code>, + <code class="literal">json</code>, and <code class="literal">yaml</code>. The default is text. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_level</code> (<code class="type">enum</code>) + <a id="id-1.11.7.13.5.3.10.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_level</code> selects the log level at which + auto_explain will log the query plan. + Valid values are <code class="literal">DEBUG5</code>, <code class="literal">DEBUG4</code>, + <code class="literal">DEBUG3</code>, <code class="literal">DEBUG2</code>, + <code class="literal">DEBUG1</code>, <code class="literal">INFO</code>, + <code class="literal">NOTICE</code>, <code class="literal">WARNING</code>, + and <code class="literal">LOG</code>. The default is <code class="literal">LOG</code>. + Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.log_nested_statements</code> (<code class="type">boolean</code>) + <a id="id-1.11.7.13.5.3.11.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.log_nested_statements</code> causes nested + statements (statements executed inside a function) to be considered + for logging. When it is off, only top-level query plans are logged. This + parameter is off by default. Only superusers can change this setting. + </p></dd><dt><span class="term"> + <code class="varname">auto_explain.sample_rate</code> (<code class="type">real</code>) + <a id="id-1.11.7.13.5.3.12.1.3" class="indexterm"></a> + </span></dt><dd><p> + <code class="varname">auto_explain.sample_rate</code> causes auto_explain to only + explain a fraction of the statements in each session. The default is 1, + meaning explain all the queries. In case of nested statements, either all + will be explained or none. Only superusers can change this setting. + </p></dd></dl></div><p> + In ordinary usage, these parameters are set + in <code class="filename">postgresql.conf</code>, although superusers can alter them + on-the-fly within their own sessions. + Typical usage might be: + </p><pre class="programlisting"> +# postgresql.conf +session_preload_libraries = 'auto_explain' + +auto_explain.log_min_duration = '3s' +</pre></div><div class="sect2" id="id-1.11.7.13.6"><div class="titlepage"><div><div><h3 class="title">F.4.2. Example</h3></div></div></div><pre class="programlisting"> +postgres=# LOAD 'auto_explain'; +postgres=# SET auto_explain.log_min_duration = 0; +postgres=# SET auto_explain.log_analyze = true; +postgres=# SELECT count(*) + FROM pg_class, pg_index + WHERE oid = indrelid AND indisunique; +</pre><p> + This might produce log output such as: + </p><pre class="screen"> +LOG: duration: 3.651 ms plan: + Query Text: SELECT count(*) + FROM pg_class, pg_index + WHERE oid = indrelid AND indisunique; + Aggregate (cost=16.79..16.80 rows=1 width=0) (actual time=3.626..3.627 rows=1 loops=1) + -> Hash Join (cost=4.17..16.55 rows=92 width=0) (actual time=3.349..3.594 rows=92 loops=1) + Hash Cond: (pg_class.oid = pg_index.indrelid) + -> Seq Scan on pg_class (cost=0.00..9.55 rows=255 width=4) (actual time=0.016..0.140 rows=255 loops=1) + -> Hash (cost=3.02..3.02 rows=92 width=4) (actual time=3.238..3.238 rows=92 loops=1) + Buckets: 1024 Batches: 1 Memory Usage: 4kB + -> Seq Scan on pg_index (cost=0.00..3.02 rows=92 width=4) (actual time=0.008..3.187 rows=92 loops=1) + Filter: indisunique +</pre></div><div class="sect2" id="id-1.11.7.13.7"><div class="titlepage"><div><div><h3 class="title">F.4.3. Author</h3></div></div></div><p> + Takahiro Itagaki <code class="email"><<a class="email" href="mailto:itagaki.takahiro@oss.ntt.co.jp">itagaki.takahiro@oss.ntt.co.jp</a>></code> + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="auth-delay.html" title="F.3. auth_delay">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="basebackup-to-shell.html" title="F.5. basebackup_to_shell">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.3. auth_delay </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.5. basebackup_to_shell</td></tr></table></div></body></html>
\ No newline at end of file |