Re: Locally managed tablespaces - autoallocate vs. uniform

Fragmentation of free space is *impossible* with uniform extent sizes.  It
is merely *rare* with automatic extent sizes, but definitely *achievable*.

With automatic extent sizes, the database has a small number of extent sizes
to choose from, but as soon as you have more than 1 choice, fragmentation is
possible.   I have had very good (better than ever expected!) results with
automatic extent sizes myself, but I *can* imagine how these *could* be used
to fragment a tablespace.

I not certain how to do it, but this is probably a pretty good recipe for
fragmentation:  Create a bunch of small segments.  Grow them to 100x or
1000x their initial size (allocating lots of extents of varying sizes).
Drop.  Repeat.  Happily, few (sane) applications will follow a pattern like
this.

For exactly this reason, I prefer to use uniform extent sizes whenever I can
find one that fits reasonably.  It is not always a viable option, though.

On Tue, Jul 28, 2009 at 12:52 PM, Schauss, R. Peter (IT Solutions) <
peter.schauss@xxxxxxx> wrote:

> How did the product cause free space fragmentation?
>
> - Peter Schauss
>
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx
> [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Powell, Mark D
> Sent: Tuesday, July 28, 2009 2:04 PM
> To: Oracle L
> Subject: RE: Locally managed tablespaces - autoallocate vs. uniform
>
> ...
> ...
>  With one exception where the product actually managed to create a free
> space fragmentation condition the feature works well.  For that one
> product we converted the tablespace to using uniform extents and have
> not had an issue since.
>
>
> -- Mark D Powell --
> Phone (313) 592-5148
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>


-- 
Cheers,
-- Mark Brinsmead
  Senior DBA,
  The Pythian Group
  http://www.pythian.com/blogs

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