On Wed, Jan 15, 2014 at 1:53 AM, KONDO Mitsumasa <kondo.mitsumasa@lab.ntt.co.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. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company