| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Jim Nasby <jim(at)nasby(dot)net> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Mel Gorman <mgorman(at)suse(dot)de>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Joshua Drake <jd(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, "lsf-pc(at)lists(dot)linux-foundation(dot)org" <lsf-pc(at)lists(dot)linux-foundation(dot)org> |
| Subject: | Re: Linux kernel impact on PostgreSQL performance |
| Date: | 2014-01-13 20:37:21 |
| Message-ID: | CAGTBQpbs8h6Fe=L8+hzkHHFcRroNDrmKD9mDp-WZS_OAr_w92g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jan 13, 2014 at 5:32 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
>>
>> That's my point. In terms of kernel-postgres interaction, it's fairly
>> simple.
>>
>> What's not so simple, is figuring out what policy to use. Remember,
>> you cannot tell the kernel to put some page in its page cache without
>> reading it or writing it. So, once you make the kernel forget a page,
>> evicting it from shared buffers becomes quite expensive.
>
>
> Well, if we were to collaborate with the kernel community on this then
> presumably we can do better than that for eviction... even to the extent of
> "here's some data from this range in this file. It's (clean|dirty). Put it
> in your cache. Just trust me on this."
If I had a kernel developer hat, I'd put it on to say: I don't think
allowing that last bit is wise for a kernel.
It would violate oh-so-many separation rules and open an oh-so-big can-o-worms.
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