Re: [GENERAL] Shared WAL archive between master and standby: WALs notalways 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.klaver@aklaver.com
> <mailto:adrian.klaver@aklaver.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.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>
>


--
Adrian Klaver
adrian.klaver@aklaver.com