Message-ID: <aa626ffb-2cb1-8683-5188-dad6031a4623@gmail.com>
Date: Tue, 15 Nov 2022 10:02:17 +0100
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Subject: Re: Synchronizing slots from primary to standby
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To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
 Bruce Momjian <bruce@momjian.us>, Ashutosh Sharma <ashu.coek88@gmail.com>
Cc: Andres Freund <andres@anarazel.de>,
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From: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
In-Reply-To: <ac40e8f8-46f5-7bb4-c08b-df3c9e6f1599@enterprisedb.com>
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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