> The whole thing runs 24 hours a day, 7 days a week. Most of the tables
> rarely get vacuumed (they have tens of thousands of rows and only inserts
> get done to them - the optimiser makes good choices for most of these) -
> however we have 5 tables which get vacuum at midnight each day, we drop
> all the indexes, vacuum, then recreate. If we don't do the index thing,
> the vacuum can take tens of minutes, which is not acceptable - the tables
> contain about 20000 rows, each of which gets updated about 3 times during
> the day. I sent an email a while back about vacuum performance, and this
> hack is the only way around it.
6.5 beta speeds up vacuuming with existing indexes, thanks to Vadim.
Also, accessing during vacuuming may be better too.
> While I'm asking some questions here, I should tell you about some of the
> other wierd things I've encountered, many of them are related to shared
> memory and hash tables, which is making me think more and more that all
> the problems I am having are somehow related.
6.5 beta has some _major_ hash fixes. We always knew there were hash
problems, but now Tom has fixed many of them.
> I would assume that the above one which uses indexes would be a lot
> better, but why did the optimiser chose the seq scan - do the indexes help
> when doing joins and at the same time all rows are being returned back? I
> understand that the optimiser will choose not to use indexes if it feels
> that it will return most of the rows anyway and so a seq scan is better.
6.5 beta also has a faster and smarter optimizer.
It may be wise for you to test 6.5beta to see how many problems we fix.
-- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
