Re: Deadlock in XLogInsert at AIX

Hi Konstantin

XLC.

I'm on AIX 7.1 for now.

I'm using this version of XLC v13:

# xlc -qversion
IBM XL C/C++ for AIX, V13.1.3 (5725-C72, 5765-J07)
Version: 13.01.0003.0003

With this version, I have (at least, since I tested with "check" and not "check-world" at that time) 2 failing tests: create_aggregate , aggregates .

With the following XLC v12 version, I have NO test failure:

# /usr/vac/bin/xlc -qversion
IBM XL C/C++ for AIX, V12.1 (5765-J02, 5725-C72)
Version: 12.01.0000.0016

So maybe you are not using XLC v13.1.3.3, rather another sub-version. Unless you are using more options for the configure ?

Configure.

What are the options that you give to the configure ?

Hard load & 64 cores ? OK. That clearly explains why I do not see this issue.

pgbench ? I wanted to run it. However, I'm still looking where to get it plus a guide for using it for testing. I would add such tests when building my PostgreSQL RPMs on AIX. So any help is welcome !

Performance.

- Also, I'd like to compare PostgreSQL performance on AIX vs Linux/PPC64. Any idea how I should proceed ? Any PostgreSQL performance benchmark that I could find and use ? pgbench ?

- I'm interested in any information for improving the performance & quality of my PostgreSQM RPMs on AIX. (As I already said, BullFreeware RPMs for AIX are free and can be used by anyone, like Perzl RPMs are. My company (ATOS/Bull) sells IBM Power machines under the Escala brand since ages (25 years this year)).

How to help ?

How could I help for improving the quality and performance of PostgreSQL on AIX ?
I may have access to very big machines for even more deeply testing of PostgreSQL. I just need to know how to run tests.

Thanks!

Regards,

Tony

Le 01/02/2017 à 14:48, Konstantin Knizhnik a écrit :
Hi,

We are using 13.1.3 version of XLC. All tests are passed.
Please notice that is is synchronization bug which can be reproduced only under hard load.
Our server has 64 cores and it is necessary to run pgbench with 100 connections during several minutes to reproduce the problem.
So may be you just didn't notice it;)

On 01.02.2017 16:29, REIX, Tony wrote:

Hi,

I'm now working on the port of PostgreSQL on AIX.
(RPMs can be found, as free OpenSource work, at <http://http://bullfreeware.com/> http://http://bullfreeware.com/ .
http://bullfreeware.com/search.php?package=postgresql )

I was not aware of any issue with XLC v12 on AIX for atomic operations.
(XLC v13 generates at least 2 tests failures)

For now, with version 9.6.1, all tests "check-world", plus numeric_big test, are OK, in both 32 & 64bit versions.

Am I missing something ?

I configure the build of PostgreSQL with (in 64bits):

./configure
--prefix=/opt/freeware
--libdir=/opt/freeware/lib64
--mandir=/opt/freeware/man
--with-perl
--with-tcl
--with-tclconfig=/opt/freeware/lib
--with-python
--with-ldap
--with-openssl
--with-libxml
--with-libxslt
--enable-nls
--enable-thread-safety
--sysconfdir=/etc/sysconfig/postgresql

Am I missing some option for more optimization on AIX ?

Thanks

Regards,

Tony

Le 01/02/2017 à 12:07, Konstantin Knizhnik a écrit :
Attached please find my patch for XLC/AIX.
The most critical fix is adding __sync to pg_atomic_fetch_add_u32_impl.
The comment in this file says that:

* __fetch_and_add() emits a leading "sync" and trailing "isync",
thereby
* providing sequential consistency. This is undocumented.

But it is not true any more (I checked generated assembler code in
debugger).
This is why I have added __sync() to this function. Now pgbench working
normally.

Also there is mysterious disappearance of assembler section function
with sync instruction from pg_atomic_compare_exchange_u32_impl.
I have fixed it by using __sync() built-in function instead.

Thanks to everybody who helped me to locate and fix this problem.

--

Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

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--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company