Re: pg_stat_replication log positions vs base backups

On Wed, Nov 25, 2015 at 7:18 PM, Magnus Hagander <magnus@hagander.net> wrote:

On Wed, Nov 25, 2015 at 10:19 AM, Magnus Hagander <magnus@hagander.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.