On Mon, Mar 10, 2014 at 9:24 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> Hi,
>
> On 2014-03-10 21:06:53 +0900, Michael Paquier wrote:
>> I have been playing a bit with the replication slots, and I noticed a
>> weird behavior in such a scenario:
>> 1) Create a master/slave cluster, and have slave use a replication slot
>> 2) Stop the master
>> 3) Create a certain amount of WAL, during my tests I played with 4~5GB of WAL
>> 4) Restart the slave, it catches up with the WALs that master has
>> retained in pg_xlog.
>> I noticed that while the standby using the replication slot catches
>> up, it is not visible in pg_stat_replication on master. This makes
>> monitoring of the replication lag difficult to follow, particularly in
>> the case where the standby disconnects from the master. Once the
>> standby has caught up, it reappears once again in pg_stat_replication.
>> I didn't have a look at the code to see what is happening, but is this
>> behavior expected?
>
> Does the use of replication slots actually alter the behaviour? I don't
> see how the slot code could influence things to that degree here. Could
> it be that it's just restoring code from the standby's pg_xlog or using
> restore_command?
Sorry for the noise, I'm feeling stupid. Yes the standby was using a
restore_command so it recovered the WAL from archives before reporting
activity back to master.
--
Michael