From: | Michael Paquier <michael(at)paquier(dot)xyz> |
---|---|
To: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
Cc: | Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Can there ever be out of sequence WAL files? |
Date: | 2022-01-12 04:10:25 |
Message-ID: | Yd5UscDRILBP1+sb@paquier.xyz |
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Lists: | pgsql-hackers |
On Wed, Jan 12, 2022 at 10:18:11AM +0800, Julien Rouhaud wrote:
> On Wed, Jan 12, 2022 at 07:19:48AM +0530, Bharath Rupireddy wrote:
>>> Can the postgres server ever have/generate out of sequence WAL files?
>>> For instance, 000000010000020C000000A2, 000000010000020C000000A3,
>>> 000000010000020C000000A5 and so on, missing 000000010000020C000000A4.
>>> Manual/Accidental deletion of the WAL files can happes, but are there
>>> any other extreme situations (like recycling, removing old WAL files
>>> etc.) caused by the postgres server leading to missing WAL files?
>
> By definition there shouldn't be such situation, as it would otherwise be a
> (critical) bug.
I have seen that in the past, in cases where a system got harshly
deplugged then replugged where a segment file flush got missing. But
that was just a flacky system, Postgres relied just on something
wrong. So the answer is that this should not happen.
>>> What happens when postgres server finds missing WAL file during
>>> crash/standby recovery?
>
> The recovery should fail.
xlog.c can be a good read to check the assumptions WAL replay relies
on, with things like CheckRecoveryConsistency() or
reachedConsistency.
--
Michael
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