Alvaro Herrera wrote: > Bruce Momjian wrote: > > > > Yep, agreed on the random I/O issue. The larger question is if you have > > a huge table, do you care to reclaim 3% of the table size, rather than > > just vacuum it when it gets to 10% dirty? I realize the vacuum is going > > to take a lot of time, but vacuuming to relaim 3% three times seems like > > it is going to be more expensive than just vacuuming the 10% once. And > > vacuuming to reclaim 1% ten times seems even more expensive. The > > partial vacuum idea is starting to look like a loser to me again. > > But if the partial vacuum is able to clean the busiest pages and reclaim > useful space, currently-running transactions will be able to use that > space and thus not have to extend the table. Not that extension is a > problem on itself, but it'll keep your working set smaller. Yes, but my point is that if you are trying to avoid vacuuming the table, I am afraid the full index scan is going to be painful too. I can see corner cases where partial vacuum is a win (I only have 4 hours of idle I/O), but for the general case I am still worried that partial vacuum will not be that useful as long as we have to scan the indexes. -- Bruce Momjian bruce@xxxxxxxxxx EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. +
