From: | Alexander Lakhin <exclusion(at)gmail(dot)com> |
---|---|
To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Michael Paquier <michael(at)paquier(dot)xyz>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
Subject: | Re: WAL record CRC calculated incorrectly because of underlying buffer modification |
Date: | 2024-05-11 05:00:00 |
Message-ID: | 35e2c2f8-f65a-f93a-ea23-957bb67a2d42@gmail.com |
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Lists: | pgsql-hackers |
11.05.2024 07:25, Thomas Munro wrote:
> On Sat, May 11, 2024 at 4:00 PM Alexander Lakhin <exclusion(at)gmail(dot)com> wrote:
>> 11.05.2024 06:26, Thomas Munro wrote:
>>> Perhaps a no-image, no-change registered buffer should not be
>>> including an image, even for XLR_CHECK_CONSISTENCY? It's actually
>>> useless for consistency checking too I guess, this issue aside,
>>> because it doesn't change anything so there is nothing to check.
>> Yes, I think something wrong is here. I've reduced the reproducer to:
> Does it reproduce if you do this?
>
> - include_image = needs_backup || (info &
> XLR_CHECK_CONSISTENCY) != 0;
> + include_image = needs_backup ||
> + ((info & XLR_CHECK_CONSISTENCY) != 0 &&
> + (regbuf->flags & REGBUF_NO_CHANGE) == 0);
No, it doesn't (at least with the latter, more targeted reproducer).
> Unfortunately the back branches don't have that new flag from 00d7fb5e
> so, even if this is the right direction (not sure, I don't understand
> this clean registered buffer trick) then ... but wait, why are there
> are no failures like this in the back branches (yet at least)? Does
> your reproducer work for 16? I wonder if something relevant changed
> recently, like f56a9def. CC'ing Michael and Amit K for info.
Maybe it's hard to hit (autovacuum needs to process the index page in a
narrow time frame), but locally I could reproduce the issue even on
ac27c74de(~1 too) from 2018-09-06 (I tried several last commits touching
hash indexes, didn't dig deeper).
Best regards,
Alexander
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