| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Dave Chinner <david(at)fromorbit(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, James Bottomley <James(dot)Bottomley(at)hansenpartnership(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, "lsf-pc(at)lists(dot)linux-foundation(dot)org" <lsf-pc(at)lists(dot)linux-foundation(dot)org>, Kevin Grittner <kgrittn(at)ymail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Joshua Drake <jd(at)commandprompt(dot)com>, Mel Gorman <mgorman(at)suse(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Trond Myklebust <trondmy(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net> |
| Subject: | Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance |
| Date: | 2014-01-14 14:57:20 |
| Message-ID: | CA+TgmoaoiT68azOvVs9nWSQX7ov=CC3W0iFTY5cOQ=A6Mkpr_w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 14, 2014 at 3:39 AM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> On Tue, Jan 14, 2014 at 5:08 AM, Hannu Krosing <hannu(at)2ndquadrant(dot)com> wrote:
>> Again, as said above the linux file system is doing fine. What we
>> want is a few ways to interact with it to let it do even better when
>> working with postgresql by telling it some stuff it otherwise would
>> have to second guess and by sometimes giving it back some cache
>> pages which were copied away for potential modifying but ended
>> up clean in the end.
>
> You don't need new interfaces. Only a slight modification of what
> fadvise DONTNEED does.
Yeah. DONTREALLYNEEDALLTHATTERRIBLYMUCH.
> This insistence in injecting pages from postgres to kernel is just a
> bad idea. At the very least, it still needs postgres to know too much
> of the filesystem (block layout) to properly work. Ie: pg must be
> required to put entire filesystem-level blocks into the page cache,
> since that's how the page cache works. At the very worst, it may
> introduce serious security and reliability implications, when
> applications can destroy the consistency of the page cache (even if
> full access rights are checked, there's still the possibility this
> inconsistency might be exploitable).
I agree with all that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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