Re: Postgresql Split Brain: Which one is latest - Mailing list pgsql-general

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.klaver@aklaver.com
> <mailto:adrian.klaver@aklaver.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.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>      > <mailto:adrian.klaver@aklaver.com
>     <mailto:adrian.klaver@aklaver.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.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>     <mailto:adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>>
>      >
>      >
>
>
>     --
>     Adrian Klaver
>     adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>


--
Adrian Klaver
adrian.klaver@aklaver.com