Re: Replication Syatem

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

Greg Smith <gsmith(at)gregsmith(dot)com> writes:
> The model here assumes that you'll need that space again for the next time 
> you UPDATE or INSERT a row.  So instead VACUUM just keeps those available 
> for database reuse rather than returning it to the operating system.

> Now, if you don't VACUUM frequently enough, this model breaks down, and 
> the table can get bigger with space that may never get reused.  The idea 
> is that you should be VACUUMing up now unneeded rows at about the same 
> rate they're being re-used.  When you don't keep up, the database can 
> expand in space that you don't get back again.  The right answer to this 
> problem is not to use VACUUM FULL; it's to use regular VACUUM more often.

Also, you need to make sure you have the FSM parameters set high enough
so that all the free space found by a VACUUM run can be remembered.

The less often you run VACUUM, the more FSM space you need, because
there'll be more free space reclaimed per run.

			regards, tom lane