Re: Synch failover WAS: Support for N synchronous standby servers - take 2

On Fri, Jul 3, 2015 at 6:23 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Fri, Jul 3, 2015 at 5:59 PM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> Yeah, quorum commit is helpful for minimizing data loss in comparison
>> with today replication.
>> But in this your case, how can we know which server we should use as
>> the next master server, after local data center got down?
>> If we choose a wrong one, we would get the data loss.
>
> Check the progress of each server, e.g., by using
> pg_last_xlog_replay_location(),
> and choose the server which is ahead of as new master.
>

Thanks. So we can choice the next master server using by checking the
progress of each server, if hot standby is enabled.
And a such procedure is needed even today replication.

I think that the #2 problem which is Josh pointed out seems to be solved;
1. I need to ensure that data is replicated to X places.
2. I need to *know* which places data was synchronously replicated
to when the master goes down.
And we can address #1 problem using quorum commit.

Thought?

Regards,

--
Sawada Masahiko