Re: Pg_stat_replication shows sync standby with flush location behind primary in 9.1.5

On 04/10/12 19:06, Simon Riggs wrote:
> On 4 October 2012 05:32, Mark Kirkwood <mark.kirkwood@catalyst.net.nz> wrote:
>> I am seeing the situation where the reported flush location for the sync
>> standby (standby1 below) is *behind* the reported current xlog location of
>> the primary. This is Postgres 9.1.5 , and I was under the impression that
>> transactions initiated on the master do not commit until the corresponding
>> wal is flushed on the sync standby.
>>
>> Now the standby is definitely working in sync mode, because stopping it
>> halts all write transactions on the primary (sync_standby_names contains
>> only standby1). So is the reported lag in flush location merely an artifact
>> of timing in the query, or is there something else going on? [1]
>
> The writing of new WAL is independent of the wait that occurs on
> commit, so it is entirely possible, even desirable, that the observed
> effect occurs.
>

Ah right - it did occur to me (after posting of course), that *other*
non commit wal could be causing the effect... thank you for clarifying!

This could be worth mentioning in docs for the view - as the context
I've encountered this effect is folks writing scripts for replication
lag etc.

Cheers

Mark