On 07/26/2013 11:42 AM, Greg Smith wrote: > On 7/25/13 6:02 PM, didier wrote: >> It was surely already discussed but why isn't postresql writing >> sequentially its cache in a temporary file? > > If you do that, reads of the data will have to traverse that temporary > file to assemble their data. You'll make every later reader pay the > random I/O penalty that's being avoided right now. Checkpoints are > already postponing these random writes as long as possible. You have > to take care of them eventually though. > Well, SSD disks do it in the way proposed by didier (AFAIK), by putting "random" fs pages on one large disk page and having an extra index layer for resolving random-to-sequential ordering.
I would not dismiss the idea without more tests and discussion. We could have a system where "checkpoint" does sequential writes of dirty wal buffers to alternating synced holding files (a "checkpoint log" :) ) and only background writer does random writes with no forced sync at all -- Hannu Krosing PostgreSQL Consultant Performance, Scalability and High Availability 2ndQuadrant Nordic OÜ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
