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