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Add archive_mode='always' option.

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In 'always' mode, the standby independently archives all files it receives
from the primary.

Original patch by Fujii Masao, docs and review by me.
This commit is contained in:
Heikki Linnakangas
2015-05-15 18:55:24 +03:00
parent f6d65f0c70
commit ffd37740ee
9 changed files with 133 additions and 29 deletions
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13
doc/src/sgml/config.sgml
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@ -2521,7 +2521,7 @@ include_dir 'conf.d'
<variablelist>
<varlistentry id="guc-archive-mode" xreflabel="archive_mode">
<term><varname>archive_mode</varname> (<type>boolean</type>)
<term><varname>archive_mode</varname> (<type>enum</type>)
<indexterm>
<primary><varname>archive_mode</> configuration parameter</primary>
</indexterm>
@ -2530,7 +2530,16 @@ include_dir 'conf.d'
<para>
When <varname>archive_mode</> is enabled, completed WAL segments
are sent to archive storage by setting
<xref linkend="guc-archive-command">.
<xref linkend="guc-archive-command">. In addition to <literal>off</>,
to disable, there are two modes: <literal>on</>, and
<literal>always</>. During normal operation, there is no
difference between the two modes, but when set to <literal>always</>
the WAL archiver is enabled also during archive recovery or standby
mode. In <literal>always</> mode, all files restored from the archive
or streamed with streaming replication will be archived (again). See
<xref linkend="continuous-archiving-in-standby"> for details.
</para>
<para>
<varname>archive_mode</> and <varname>archive_command</> are
separate variables so that <varname>archive_command</> can be
changed without leaving archiving mode.

39
doc/src/sgml/high-availability.sgml
View File

@ -1220,6 +1220,45 @@ primary_slot_name = 'node_a_slot'
</sect3>
</sect2>
<sect2 id="continuous-archiving-in-standby">
<title>Continuous archiving in standby</title>
<indexterm>
<primary>continuous archiving</primary>
<secondary>in standby</secondary>
</indexterm>
<para>
When continuous WAL archiving is used in a standby, there are two
different scenarios: the WAL archive can be shared between the primary
and the standby, or the standby can have its own WAL archive. When
the standby has its own WAL archive, set <varname>archive_mode</varname>
to <literal>always</literal>, and the standby will call the archive
command for every WAL segment it receives, whether it's by restoring
from the archive or by streaming replication. The shared archive can
be handled similarly, but the archive_command must test if the file
being archived exists already, and if the existing file has identical
contents. This requires more care in the archive_command, as it must
be careful to not overwrite an existing file with different contents,
but return success if the exactly same file is archived twice. And
all that must be done free of race conditions, if two servers attempt
to archive the same file at the same time.
</para>
</para>
If <varname>archive_mode</varname> is set to <literal>on</>, the
archiver is not enabled during recovery or standby mode. If the standby
server is promoted, it will start archiving after the promotion, but
will not archive any WAL it did not generate itself. To get a complete
series of WAL files in the archive, you must ensure that all WAL is
archived, before it reaches the standby. This is inherently true with
file-based log shipping, as the standby can only restore files that
are found in the archive, but not if streaming replication is enabled.
When a server is not in recovery mode, there is no difference between
<literal>on</literal> and <literal>always</literal> modes.
</para>
</sect2>
</sect1>
<sect1 id="warm-standby-failover">