Ryan Wexler <ryan@xxxxxxxxxxxxxxxx> wrote: > It still amazes me that it would account for a 5x change in IO. If you were doing one INSERT per database transaction, for instance, that would not be at all surprising. If you were doing one COPY in of a million rows, it would be a bit more surprising. Each COMMIT of a database transaction, without caching, requires that you wait for the disk to rotate around to the right position. Compared to the speed of RAM, that can take quite a long time. With write caching, you might write quite a few adjacent disk sectors to the cache, which can then all be streamed to disk on one rotation. It can also do tricks like writing a bunch of sectors on one part of the disk before pulling the heads all the way over to another portion of the disk to write a bunch of sectors. It is very good for performance to cache writes. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
