Re: BUG #17064: Parallel VACUUM operations cause the error "global/pg_filenode.map contains incorrect checksum"

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alexander Lakhin <exclusion(at)gmail(dot)com>, PostgreSQL mailing lists <pgsql-bugs(at)lists(dot)postgresql(dot)org>
Subject: Re: BUG #17064: Parallel VACUUM operations cause the error "global/pg_filenode.map contains incorrect checksum"
Date: 2021-06-24 08:31:01
Message-ID: f0d05962-9058-b583-706c-af1c788fc3cb@iki.fi
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On 24/06/2021 11:06, Thomas Munro wrote:
> On Thu, Jun 24, 2021 at 7:52 PM Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>> On 23/06/2021 12:45, Thomas Munro wrote:
>>> On Wed, Jun 23, 2021 at 7:46 PM Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>>>> Let's just add the lock there.
>>>
>>> +1, no doubt about that.
>>
>> Committed that. Thanks for the report, Alexander!
>
> I think you missed relmap_redo (including a misleading comment).

Fixed, thanks!

>> If anyone wants a write a patch for that, I'd be happy to review it. And
>> if anyone has access to a system with pmem hardware, it would be
>> interesting to try to reproduce a torn sector and broken control file by
>> pulling the power plug.
>
> I have been working on a kind of experimental file system for
> simulating torn sectors (and other interesting file system phenomena)
> as part of some work on recovery scenerio testing, not quite ready to
> share yet but it can simulate that exact failure...

Cool! We know what happens if pg_control file is torn, though. What I'd
like to know is whether it can happen in practice with pmem, an how
likely it is. For curiosity mostly, I think we have already established
that it can happen, and it would be nice to protect against it in any
case, even if it's rare.

- Heikki

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