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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/pgrowlocks.html

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  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>F.28. pgrowlocks</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 V1.79.1" /><link rel="prev" href="pgprewarm.html" title="F.27. pg_prewarm" /><link rel="next" href="pgstatstatements.html" title="F.29. pg_stat_statements" /></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.28. pgrowlocks</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgprewarm.html" title="F.27. pg_prewarm">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 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgstatstatements.html" title="F.29. pg_stat_statements">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PGROWLOCKS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.28. pgrowlocks</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgrowlocks.html#id-1.11.7.37.5">F.28.1. Overview</a></span></dt><dt><span class="sect2"><a href="pgrowlocks.html#id-1.11.7.37.6">F.28.2. Sample Output</a></span></dt><dt><span class="sect2"><a href="pgrowlocks.html#id-1.11.7.37.7">F.28.3. Author</a></span></dt></dl></div><a id="id-1.11.7.37.2" class="indexterm"></a><p>

  3.   The <code class="filename">pgrowlocks</code> module provides a function to show row

  4.   locking information for a specified table.

  5.  </p><p>

  6.   By default use is restricted to superusers, members of the

  7.   <code class="literal">pg_stat_scan_tables</code> role, and users with

  8.   <code class="literal">SELECT</code> permissions on the table.

  9.  </p><div class="sect2" id="id-1.11.7.37.5"><div class="titlepage"><div><div><h3 class="title">F.28.1. Overview</h3></div></div></div><a id="id-1.11.7.37.5.2" class="indexterm"></a><pre class="synopsis">

  10. pgrowlocks(text) returns setof record

  11. </pre><p>

  12.    The parameter is the name of a table.  The result is a set of records,

  13.    with one row for each locked row within the table.  The output columns

  14.    are shown in <a class="xref" href="pgrowlocks.html#PGROWLOCKS-COLUMNS" title="Table F.20. pgrowlocks Output Columns">Table F.20</a>.

  15.   </p><div class="table" id="PGROWLOCKS-COLUMNS"><p class="title"><strong>Table F.20. <code class="function">pgrowlocks</code> Output Columns</strong></p><div class="table-contents"><table class="table" summary="pgrowlocks Output Columns" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">locked_row</code></td><td><code class="type">tid</code></td><td>Tuple ID (TID) of locked row</td></tr><tr><td><code class="structfield">locker</code></td><td><code class="type">xid</code></td><td>Transaction ID of locker, or multixact ID if multitransaction</td></tr><tr><td><code class="structfield">multi</code></td><td><code class="type">boolean</code></td><td>True if locker is a multitransaction</td></tr><tr><td><code class="structfield">xids</code></td><td><code class="type">xid[]</code></td><td>Transaction IDs of lockers (more than one if multitransaction)</td></tr><tr><td><code class="structfield">modes</code></td><td><code class="type">text[]</code></td><td>Lock mode of lockers (more than one if multitransaction),

  16.        an array of <code class="literal">Key Share</code>, <code class="literal">Share</code>,

  17.        <code class="literal">For No Key Update</code>, <code class="literal">No Key Update</code>,

  18.        <code class="literal">For Update</code>, <code class="literal">Update</code>.</td></tr><tr><td><code class="structfield">pids</code></td><td><code class="type">integer[]</code></td><td>Process IDs of locking backends (more than one if multitransaction)</td></tr></tbody></table></div></div><br class="table-break" /><p>

  19.    <code class="function">pgrowlocks</code> takes <code class="literal">AccessShareLock</code> for the

  20.    target table and reads each row one by one to collect the row locking

  21.    information.  This is not very speedy for a large table.  Note that:

  22.   </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>

  23.     If the table as a whole is exclusive-locked by someone else,

  24.     <code class="function">pgrowlocks</code> will be blocked.

  25.     </p></li><li class="listitem"><p>

  26.      <code class="function">pgrowlocks</code> is not guaranteed to produce a

  27.      self-consistent snapshot.  It is possible that a new row lock is taken,

  28.      or an old lock is freed, during its execution.

  29.     </p></li></ol></div><p>

  30.    <code class="function">pgrowlocks</code> does not show the contents of locked

  31.    rows. If you want to take a look at the row contents at the same time, you

  32.    could do something like this:

  33. 

  34. </p><pre class="programlisting">

  35. SELECT * FROM accounts AS a, pgrowlocks('accounts') AS p

  36.   WHERE p.locked_row = a.ctid;

  37. </pre><p>

  38. 

  39.    Be aware however that such a query will be very inefficient.

  40.   </p></div><div class="sect2" id="id-1.11.7.37.6"><div class="titlepage"><div><div><h3 class="title">F.28.2. Sample Output</h3></div></div></div><pre class="screen">

  41. =# SELECT * FROM pgrowlocks('t1');

  42.  locked_row | locker | multi | xids  |     modes      |  pids

  43. ------------+--------+-------+-------+----------------+--------

  44.  (0,1)      |    609 | f     | {609} | {"For Share"}  | {3161}

  45.  (0,2)      |    609 | f     | {609} | {"For Share"}  | {3161}

  46.  (0,3)      |    607 | f     | {607} | {"For Update"} | {3107}

  47.  (0,4)      |    607 | f     | {607} | {"For Update"} | {3107}

  48. (4 rows)

  49. </pre></div><div class="sect2" id="id-1.11.7.37.7"><div class="titlepage"><div><div><h3 class="title">F.28.3. Author</h3></div></div></div><p>

  50.    Tatsuo Ishii

  51.   </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pgprewarm.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pgstatstatements.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.27. pg_prewarm </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> F.29. pg_stat_statements</td></tr></table></div></body></html>
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