Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance

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 ?)

Cheers

-- 
Hannu Krosing
PostgreSQL Consultant
Performance, Scalability and High Availability
2ndQuadrant Nordic OÜ