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doc: Additional information about timeline ID hexadecimal format

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Timeline IDs are sometimes presented to the user in hexadecimal format
(for example in WAL file names).  Add a few bits of information to
clarify this.

Author: Sébastien Lardière <sebastien@lardiere.net>
Discussion: https://www.postgresql.org/message-id/flat/8fef346e-2541-76c3-d768-6536ae052993@lardiere.net
This commit is contained in:
Peter Eisentraut 2023-03-20 08:48:46 +01:00
parent 785f709576
commit 0b51d423e9
2 changed files with 18 additions and 1 deletions
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11
doc/src/sgml/backup.sgml
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@ -1309,7 +1309,16 @@ restore_command = 'cp /mnt/server/archivedir/%f %p'
a new timeline is created to identify the series of WAL records
generated after that recovery. The timeline
ID number is part of WAL segment file names so a new timeline does
not overwrite the WAL data generated by previous timelines. It is
not overwrite the WAL data generated by previous timelines.
For example, in the WAL file name
<filename>0000000100001234000055CD</filename>, the leading
<literal>00000001</literal> is the timeline ID in hexadecimal. (Note that
in other contexts, such as server log messages, timeline IDs are
usually printed in decimal.)
</para>
<para>
It is
in fact possible to archive many different timelines. While that might
seem like a useless feature, it's often a lifesaver. Consider the
situation where you aren't quite sure what point-in-time to recover to,

8
doc/src/sgml/config.sgml
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@ -4113,6 +4113,14 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
a standby server. <literal>latest</literal> is the default.
</para>
<para>
To specify a timeline ID in hexadecimal (for example, if extracted
from a WAL file name or history file), prefix it with a
<literal>0x</literal>. For instance, if the WAL file name is
<filename>00000011000000A10000004F</filename>, then the timeline ID is
<literal>0x11</literal> (or 17 decimal).
</para>
<para>
You usually only need to set this parameter
in complex re-recovery situations, where you need to return to