| From: | Hannu Krosing <hannu(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Hannu Krosing <hannu(at)2ndQuadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, James Bottomley <James(dot)Bottomley(at)hansenpartnership(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(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>, Claudio Freire <klaussfreire(at)gmail(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: | 2014-01-15 11:23:45 |
| Message-ID: | 52D66FC1.9060809@2ndQuadrant.com |
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| Thread: | |
| Lists: | pgsql-hackers |
On 01/15/2014 12:16 PM, Hannu Krosing wrote:
> On 01/14/2014 06:12 PM, Robert Haas wrote:
>> This would be pretty similar to copy-on-write, except
>> without the copying. It would just be
>> forget-from-the-buffer-pool-on-write.
> +1
>
> A version of this could probably already be implement using MADV_DONTNEED
> and MADV_WILLNEED
>
> Thet is, just after reading the page in, use MADV_DONTNEED on it. When
> evicting
> a clean page, check that it is still in cache and if it is, then
> MADV_WILLNEED it.
>
> Another nice thing to do would be dynamically adjusting kernel
> dirty_background_ratio
> and other related knobs in real time based on how many buffers are dirty
> inside postgresql.
> Maybe in background writer.
>
> Question to LKM folks - will kernel react well to frequent changes to
> /proc/sys/vm/dirty_* ?
> How frequent can they be (every few second? every second? 100Hz ?)
One obvious use case of this would be changing dirty_background_bytes
linearly to almost zero during a checkpoint to make final fsync fast.
Cheers
--
Hannu Krosing
PostgreSQL Consultant
Performance, Scalability and High Availability
2ndQuadrant Nordic OÜ
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