Mike Glover <mpg4(at)duluoz(dot)net> writes:
> You should bump sort_mem as high as you can stand. with only 8MB sort
> memory available, you're swapping intermediate sort pages to disk --
> a lot. Try the query with sort_mem set to 75MB (to do the entire sort in
> memory).
7.4 will probably flip over to a hash-based aggregation method, and not
sort at all, once you make sort_mem large enough that it thinks the hash
table will fit in sort_mem.
regards, tom lane