Add ps display while waiting for wal in read_local_xlog_page_guts
Hi,
pg_create_logical_replication_slot can take longer than usual on a standby
when there is no activity on the primary. We don't have enough information
in the pg_stat_activity or process title to debug why this is taking so
long. Attached a small patch to update the process title while waiting for
the wal in read_local_xlog_page_guts. Any thoughts on introducing a new
wait event too?
For example, in my setup, slot creation took 8 minutes 13 seconds. It only
succeeded after I ran select txid_current() on primary.
postgres=# select pg_create_logical_replication_slot('s1','test_decoding');
pg_create_logical_replication_slot
------------------------------------
(s1,0/C096D10)
(1 row)
Time: 493365.995 ms (08:13.366)
Thanks,
Sirisha
Attachments:
0001-set-ps-display_while-waiting-for-wal.patchapplication/octet-stream; name=0001-set-ps-display_while-waiting-for-wal.patchDownload+7-2
sirisha chamarthi <sirichamarthi22@gmail.com> writes:
pg_create_logical_replication_slot can take longer than usual on a standby
when there is no activity on the primary. We don't have enough information
in the pg_stat_activity or process title to debug why this is taking so
long. Attached a small patch to update the process title while waiting for
the wal in read_local_xlog_page_guts. Any thoughts on introducing a new
wait event too?
set_ps_display is a fairly expensive operation on a lot of platforms,
so I'm concerned about the overhead this proposal would add. However,
getting rid of that pg_usleep in favor of a proper wait event seems
like a good idea.
regards, tom lane
Hi,
On 4/13/23 12:43 AM, sirisha chamarthi wrote:
Hi,
pg_create_logical_replication_slot can take longer than usual on a standby when there is no activity on the primary. We don't have enough information in the pg_stat_activity or process title to debug why this is taking so long. Attached a small patch to update the process title while waiting for the wal in read_local_xlog_page_guts. Any thoughts on introducing a new wait event too?
For example, in my setup, slot creation took 8 minutes 13 seconds. It only succeeded after I ran select txid_current() on primary.
FWIW, this behavior has been mentioned in 0fdab27ad6 and a new function (pg_log_standby_snapshot()) has been created/documented to accelerate the slot creation on the standby.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
Hi,
On 4/13/23 4:29 AM, Tom Lane wrote:
sirisha chamarthi <sirichamarthi22@gmail.com> writes:
pg_create_logical_replication_slot can take longer than usual on a standby
when there is no activity on the primary. We don't have enough information
in the pg_stat_activity or process title to debug why this is taking so
long. Attached a small patch to update the process title while waiting for
the wal in read_local_xlog_page_guts.
Thanks for the patch!
Any thoughts on introducing a new
wait event too?
set_ps_display is a fairly expensive operation on a lot of platforms,
so I'm concerned about the overhead this proposal would add. However,
getting rid of that pg_usleep in favor of a proper wait event seems
like a good idea.
+1 for adding a proper wait event.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com