Re: Should we cacheline align PGXACT?

From: Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>
To: Bernd Helmle <mailings(at)oopsware(dot)de>
Cc: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Should we cacheline align PGXACT?
Date: 2017-02-13 17:02:04
Message-ID: CAE9k0PnnwqxW1AmUs2+QrcXLyWRnscLc2uTBjW=tWT6-gr7a+Q@mail.gmail.com
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Hi All,

I too have performed benchmarking of this patch on a large machine
(with 128 CPU(s), 520GB RAM, intel x86-64 architecture) and would like
to share my observations for the same (Please note that, as I had to
reverify readings on few client counts, it did take some time for me
to share these test-results.)

Case1: Data fits in shared buffer, Read Only workload:
-------------------------------------------------------------------------------
For data fits in shared buffer, I have taken readings at 300 SF. The
result sheet 'results-readonly-300-1000-SF' containing the median of 3
runs is attached with this mail. In this case, I could see very good
performance improvement with the patch basically at high client counts
(156 - 256).

Case2: Data doesn't fit in shared buffer, Read Only workload:
--------------------------------------------------------------------------------------
For data doesn't fit in shared buffer, I have taken readings at 1000
SF. The result sheet 'results-readonly-300-1000-SF' is attached with
this mail. In this case, the performance improvement is not as in
Case1, Infact it just varies in the range of 2-7%. but the good thing
is that there is no regression.

Case3: Data fits in shared buffer, Read-write workload:
-----------------------------------------------------------------------------
In this case, I could see that the tps on head and patch are very
close to each other with a small variation of (+-)3-4% which i assume
is a run-to-run variation. PFA result sheet
'results-readwrite-300-1000-SF' containing the test-results.

Case4: Data doesn't fit in shared buffer, Read-write workload:
----------------------------------------------------------------------------------------
In this case as well, tps on head and patch are very close to each
other with small variation of 1-2% which again is a run-to-run
variation. PFA result sheet 'results-readwrite-300-1000-SF' containing
the test-results.

Please note that details on the non-default guc params and pgbench is
all provided in the result sheets attached with this mail. Also, I
have not used pg_prewarm in my test script. Thank you.

On Mon, Feb 13, 2017 at 9:43 PM, Bernd Helmle <mailings(at)oopsware(dot)de> wrote:
> Am Montag, den 13.02.2017, 16:55 +0300 schrieb Alexander Korotkov:
>>
>> Thank you for testing.
>>
>> Yes, influence seems to be low. But nevertheless it's important to
>> insure
>> that there is no regression here.
>> Despite pg_prewarm'ing and running tests 300s, there is still
>> significant
>> variation.
>> For instance, with clients count = 80:
>> * pgxact-result-2.txt – 474704
>> * pgxact-results.txt – 574844
>
>> Could some background processes influence the tests? Or could it be
>> another virtual machine?
>> Also, I wonder why I can't see this variation on the graphs.
>> Another issue with graphs is that we can't see details of read and
>> write
>
> Whoops, good catch. I've mistakenly copied the wrong y-axis for these
> results in the gnuplot script, shame on me. New plots attached.
>
> You're right, the 2nd run with the pgxact alignment patch is notable.
> I've realized that there was a pgbouncer instance running from a
> previous test, but not sure if that could explain the difference.
>
>> TPS variation on the same scale, because write TPS values are too
>> low. I
>> think you should draw write benchmark on the separate graph.
>>
>
> The Linux LPAR is the only one used atm. We got some more time for
> Linux now and i'm going to prepare Tomas' script to run. Not sure i can
> get to it today, though.
>
>
>
>
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Attachment Content-Type Size
results-readonly-300-1000-SF.xlsx application/vnd.openxmlformats-officedocument.spreadsheetml.sheet 7.3 KB
results-readwrite-300-1000-SF.xlsx application/vnd.openxmlformats-officedocument.spreadsheetml.sheet 10.9 KB

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