Re: Extents

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
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Practical Oracle 8i: Building Efficient Databases

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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.

>