Here is a patch for TODO item, "Consider sorting writes during checkpoint". It writes dirty buffers in the order of block number during checkpoint so that buffers are written sequentially.
I proposed the patch before, but it was rejected because 8.3 feature has been frozen already at that time. http://archives.postgresql.org/pgsql-hackers/2007-06/msg00541.php I rewrote it to be applied cleanly against current HEAD, but the concept is not changed at all -- Memorizing pairs of (buf_id, BufferTag) for each dirty buffer into an palloc-ed array at the start of checkpoint. Sorting the array in BufferTag order and writing buffers in the order. There are 10% of performance win in pgbench on my machine with RAID-0 disks. There can be more benefits on RAID-5 disks, because random writes are slower than sequential writes there. [HEAD] tps = 1134.233955 (excluding connections establishing) [HEAD with patch] tps = 1267.446249 (excluding connections establishing) [pgbench] transaction type: TPC-B (sort of) scaling factor: 100 query mode: simple number of clients: 32 number of transactions per client: 100000 number of transactions actually processed: 3200000/3200000 [hardware] 2x Quad core Xeon, 16GB RAM, 4x HDD (RAID-0) [postgresql.conf] shared_buffers = 2GB wal_buffers = 4MB checkpoint_segments = 64 checkpoint_timeout = 5min checkpoint_completion_target = 0.5 Regards, --- ITAGAKI Takahiro NTT Open Source Software Center
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