| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tatsuo Ishii <ishii(at)postgresql(dot)org>, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, Magnus Hagander <magnus(at)hagander(dot)net>, Josh Berkus <josh(at)agliodbs(dot)com>, Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Why we are going to have to go DirectIO |
| Date: | 2013-12-11 03:31:56 |
| Message-ID: | CAGTBQpZbcTWzDGN99zF+Dt5giTMspBh_8_ukbVV5aeQ82V5UbA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Dec 10, 2013 at 11:33 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Tuesday, December 10, 2013, Tom Lane wrote:
>>
>> Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
>> > On Tue, Dec 3, 2013 at 11:39 PM, Claudio Freire
>> > <klaussfreire(at)gmail(dot)com>wrote:
>> >> Problem is, Postgres relies on a working kernel cache for checkpoints.
>> >> Checkpoint logic would have to be heavily reworked to account for an
>> >> impaired kernel cache.
>>
>> > I don't think it would need anything more than a sorted checkpoint.
>>
>> Nonsense. We don't have access to the physical-disk-layout information
>> needed to do reasonable sorting; to say nothing of doing something
>> intelligent in a multi-spindle environment, or whenever any other I/O
>> is going on concurrently.
>
>
> The proposal I was responding to was simply to increase shared_buffers to
> 80% of RAM *instead of* implementing directIO.
If you do not leave a reasonable amount of RAM, writes will be direct
and synchronous.
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