Re: What's The Difference Between VACUUM and VACUUM ANALYZE?

On Tue, 8 May 2007, Y Sidhu wrote:

> I am trying to follow a message thread. One guy says we should be running
> vacuum analyze daily and the other says we should be running vacuum multiple
> times a day. I have tried looking for what a vacuum analyze is to help me
> understand but no luck.

vaccum frees tuples that are no longer refrenced
vaccum analyse does the same thing, but then does some additional
information gathering about what data is in the tables Postgres uses this
data to adjust it's estimates of how long various things will take
(sequential scan, etc). if these estimates are off by a huge amount
(especially if you have never done a vaccum analyse after loading your
table) then it's very likely that postgres will be slow becouse it's doing
expensive operations that it thinks are cheap.

David Lang