Tomas Vondra <tv@xxxxxxxx> writes: > Yes, I understand why MCV is not used in case of col_b, and I do > understand that the estimate may not be precise. But I'm wondering > what's a better estimate in such cases - 1, 5000, any constant, or > something related to a the histogram? It is doing it off the histogram. The logic is actually quite good I think for cases where the data granularity is small compared to the histogram bucket width. For cases like we have here, the assumption of a continuous distribution fails rather badly --- but it's pretty hard to see how to improve it without inserting a lot of type-specific assumptions. > BTW I think the default estimate used to be 1000, so it was changed in > one of the 8.x releases? Can you point me to the docs? I've even tried > to find that in the sources, but unsuccessfully. It's DEFAULT_RANGE_INEQ_SEL, and AFAIR it hasn't changed in quite a while. But I wouldn't be surprised if the behavior of this example changed when we boosted the default statistics target. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
