Re: Autovacuum / full vacuum

Michael Riess wrote:
> Hi,
> 
> yes, some heavily used tables contain approx. 90% free space after a
> week. I'll try to increase FSM even more, but I think that I will
> still have to run a full vacuum every week. Prior to 8.1 I was using
> 7.4 and ran a full vacuum every day, so the autovacuum has helped a
> lot. 
> 
> But actually I never understood why the database system slows down at
> all when there is much unused space in the files. Are the unused pages
> cached by the system, or is there another reason for the impact on the
> performance?

The reason is that the system needs to LOOK at the pages/tuples to see
if the tuples
are dead or not. 

So, the number of dead tuples impacts the scans.

LER

> 
> Mike
-- 
Larry Rosenman		
Database Support Engineer

PERVASIVE SOFTWARE. INC.
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