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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-13 13:44:03 +0000 |
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| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-13 13:44:03 +0000 |
| commit | 293913568e6a7a86fd1479e1cff8e2ecb58d6568 (patch) | |
| tree | fc3b469a3ec5ab71b36ea97cc7aaddb838423a0c /doc/src/sgml/html/pgwalinspect.html | |
| parent | Initial commit. (diff) | |
| download | postgresql-16-293913568e6a7a86fd1479e1cff8e2ecb58d6568.tar.xz postgresql-16-293913568e6a7a86fd1479e1cff8e2ecb58d6568.zip | |
Adding upstream version 16.2.upstream/16.2
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/src/sgml/html/pgwalinspect.html')
| -rw-r--r-- | doc/src/sgml/html/pgwalinspect.html | 211 |
1 files changed, 211 insertions, 0 deletions
diff --git a/doc/src/sgml/html/pgwalinspect.html b/doc/src/sgml/html/pgwalinspect.html new file mode 100644 index 0000000..39e80fd --- /dev/null +++ b/doc/src/sgml/html/pgwalinspect.html @@ -0,0 +1,211 @@ +<?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 — low-level WAL inspection</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 — visibility map information and utilities" /><link rel="next" href="postgres-fdw.html" title="F.38. postgres_fdw — access data stored in external PostgreSQL servers" /></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 — low-level WAL inspection</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgvisibility.html" title="F.36. pg_visibility — visibility map information and utilities">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="postgres-fdw.html" title="F.38. postgres_fdw — access data stored in external PostgreSQL servers">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 — low-level WAL inspection <a href="#PGWALINSPECT" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgwalinspect.html#PGWALINSPECT-FUNCS">F.37.1. General Functions</a></span></dt><dt><span class="sect2"><a href="pgwalinspect.html#PGWALINSPECT-AUTHOR">F.37.2. Author</a></span></dt></dl></div><a id="id-1.11.7.47.2" 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 + server's current timeline ID. + </p><div class="note"><h3 class="title">Note</h3><p> + The <code class="filename">pg_walinspect</code> functions are often called + using an LSN argument that specifies the location at which a known + WAL record of interest <span class="emphasis"><em>begins</em></span>. However, 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 that was just + inserted. + </p></div><div class="tip"><h3 class="title">Tip</h3><p> + All of the <code class="filename">pg_walinspect</code> functions that show + information about records that fall within a certain LSN range are + permissive about accepting <em class="replaceable"><code>end_lsn</code></em> + arguments that are after the server's current LSN. Using an + <em class="replaceable"><code>end_lsn</code></em> <span class="quote">“<span class="quote">from the future</span>”</span> + will not raise an error. + </p><p> + It may be convenient to provide the value + <code class="literal">FFFFFFFF/FFFFFFFF</code> (the maximum valid + <code class="type">pg_lsn</code> value) as an <em class="replaceable"><code>end_lsn</code></em> + argument. This is equivalent to providing an + <em class="replaceable"><code>end_lsn</code></em> argument matching the server's + current LSN. + </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="PGWALINSPECT-FUNCS"><div class="titlepage"><div><div><h3 class="title">F.37.1. General Functions <a href="#PGWALINSPECT-FUNCS" class="id_link">#</a></h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="PGWALINSPECT-FUNCS-PG-GET-WAL-RECORD-INFO"><span class="term"> + <code class="function">pg_get_wal_record_info(in_lsn pg_lsn) returns record</code> + </span> <a href="#PGWALINSPECT-FUNCS-PG-GET-WAL-RECORD-INFO" class="id_link">#</a></dt><dd><p> + Gets WAL record information about a record that is located at or + after the <em class="replaceable"><code>in_lsn</code></em> argument. For + example: +</p><pre class="screen"> +postgres=# SELECT * FROM pg_get_wal_record_info('0/E419E28'); +-[ RECORD 1 ]----+------------------------------------------------- +start_lsn | 0/E419E28 +end_lsn | 0/E419E68 +prev_lsn | 0/E419D78 +xid | 0 +resource_manager | Heap2 +record_type | VACUUM +record_length | 58 +main_data_length | 2 +fpi_length | 0 +description | nunused: 5, unused: [1, 2, 3, 4, 5] +block_ref | blkref #0: rel 1663/16385/1249 fork main blk 364 +</pre><p> + </p><p> + If <em class="replaceable"><code>in_lsn</code></em> isn't at the start of a WAL + record, information about the next valid WAL record is shown + instead. If there is no next valid WAL record, the function + raises an error. + </p></dd><dt id="PGWALINSPECT-FUNCS-PG-GET-WAL-RECORDS-INFO"><span class="term"> + <code class="function"> + pg_get_wal_records_info(start_lsn pg_lsn, end_lsn pg_lsn) + returns setof record + </code> + </span> <a href="#PGWALINSPECT-FUNCS-PG-GET-WAL-RECORDS-INFO" class="id_link">#</a></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. 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><p> + The function raises an error if + <em class="replaceable"><code>start_lsn</code></em> is not available. + </p></dd><dt id="PGWALINSPECT-FUNCS-PG-GET-WAL-BLOCK-INFO"><span class="term"> + <code class="function">pg_get_wal_block_info(start_lsn pg_lsn, end_lsn pg_lsn, show_data boolean DEFAULT true) returns setof record</code> + </span> <a href="#PGWALINSPECT-FUNCS-PG-GET-WAL-BLOCK-INFO" class="id_link">#</a></dt><dd><p> + Gets information about each block reference from all the valid + WAL records between <em class="replaceable"><code>start_lsn</code></em> and + <em class="replaceable"><code>end_lsn</code></em> with one or more block + references. Returns one row per block reference per WAL record. + For example: +</p><pre class="screen"> +postgres=# SELECT * FROM pg_get_wal_block_info('0/1230278', '0/12302B8'); +-[ RECORD 1 ]-----+----------------------------------- +start_lsn | 0/1230278 +end_lsn | 0/12302B8 +prev_lsn | 0/122FD40 +block_id | 0 +reltablespace | 1663 +reldatabase | 1 +relfilenode | 2658 +relforknumber | 0 +relblocknumber | 11 +xid | 341 +resource_manager | Btree +record_type | INSERT_LEAF +record_length | 64 +main_data_length | 2 +block_data_length | 16 +block_fpi_length | 0 +block_fpi_info | +description | off: 46 +block_data | \x00002a00070010402630000070696400 +block_fpi_data | +</pre><p> + </p><p> + This example involves a WAL record that only contains one block + reference, but many WAL records contain several block + references. Rows output by + <code class="function">pg_get_wal_block_info</code> are guaranteed to + have a unique combination of + <em class="replaceable"><code>start_lsn</code></em> and + <em class="replaceable"><code>block_id</code></em> values. + </p><p> + Much of the information shown here matches the output that + <code class="function">pg_get_wal_records_info</code> would show, given + the same arguments. However, + <code class="function">pg_get_wal_block_info</code> unnests the + information from each WAL record into an expanded form by + outputting one row per block reference, so certain details are + tracked at the block reference level rather than at the + whole-record level. This structure is useful with queries that + track how individual blocks changed over time. Note that + records with no block references (e.g., + <code class="literal">COMMIT</code> WAL records) will have no rows + returned, so <code class="function">pg_get_wal_block_info</code> may + actually return <span class="emphasis"><em>fewer</em></span> rows than + <code class="function">pg_get_wal_records_info</code>. + </p><p> + The <code class="structfield">reltablespace</code>, + <code class="structfield">reldatabase</code>, and + <code class="structfield">relfilenode</code> parameters reference + <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>, + <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>, and + <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> + respectively. The <code class="structfield">relforknumber</code> + field is the fork number within the relation for the block + reference; see <code class="filename">common/relpath.h</code> for + details. + </p><div class="tip"><h3 class="title">Tip</h3><p> + The <code class="function">pg_filenode_relation</code> function (see + <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBLOCATION" title="Table 9.97. Database Object Location Functions">Table 9.97</a>) can help you to + determine which relation was modified during original execution. + </p></div><p> + It is possible for clients to avoid the overhead of + materializing block data. This may make function execution + significantly faster. When <em class="replaceable"><code>show_data</code></em> + is set to <code class="literal">false</code>, <code class="structfield">block_data</code> + and <code class="structfield">block_fpi_data</code> values are omitted + (that is, the <code class="structfield">block_data</code> and + <code class="structfield">block_fpi_data</code> <code class="literal">OUT</code> + arguments are <code class="literal">NULL</code> for all rows returned). + Obviously, this optimization is only feasible with queries where + block data isn't truly required. + </p><p> + The function raises an error if + <em class="replaceable"><code>start_lsn</code></em> is not available. + </p></dd><dt id="PGWALINSPECT-FUNCS-PG-GET-WAL-STATS"><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> <a href="#PGWALINSPECT-FUNCS-PG-GET-WAL-STATS" class="id_link">#</a></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>. + 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><p> + The function raises an error if + <em class="replaceable"><code>start_lsn</code></em> is not available. + </p></dd></dl></div></div><div class="sect2" id="PGWALINSPECT-AUTHOR"><div class="titlepage"><div><div><h3 class="title">F.37.2. Author <a href="#PGWALINSPECT-AUTHOR" class="id_link">#</a></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 — visibility map information and utilities">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="postgres-fdw.html" title="F.38. postgres_fdw — access data stored in external PostgreSQL servers">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.36. pg_visibility — visibility map information and utilities </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.38. postgres_fdw — + access data stored in external <span class="productname">PostgreSQL</span> + servers</td></tr></table></div></body></html>
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