On Thu, 29 Apr 2010, Tom Lane wrote:
Teodor Sigaev <teo...@sigaev.ru> writes:
[ planner prefers ]
-> Seq Scan on foo (cost=0.00..5805.00 rows=4907 width=0)
to
-> Bitmap Heap Scan on foo (cost=942.46..5755.08 rows=4907 width=0)
Why does pgsql choose seqscan (5817.28) instead of bitmap one (5767.36)?
There's a fuzz factor of (IIRC) 1% in path cost comparisons. It's
deciding that the seqscan and bitmapscan total costs are not
meaningfully different; then since the startup costs *are* meaningfully
different, it's making the choice on the basis of cheaper startup cost.
hmm, what if we add index scan preference inside 1% tolerance ?
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: o...@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83
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