Re: per backend WAL statistics

Hi,

Thank you for working on this!

I just started reading the code and have a couple of questions.

I think that every time we flush IO or WAL stats, we want(?) to flush
backend stats as well, so would it make sense to move
pgstat_flush_backend() calls to inside of pgstat_flush_io() and
pgstat_wal_flush_cb()? I see that backend statistics are not collected
for some of the backend types but that is already checked in the
pgstat_flush_backend() with pgstat_tracks_backend_bktype().

Also, is there a chance that wal_bytes gets incremented without
wal_records getting incremented? I searched the code and did not find
any example of that but I just wanted to be sure. If there is a case
like that, then pgstat_backend_wal_have_pending() needs to check
wal_bytes instead of wal_records.

--
Regards,
Nazir Bilal Yavuz
Microsoft