From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | vignesh C <vignesh21(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Failed Assert in pgstat_assoc_relation |
Date: | 2022-11-28 18:50:13 |
Message-ID: | 20221128185013.xnvimyu6woplhrqi@awork3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2022-11-28 13:37:16 -0500, Tom Lane wrote:
> vignesh C <vignesh21(at)gmail(dot)com> writes:
> > I could reproduce this issue with the following steps:
> > create table t1(c int);
> > BEGIN;
> > CREATE TABLE t (c int);
> > SAVEPOINT q;
> > CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD SELECT * FROM t1;
> > select * from t;
> > ROLLBACK TO q;
> > CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD SELECT * FROM t1;
> > ROLLBACK;
>
> Uh-huh. I've not bothered to trace this in detail, but presumably
> what is happening is that the first CREATE RULE converts the table
> to a view, and then the ROLLBACK undoes that so far as the catalogs
> are concerned, but probably doesn't undo related pg_stats state
> changes fully. Then we're in a bad state that will cause problems.
> (It still crashes if you replace the second CREATE RULE with
> "select * from t".)
Yea. I haven't yet fully traced through this, but presumably relcache inval
doesn't fix this because we don't want to loose pending stats after DDL.
Perhaps we need to add a rule about not swapping pgstat* in
RelationClearRelation() when relkind changes?
> As far as HEAD is concerned, maybe it's time to nuke the whole
> convert-table-to-view kluge entirely? Only pg_dump older than
> 9.4 will emit such code, so we're really about out of reasons
> to keep on maintaining it.
Sounds good to me.
> However, I'm not sure that removing that code in v15 will fly,
Agreed, at the very least that'd increase memory usage.
> so maybe we need to make the new pg_stats code a little more
> robust against the possibility of a relkind change.
Possibly via the relcache code.
Greetings,
Andres Freund
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