While replying to the "Improving count(*)" thread, the following occured to me:
Vacuuming a table is only useful if we're nearing xid-wrap or if new tuples are being created in the table. One way to detect the later case is to monitor how many pages that table has in the FSM. Of course there's other ways to do this, but I think there's a distinct advantage to monitoring FSM: it allows us to vacuum at the rate that the space marked as being available by a vacuum is actually being used. So for example, we could set a threshold of keeping X pages is the FSM for each table. When the number of pages in the FSM falls below X for a table, a vacuum would be run against that table. But if we only want X pages in the FSM for that table, we could stop the vacuum once we reach X pages in the FSM. Unfortunately, I think that might leave us pretty succeptable to index bloat from deleted tuples, but maybe there's some clever way around that. If the proposal to track heap block-level metadata happens, that might make this idea a lot more doable. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
