Re: Synchronizing slots from primary to standby

Hi,

On 2/11/22 3:26 PM, Peter Eisentraut wrote:
> On 10.02.22 22:47, Bruce Momjian wrote:
>> On Tue, Feb  8, 2022 at 08:27:32PM +0530, Ashutosh Sharma wrote:
>>>> Which means that if e.g. the standby_slot_names GUC differs from
>>>> synchronize_slot_names on the physical replica, the slots
>>>> synchronized on the
>>>> physical replica are not going to be valid.  Or if the primary drops
>>>> its
>>>> logical slots.
>>>>
>>>>
>>>>> Should the redo function for the drop replication slot have the
>>>>> capability
>>>>> to drop it on standby and its subscribers (if any) as well?
>>>>
>>>> Slots are not WAL logged (and shouldn't be).
>>>>
>>>> I think you pretty much need the recovery conflict handling
>>>> infrastructure I
>>>> referenced upthread, which recognized during replay if a record has
>>>> a conflict
>>>> with a slot on a standby.  And then ontop of that you can build
>>>> something like
>>>> this patch.
>>>>
>>>
>>> OK. Understood, thanks Andres.
>>
>> I would love to see this feature in PG 15.  Can someone explain its
>> current status?  Thanks.
>
> The way I understand it:
>
> 1. This feature (probably) depends on the "Minimal logical decoding on
> standbys" patch.  The details there aren't totally clear (to me).  That
> patch had some activity lately but I don't see it in a state that it's
> nearing readiness.
>

FWIW, a proposal has been submitted in [1] to add information in the WAL
records in preparation for logical slot conflict handling.

[1]:
https://www.postgresql.org/message-id/178cf7da-9bd7-e328-9c49-e28ac4701352@gmail.com

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com