Re: Does the number of extents affect the performance?

Roald van Geleuken <roald_at_xs4all.nl> wrote in article <5vjpng$6u2$1_at_news2.xs4all.nl>...
> I don't agree with this. I'm working on a project where we found that
 when
> the number of extents exceeded about 40 (differs per table), we got a
> significant performance loss. After export/import to a single extent, the
> performance would go up again, until again the extent count would go over
> the magic mark.

When you Export/Import, you re-pack the rows. They are stored as efficiently as
they ever will be, with no row chaining. More importantly, you're probably rebuilding
your indexes as well - an important maintenance activity. These acts alone usually
generate the perceived performance improvement.

There's a simple way to test this out. Do your Export, drop your tables, and rebuild
them with minextents 40, and Import, then check your performance.
>
> It seems that the recordsize of the table has something to do with it.

Sure, because that affects chaining.

Kevin Loney. Received on Tue Sep 16 1997 - 00:00:00 CDT