Re: Shared WAL archive between master and standby: WALs not always identical

On 02/27/2017 05:29 PM, Sasa Vilic wrote:
> Master is streaming directly to standby. Both master and standby are
> pushing WALs to archive.
>
> My point is that in case that master crashed completely (and we failover
> to standby) and wal archiver on master didn't push everything to wal
> archive, we would still have a wal pushed from slave. Therefore there is
> no interruption in WAL stream.

Still failing to see how the standby can have more information then what
the master had sent to it at the time of the crash.

>
> Regards,
> Sasa
>
> On 28 February 2017 at 01:57, Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
>
> On 02/27/2017 04:40 PM, Sasa Vilic wrote:
>
> Hallo,
>
> I am trying to setup shared WAL archive between master and standby.
> Standby is synchronously streaming from master and both servers
> run with
> archive_mode = always. The ideas is that when promoting standby to
> master we would not missed WALs.
>
>
> I seem to be missing the point of duplicating your effort.
>
> You are doing this, correct?:
>
> Master WAL --> WAL archive <--
> |
> Master stream --> Standby --> |
>
> I can't see how the Standby contributes anything to the archive that
> it does not already have from the Master?
>
>
>
> My problem is that sometimes WAL uploaded from master and from
> slave are
> not 100% identical. In most cases they are but occasionally they are
> not. I have written small script that ensures that upload is free of
> race condition and I log md5 sum of each WAL. Aren't WALs from
> master
> and standby supposed to be identical? After all, standby is just
> consuming WAL that it is receiving from master ...
>
> Or do you have any better suggestion on how to achieve continuous
> incremental backup?
>
> Thanks in advance
>
>
>
> --
> 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