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Add contrib/pg_logicalinspect.

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This module provides SQL functions that allow to inspect logical
decoding components.

It currently allows to inspect the contents of serialized logical
snapshots of a running database cluster, which is useful for debugging
or educational purposes.

Author: Bertrand Drouvot
Reviewed-by: Amit Kapila, Shveta Malik, Peter Smith, Peter Eisentraut
Reviewed-by: David G. Johnston
Discussion: https://postgr.es/m/ZscuZ92uGh3wm4tW%40ip-10-97-1-34.eu-west-3.compute.internal
This commit is contained in:
Masahiko Sawada
2024-10-14 17:22:02 -07:00
parent e2fd615ecc
commit 7cdfeee320
18 changed files with 598 additions and 39 deletions
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1
doc/src/sgml/contrib.sgml
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@@ -154,6 +154,7 @@ CREATE EXTENSION <replaceable>extension_name</replaceable>;
&pgbuffercache;
&pgcrypto;
&pgfreespacemap;
&pglogicalinspect;
&pgprewarm;
&pgrowlocks;
&pgstatstatements;

1
doc/src/sgml/filelist.sgml
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@@ -143,6 +143,7 @@
<!ENTITY pgbuffercache SYSTEM "pgbuffercache.sgml">
<!ENTITY pgcrypto SYSTEM "pgcrypto.sgml">
<!ENTITY pgfreespacemap SYSTEM "pgfreespacemap.sgml">
<!ENTITY pglogicalinspect SYSTEM "pglogicalinspect.sgml">
<!ENTITY pgprewarm SYSTEM "pgprewarm.sgml">
<!ENTITY pgrowlocks SYSTEM "pgrowlocks.sgml">
<!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">

143
doc/src/sgml/pglogicalinspect.sgml Normal file
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@@ -0,0 +1,143 @@
<!-- doc/src/sgml/pglogicalinspect.sgml -->
<sect1 id="pglogicalinspect" xreflabel="pg_logicalinspect">
<title>pg_logicalinspect &mdash; logical decoding components inspection</title>
<indexterm zone="pglogicalinspect">
<primary>pg_logicalinspect</primary>
</indexterm>
<para>
The <filename>pg_logicalinspect</filename> module provides SQL functions
that allow you to inspect the contents of logical decoding components. It
allows the inspection of serialized logical snapshots of a running
<productname>PostgreSQL</productname> database cluster, which is useful
for debugging or educational purposes.
</para>
<para>
By default, use of these functions is restricted to superusers and members of
the <literal>pg_read_server_files</literal> role. Access may be granted by
superusers to others using <command>GRANT</command>.
</para>
<sect2 id="pglogicalinspect-funcs">
<title>Functions</title>
<variablelist>
<varlistentry id="pglogicalinspect-funcs-pg-get-logical-snapshot-meta">
<term>
<function>pg_get_logical_snapshot_meta(filename text) returns record</function>
</term>
<listitem>
<para>
Gets logical snapshot metadata about a snapshot file that is located in
the server's <filename>pg_logical/snapshots</filename> directory.
The <replaceable>filename</replaceable> argument represents the snapshot
file name.
For example:
<screen>
postgres=# SELECT * FROM pg_ls_logicalsnapdir();
-[ RECORD 1 ]+-----------------------
name | 0-40796E18.snap
size | 152
modification | 2024-08-14 16:36:32+00
postgres=# SELECT * FROM pg_get_logical_snapshot_meta('0-40796E18.snap');
-[ RECORD 1 ]--------
magic | 1369563137
checksum | 1028045905
version | 6
postgres=# SELECT ss.name, meta.* FROM pg_ls_logicalsnapdir() AS ss,
pg_get_logical_snapshot_meta(ss.name) AS meta;
-[ RECORD 1 ]-------------
name | 0-40796E18.snap
magic | 1369563137
checksum | 1028045905
version | 6
</screen>
</para>
<para>
If <replaceable>filename</replaceable> does not match a snapshot file, the
function raises an error.
</para>
</listitem>
</varlistentry>
<varlistentry id="pglogicalinspect-funcs-pg-get-logical-snapshot-info">
<term>
<function>pg_get_logical_snapshot_info(filename text) returns record</function>
</term>
<listitem>
<para>
Gets logical snapshot information about a snapshot file that is located in
the server's <filename>pg_logical/snapshots</filename> directory.
The <replaceable>filename</replaceable> argument represents the snapshot
file name.
For example:
<screen>
postgres=# SELECT * FROM pg_ls_logicalsnapdir();
-[ RECORD 1 ]+-----------------------
name | 0-40796E18.snap
size | 152
modification | 2024-08-14 16:36:32+00
postgres=# SELECT * FROM pg_get_logical_snapshot_info('0-40796E18.snap');
-[ RECORD 1 ]------------+-----------
state | consistent
xmin | 751
xmax | 751
start_decoding_at | 0/40796AF8
two_phase_at | 0/40796AF8
initial_xmin_horizon | 0
building_full_snapshot | f
in_slot_creation | f
last_serialized_snapshot | 0/0
next_phase_at | 0
committed_count | 0
committed_xip |
catchange_count | 2
catchange_xip | {751,752}
postgres=# SELECT ss.name, info.* FROM pg_ls_logicalsnapdir() AS ss,
pg_get_logical_snapshot_info(ss.name) AS info;
-[ RECORD 1 ]------------+----------------
name | 0-40796E18.snap
state | consistent
xmin | 751
xmax | 751
start_decoding_at | 0/40796AF8
two_phase_at | 0/40796AF8
initial_xmin_horizon | 0
building_full_snapshot | f
in_slot_creation | f
last_serialized_snapshot | 0/0
next_phase_at | 0
committed_count | 0
committed_xip |
catchange_count | 2
catchange_xip | {751,752}
</screen>
</para>
<para>
If <replaceable>filename</replaceable> does not match a snapshot file, the
function raises an error.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="pglogicalinspect-author">
<title>Author</title>
<para>
Bertrand Drouvot <email>bertranddrouvot.pg@gmail.com</email>
</para>
</sect2>
</sect1>