Re: Postgresql Split Brain: Which one is latest

On 04/10/2018 09:47 AM, Vikas Sharma wrote:
> Thanks Adrian and Edison, I also think so. At the moment I have 2
> masters, as soon as slave is promoted to master it starts its own
> timeline and application might have added data to either of them or
> both, only way to find out correct master now is the instance with max
> count of data in tables which could incur data loss as well. Correct me
> if wrong please?

Not sure max count is necessarily a valid indicator:

1) What if there was a legitimate large delete process?

2) The application/end users where looking at two different views of the
data at different points in time. Just because the count is higher does
not mean the data is actually valid.

>
> Thanks and Regards
> Vikas
>
> On Tue, Apr 10, 2018, 17:29 Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
>
> On 04/10/2018 08:04 AM, Vikas Sharma wrote:
> > Hi Adrian,
> >
> > This can be a good example: Application server e.g. tomcat having two
> > entries to connect to databases, one for master and 2nd for Slave
> > (ideally used when slave becomes master). If application is not
> able to
> > connect to first, it will try to connect to 2nd.
>
> So the application server had a way of seeing the new master(old slave),
> in spite of the network glitch, that the original master database
> did not?
>
> If so and it was distributing data between the two masters on an unknown
> schedule, then as Edison pointed out in another post, you really have a
> split brain issue. Each master would have it's own view of the data and
> latest update would really only be relevant for that master.
>
> >
> > Regards
> > Vikas
> >
> > On 10 April 2018 at 15:26, Adrian Klaver
> <adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
> > <mailto:adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>>> wrote:
> >
> >     On 04/10/2018 06:50 AM, Vikas Sharma wrote:
> >
> >         Hi,
> >
> >         We have postgresql 9.5 with streaming
> replication(Master-slave)
> >         and automatic failover. Due to network glitch we are in
> >         master-master situation for quite some time. Please,
> could you
> >         advise best way to confirm which node is latest in terms of
> >         updates to the postgres databases.
> >
> >
> >     It might help to know how the two masters received data when they
> >     where operating independently.
> >
> >
> >         Regards
> >         Vikas Sharma
> >
> >
> >
> >     --
> >     Adrian Klaver
> > adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
> <mailto:adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>>
> >
> >
>
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com