Re: Linux kernel impact on PostgreSQL performance

On 1/13/14, 2:19 PM, Claudio Freire wrote:
> On Mon, Jan 13, 2014 at 5:15 PM, Robert Haas <robertmhaas@gmail.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
corollaryto 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@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net