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List:       postgresql-hackers
Subject:    Re: Synchronizing slots from primary to standby
From:       Ajin Cherian <itsajin () gmail ! com>
Date:       2023-11-30 12:06:57
Message-ID: CAFPTHDb8LW4i9-nyvz+XVkJmmciZwYGivpH=aDOrDkBfHR_q9w () mail ! gmail ! com
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On Wed, Nov 29, 2023 at 8:17 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> This has been fixed.
>
> Best Regards,
> Hou zj

Thanks for addressing my comments. Some comments from my testing of patch v41

1. In my opinion, the second message "aborting the wait...moving to
the next slot" does not hold much value. There might not even be a
"next slot", there might be just one slot. I think the first LOG is
enough to indicate that the sync-slot is waiting as it repeats this
log till the slot catches up. I know these messages hold great value
for debugging but in production,  "waiting..", "aborting the wait.."
might not be as helpful, maybe change it to debug?

2023-11-30 05:13:49.811 EST [6115] LOG:  waiting for remote slot
"sub1" LSN (0/3047A90) and catalog xmin (745) to pass local slot LSN
(0/3047AC8) and catalog xmin (745)
2023-11-30 05:13:57.909 EST [6115] LOG:  aborting the wait for remote
slot "sub1" and moving to the next slot, will attempt creating it
again
2023-11-30 05:14:07.921 EST [6115] LOG:  waiting for remote slot
"sub1" LSN (0/3047A90) and catalog xmin (745) to pass local slot LSN
(0/3047AC8) and catalog xmin (745)


2. If a slot on the standby is in the "i" state as it hasn't been
synced and it was invalidated on the primary, should you continuously
retry creating this invalidated slot on the standby?

2023-11-30 06:21:41.844 EST [10563] LOG:  waiting for remote slot
"sub1" LSN (0/0) and catalog xmin (785) to pass local slot LSN
(0/EED9330) and catalog xmin (785)
2023-11-30 06:21:41.845 EST [10563] WARNING:  slot "sub1" invalidated
on the primary server, slot creation aborted
2023-11-30 06:21:51.892 EST [10563] LOG:  waiting for remote slot
"sub1" LSN (0/0) and catalog xmin (785) to pass local slot LSN
(0/EED9330) and catalog xmin (785)
2023-11-30 06:21:51.893 EST [10563] WARNING:  slot "sub1" invalidated
on the primary server, slot creation aborted

3. If creation of a slot on the standby fails for one slot because a
slot of the same name exists, then thereafter no new sync slots are
created on standby. Is this expected? I do see that previously created
slots are kept up to date, just that no new slots are created after
that.

regards,
Ajin Cherian
Fujitsu australia


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