Re: Problem with bitmap-index-scan plan

jkapad@csd.uoc.gr writes:
> ... is quite reasonable.The table has 1.000.000 rows (17.242 pages). From
> pg_stat_get_blocks_fetched I can see that there were 102 page requests for
> table. So all things seem to work great here!

> But if I multiply the size of the table ten-times (10.000.000 rows - 172.414
> pages) and run the same query I get:
> ...
> which is slower even than a seq scan. Now I get that there were 131.398 page
> requests for table in order to retrieve almost 1250 tuples!Can someone explain
> why this is happening? All memory parameters are set to default.

You probably need to increase work_mem so that the bitmaps don't become
lossy ...

            regards, tom lane