Re: [HACKERS] Should we cacheline align PGXACT?

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От Alexander Korotkov
Тема Re: [HACKERS] Should we cacheline align PGXACT?
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Msg-id CAPpHfdtwufWG=WD0LtnnC_LW+VPXu2B1hZxHH4J_cX8NNda6=Q@mail.gmail.com
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Ответ на Re: [HACKERS] Should we cacheline align PGXACT?  (Ashutosh Sharma <ashu.coek88@gmail.com>)
Ответы Re: [HACKERS] Should we cacheline align PGXACT?  (Alexander Korotkov <a.korotkov@postgrespro.ru>)
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Hi!

On Mon, Feb 13, 2017 at 8:02 PM, Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
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.)
 
Great! Thank you very much for testing.

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.

I wouldn't say it's just a variation.  It looks like relatively small but noticeable regression in the patch.
According to Andres comment [1] I made a version of patch (pgxact-align-3.patch) which align PGXACT to 16 bytes.
That excludes situation when single PGXACT is spread over 2 cache lines.
Results of read-only tests are attached.  We can see that 16-byte alignment gives speedup in read-only tests, but it's a bit less than speedup of cache line alignment version.
Read-write tests are now running.  Hopefully 16-byte alignment version of patch wouldn't cause regression in read-write benchmark.


------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
 
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