| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | James Bottomley <James(dot)Bottomley(at)hansenpartnership(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Trond Myklebust <trondmy(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Dave Chinner <david(at)fromorbit(dot)com>, 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>, "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: | 2014-01-14 17:15:20 |
| Message-ID: | CAGTBQpadbNnBp4F-0ac8wrYar+8dGUa85=pi35D1+pRSLDkPEg@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Tue, Jan 14, 2014 at 2:12 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> In terms of avoiding double-buffering, here's my thought after reading
> what's been written so far. Suppose we read a page into our buffer
> pool. Until the page is clean, it would be ideal for the mapping to
> be shared between the buffer cache and our pool, sort of like
> copy-on-write. That way, if we decide to evict the page, it will
> still be in the OS cache if we end up needing it again (remember, the
> OS cache is typically much larger than our buffer pool). But if the
> page is dirtied, then instead of copying it, just have the buffer pool
> forget about it, because at that point we know we're going to write
> the page back out anyway before evicting it.
>
> This would be pretty similar to copy-on-write, except without the
> copying. It would just be forget-from-the-buffer-pool-on-write.
But... either copy-on-write or forget-on-write needs a page fault, and
thus a page mapping.
Is a page fault more expensive than copying 8k?
(I really don't know).
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Robert Haas | 2014-01-14 17:17:57 | Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance |
| Previous Message | Tom Lane | 2014-01-14 17:15:08 | Re: plpgsql.consistent_into |