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Add pg_dissect_walfile_name()

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This function takes in input a WAL segment name and returns a tuple made
of the segment sequence number (dependent on the WAL segment size of the
cluster) and its timeline, as of a thin SQL wrapper around the existing
XLogFromFileName().

This function has multiple usages, like being able to compile a LSN from
a file name and an offset, or finding the timeline of a segment without
having to do to some maths based on the first eight characters of the
segment.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Kyotaro Horiguchi, Maxim Orlov, Michael
Paquier
Discussion: https://postgr.es/m/CALj2ACWV=FCddsxcGbVOA=cvPyMr75YCFbSQT6g4KDj=gcJK4g@mail.gmail.com
This commit is contained in:
Michael Paquier
2022-12-20 13:36:27 +09:00
parent b3bb7d12af
commit cca1863489
6 changed files with 125 additions and 1 deletions
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33
doc/src/sgml/func.sgml
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@ -26098,6 +26098,22 @@ LOG: Grand total: 1651920 bytes in 201 blocks; 622360 free (88 chunks); 1029560
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_dissect_walfile_name</primary>
</indexterm>
<function>pg_dissect_walfile_name</function> ( <parameter>file_name</parameter> <type>text</type> )
<returnvalue>record</returnvalue>
( <parameter>segno</parameter> <type>numeric</type>,
<parameter>timeline_id</parameter> <type>bigint</type> )
</para>
<para>
Extracts the file sequence number and timeline ID from a WAL file
name.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
@ -26155,6 +26171,23 @@ postgres=# SELECT * FROM pg_walfile_name_offset((pg_backup_stop()).lsn);
needs to be archived.
</para>
<para>
<function>pg_dissect_walfile_name</function> is useful to compute a
<acronym>LSN</acronym> from a file offset and WAL file name, for example:
<programlisting>
postgres=# \set file_name '000000010000000100C000AB'
postgres=# \set offset 256
postgres=# SELECT '0/0'::pg_lsn + pd.segno * ps.setting::int + :offset AS lsn
FROM pg_dissect_walfile_name(:'file_name') pd,
pg_show_all_settings() ps
WHERE ps.name = 'wal_segment_size';
lsn
---------------
C001/AB000100
(1 row)
</programlisting>
</para>
</sect2>
<sect2 id="functions-recovery-control">