| From: | Jim Nasby <jim(at)nasby(dot)net> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | 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 20:23:30 |
| Message-ID: | 52D44B42.1020002@nasby.net |
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| Lists: | pgsql-hackers |
On 1/13/14, 2:19 PM, Claudio Freire wrote:
> On Mon, Jan 13, 2014 at 5:15 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On a related note, there's also the problem of double-buffering. When
>> we read a page into shared_buffers, we leave a copy behind in the OS
>> buffers, and similarly on write-out. It's very unclear what to do
>> about this, since the kernel and PostgreSQL don't have intimate
>> knowledge of what each other are doing, but it would be nice to solve
>> somehow.
>
>
> There you have a much harder algorithmic problem.
>
> You can basically control duplication with fadvise and WONTNEED. The
> problem here is not the kernel and whether or not it allows postgres
> to be smart about it. The problem is... what kind of smarts
> (algorithm) to use.
Isn't this a fairly simple matter of when we read a page into shared buffers tell the kernel do forget that page? And a corollary to that for when we dump a page out of shared_buffers (here kernel, please put this back into your cache).
--
Jim C. Nasby, Data Architect jim(at)nasby(dot)net
512.569.9461 (cell) http://jim.nasby.net
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