From: Tom Lane <tgl@sss.pgh.pa.us>
To: Amit Kapila <akapila@postgresql.org>
cc: pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Avoid creation of the free space map for small heap
 relations, t
In-reply-to: <E1gqTuL-0004Wj-U7@gemulon.postgresql.org>
References: <E1gqTuL-0004Wj-U7@gemulon.postgresql.org>
Comments: In-reply-to Amit Kapila <akapila@postgresql.org>
	message dated "Mon, 04 Feb 2019 02:22:49 +0000"
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Date: Mon, 25 Feb 2019 12:02:00 -0500
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Amit Kapila <akapila@postgresql.org> writes:
> Avoid creation of the free space map for small heap relations, take 2.

I think this patch still has some issues.  Note the following two
recent buildfarm failures:

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Dpetalura&dt=3D20=
19-02-20%2004%3A20%3A01
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Ddragonet&dt=3D20=
19-02-24%2022%3A48%3A02

Both of them failed in an assertion added by this patch:

TRAP: FailedAssertion("!((rel->rd_rel->relkind =3D=3D 'r' || rel->rd_rel->=
relkind =3D=3D 't') && fsm_local_map.map[oldPage] =3D=3D 0x01)", File: "/h=
ome/bf/build/buildfarm-petalura/HEAD/pgsql.build/../pgsql/src/backend/stor=
age/freespace/freespace.c", Line: 229)
...
2019-02-20 06:23:26.660 CET [5c6ce440.3bd2:4] LOG:  server process (PID 17=
981) was terminated by signal 6: Aborted
2019-02-20 06:23:26.660 CET [5c6ce440.3bd2:5] DETAIL:  Failed process was =
running: INSERT INTO T VALUES ( $1 )

I can even offer you a theory as to why we're managing to get through all
the core regression tests and then failing in ecpg: the failing test is
ecpg/test/thread/prep.pgc, and I think that may be the only place in our
tests where we stress concurrent insertions into a single small table.
So I think you've got race-condition issues here.

It might or might not be significant that these two animals are part
of Andres' JIT-enabled menagerie.  I could see that affecting test
timing to the point of showing a symptom that's otherwise hard to hit.

			regards, tom lane