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"standby promote": add check for WAL replay status if replay is paused

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If WAL replay is paused but WAL is still pending replay, PostgreSQL will ignore
the promote request until WAL replay is unpaused. This may lead to the standby
being promoted at an unpredictable point in time outside of repmgr's
control. Moreover it may not be obvious that this is happening, or why, and
it will appear that an apparently successful promotion attempt has not
actually worked.

To prevent this from happening, repmgr will now refuse to promote the
standy if WAL replay is paused *and* WAL is still pending replay.

GitHub #540.
This commit is contained in:
Ian Barwick
2019-02-05 13:25:21 +09:00
parent d8048060a2
commit 701944c194
4 changed files with 218 additions and 14 deletions
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147
doc/repmgr-standby-promote.sgml
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@@ -33,21 +33,21 @@
Both values can be defined in <filename>repmgr.conf</filename>.
</para>
<note>
<para>
If WAL replay is paused on the standby, and not all WAL files on the standby have been
replayed, &repmgr; will not attempt to promote it.
</para>
<para>
This is because if WAL replay is paused, PostgreSQL itself will not react to a promote command
until WAL replay is resumed and all pending WAL has been replayed. This means
attempting to promote PostgreSQL in this state will leave PostgreSQL in a condition where the
promotion may occur at a unpredictable point in the future.
</para>
</note>
</refsect1>
<refsect1>
<title>Options</title>
<variablelist>
<varlistentry>
<term><option>--dry-run</option></term>
<listitem>
<para>
Check if this node can be promoted, but don't carry out the promotion
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Example</title>
@@ -64,6 +64,127 @@
</refsect1>
<refsect1>
<title>Options</title>
<variablelist>
<varlistentry>
<term><option>--dry-run</option></term>
<listitem>
<para>
Check if this node can be promoted, but don't carry out the promotion
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Configuration file settings</title>
<para>
The following parameters in <filename>repmgr.conf</filename> are relevant to the
promote operation:
</para>
<para>
<itemizedlist spacing="compact" mark="bullet">
<listitem>
<indexterm>
<primary>promote_check_interval</primary>
<secondary>with &quot;repmgr standby promote &quot;</secondary>
</indexterm>
<simpara>
<literal>promote_check_interval</literal>:
interval (in seconds, default: 1 seconds) to wait between each check
to determine whether the standby has been promoted.
</simpara>
</listitem>
<listitem>
<indexterm>
<primary>promote_check_timeout</primary>
<secondary>with &quot;repmgr standby promote &quot;</secondary>
</indexterm>
<simpara>
<literal>promote_check_timeout</literal>:
time (in seconds, default: 60 seconds) to wait to verify that the standby has been promoted
before exiting with <literal>ERR_PROMOTION_FAIL</literal>.
</simpara>
</listitem>
</itemizedlist>
</para>
</refsect1>
<refsect1>
<title>Exit codes</title>
<para>
Following exit codes can be emitted by <command>repmgr standby promote</command>:
</para>
<variablelist>
<varlistentry>
<term><option>SUCCESS (0)</option></term>
<listitem>
<para>
The standby was successfully promoted to primary.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>ERR_DB_CONN (6)</option></term>
<listitem>
<para>
&repmgr; was unable to connect to the local PostgreSQL node.
</para>
<para>
PostgreSQL must be running before the node can be promoted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>ERR_PROMOTION_FAIL (8)</option></term>
<listitem>
<para>
The node could not be promoted to primary for one of the following
reasons:
<itemizedlist spacing="compact" mark="bullet">
<listitem>
<simpara>
there is an existing primary node in the replication cluster
</simpara>
</listitem>
<listitem>
<simpara>
the node is not a standby
</simpara>
</listitem>
<listitem>
<simpara>
WAL replay is paused on the node
</simpara>
</listitem>
<listitem>
<simpara>
execution of the PostgreSQL promote command failed
</simpara>
</listitem>
</itemizedlist>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="repmgr-standby-promote-events">
<title>Event notifications</title>
<para>