RE: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly - Mailing list pgsql-hackers

From Hayato Kuroda (Fujitsu)
Subject RE: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly
Date
Msg-id OSCPR01MB14966F3D6F2E8B6C982890880F572A@OSCPR01MB14966.jpnprd01.prod.outlook.com
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In response to Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly  ("Vitaly Davydov" <v.davydov@postgrespro.ru>)
List pgsql-hackers
Dear Vitaly,

I've been working on the bug...

> This assert was introduced in the patch. Now, I think, it is a wrong one. Let me
> please explain one of the possible scenarios when it can be triggered. In case
> of physical replication, when walsender receives a standby reply message, it
> calls PhysicalConfirmReceivedLocation function which updates slots' restart_lsn
> from received flush_lsn value. This value may be older than the saved value. 

To confirm, can you tell me the theory why the walsender received old LSN?
It is sent by the walreceiver, so is there a case that LogstreamResult.Flush can go backward?
Not sure we can accept the situation.

Best regards,
Hayato Kuroda
FUJITSU LIMITED


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