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diff --git a/doc/src/sgml/html/pgbuffercache.html b/doc/src/sgml/html/pgbuffercache.html new file mode 100644 index 0000000..8fa29c4 --- /dev/null +++ b/doc/src/sgml/html/pgbuffercache.html @@ -0,0 +1,233 @@ +<?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.27. pg_buffercache — inspect PostgreSQL buffer cache state</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.26. passwordcheck — verify password strength" /><link rel="next" href="pgcrypto.html" title="F.28. pgcrypto — cryptographic functions" /></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.27. pg_buffercache — inspect <span class="productname">PostgreSQL</span> + buffer cache state</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="passwordcheck.html" title="F.26. passwordcheck — verify password strength">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgcrypto.html" title="F.28. pgcrypto — cryptographic functions">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGBUFFERCACHE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.27. pg_buffercache — inspect <span class="productname">PostgreSQL</span> + buffer cache state <a href="#PGBUFFERCACHE" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgbuffercache.html#PGBUFFERCACHE-PG-BUFFERCACHE">F.27.1. The <code class="structname">pg_buffercache</code> View</a></span></dt><dt><span class="sect2"><a href="pgbuffercache.html#PGBUFFERCACHE-SUMMARY">F.27.2. The <code class="function">pg_buffercache_summary()</code> Function</a></span></dt><dt><span class="sect2"><a href="pgbuffercache.html#PGBUFFERCACHE-USAGE-COUNTS">F.27.3. The <code class="function">pg_buffercache_usage_counts()</code> Function</a></span></dt><dt><span class="sect2"><a href="pgbuffercache.html#PGBUFFERCACHE-SAMPLE-OUTPUT">F.27.4. Sample Output</a></span></dt><dt><span class="sect2"><a href="pgbuffercache.html#PGBUFFERCACHE-AUTHORS">F.27.5. Authors</a></span></dt></dl></div><a id="id-1.11.7.37.2" 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-1.11.7.37.4" class="indexterm"></a><a id="id-1.11.7.37.5" class="indexterm"></a><p> + This module provides the <code class="function">pg_buffercache_pages()</code> + function (wrapped in the <code class="structname">pg_buffercache</code> view), + the <code class="function">pg_buffercache_summary()</code> function, and the + <code class="function">pg_buffercache_usage_counts()</code> function. + </p><p> + The <code class="function">pg_buffercache_pages()</code> function returns a set of + records, each row describing the state of one shared buffer entry. The + <code class="structname">pg_buffercache</code> view wraps the function for + convenient use. + </p><p> + The <code class="function">pg_buffercache_summary()</code> function returns a single + row summarizing the state of the shared buffer cache. + </p><p> + The <code class="function">pg_buffercache_usage_counts()</code> function returns a set + of records, each row describing the number of buffers with a given usage + count. + </p><p> + By default, use is restricted to superusers and roles with privileges 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="PGBUFFERCACHE-PG-BUFFERCACHE"><div class="titlepage"><div><div><h3 class="title">F.27.1. The <code class="structname">pg_buffercache</code> View <a href="#PGBUFFERCACHE-PG-BUFFERCACHE" class="id_link">#</a></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 /></colgroup><thead><tr><th class="catalog_table_entry"><p class="column_definition"> + Column Type + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">bufferid</code> <code class="type">integer</code> + </p> + <p> + ID, in the range 1..<code class="varname">shared_buffers</code> + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">relfilenode</code> <code class="type">oid</code> + (references <a class="link" href="catalog-pg-class.html" title="53.11. pg_class"><code class="structname">pg_class</code></a>.<code class="structfield">relfilenode</code>) + </p> + <p> + Filenode number of the relation + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">reltablespace</code> <code class="type">oid</code> + (references <a class="link" href="catalog-pg-tablespace.html" title="53.56. pg_tablespace"><code class="structname">pg_tablespace</code></a>.<code class="structfield">oid</code>) + </p> + <p> + Tablespace OID of the relation + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">reldatabase</code> <code class="type">oid</code> + (references <a class="link" href="catalog-pg-database.html" title="53.15. pg_database"><code class="structname">pg_database</code></a>.<code class="structfield">oid</code>) + </p> + <p> + Database OID of the relation + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">relforknumber</code> <code class="type">smallint</code> + </p> + <p> + Fork number within the relation; see + <code class="filename">common/relpath.h</code> + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">relblocknumber</code> <code class="type">bigint</code> + </p> + <p> + Page number within the relation + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">isdirty</code> <code class="type">boolean</code> + </p> + <p> + Is the page dirty? + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">usagecount</code> <code class="type">smallint</code> + </p> + <p> + Clock-sweep access count + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">pinning_backends</code> <code class="type">integer</code> + </p> + <p> + Number of backends pinning this buffer + </p></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="PGBUFFERCACHE-SUMMARY"><div class="titlepage"><div><div><h3 class="title">F.27.2. The <code class="function">pg_buffercache_summary()</code> Function <a href="#PGBUFFERCACHE-SUMMARY" class="id_link">#</a></h3></div></div></div><p> + The definitions of the columns exposed by the function are shown in <a class="xref" href="pgbuffercache.html#PGBUFFERCACHE-SUMMARY-COLUMNS" title="Table F.16. pg_buffercache_summary() Output Columns">Table F.16</a>. + </p><div class="table" id="PGBUFFERCACHE-SUMMARY-COLUMNS"><p class="title"><strong>Table F.16. <code class="function">pg_buffercache_summary()</code> Output Columns</strong></p><div class="table-contents"><table class="table" summary="pg_buffercache_summary() Output Columns" border="1"><colgroup><col /></colgroup><thead><tr><th class="catalog_table_entry"><p class="column_definition"> + Column Type + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">buffers_used</code> <code class="type">int4</code> + </p> + <p> + Number of used shared buffers + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">buffers_unused</code> <code class="type">int4</code> + </p> + <p> + Number of unused shared buffers + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">buffers_dirty</code> <code class="type">int4</code> + </p> + <p> + Number of dirty shared buffers + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">buffers_pinned</code> <code class="type">int4</code> + </p> + <p> + Number of pinned shared buffers + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">usagecount_avg</code> <code class="type">float8</code> + </p> + <p> + Average usage count of used shared buffers + </p></td></tr></tbody></table></div></div><br class="table-break" /><p> + The <code class="function">pg_buffercache_summary()</code> function returns a + single row summarizing the state of all shared buffers. Similar and more + detailed information is provided by the + <code class="structname">pg_buffercache</code> view, but + <code class="function">pg_buffercache_summary()</code> is significantly cheaper. + </p><p> + Like the <code class="structname">pg_buffercache</code> view, + <code class="function">pg_buffercache_summary()</code> does not acquire buffer + manager locks. Therefore concurrent activity can lead to minor inaccuracies + in the result. + </p></div><div class="sect2" id="PGBUFFERCACHE-USAGE-COUNTS"><div class="titlepage"><div><div><h3 class="title">F.27.3. The <code class="function">pg_buffercache_usage_counts()</code> Function <a href="#PGBUFFERCACHE-USAGE-COUNTS" class="id_link">#</a></h3></div></div></div><p> + The definitions of the columns exposed by the function are shown in + <a class="xref" href="pgbuffercache.html#PGBUFFERCACHE_USAGE_COUNTS-COLUMNS" title="Table F.17. pg_buffercache_usage_counts() Output Columns">Table F.17</a>. + </p><div class="table" id="PGBUFFERCACHE_USAGE_COUNTS-COLUMNS"><p class="title"><strong>Table F.17. <code class="function">pg_buffercache_usage_counts()</code> Output Columns</strong></p><div class="table-contents"><table class="table" summary="pg_buffercache_usage_counts() Output Columns" border="1"><colgroup><col /></colgroup><thead><tr><th class="catalog_table_entry"><p class="column_definition"> + Column Type + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">usage_count</code> <code class="type">int4</code> + </p> + <p> + A possible buffer usage count + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">buffers</code> <code class="type">int4</code> + </p> + <p> + Number of buffers with the usage count + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">dirty</code> <code class="type">int4</code> + </p> + <p> + Number of dirty buffers with the usage count + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">pinned</code> <code class="type">int4</code> + </p> + <p> + Number of pinned buffers with the usage count + </p></td></tr></tbody></table></div></div><br class="table-break" /><p> + The <code class="function">pg_buffercache_usage_counts()</code> function returns a + set of rows summarizing the states of all shared buffers, aggregated over + the possible usage count values. Similar and more detailed information is + provided by the <code class="structname">pg_buffercache</code> view, but + <code class="function">pg_buffercache_usage_counts()</code> is significantly cheaper. + </p><p> + Like the <code class="structname">pg_buffercache</code> view, + <code class="function">pg_buffercache_usage_counts()</code> does not acquire buffer + manager locks. Therefore concurrent activity can lead to minor inaccuracies + in the result. + </p></div><div class="sect2" id="PGBUFFERCACHE-SAMPLE-OUTPUT"><div class="titlepage"><div><div><h3 class="title">F.27.4. Sample Output <a href="#PGBUFFERCACHE-SAMPLE-OUTPUT" class="id_link">#</a></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) + + +regression=# SELECT * FROM pg_buffercache_summary(); + buffers_used | buffers_unused | buffers_dirty | buffers_pinned | usagecount_avg +--------------+----------------+---------------+----------------+---------------- + 248 | 2096904 | 39 | 0 | 3.141129 +(1 row) + + +regression=# SELECT * FROM pg_buffercache_usage_counts(); + usage_count | buffers | dirty | pinned +-------------+---------+-------+-------- + 0 | 14650 | 0 | 0 + 1 | 1436 | 671 | 0 + 2 | 102 | 88 | 0 + 3 | 23 | 21 | 0 + 4 | 9 | 7 | 0 + 5 | 164 | 106 | 0 +(6 rows) +</pre></div><div class="sect2" id="PGBUFFERCACHE-AUTHORS"><div class="titlepage"><div><div><h3 class="title">F.27.5. Authors <a href="#PGBUFFERCACHE-AUTHORS" class="id_link">#</a></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 class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="passwordcheck.html" title="F.26. passwordcheck — verify password strength">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. 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