Re: [HACKERS] Deadlock in XLogInsert at AIX

On Tue, Jan 16, 2018 at 08:25:51AM +0000, REIX, Tony wrote:
> My team and my company (ATOS/Bull) are involved in improving the
> quality of PostgreSQL on AIX.

Cool to hear that!

> We have AIX 6.1, 7.1, and 7.2 Power8 systems, with several
> logical/physical processors. And I plan to have a more powerful (more
> processors) machine for running PostgreSQL stress tests.
> A DB-expert colleague has started to write some new not-too-complex
> stress tests that we'd like to submit to PostgreSQL project later.
> For now, using latest versions of XLC 12 (12.1.0.19) and 13 (13.1.3.4
> with a patch), we have only (on AIX 6.1 and 7.2) one remaining random
> failure (dealing with src/bin/pgbench/t/001_pgbench.pl test), for
> PostgreSQL 9.6.6 and 10.1 . And, on AIX 7.1, we have one more
> remaining failure that may be due to some other dependent
> software. Investigating.
> XLC 13.1.3.4 shows an issue with -O2 and I have a work-around that
> fixes it in ./src/backend/parser/gram.c . We have opened a PMR
> (defect) against XLC. Note that our tests are now executed without the
> PG_FORCE_DISABLE_INLINE "inline" trick in src/include/port/aix.h that
> suppresses the inlining of routines on AIX. I think that older
> versions of XLC have shown issues that have now disappeared (or, at
> least, many of them).
> I've been able to compare PostgreSQL compiled with XLC vs GCC 7.1 and,
> using times outputs provided by PostgreSQL tests, XLC seems to provide
> at least 8% more speed. We also plan to run professional performance
> tests in order to compare PostgreSQL 10.1 on AIX vs Linux/Power. I saw
> some 2017 performance slides, made with older versions of PostgreSQL
> and XLC, that show bad PostgreSQL performance on AIX vs Linux/Power,
> and I cannot believe it. We plan to investigate this.

That's interesting investigation. The community is always interested in
such stories. You could have material for a conference talk.

> Though I have very very little skills about PostgreSQL (I'm porting
> too now GCC Go on AIX), we can help, at least by
> compiling/testing/investigating/stressing in a different AIX
> environment than the AIX ones (32/64bit, XLC/GCC) you have in your
> BuildFarm.

Setting up a buildfarm member with the combination of compiler and
environment where you are seeing the failures would be the best answer
in my opinion:
https://wiki.postgresql.org/wiki/PostgreSQL_Buildfarm_Howto

This does not require special knowledge of PostgreSQL internals, and the
in-core testing framework has improved the last couple of years to allow
for more advanced tests. I do use it as well for some tests on my own
modules (company stuff). The buildfarm code has also followed the pace,
which really helps a lot, thanks to Andrew Dunstan.

Developers and committers are more pro-active if they can see automated
tests failing in the central community place. And buildfarm animals
usually don't stay red for more than a couple of days.
--
Michael