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docs: expand witness documentation

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Ian Barwick
2017-11-17 11:00:43 +09:00
parent e2b94adec3
commit 5b4c92392c
9 changed files with 123 additions and 34 deletions
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49
doc/overview.sgml
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@@ -87,6 +87,30 @@
</simpara>
</listitem>
</varlistentry>
<varlistentry id="witness-server">
<term>witness server</term>
<listitem>
<para>
&repmgr; provides functionality to set up a so-called "witness server" to
assist in determining a new primary server in a failover situation with more
than one standby. The witness server itself is not part of the replication
cluster, although it does contain a copy of the repmgr metadata schema.
</para>
<para>
The purpose of a witness server is to provide a "casting vote" where servers
in the replication cluster are split over more than one location. In the event
of a loss of connectivity between locations, the presence or absence of
the witness server will decide whether a server at that location is promoted
to primary; this is to prevent a "split-brain" situation where an isolated
location interprets a network outage as a failure of the (remote) primary and
promotes a (local) standby.
</para>
<para>
A witness server only needs to be created if <application>repmgrd</application>
is in use.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect1>
@@ -145,31 +169,6 @@
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>witness server</term>
<listitem>
<para>
&repmgr; provides functionality to set up a so-called "witness server" to
assist in determining a new primary server in a failover situation with more
than one standby. The witness server itself is not part of the replication
cluster, although it does contain a copy of the repmgr metadata schema
(see below).
</para>
<para>
The purpose of a witness server is to provide a "casting vote" where servers
in the replication cluster are split over more than one location. In the event
of a loss of connectivity between locations, the presence or absence of
the witness server will decide whether a server at that location is promoted
to primary; this is to prevent a "split-brain" situation where an isolated
location interprets a network outage as a failure of the (remote) primary and
promotes a (local) standby.
</para>
<para>
A witness server only needs to be created if <application>repmgrd</application>
is in use.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect1>