Move unused buffers to freelist

As discussed and concluded in mail thread (http://www.postgresql.org/message-id/006f01ce34f0$d6fa8220$84ef8660$@kapila@huawei.com), for moving unused buffer’s to freelist end,

I having implemented the idea and taken some performance data.

In the attached patch, bgwriter/checkpointer moves unused (usage_count =0 && refcount = 0) buffer’s to end of freelist. I have implemented a new API StrategyMoveBufferToFreeListEnd() to

move buffer’s to end of freelist.

Performance Data :

Configuration Details

O/S – Suse-11

RAM – 24GB

Number of Cores – 8

Server Conf – checkpoint_segments = 256; checkpoint_timeout = 25 min, synchronous_commit = 0FF, shared_buffers = 5GB

Pgbench – Select-only

Scalefactor – 1200

Time – Each run is of 20 mins

Below data is for average 3 runs of 20 minutes

                        8C-8T                16C-16T            32C-32T            64C-64T

HEAD               11997               8455                 4989                 2757

After Patch        19807               13296               8388                 2821

Detailed each run data is attached with mail.

This is just the initial data, I will collect more data based on different configuration of shared buffers and other configurations.

Feedback/Suggesions?

With Regards,

Amit Kapila.