Horton

Re: pgsql: Avoid improbable PANIC during heap_update.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jaime Casanova <jcasanov@systemguards.com.ec>, pgsql-committers@lists.postgresql.org
Date: 2022-10-01T01:29:28Z
Lists: pgsql-hackers 
On Fri, Sep 30, 2022 at 5:09 PM Peter Geoghegan <pg@bowt.ie> wrote:
> In any case we cannot really treat the information that we have about
> that as a bug report -- not as things stand. Why should the question
> of whether or not we ever set a page PD_ALL_VISIBLE without a cleanup
> lock on v13 be a mystery at all? Why wouldn't a simple grep get to the
> bottom of it? I have to imagine that the true explanation is very
> simple and boring.

I talked to Robins about this privately. I was wrong; there isn't a
simple or boring explanation.

Robins set out to find bugs like this in Postgres via stress-testing.
He used a lab environment for this, and was quite methodical. So there
is no reason to doubt that a PANIC happened on v13 at least once.
There must be some relatively complicated explanation for that, but
right now I can only speculate.

--
Peter Geoghegan

Commits

  1. Avoid improbable PANIC during heap_update, redux.

  2. Fix race condition where heap_delete() fails to pin VM page.

  3. Avoid improbable PANIC during heap_update.