| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Mel Gorman <mgorman(at)suse(dot)de>, Dave Chinner <david(at)fromorbit(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Andres Freund <andres(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, 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>, James Bottomley <James(dot)Bottomley(at)hansenpartnership(dot)com>, Jim Nasby <jim(at)nasby(dot)net>, "lsf-pc(at)lists(dot)linux-foundation(dot)org" <lsf-pc(at)lists(dot)linux-foundation(dot)org>, Magnus Hagander <magnus(at)hagander(dot)net> |
| Subject: | Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance |
| Date: | 2014-01-15 18:06:22 |
| Message-ID: | CAGTBQpa-ST_V+v2rzCp73_dApHYdV12CnNj+6d9EH2-m1OABAA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Jan 15, 2014 at 2:52 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> I think that the bottom line is that we're not likely to make massive
>> changes to the way that we do block caching now. Even if some other
>> scheme could work much better on Linux (and so far I'm unconvinced
>> that any of the proposals made here would in fact work much better),
>> we aim to be portable to Windows as well as other UNIX-like systems
>> (BSD, Solaris, etc.). So using completely Linux-specific technology
>> in an overhaul of our block cache seems to me to have no future.
>
> Unfortunately, I have to agree with this. Even if there were a way to
> merge our internal buffers with the kernel's, it would surely be far
> too invasive to coexist with buffer management that'd still work on
> more traditional platforms.
>
> But we could add hint calls, or modify the I/O calls we use, and that
> ought to be a reasonably localized change.
That's what's pretty nice with the zero-copy read idea. It's almost
transparent. You read to a page-aligned address, and it works. The
only code change would be enabling zero-copy reads, which I'm not sure
will be low-overhead enough to leave enabled by default.
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