Sam Mason <sam@xxxxxxxxxxxxx> writes: > On Tue, Nov 18, 2008 at 04:49:35PM +0000, Scara Maccai wrote: >> It makes sense to me, >> but I don't understand is how other databases (such as Oracle) do it. > I believe Oracle maintains a separate log (not sure how it's structured) > that contains this information and all the data in both the main table > and index can be considered committed. FWIW, I believe that count(*) is pretty slow in Oracle too. The DBs that can do it fast are the ones that maintain a centralized counter of the number of rows in each table. Which makes count(*) nice and fast, at the cost of horrendous concurrency impacts for updates; plus there's no chance of real MVCC operation. (In an MVCC world the correct answer for count(*) can vary depending on who's asking --- there's no hope of doing that with a single counter.) 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
