Re: Deadlock in XLogInsert at AIX

On 02/01/2017 08:30 PM, REIX, Tony wrote:
>
> Hi Konstantin,
>
> Please run:*/opt/IBM/xlc/13.1.3/bin/xlc -qversion*  so that I know your exact XLC v13 version.
>
IBM XL C/C++ for AIX, V13.1.3 (5725-C72, 5765-J07)

> I'm building on Power7 and not giving any architecture flag to XLC.
>
> I'm not using *-qalign=natural* . Thus, by default, XLC use -qalign=power, which is close to natural, as explained at:
>          https://www.ibm.com/support/knowledgecenter/SSGH2K_13.1.0/com.ibm.xlc131.aix.doc/compiler_ref/opt_align.html
> Why are you using this flag ?
>

Because otherwise double type is aligned on 4 bytes.

> Thanks for info about *pgbench*. PostgreSQL web-site contains a lot of old information...
>
> If you could*share scripts or instructions about the tests you are doing with pgbench*, I would reproduce here.
>

You do not need any script.
Just two simple commands.
One to initialize database:

pgbench -i -s 1000

And another to run benchmark itself:

pgbench -c 100 -j 20 -P 1 -T 1000000000


> I have no "real" application. My job consists in porting OpenSource packages on AIX. Many packages. Erlang, Go, these days. I just want to make PostgreSQL RPMs as good as possible... within the limited amount of time I can give to this package, before
> moving to another one.
>
> About the *zombie* issue, I've discussed with my colleagues. Looks like the process keeps zombie till the father looks at its status. However, though I did that several times, I  do not remember well the details. And that should be not specific to AIX.
> I'll discuss with another colleague, tomorrow, who should understand this better than me.
>

1. Process is not in zomby state (according to ps). It is in <exiting> state... It is something AIX specific, I have not see processes in this state at Linux.
2. I have implemented simple test - forkbomb. It creates 1000 children and then wait for them. It is about ten times slower than at Intel/Linux, but still much faster than 100 seconds. So there is some difference between postgress backend and dummy process
doing nothing - just immediately terminating after return from fork()
>
> *Patch for Large Files*: When building PostgreSQL, I found required to use the following patch so that PostgreSQL works with large files. I do not remember the details. Do you agree with such a patch ? 1rst version (new-...) shows the exact places where
>   define _LARGE_FILES 1  is required.  2nd version (new2-...) is simpler.
>
> I'm now experimenting with your patch for dead lock. However, that should be invisible with the  "check-world" tests I guess.
>
> Regards,
>
> Tony
>
>
> Le 01/02/2017 à 16:59, Konstantin Knizhnik a écrit :
>> Hi Tony,
>>
>> On 01.02.2017 18:42, REIX, Tony wrote:
>>>
>>> Hi Konstantin
>>>
>>> *XLC.*
>>>
>>> I'm on AIX 7.1 for now.
>>>
>>> I'm using this version of *XL**C 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 ?
>>>
>>>
>> export CC="/opt/IBM/xlc/13.1.3/bin/xlc"
>> export CFLAGS="-qarch=pwr8 -qtune=pwr8 -O2 -qalign=natural -q64 "
>> export LDFLAGS="-Wl,-bbigtoc,-b64"
>> export AR="/usr/bin/ar -X64"
>> export LD="/usr/bin/ld -b64 "
>> export NM="/usr/bin/nm -X64"
>> ./configure --prefix="/opt/postgresql/xlc-debug/9.6"
>>
>>
>>> *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.
>>>
>>
>> pgbench is part of Postgres distributive (src/bin/pgbench)
>>
>>
>>> 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 ?
>>>
>> pgbench is most widely used tool simulating OLTP workload. Certainly it is quite primitive and its results are rather artificial. TPC-C seems to be better choice.
>> But the best case is to implement your own benchmark simulating actual workload of your real application.
>>
>>> - 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 compa//ny (ATOS/Bull) sells IBM
>>> Power machines under the Escala brand s//ince ages (25 years this year)//)/.
>>>
>>>
>>> *How to help ?*
>>>
>>> How could I help for improving the quality and performance of PostgreSQL on AIX ?
>>>
>>
>> We still have one open issue at AIX: see https://www.mail-archive.com/pgsql-hackers@postgresql.org/msg303094.html
>> It will be great if you can somehow help to fix this problem.
>>
>>
>>
>> -- 
>> Konstantin Knizhnik
>> Postgres Professional: http://www.postgrespro.com
>> The Russian Postgres Company 
>


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