Re: pg_stat_replication log positions vs base backups

On Wed, Nov 25, 2015 at 7:18 PM, Magnus Hagander <magnus(at)hagander(dot)net>
wrote:

>
> On Wed, Nov 25, 2015 at 10:19 AM, Magnus Hagander <magnus(at)hagander(dot)net>
> wrote:
>
>> Are the values for the log locations really relevant for backup
>> connections? And if they are, we need to document it :) ISTM we are just
>> more or less leaking random data out there?
>>
>> I'm talking about the actual state=backup connection - not the connection
>> if we're using -x with pg_basebackup. Where we have output like:
>>
>> state | backup
>> sent_location | 0/0
>> write_location | 2/76CE0000
>> flush_location | 2/76CC0000
>> replay_location | 2/76CBF938
>>
>> I'm thinking those fields should probably all be NULL for state=backup?
>>
>
Hm. You would basically get that when a backup WAL sender is reusing the
sender of another node that is not here anymore.

> In particular, it seems that in InitWalSenderSlot, we only initialize the
> sent location. Perhaps this is needed?
>

Yes, that would be nice to start with a clean state. At the same time, I am
noticing that pg_stat_get_wal_senders() is comparing flush, apply and write
directly with 0. I think those should be InvalidXLogRecPtr. Combined with
your patch it gives the attached.
--
Michael