Re: Why vacuum?

The Hermit Hacker wrote:
>
> On Wed, 13 Dec 2000, bpalmer wrote:
>
> > > Yes, postgresql requires vacuum quite often otherwise queries and
> > > updates start taking ungodly amounts of time to complete. If you're
> > > having problems because vacuum locks up your tables for too long
> > > you might want to check out:
> >
> > But why? I don't know of other databases that need to be 'vacuum'ed. Do
> > all others just do it internaly on a regular basis?
> >
> > What am I missing here?
>
> PgSQL's storage manager is currently such that it doesn't overwrite
> 'deleted' records, but just keeps appending to the end of the table
> ... so, for instance, a client of ours whose table had 5 records in it
> that are updated *alot* grew a table to 64Meg that only contains ~8k worth
> of data ...
>
> vacuum'ng cleans out the cruft and truncates the file ...
>
> vadim, for v7.2, is planning on re-writing the storage manager to do
> proper overwriting of deleted space, which will reduce the requirement for
> vacuum to almost never ...

I hope that he does it in a way that allows it to retain the old
behaviour
for some tables if there is need for it.

Also, vacuum and analyze should be separated (i.e. one should be able to
analyze a table without vacuuming it.)

Maybe use "ALTER TABLE/DATABASE UPDATE STATISTICS" for VACUUM ANALYZE as
syntax.

Time travel is/was an useful feature that is difficult to emulate
efficiently
using "other" means like rules/triggers

------------
Hannu