In article <b42b73150804150715r83cad1doa166230ec509f0d@xxxxxxxxxxxxxx>, "Merlin Moncure" <mmoncure@xxxxxxxxx> writes: > On Mon, Apr 14, 2008 at 5:21 AM, Harald Fuchs <hari.fuchs@xxxxxxxxxxxxxx> wrote: >> I think there's something sub-optimal with generate_series. >> In the following, "documents" is a table with more than 120000 rows, >> vacuumed and analyzed before the queries. > everything is working exactly as intended. while it's obvious to you > that the generate series function returns a particular number of rows > based on your supplied inputs, it's not (yet) obvious to the planner. Which was exactly my point. Since generate_series is a builtin function, the planner could theoretically know the number of rows returned, thus choosing a better plan. OTOH, the difference between theory and reality is in theory smaller than in reality. > your genser function supplies the hint the planner needs and it > adjusts the plan. most set returning functions (particularly > non-immutable ones) are not so easy to determine the # of rows from > the input parameters anyways. Yes, of course. I used "genser" just to show that there is a better plan.
