Arnau <arnaulist@andromeiberica.com> writes:
> I have done the same tests on 8.1.0.
Bitmap scans are a totally different animal that doesn't exist in 7.4.
A plain indexscan, such as 7.4 knows about, is generally not effective
for fetching more than a percent or two of the table. The crossover
point for a bitmap scan is much higher (don't know exactly, but probably
something like 30-50%).
regards, tom lane
