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<?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.37. pg_walinspect</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="pgvisibility.html" title="F.36. pg_visibility" /><link rel="next" href="postgres-fdw.html" title="F.38. postgres_fdw" /></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.37. pg_walinspect</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgvisibility.html" title="F.36. pg_visibility">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 15.7 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="postgres-fdw.html" title="F.38. postgres_fdw">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGWALINSPECT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.37. pg_walinspect</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgwalinspect.html#id-1.11.7.46.8">F.37.1. General Functions</a></span></dt><dt><span class="sect2"><a href="pgwalinspect.html#id-1.11.7.46.9">F.37.2. Author</a></span></dt></dl></div><a id="id-1.11.7.46.2" class="indexterm"></a><p>
The <code class="filename">pg_walinspect</code> module provides SQL functions that
allow you to inspect the contents of write-ahead log of
a running <span class="productname">PostgreSQL</span> database cluster at a low
level, which is useful for debugging, analytical, reporting or
educational purposes. It is similar to <a class="xref" href="pgwaldump.html" title="pg_waldump"><span class="refentrytitle"><span class="application">pg_waldump</span></span></a>, but
accessible through SQL rather than a separate utility.
</p><p>
All the functions of this module will provide the WAL information using the
current server's timeline ID.
</p><p>
All the functions of this module will try to find the first valid WAL record
that is at or after the given <em class="replaceable"><code>in_lsn</code></em> or
<em class="replaceable"><code>start_lsn</code></em> and will emit error if no such record
is available. Similarly, the <em class="replaceable"><code>end_lsn</code></em> must be
available, and if it falls in the middle of a record, the entire record must
be available.
</p><div class="note"><h3 class="title">Note</h3><p>
Some functions, such as <code class="function"><a class="link" href="functions-admin.html#PG-LOGICAL-EMIT-MESSAGE">pg_logical_emit_message</a></code>,
return the LSN <span class="emphasis"><em>after</em></span> the record just
inserted. Therefore, if you pass that LSN as
<em class="replaceable"><code>in_lsn</code></em> or <em class="replaceable"><code>start_lsn</code></em>
to one of these functions, it will return the <span class="emphasis"><em>next</em></span>
record.
</p></div><p>
By default, use of these functions is restricted to superusers and members of
the <code class="literal">pg_read_server_files</code> role. Access may be granted by
superusers to others using <code class="command">GRANT</code>.
</p><div class="sect2" id="id-1.11.7.46.8"><div class="titlepage"><div><div><h3 class="title">F.37.1. General Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="function">pg_get_wal_record_info(in_lsn pg_lsn) returns record</code>
</span></dt><dd><p>
Gets WAL record information of a given LSN. If the given LSN isn't
at the start of a WAL record, it gives the information of the next
available valid WAL record; or an error if no such record is found.
For example, usage of the function is as
follows:
</p><pre class="screen">
postgres=# SELECT * FROM pg_get_wal_record_info('0/1E826E98');
-[ RECORD 1 ]----+----------------------------------------------------
start_lsn | 0/1E826F20
end_lsn | 0/1E826F60
prev_lsn | 0/1E826C80
xid | 0
resource_manager | Heap2
record_type | PRUNE
record_length | 58
main_data_length | 8
fpi_length | 0
description | snapshotConflictHorizon 33748 nredirected 0 ndead 2
block_ref | blkref #0: rel 1663/5/60221 fork main blk 2
</pre><p>
</p></dd><dt><span class="term">
<code class="function">
pg_get_wal_records_info(start_lsn pg_lsn, end_lsn pg_lsn)
returns setof record
</code>
</span></dt><dd><p>
Gets information of all the valid WAL records between
<em class="replaceable"><code>start_lsn</code></em> and <em class="replaceable"><code>end_lsn</code></em>.
Returns one row per WAL record. If <em class="replaceable"><code>start_lsn</code></em>
or <em class="replaceable"><code>end_lsn</code></em> are not yet available, the
function will raise an error. For example:
</p><pre class="screen">
postgres=# SELECT * FROM pg_get_wal_records_info('0/1E913618', '0/1E913740') LIMIT 1;
-[ RECORD 1 ]----+--------------------------------------------------------------
start_lsn | 0/1E913618
end_lsn | 0/1E913650
prev_lsn | 0/1E9135A0
xid | 0
resource_manager | Standby
record_type | RUNNING_XACTS
record_length | 50
main_data_length | 24
fpi_length | 0
description | nextXid 33775 latestCompletedXid 33774 oldestRunningXid 33775
block_ref |
</pre><p>
</p></dd><dt><span class="term">
<code class="function">
pg_get_wal_records_info_till_end_of_wal(start_lsn pg_lsn)
returns setof record
</code>
</span></dt><dd><p>
This function is the same as <code class="function">pg_get_wal_records_info()</code>,
except that it gets information of all the valid WAL records from
<em class="replaceable"><code>start_lsn</code></em> till the end of WAL.
</p></dd><dt><span class="term">
<code class="function">
pg_get_wal_stats(start_lsn pg_lsn, end_lsn pg_lsn, per_record boolean DEFAULT false)
returns setof record
</code>
</span></dt><dd><p>
Gets statistics of all the valid WAL records between
<em class="replaceable"><code>start_lsn</code></em> and
<em class="replaceable"><code>end_lsn</code></em>. By default, it returns one row per
<em class="replaceable"><code>resource_manager</code></em> type. When
<em class="replaceable"><code>per_record</code></em> is set to <code class="literal">true</code>,
it returns one row per <em class="replaceable"><code>record_type</code></em>.
If <em class="replaceable"><code>start_lsn</code></em>
or <em class="replaceable"><code>end_lsn</code></em> are not yet available, the
function will raise an error. For example:
</p><pre class="screen">
postgres=# SELECT * FROM pg_get_wal_stats('0/1E847D00', '0/1E84F500')
WHERE count > 0 AND
"resource_manager/record_type" = 'Transaction'
LIMIT 1;
-[ RECORD 1 ]----------------+-------------------
resource_manager/record_type | Transaction
count | 2
count_percentage | 8
record_size | 875
record_size_percentage | 41.23468426013195
fpi_size | 0
fpi_size_percentage | 0
combined_size | 875
combined_size_percentage | 2.8634072910530795
</pre><p>
</p></dd><dt><span class="term">
<code class="function">
pg_get_wal_stats_till_end_of_wal(start_lsn pg_lsn, per_record boolean DEFAULT false)
returns setof record
</code>
</span></dt><dd><p>
This function is the same as <code class="function">pg_get_wal_stats()</code>,
except that it gets statistics of all the valid WAL records from
<em class="replaceable"><code>start_lsn</code></em> till end of WAL.
</p></dd></dl></div></div><div class="sect2" id="id-1.11.7.46.9"><div class="titlepage"><div><div><h3 class="title">F.37.2. Author</h3></div></div></div><p>
Bharath Rupireddy <code class="email"><<a class="email" href="mailto:bharath.rupireddyforpostgres@gmail.com">bharath.rupireddyforpostgres@gmail.com</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="pgvisibility.html" title="F.36. pg_visibility">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="postgres-fdw.html" title="F.38. postgres_fdw">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.36. pg_visibility </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.38. postgres_fdw</td></tr></table></div></body></html>
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