| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, Peter Geoghegan <pg(at)heroku(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Misaligned BufferDescriptors causing major performance problems on AMD |
| Date: | 2015-01-27 02:08:25 |
| Message-ID: | CA+TgmoZsBKAA3DCwXh_aGv2y=JWbBB5y--Ozzs9dg7C2TUSWqw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jan 26, 2015 at 8:04 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2015-01-26 19:58:25 -0500, Bruce Momjian wrote:
>> On Tue, Jan 27, 2015 at 01:43:41AM +0100, Andres Freund wrote:
>> > master + 32align.patch:
>> > -c max_connections=400
>> > tps = 183791.872359 (high run vs. run variability)
>> > -c max_connections=401
>> > tps = 185494.98244 (high run vs. run variability)
>> >
>> > master + 64align.patch:
>> > -c max_connections=400
>> > tps = 489257.195570
>> > -c max_connections=401
>> > tps = 490496.520632
>> >
>> > Pretty much as expected, rigth?
>>
>> Yes, I am convinced. Let's work on a patch now.
>
> Since I can reproduce some minor (1-3%) performance *regressions* at low
> client counts when aligning every shmem allocation, I'm inclined to just
> add special case code to BufferShmemSize()/InitBufferPool() to align
> descriptors to PG_CACHE_LINE_SIZE. That's really unlikely to regress
> anythign as it basically can't be a bad idea to align buffer
> descriptors.
>
> Contrary opinions? Robert?
I'm totally OK with further aligning just that one allocation.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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