Re: Algorithm for calculating extent size in LMT

Hi Mark.

I agree. Uniform size is so easy to do, I can't think why anyone would want to use autoallocate for their own tablespaces (something in the back of my head tells me 9i Release 2 uses autoallocate for SYSTEM. I may have got my neurons crossed, though. And undo tablespaces are autoallocate, of course).

On the other hand, the autoallocate policy is not as crazy as ye olde PCTINCREASE, and the possible fragmentation penalties seem less severe.

Regards
HJR

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Resources for Oracle: http://www.hjrdba.com
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"Mark D Powell" <mark.powell_at_eds.com> wrote in message
news:178d2795.0203040905.5460dbda_at_posting.google.com...
> "Howard J. Rogers" <dba_at_hjrdba.com> wrote in message
news:<a5u9is$1r7$1_at_lust.ihug.co.nz>...


> > There *is* such a thing, of course... there is an 'autoallocate' policy

for


> > locally managed tablespaces, and as best I can tell it goes something

like


> > this:

> >

> > The first 16 extents of a segment will be 64K in size.

> > The next 64 extents will be 1M in size

> > Then extents become 8M in size.

> > At the 200th extent, you get 64M extents.

> > After that, I can't tell you... because I ran out of disk space!

> >

> > What Daniel is hinting at, I guess, is that having odd-sized extents

within


> > a tablespace is not a good idea, because it risks fragmentation.  I

agree


> > with him that 'autoallocate' is not a terribly good idea for your own

> > tablespaces, and that you should take charge of the extent allocation

> > policy.

> >

> > The essential feature of locally managed tablespace is that we no longer

> > really give a damn how many extents a segment acquires, because extent

> > allocation is now a trivial operation for the database (though I agree

that


> > having the extent map for a segment fit into one block makes for some

small


> > performance improvement, and therefore limiting the number to the old

hard


> > limits (121 for 2K blocks, 504 for 8K blocks and so on) is still not a

bad


> > idea).

> >

> > Regards

> > HJR

> > --

> > ----------------------------------------------

> > Resources for Oracle: http://www.hjrdba.com

> > ===============================

> >

>
> Howard, thanks for posting your findings.  I find the results
> interesting, and potentially good to have in the back of my mind in
> case I encounter auto extent in use.  I perfer to either use uniform
> extents or manage them manually using a limited set of extents, but
> you never know what you will encounter.
>
> -- Mark D Powell --