Horton

Re: snapbuild woes

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: Petr Jelinek <petr.jelinek@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Erik Rijkers <er@xs4all.nl>, David Steele <david@pgmasters.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Robert Haas <robertmhaas@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, pgsql-hackers-owner@postgresql.org
Date: 2017-04-29T21:42:01Z
Lists: pgsql-hackers 
On Fri, Apr 21, 2017 at 10:34:58PM -0700, Andres Freund wrote:
> I've a bunch of tests, but I don't quite know whether we can expose all
> of them via classical tests.  There are several easy ones that I
> definitely want to add (import "empty" snapshot; import snapshot with
> running xacts; create snapshot, perform some ddl, import snapshot,
> perform some ddl, check things work reasonably crazy), but there's
> enough others that are just probabilistic.  I was wondering about adding
> a loop that simply runs for like 30s and then quits or such, but who
> knows.

If the probabilistic test catches the bug even 5% of the time in typical
configurations, the buildfarm will rapidly identify any regression.  I'd
choose a 7s test that detects the bug 5% of the time over a 30s test that
detects it 99% of the time.  (When I wrote src/bin/pgbench/t/001_pgbench.pl
for a probabilistic bug, I sized that test to finish in 1s and catch its bug
half the time.  In its case, only two buildfarm members were able to
demonstrate the original bug, so 5% detection would have been too low.)

Commits

  1. Fix thinko introduced in 2bef06d516460 et al.

  2. Avoid superfluous work for commits during logical slot creation.

  3. Fix race condition leading to hanging logical slot creation.

  4. Don't use on-disk snapshots for exported logical decoding snapshot.

  5. Preserve required !catalog tuples while computing initial decoding snapshot.