Re: Issues with Quorum Commit

On 10/08/2010 05:41 AM, Fujii Masao wrote:
> But, even with quorum commit, if you choose wait-forever option,
> failover would decrease availability. Right after the failover,
> no standby has connected to new master, so if quorum >= 1, all
> the transactions must wait for a while.

That's a point, yes. But again, this is just write-availability, you can
happily read from all active standbies. And connection time is certainly
negligible compared to any kind of timeout (which certainly needs to be
way bigger than a couple of network round-trips).

> Basically we need to take a base backup from new master to start
> the standbys and make them connect to new master. This might take
> a long time. Since transaction commits cannot advance for that time,
> availability would goes down.

Just don't increase your quorum_commit to unreasonable values which your
hardware cannot possible satisfy. It doesn't make sense to set a
quorum_commit of 1 or even bigger, if you don't already have a standby
attached.

Start with 0 (i.e. replication off), then add standbies, then increase
quorum_commit to your new requirements.

> Or you think that wait-forever option is applied only when the
> standby goes down?

That wouldn't work in case of a full-cluster crash, where the
wait-forever option is required again. Otherwise you risk a split-brain
situation.

Regards

Markus Wanner