Re: Standalone synchronous master

On 2014-01-08 17:56:37 -0500, Stephen Frost wrote:
> * Andres Freund (andres(at)2ndquadrant(dot)com) wrote:
> > That's why you should configure a second standby as another (candidate)
> > synchronous replica, also listed in synchronous_standby_names.
>
> Perhaps we should stress in the docs that this is, in fact, the *only*
> reasonable mode in which to run with sync rep on? Where there are
> multiple replicas, because otherwise Drake is correct that you'll just
> end up having both nodes go offline if the slave fails.

Which, as it happens, is actually documented.

http://www.postgresql.org/docs/devel/static/warm-standby.html#SYNCHRONOUS-REPLICATION
25.2.7.3. Planning for High Availability

"Commits made when synchronous_commit is set to on or remote_write will
wait until the synchronous standby responds. The response may never
occur if the last, or only, standby should crash.

The best solution for avoiding data loss is to ensure you don't lose
your last remaining synchronous standby. This can be achieved by naming
multiple potential synchronous standbys using
synchronous_standby_names. The first named standby will be used as the
synchronous standby. Standbys listed after this will take over the role
of synchronous standby if the first one should fail."

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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