Murat Tasan <mmuurr@xxxxxxxxx> writes: > p.s. on the 8.4 version EXPLAIN ANALYZE *still* tells me that an > external merge on disk is happening, despite my setting of work_mem to > a full 16 MB this time. When we have to push sort data to disk, it's written in a form that's noticeably more compact than what's used in-memory. So it can be expected that an in-memory sort will need significantly more memory than what an external merge reports using on-disk. I'd try cranking up work_mem to at least 10X the on-disk size if you want to be sure of seeing an in-memory sort. However, so far as I can see the sort is taking much less time than the scan and join steps anyway, so you're not likely to get much improvement this way. The unstable performance is a result of caching effects for the table data, not of how the sort is done. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
