"Markus Wollny" <Markus.Wollny@xxxxxxxxxxx> writes: >> ... What I find interesting though is >> that the plain index scan in 8.0 is so enormously cheaper >> than it's estimated to be. Perhaps the answer table in your >> 8.0 installation is almost perfectly ordered by session_id? > Not quite - there may be several concurrent sessions at any one time, but ordinarily the answers for one session-id would be quite close together, in a lot of cases even in perfect sequence, so "almost perfectly" might be a fair description, depending on the exact definition of "almost" :) Could we see the pg_stats row for answer.session_id in both 8.0 and 8.1? > I had set random_page_cost to 1.4 already, so I doubt that it would do much good to further reduce the value - reading the docs and the suggestions for tuning I would have thought that I should actually consider increasing this value a bit, as not all of my data will fit in memory any more. Do you nevertheless want me to try what happens if I reduce random_page_cost even further? No, that's probably quite low enough already ... regards, tom lane
