Re: Extents

Jonathan Lewis wrote:
>
> Oracle 9 may have re-introduced the number of
> extents as an issue.
>
> If you use 'segment space management auto',
> the typical action is to produce a 1st level
> bitmap block as the first block of every extent -
> although my first experiment creating a large
> table table with a small extent size resulted
> in lots of 1st level blocks covering 4 extents,
> and one 2nd level block covering all the first
> level blocks.
>
> Upshot - in a table with 512 blocks, I had
> 24 blocks allocated to space management,
> whereas previously I would have had only
> one (the segment header block) or a max
> of 5 if I had thought multiple free list groups
> were necessary.
>
> It's a small percentage - but those blocks
> still impact on rollback, redo, and I/O.
>
> --
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> Host to The Co-Operative Oracle Users' FAQ
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
>
> Author of:
> Practical Oracle 8i: Building Efficient Databases
>
> Screen saver or Life saver: http://www.ud.com
> Use spare CPU to assist in cancer research.
>
> Connor McDonald wrote in message <3BFCCB89.7D33_at_yahoo.com>...
> >What you want is (on a per tablespace basis) identically sized extents.
> >This is easiest to do with locally managed tablespaces.
> >
> >After that, it really doesn't matter how many extents you have. If
> >anything, more extents gives you greater granularity at trending the
> >growth of the segments in the database.
> >

Have to admit, I'm still not convinced on the granularity thats being offered with the bitmap mgt, ie 0-25%, 25-50, 50-75, 75-100.

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."