Re: Test slots invalidations in only if dead rows are removed

From: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Alexander Lakhin <exclusion(at)gmail(dot)com>, "Yu Shi (Fujitsu)" <shiy(dot)fnst(at)fujitsu(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Test slots invalidations in only if dead rows are removed
Date: 2024-01-23 08:07:36
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On Tue, Jan 23, 2024 at 02:50:06PM +0900, Michael Paquier wrote:
> On Mon, Jan 22, 2024 at 09:07:45AM +0000, Bertrand Drouvot wrote:
> I've rewritten some of that, and applied the patch down to v16.


> > Yeah, I can clearly see how this patch helps from a theoritical perspective but
> > rely on Alexander's testing to see how it actually stabilizes the test.
> Anyway, that's not the end of it. What should we do for snapshot
> snapshot records coming from the bgwriter?

I've mixed feeling about it. On one hand we'll decrease even more the risk of
seeing a xl_running_xacts in the middle of a test, but on the other hand I agree
with Tom's concern [1]: I think that we could miss "corner cases/bug" detection
(like the one reported in [2]).

What about?

1) Apply "wait_until_vacuum_can_remove() + autovacuum disabled" where it makes
sense and for tests that suffers from random xl_running_xacts. I can look at, do you have others in mind?
2) fix [2]
3) depending on how stabilized this test (and others that suffer from "random"
xl_running_xacts) is, then think about the bgwriter.



Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services:

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