From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Rahila Syed <rahilasyed90(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [REVIEW] Re: Compression of full-page-writes |
Date: | 2014-12-12 13:27:59 |
Message-ID: | CA+Tgmobae_QcdxacO5AGBQjq_dpMo-_XP6Pm+VqF09OOWBdqag@mail.gmail.com |
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On Thu, Dec 11, 2014 at 11:34 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> compression = 'on' : 1838 secs
>> = 'off' : 1701 secs
>>
>> Different is around 140 secs.
>
> OK, so the compression took 2x the cpu and was 8% slower. The only
> benefit is WAL files are 35% smaller?
Compression didn't take 2x the CPU. It increased user CPU from 354.20
s to 562.67 s over the course of the run, so it took about 60% more
CPU.
But I wouldn't be too discouraged by that. At least AIUI, there are
quite a number of users for whom WAL volume is a serious challenge,
and they might be willing to pay that price to have less of it. Also,
we have talked a number of times before about incorporating Snappy or
LZ4, which I'm guessing would save a fair amount of CPU -- but the
decision was made to leave that out of the first version, and just use
pg_lz, to keep the initial patch simple. I think that was a good
decision.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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