Re: Synchronizing slots from primary to standby - Mailing list pgsql-hackers

On Tue, Jan 23, 2024 at 2:38 PM Ajin Cherian <itsajin@gmail.com> wrote:
>
> I was doing some testing on this. What I noticed is that creating subscriptions with failover enabled is taking a lot
longercompared with a subscription with failover disabled. The setup has primary configured with standby_slot_names and
thatstandby is enabled with enable_synclot turned on. 
>

Thanks Ajin for testing the patch. PFA v66 which fixes this issue.

The overall changes in this version are:

patch 001
1) Restricted enabling failover for user created slots on standby.
2) Fixed a wrong NOTICE during alter-sub which was always saying that
'changed the failover state to false' even if it was switched to true.

patch 002:
3) Addressed Peter's comment in [1]

patch 003:
4) Fixed the drop-db issue reported by Swada-San in [2]
5) Added other signal-handlers.
6) Fixed CFBot Windows compilation failure.

patch 004:
7) Fixed the issue reported by Ajin above in [3]. The performance
issue was due to the additional wait in WalSndWaitForWal() for
failover slots. Create Subscription calls
DecodingContextFindStartpoint() which then reads WALs to build the
initial snapshot which ends up calling WalSndWaitForWal() which waits
for standby confirmation for the case of failover slots. Addressed it
by skipping the wait during Create Sub as it is not needed there. We
now wait only if 'replication_active' is true.

Thanks Nisha for reporting the NOTICE issue (addressed in 2) and
working on issue #6.

Thanks Hou-San for working on #7.

[1]: https://www.postgresql.org/message-id/CAHut%2BPs6p6Km8_Hfy6X0KTuyqBKkhC84u23sQnnkhqkHuDL%2BDQ%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/CAD21AoBgzONdt3o5mzbQ4MtqAE%3DWseiXUOq0LMqne-nWGjZBsA%40mail.gmail.com
[3]: https://www.postgresql.org/message-id/CAFPTHDbsZ%2BpxAubb9d9BwVNt5OB3_2s77bG6nHcAgUPPhEVmMQ%40mail.gmail.com

thanks
Shveta