| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, 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 16:15:46 |
| Message-ID: | CA+TgmoYfKjU3KrJEASWvkM4s-uOcA6Hg9VyU2=1DxCo+KOvm2w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Dec 12, 2014 at 11:12 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2014-12-12 11:08:52 -0500, Robert Haas wrote:
>> Unless I'm missing something, this test is showing that FPW
>> compression saves 298MB of WAL for 17.3 seconds of CPU time, as
>> against master. And compressing the whole record saves a further 1MB
>> of WAL for a further 13.39 seconds of CPU time. That makes
>> compressing the whole record sound like a pretty terrible idea - even
>> if you get more benefit by reducing the lower boundary, you're still
>> burning a ton of extra CPU time for almost no gain on the larger
>> records. Ouch!
>
> Well, that test pretty much doesn't have any large records besides FPWs
> afaics. So it's unsurprising that it's not beneficial.
"Not beneficial" is rather an understatement. It's actively harmful,
and not by a small margin.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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