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, because the latter representation is > optimized to be small and the in-memory representation not so much. > I haven't seen a 3X differential before, but it's not outside the realm > of reason, especially for narrow rows like these where it's all about > the overhead. I suspect if you crank work_mem up still more, you'll see > it switch over. It flips to on-disk sort when the in-memory > representation exceeds the limit ... 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? Andreas -- Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect. (Linus Torvalds) "If I was god, I would recompile penguin with --enable-fly." (unknown) Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889° -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
