On Aug 13, 2008, at 10:45 PM, Andrew Gierth wrote:
You could likely expose a difference using LIMIT 1 in the subselect, but that doesn't tell us anything we didn't already know (which is that yes, index scan is much faster than seqscan even for 1-block tables, except in the rare case when neither the index page nor the table page are in cache, causing the indexscan to take two page fetches rather than just one).Oddly enough, when I try it with LIMIT 1, it _does_ show a significant speed difference according to the row position, _but_ the index scan is still twice as fast even when fetching only row 1 (which is indeed physically first).
So the question is: why?? How can it be cheaper to hit 2 buffers than 1?Though, unless we can improve the speed of seqscanning an entire page vs pulling the exact row we need it's probably still a moot point.
-- Decibel!, aka Jim C. Nasby, Database Architect [EMAIL PROTECTED] Give your computer some brain candy! www.distributed.net Team #1828
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