am Thu, dem 06.03.2008, um 1:26:46 -0500 mailte Mark Mielke folgendes: > > > There aren't a general solution. If you realy need the exact count of > tuples than you can play with a TRIGGER and increase/decrease the > tuple-count for this table in an extra table. > > > Of course, this means accepting the cost of obtaining update locks on the count > table. > > The original poster should understand that they can either get a fast estimated > count, or they can get a slow accurate count (either slow in terms of select > using count(*) or slow in terms of updates using triggers and locking). > > Other systems have their own issues. An index scan may be faster than a table > scan for databases that can accurately determine counts using only the index, No. The current index-implementation contains no information about the row-visibility within the current transaction. You need to scan the whole data-table to obtain if the current row are visible within the current transaction. > but it's still a relatively slow operation, and people don't normally need an > accurate count for records in the range of 100,000+? :-) right. Andreas -- Andreas Kretschmer Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header) GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.org&extra=pgsql-performance
