<?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.24. pg_buffercache</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="passwordcheck.html" title="F.23. passwordcheck" /><link rel="next" href="pgcrypto.html" title="F.25. pgcrypto" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.24. pg_buffercache</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="passwordcheck.html" title="F.23. passwordcheck">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 11.12 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgcrypto.html" title="F.25. pgcrypto">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PGBUFFERCACHE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.24. pg_buffercache</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgbuffercache.html#id-1.11.7.33.7">F.24.1. The <code class="structname">pg_buffercache</code> View</a></span></dt><dt><span class="sect2"><a href="pgbuffercache.html#id-1.11.7.33.8">F.24.2. Sample Output</a></span></dt><dt><span class="sect2"><a href="pgbuffercache.html#id-1.11.7.33.9">F.24.3. Authors</a></span></dt></dl></div><a id="id-1.11.7.33.2" class="indexterm"></a><p> The <code class="filename">pg_buffercache</code> module provides a means for examining what's happening in the shared buffer cache in real time. </p><a id="id-1.11.7.33.4" class="indexterm"></a><p> The module provides a C function <code class="function">pg_buffercache_pages</code> that returns a set of records, plus a view <code class="structname">pg_buffercache</code> that wraps the function for convenient use. </p><p> By default, use is restricted to superusers and members of the <code class="literal">pg_monitor</code> role. Access may be granted to others using <code class="command">GRANT</code>. </p><div class="sect2" id="id-1.11.7.33.7"><div class="titlepage"><div><div><h3 class="title">F.24.1. The <code class="structname">pg_buffercache</code> View</h3></div></div></div><p> The definitions of the columns exposed by the view are shown in <a class="xref" href="pgbuffercache.html#PGBUFFERCACHE-COLUMNS" title="Table F.15. pg_buffercache Columns">Table F.15</a>. </p><div class="table" id="PGBUFFERCACHE-COLUMNS"><p class="title"><strong>Table F.15. <code class="structname">pg_buffercache</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_buffercache Columns" border="1"><colgroup><col /><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>References</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">bufferid</code></td><td><code class="type">integer</code></td><td> </td><td>ID, in the range 1..<code class="varname">shared_buffers</code></td></tr><tr><td><code class="structfield">relfilenode</code></td><td><code class="type">oid</code></td><td><code class="literal">pg_class.relfilenode</code></td><td>Filenode number of the relation</td></tr><tr><td><code class="structfield">reltablespace</code></td><td><code class="type">oid</code></td><td><code class="literal">pg_tablespace.oid</code></td><td>Tablespace OID of the relation</td></tr><tr><td><code class="structfield">reldatabase</code></td><td><code class="type">oid</code></td><td><code class="literal">pg_database.oid</code></td><td>Database OID of the relation</td></tr><tr><td><code class="structfield">relforknumber</code></td><td><code class="type">smallint</code></td><td> </td><td>Fork number within the relation; see <code class="filename">include/common/relpath.h</code></td></tr><tr><td><code class="structfield">relblocknumber</code></td><td><code class="type">bigint</code></td><td> </td><td>Page number within the relation</td></tr><tr><td><code class="structfield">isdirty</code></td><td><code class="type">boolean</code></td><td> </td><td>Is the page dirty?</td></tr><tr><td><code class="structfield">usagecount</code></td><td><code class="type">smallint</code></td><td> </td><td>Clock-sweep access count</td></tr><tr><td><code class="structfield">pinning_backends</code></td><td><code class="type">integer</code></td><td> </td><td>Number of backends pinning this buffer</td></tr></tbody></table></div></div><br class="table-break" /><p> There is one row for each buffer in the shared cache. Unused buffers are shown with all fields null except <code class="structfield">bufferid</code>. Shared system catalogs are shown as belonging to database zero. </p><p> Because the cache is shared by all the databases, there will normally be pages from relations not belonging to the current database. This means that there may not be matching join rows in <code class="structname">pg_class</code> for some rows, or that there could even be incorrect joins. If you are trying to join against <code class="structname">pg_class</code>, it's a good idea to restrict the join to rows having <code class="structfield">reldatabase</code> equal to the current database's OID or zero. </p><p> Since buffer manager locks are not taken to copy the buffer state data that the view will display, accessing <code class="structname">pg_buffercache</code> view has less impact on normal buffer activity but it doesn't provide a consistent set of results across all buffers. However, we ensure that the information of each buffer is self-consistent. </p></div><div class="sect2" id="id-1.11.7.33.8"><div class="titlepage"><div><div><h3 class="title">F.24.2. Sample Output</h3></div></div></div><pre class="screen"> regression=# SELECT n.nspname, c.relname, count(*) AS buffers FROM pg_buffercache b JOIN pg_class c ON b.relfilenode = pg_relation_filenode(c.oid) AND b.reldatabase IN (0, (SELECT oid FROM pg_database WHERE datname = current_database())) JOIN pg_namespace n ON n.oid = c.relnamespace GROUP BY n.nspname, c.relname ORDER BY 3 DESC LIMIT 10; nspname | relname | buffers ------------+------------------------+--------- public | delete_test_table | 593 public | delete_test_table_pkey | 494 pg_catalog | pg_attribute | 472 public | quad_poly_tbl | 353 public | tenk2 | 349 public | tenk1 | 349 public | gin_test_idx | 306 pg_catalog | pg_largeobject | 206 public | gin_test_tbl | 188 public | spgist_text_tbl | 182 (10 rows) </pre></div><div class="sect2" id="id-1.11.7.33.9"><div class="titlepage"><div><div><h3 class="title">F.24.3. Authors</h3></div></div></div><p> Mark Kirkwood <code class="email"><<a class="email" href="mailto:markir@paradise.net.nz">markir@paradise.net.nz</a>></code> </p><p> Design suggestions: Neil Conway <code class="email"><<a class="email" href="mailto:neilc@samurai.com">neilc@samurai.com</a>></code> </p><p> Debugging advice: Tom Lane <code class="email"><<a class="email" href="mailto:tgl@sss.pgh.pa.us">tgl@sss.pgh.pa.us</a>></code> </p></div></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="passwordcheck.html" title="F.23. passwordcheck">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. 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