Andreas Kretschmer <akretschmer@xxxxxxxxxxxxx> writes: > Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >> Reid Thompson <Reid.Thompson@xxxxxxxx> writes: >>> What am I missing that causes this to resort to sorting on disk? >> >> The in-memory space required to sort N tuples can be significantly >> larger than the on-disk space, > Question: when is the planner making the decision between in-memory and > on-disk, at planning-time or at execution time with the knowledge about > the real amount of tuples? The planner doesn't make that decision. tuplesort.c always starts in in-memory mode, and flips to on-disk when the actual amount of data in its care exceeds work_mem. The planner guesses whether that will happen while making cost estimates, but it's only an estimate. 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
