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diff --git a/doc/src/sgml/html/pgstattuple.html b/doc/src/sgml/html/pgstattuple.html new file mode 100644 index 0000000..decbc32 --- /dev/null +++ b/doc/src/sgml/html/pgstattuple.html @@ -0,0 +1,199 @@ +<?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.33. pgstattuple</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="pgstatstatements.html" title="F.32. pg_stat_statements" /><link rel="next" href="pgsurgery.html" title="F.34. pg_surgery" /></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.33. pgstattuple</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgstatstatements.html" title="F.32. pg_stat_statements">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 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgsurgery.html" title="F.34. pg_surgery">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGSTATTUPLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.33. pgstattuple</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgstattuple.html#id-1.11.7.42.5">F.33.1. Functions</a></span></dt><dt><span class="sect2"><a href="pgstattuple.html#id-1.11.7.42.6">F.33.2. Authors</a></span></dt></dl></div><a id="id-1.11.7.42.2" class="indexterm"></a><p> + The <code class="filename">pgstattuple</code> module provides various functions to + obtain tuple-level statistics. + </p><p> + Because these functions return detailed page-level information, access is + restricted by default. By default, only the + role <code class="literal">pg_stat_scan_tables</code> has <code class="literal">EXECUTE</code> + privilege. Superusers of course bypass this restriction. After the + extension has been installed, users may issue <code class="command">GRANT</code> + commands to change the privileges on the functions to allow others to + execute them. However, it might be preferable to add those users to + the <code class="literal">pg_stat_scan_tables</code> role instead. + </p><div class="sect2" id="id-1.11.7.42.5"><div class="titlepage"><div><div><h3 class="title">F.33.1. Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term"> + <a id="id-1.11.7.42.5.2.1.1.1" class="indexterm"></a> + <code class="function">pgstattuple(regclass) returns record</code> + </span></dt><dd><p> + <code class="function">pgstattuple</code> returns a relation's physical length, + percentage of <span class="quote">“<span class="quote">dead</span>”</span> tuples, and other info. This may help users + to determine whether vacuum is necessary or not. The argument is the + target relation's name (optionally schema-qualified) or OID. + For example: +</p><pre class="programlisting"> +test=> SELECT * FROM pgstattuple('pg_catalog.pg_proc'); +-[ RECORD 1 ]------+------- +table_len | 458752 +tuple_count | 1470 +tuple_len | 438896 +tuple_percent | 95.67 +dead_tuple_count | 11 +dead_tuple_len | 3157 +dead_tuple_percent | 0.69 +free_space | 8932 +free_percent | 1.95 +</pre><p> + The output columns are described in <a class="xref" href="pgstattuple.html#PGSTATTUPLE-COLUMNS" title="Table F.22. pgstattuple Output Columns">Table F.22</a>. + </p><div class="table" id="PGSTATTUPLE-COLUMNS"><p class="title"><strong>Table F.22. <code class="function">pgstattuple</code> Output Columns</strong></p><div class="table-contents"><table class="table" summary="pgstattuple Output Columns" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">table_len</code></td><td><code class="type">bigint</code></td><td>Physical relation length in bytes</td></tr><tr><td><code class="structfield">tuple_count</code></td><td><code class="type">bigint</code></td><td>Number of live tuples</td></tr><tr><td><code class="structfield">tuple_len</code></td><td><code class="type">bigint</code></td><td>Total length of live tuples in bytes</td></tr><tr><td><code class="structfield">tuple_percent</code></td><td><code class="type">float8</code></td><td>Percentage of live tuples</td></tr><tr><td><code class="structfield">dead_tuple_count</code></td><td><code class="type">bigint</code></td><td>Number of dead tuples</td></tr><tr><td><code class="structfield">dead_tuple_len</code></td><td><code class="type">bigint</code></td><td>Total length of dead tuples in bytes</td></tr><tr><td><code class="structfield">dead_tuple_percent</code></td><td><code class="type">float8</code></td><td>Percentage of dead tuples</td></tr><tr><td><code class="structfield">free_space</code></td><td><code class="type">bigint</code></td><td>Total free space in bytes</td></tr><tr><td><code class="structfield">free_percent</code></td><td><code class="type">float8</code></td><td>Percentage of free space</td></tr></tbody></table></div></div><br class="table-break" /><div class="note"><h3 class="title">Note</h3><p> + The <code class="literal">table_len</code> will always be greater than the sum + of the <code class="literal">tuple_len</code>, <code class="literal">dead_tuple_len</code> + and <code class="literal">free_space</code>. The difference is accounted for by + fixed page overhead, the per-page table of pointers to tuples, and + padding to ensure that tuples are correctly aligned. + </p></div><p> + <code class="function">pgstattuple</code> acquires only a read lock on the + relation. So the results do not reflect an instantaneous snapshot; + concurrent updates will affect them. + </p><p> + <code class="function">pgstattuple</code> judges a tuple is <span class="quote">“<span class="quote">dead</span>”</span> if + <code class="function">HeapTupleSatisfiesDirty</code> returns false. + </p></dd><dt><span class="term"> + <code class="function">pgstattuple(text) returns record</code> + </span></dt><dd><p> + This is the same as <code class="function">pgstattuple(regclass)</code>, except + that the target relation is specified as TEXT. This function is kept + because of backward-compatibility so far, and will be deprecated in + some future release. + </p></dd><dt><span class="term"> + <a id="id-1.11.7.42.5.2.3.1.1" class="indexterm"></a> + <code class="function">pgstatindex(regclass) returns record</code> + </span></dt><dd><p> + <code class="function">pgstatindex</code> returns a record showing information + about a B-tree index. For example: +</p><pre class="programlisting"> +test=> SELECT * FROM pgstatindex('pg_cast_oid_index'); +-[ RECORD 1 ]------+------ +version | 2 +tree_level | 0 +index_size | 16384 +root_block_no | 1 +internal_pages | 0 +leaf_pages | 1 +empty_pages | 0 +deleted_pages | 0 +avg_leaf_density | 54.27 +leaf_fragmentation | 0 +</pre><p> + </p><p> + The output columns are: + + </p><div class="informaltable"><table class="informaltable" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">version</code></td><td><code class="type">integer</code></td><td>B-tree version number</td></tr><tr><td><code class="structfield">tree_level</code></td><td><code class="type">integer</code></td><td>Tree level of the root page</td></tr><tr><td><code class="structfield">index_size</code></td><td><code class="type">bigint</code></td><td>Total index size in bytes</td></tr><tr><td><code class="structfield">root_block_no</code></td><td><code class="type">bigint</code></td><td>Location of root page (zero if none)</td></tr><tr><td><code class="structfield">internal_pages</code></td><td><code class="type">bigint</code></td><td>Number of <span class="quote">“<span class="quote">internal</span>”</span> (upper-level) pages</td></tr><tr><td><code class="structfield">leaf_pages</code></td><td><code class="type">bigint</code></td><td>Number of leaf pages</td></tr><tr><td><code class="structfield">empty_pages</code></td><td><code class="type">bigint</code></td><td>Number of empty pages</td></tr><tr><td><code class="structfield">deleted_pages</code></td><td><code class="type">bigint</code></td><td>Number of deleted pages</td></tr><tr><td><code class="structfield">avg_leaf_density</code></td><td><code class="type">float8</code></td><td>Average density of leaf pages</td></tr><tr><td><code class="structfield">leaf_fragmentation</code></td><td><code class="type">float8</code></td><td>Leaf page fragmentation</td></tr></tbody></table></div><p> + </p><p> + The reported <code class="literal">index_size</code> will normally correspond to one more + page than is accounted for by <code class="literal">internal_pages + leaf_pages + + empty_pages + deleted_pages</code>, because it also includes the + index's metapage. + </p><p> + As with <code class="function">pgstattuple</code>, the results are accumulated + page-by-page, and should not be expected to represent an + instantaneous snapshot of the whole index. + </p></dd><dt><span class="term"> + <code class="function">pgstatindex(text) returns record</code> + </span></dt><dd><p> + This is the same as <code class="function">pgstatindex(regclass)</code>, except + that the target index is specified as TEXT. This function is kept + because of backward-compatibility so far, and will be deprecated in + some future release. + </p></dd><dt><span class="term"> + <a id="id-1.11.7.42.5.2.5.1.1" class="indexterm"></a> + <code class="function">pgstatginindex(regclass) returns record</code> + </span></dt><dd><p> + <code class="function">pgstatginindex</code> returns a record showing information + about a GIN index. For example: +</p><pre class="programlisting"> +test=> SELECT * FROM pgstatginindex('test_gin_index'); +-[ RECORD 1 ]--+-- +version | 1 +pending_pages | 0 +pending_tuples | 0 +</pre><p> + </p><p> + The output columns are: + + </p><div class="informaltable"><table class="informaltable" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">version</code></td><td><code class="type">integer</code></td><td>GIN version number</td></tr><tr><td><code class="structfield">pending_pages</code></td><td><code class="type">integer</code></td><td>Number of pages in the pending list</td></tr><tr><td><code class="structfield">pending_tuples</code></td><td><code class="type">bigint</code></td><td>Number of tuples in the pending list</td></tr></tbody></table></div><p> + </p></dd><dt><span class="term"> + <a id="id-1.11.7.42.5.2.6.1.1" class="indexterm"></a> + <code class="function">pgstathashindex(regclass) returns record</code> + </span></dt><dd><p> + <code class="function">pgstathashindex</code> returns a record showing information + about a HASH index. For example: +</p><pre class="programlisting"> +test=> select * from pgstathashindex('con_hash_index'); +-[ RECORD 1 ]--+----------------- +version | 4 +bucket_pages | 33081 +overflow_pages | 0 +bitmap_pages | 1 +unused_pages | 32455 +live_items | 10204006 +dead_items | 0 +free_percent | 61.8005949100872 +</pre><p> + </p><p> + The output columns are: + + </p><div class="informaltable"><table class="informaltable" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">version</code></td><td><code class="type">integer</code></td><td>HASH version number</td></tr><tr><td><code class="structfield">bucket_pages</code></td><td><code class="type">bigint</code></td><td>Number of bucket pages</td></tr><tr><td><code class="structfield">overflow_pages</code></td><td><code class="type">bigint</code></td><td>Number of overflow pages</td></tr><tr><td><code class="structfield">bitmap_pages</code></td><td><code class="type">bigint</code></td><td>Number of bitmap pages</td></tr><tr><td><code class="structfield">unused_pages</code></td><td><code class="type">bigint</code></td><td>Number of unused pages</td></tr><tr><td><code class="structfield">live_items</code></td><td><code class="type">bigint</code></td><td>Number of live tuples</td></tr><tr><td><code class="structfield">dead_tuples</code></td><td><code class="type">bigint</code></td><td>Number of dead tuples</td></tr><tr><td><code class="structfield">free_percent</code></td><td><code class="type">float</code></td><td>Percentage of free space</td></tr></tbody></table></div><p> + </p></dd><dt><span class="term"> + <a id="id-1.11.7.42.5.2.7.1.1" class="indexterm"></a> + <code class="function">pg_relpages(regclass) returns bigint</code> + </span></dt><dd><p> + <code class="function">pg_relpages</code> returns the number of pages in the + relation. + </p></dd><dt><span class="term"> + <code class="function">pg_relpages(text) returns bigint</code> + </span></dt><dd><p> + This is the same as <code class="function">pg_relpages(regclass)</code>, except + that the target relation is specified as TEXT. This function is kept + because of backward-compatibility so far, and will be deprecated in + some future release. + </p></dd><dt><span class="term"> + <a id="id-1.11.7.42.5.2.9.1.1" class="indexterm"></a> + <code class="function">pgstattuple_approx(regclass) returns record</code> + </span></dt><dd><p> + <code class="function">pgstattuple_approx</code> is a faster alternative to + <code class="function">pgstattuple</code> that returns approximate results. + The argument is the target relation's name or OID. + For example: +</p><pre class="programlisting"> +test=> SELECT * FROM pgstattuple_approx('pg_catalog.pg_proc'::regclass); +-[ RECORD 1 ]--------+------- +table_len | 573440 +scanned_percent | 2 +approx_tuple_count | 2740 +approx_tuple_len | 561210 +approx_tuple_percent | 97.87 +dead_tuple_count | 0 +dead_tuple_len | 0 +dead_tuple_percent | 0 +approx_free_space | 11996 +approx_free_percent | 2.09 +</pre><p> + The output columns are described in <a class="xref" href="pgstattuple.html#PGSTATAPPROX-COLUMNS" title="Table F.23. pgstattuple_approx Output Columns">Table F.23</a>. + </p><p> + Whereas <code class="function">pgstattuple</code> always performs a + full-table scan and returns an exact count of live and dead tuples + (and their sizes) and free space, <code class="function">pgstattuple_approx</code> + tries to avoid the full-table scan and returns exact dead tuple + statistics along with an approximation of the number and + size of live tuples and free space. + </p><p> + It does this by skipping pages that have only visible tuples + according to the visibility map (if a page has the corresponding VM + bit set, then it is assumed to contain no dead tuples). For such + pages, it derives the free space value from the free space map, and + assumes that the rest of the space on the page is taken up by live + tuples. + </p><p> + For pages that cannot be skipped, it scans each tuple, recording its + presence and size in the appropriate counters, and adding up the + free space on the page. At the end, it estimates the total number of + live tuples based on the number of pages and tuples scanned (in the + same way that VACUUM estimates pg_class.reltuples). + </p><div class="table" id="PGSTATAPPROX-COLUMNS"><p class="title"><strong>Table F.23. <code class="function">pgstattuple_approx</code> Output Columns</strong></p><div class="table-contents"><table class="table" summary="pgstattuple_approx Output Columns" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">table_len</code></td><td><code class="type">bigint</code></td><td>Physical relation length in bytes (exact)</td></tr><tr><td><code class="structfield">scanned_percent</code></td><td><code class="type">float8</code></td><td>Percentage of table scanned</td></tr><tr><td><code class="structfield">approx_tuple_count</code></td><td><code class="type">bigint</code></td><td>Number of live tuples (estimated)</td></tr><tr><td><code class="structfield">approx_tuple_len</code></td><td><code class="type">bigint</code></td><td>Total length of live tuples in bytes (estimated)</td></tr><tr><td><code class="structfield">approx_tuple_percent</code></td><td><code class="type">float8</code></td><td>Percentage of live tuples</td></tr><tr><td><code class="structfield">dead_tuple_count</code></td><td><code class="type">bigint</code></td><td>Number of dead tuples (exact)</td></tr><tr><td><code class="structfield">dead_tuple_len</code></td><td><code class="type">bigint</code></td><td>Total length of dead tuples in bytes (exact)</td></tr><tr><td><code class="structfield">dead_tuple_percent</code></td><td><code class="type">float8</code></td><td>Percentage of dead tuples</td></tr><tr><td><code class="structfield">approx_free_space</code></td><td><code class="type">bigint</code></td><td>Total free space in bytes (estimated)</td></tr><tr><td><code class="structfield">approx_free_percent</code></td><td><code class="type">float8</code></td><td>Percentage of free space</td></tr></tbody></table></div></div><br class="table-break" /><p> + In the above output, the free space figures may not match the + <code class="function">pgstattuple</code> output exactly, because the free + space map gives us an exact figure, but is not guaranteed to be + accurate to the byte. + </p></dd></dl></div></div><div class="sect2" id="id-1.11.7.42.6"><div class="titlepage"><div><div><h3 class="title">F.33.2. Authors</h3></div></div></div><p> + Tatsuo Ishii, Satoshi Nagayasu and Abhijit Menon-Sen + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pgstatstatements.html" title="F.32. pg_stat_statements">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="pgsurgery.html" title="F.34. pg_surgery">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.32. pg_stat_statements </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"> F.34. pg_surgery</td></tr></table></div></body></html>
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