Hi, thanks for your reply. The number of rows per second has been increasing rapidly, but its averaging about 1 row per second, and a far smaller number of updates. So maybe there are not such a huge number of dead rows. I hope that a normal vacuum will clean it up. Total number of rows is about 3 million. Last night before I got your reply, I noticed that the number of shared memory buffers was only 1000, so I increased shmmax and when I restart the server next, its number of buffers will be 10000. The server has 8GB of memory, so that will only be a small proportion of its total memory. I have not restarted postgres yet because a vacuum is still running. Maybe I should kill that and restart postgres? The reason I increased this is because I noticed if I did a partial count of rows (e.g. those inserted with a timestamp after midnight last night), then the first time takes about 17 seconds, and the second time 1/4 second. I started a vacuum on the table yesterday, and its still running. I guess thats because the table is live. I am pretty sure that if I take it offline, then the vacuum will complete relatively quickly. Am I right? (I don't want to take it offline unless I really need to.) On 04/01/2008, Scott Marlowe <scott.marlowe@xxxxxxxxx> wrote: > On Jan 3, 2008 6:48 AM, Brian Modra <epailty@xxxxxxxxxxxxxx> wrote: > > Hi, > > > > > > I have a pretty "live" table: rows being inserted and updated more > > than once 1 per second, though far, far more inserts than updates. > > > > There are currently over 3 million rows. > > > > It has not been vacuumed for months. > > How many rows per second? 1? all of them? Kinda makes a difference. > > If it was 1 a second updated for 3 months that's about 7million dead > rows. If it was all 3million, then that's 7million * 3million dead > rows, also know as a whole bunch of rows. > > Either way, you probably have a table so terribly bloated that a > regular vacuum will not help you in terms of speeding it up. Regular > vacuums are like brushing your teeth three times a day. If you've > forgotten for three months, brushing them once isn't likely to fix all > the cavities you've got. Same thing here. You'll either need a > vacuum full or a cluster. Cluster is often faster. Or you can try > selecting everything into a temp table, truncating the real table, and > inserting the data back in. Truncation will remove all rows, dead or > otherwise. The advantage is that it's often faster to truncate / > reload than it is to vacuum full. If you have indexes, you might want > to drop them while re-inserting and then recreated them. > -- Brian Modra Land line: +27 23 5411 462 Mobile: +27 79 183 8059 6 Jan Louw Str, Prince Albert, 6930 Postal: P.O. Box 2, Prince Albert 6930 South Africa ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
