Thomas Kellerer <spam_eater(at)gmx(dot)net> writes:
> I'm playing around with 9.2 beta4 and was looking into the new Index Only Scan feature.
> I was a bit surprised that a "count(*)" query does not use an index.
Works for me. However, the cost estimate for that is heavily dependent
on how much of the table is known all-visible. If the table is getting
a lot of churn, or even just hasn't been vacuumed since it quiesced,
the planner will prefer a seqscan for this --- and it will be right.
regards, tom lane