On Thu, 2007-05-03 at 14:33 -0700, jaba the mobzy wrote: > mycorr_100 took 11.4 s to run although it had to fetch 100000 row from > the base table. > mycorr_10 took 24.4 s to run although it had to fetch 10563 row from > the base table.
This is because the physical distribution of data is different. The mycorr_10 table has tuples in which a and b are > 15.9M spread all throughout. mycorr_100 has them all collected together at the end of the physical file. Less disk seeking. You can test this by doing a CLUSTER on both tables and run the same queries again. Regards, Jeff Davis ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org