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

On Tue, Feb 28, 2017 at 9:41 AM, Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> On 02/27/2017 11:14 PM, Sasa Vilic wrote:
> ...
>

> "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."
>

The wisdom (or not!) in archiving WAL to the same location from multiple
sources (even if they share a common ancestor) notwithstanding, I must
admit to having my curiosity piqued.

Let's assume a different situation:
- a master and one or more standby units each archiving every WAL file but
to it's own archive
- we check to see if identically named WAL files are content identical

Does it surprise anybody else that, sometimes, an identically named WAL
file from the master and from a standby have different contents? It
surprises me.

I would love to know if the differences are due to some oversight in the
WAL archiving mechanism chosen by the OP or if, in fact, a master and a
standby generate different WAL files!

What does pg_xlogdump say about the differences in the files?

--
Jon