Re: Minimal logical decoding on standbys

On Tue, Mar 23, 2021 at 8:47 AM Drouvot, Bertrand <bdrouvot(at)amazon(dot)com>
wrote:
>
> I have one remark regarding the conflicts:
>
> The logical slots are dropped if a conflict is detected.
>
> But, if the slot is not active before being dropped (say wal_level is
changed to < logical on master and a logical slot is not active on the
standby) then its corresponding
pg_stat_database_conflicts.confl_logicalslot is not incremented (as it
would be incremented "only" during the cancel of an "active" backend).
>
> I think, it should be incremented in all the cases (active or not), what
do you think?
>

Good catch... IMHO it should be incremented as well!!!

> I updated the patch to handle this scenario (see the new
pgstat_send_droplogicalslot() in
v12-0003-Handle-logical-slot-conflicts-on-standby.patch).
>

Perfect.

> I also added more tests in 023_standby_logical_decoding_conflicts.pl to
verify that pg_stat_database_conflicts.confl_logicalslot is updated as
expected (see check_confl_logicalslot() in
v12-0004-New-TAP-test-for-logical-decoding-on-standby.patch).
>

Perfect.

> Except this remark and the associated changes, then it looks good to me.
>

LGTM too... Reviewing new changes now to move it forward and make this
patch set ready for commiter review.

Regards,

--
Fabrízio de Royes Mello
PostgreSQL Developer at OnGres Inc. - https://ongres.com