On Fri, 18 Nov 2005, Simon Riggs wrote: > >From here, another proposal. We have a GUC called count_uses_estimate > that is set to off by default. If set to true, then a count(*) will use > the planner logic to estimate number of rows in the table and return > that as the answer, rather than actually count the row. Unless analyze > statistics are not available, in which case it does the real count.
I'm finishing off a tablesample patch a grad student on #postgresql was working on. template1=# select count(*)*100 from a tablesample system(1) repeatable (2); ?column? ---------- 8371100 (1 row) Time: 6366.757 ms template1=# select count(*)*50 from a tablesample system(2) repeatable (11); ?column? ---------- 8453550 (1 row) Time: 10521.871 ms template1=# select count(*)*10 from a tablesample system(10) repeatable (3); ?column? ---------- 8314350 (1 row) Time: 28744.498 ms template1=# select count(*) from a; count --------- 8388608 (1 row) Time: 33897.857 ms Seems like a better solution. I can finish the patch pretty soon. I need to contact the original author, who has disappeared, but I'll send it over to you. Gavin ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
