silly8888 escribió: > 2009/10/26 Grzegorz Jaśkiewicz <gryzman@xxxxxxxxx>: > > > > > > On Mon, Oct 26, 2009 at 10:30 AM, silly8888 <silly8888@xxxxxxxxx> wrote: > >> > >> Suppose that you have a query, say $sql_query, which is very > >> complicated and produces many rows. Which of the following is going to > >> be faser: > >> > >> $sql_query OFFSET 3000 LIMIT 12; > >> > >> or > >> > >> BEGIN; > >> DECLARE cur1 CURSOR FOR $sql_query; > >> MOVE 3000 IN cur1; > >> FETCH 12 FROM cur1; > >> COMMIT; > >> > >> Naturally, the former cannot be slower than the latter. So my question > >> essentially is whether the MOVE operation on a cursor is > >> (significantly) slower that a OFFSET on the SELECT. > > > > > > OFFSET/LIMIT. Afaik cursor always fetches everything. > > Well, in my experiments they always perform the same. I suspect that > the way SELECT/OFFSET is implemented is not much different than > cursor/MOVE. The cursor could choose a different plan due to the "fast startup" behavior that Pavel alludes to. You can actually change that by setting the cursor_tuple_fraction parameter. Whether this plan is faster or slower than the other one is problem dependent. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
