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doc: Describe calculation method of streaming start for pg_receivewal

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The documentation was imprecise about the starting LSN used for WAL
streaming if nothing can be found in the local archive directory
defined with the pg_receivewal command, so be more talkative on this
matter.

Extracted from a larger patch by the same author.

Author: Ronan Dunklau, Michael Paquier
Discussion: https://postgr.es/m/18708360.4lzOvYHigE@aivenronan
Backpatch-through: 10
This commit is contained in:
Michael Paquier
2021-10-23 14:43:48 +09:00
parent 52b927a731
commit fb1aa489e4
1 changed files with 23 additions and 0 deletions
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23
doc/src/sgml/ref/pg_receivewal.sgml
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@@ -76,6 +76,29 @@ PostgreSQL documentation
leave at least one session available for the stream.
</para>
<para>
The starting point of the write-ahead log streaming is calculated when
<application>pg_receivewal</application> starts:
<orderedlist>
<listitem>
<para>
First, scan the directory where the WAL segment files are written and
find the newest completed segment file, using as starting point the
beginning of the next WAL segment file. This is calculated independently
on the compression method used to compress each segment.
</para>
</listitem>
<listitem>
<para>
If a starting point cannot be calculated with the previous method,
the latest WAL flush location is used as reported by the server from
a <literal>IDENTIFY_SYSTEM</literal> command.
</para>
</listitem>
</orderedlist>
</para>
<para>
If the connection is lost, or if it cannot be initially established,
with a non-fatal error, <application>pg_receivewal</application> will