Re: drop duplicate buffers in OS

(2014/01/16 3:34), Robert Haas wrote:
> On Wed, Jan 15, 2014 at 1:53 AM, KONDO Mitsumasa
> <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> I create patch that can drop duplicate buffers in OS using usage_count
>> alogorithm. I have developed this patch since last summer. This feature seems to
>> be discussed in hot topic, so I submit it more faster than my schedule.
>>
>> When usage_count is high in shared_buffers, they are hard to drop from
>> shared_buffers. However, these buffers wasn't required in file cache. Because
>> they aren't accessed by postgres(postgres access to shared_buffers).
>> So I create algorithm that dropping file cache which is high usage_count in
>> shared_buffers and is clean state in OS. If file cache are clean state in OS, and
>> executing posix_fadvice DONTNEED, it can only free in file cache without writing
>> physical disk. This algorithm will solve double-buffered situation problem and
>> can use memory more efficiently.
>>
>> I am testing DBT-2 benchmark now...
>
> The thing about this is that our usage counts for shared_buffers don't
> really work right now; it's common for everything, or nearly
> everything, to have a usage count of 5. So I'm reluctant to rely on
> that for much of anything.
This patch aims to large shared_buffers situations, so 10% memory shared_buffers
situaition
might be not effective. This patch is in experimental and to show how to solve
the double-buffers for one of a example.

Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center