| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | 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 20:19:22 |
| Message-ID: | CAGTBQpaZTxnFdpdCoid+pxLjKhor8BpHxKujaVc=GxtgCD+gRg@mail.gmail.com |
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| Lists: | pgsql-hackers |
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.
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