Re: 8.1.7 LMTs Autoallocate vs Uniform Extents

There's a note on my website in the errata and addenda to the book, chapter 8, about this. 64MB extents kick in when the segment has grown to about 1GB.

However, oddities occur all over the place, particularly when the tablespace has been exercised for a while. It is possible for Oracle to be pretty arbitrary about how many of each of the 'legal' extent sizes it uses if (a) you specify a table with a large initial extent
(notes about that on the same addendum page) and/or
if there are available holes near the start of the tablespace which are waiting to be used up.

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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Practical Oracle 8i: Building Efficient Databases

-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 26 March 2002 20:59

Sundeep,

Major differences between AUTOALLOCATE and UNIFORM is the fact that extent
sizes in AUTOALLOCATE tablespace are not uniformly-sized.

I've been working in v9.0.1 (not 8.1.7 -- don't have one of those!) and
noticed the following pattern in non-partitioned tables and range-partitioned tables:

    first 16 extents = 64K (8 blocks of 8K apiece)
    next 63 extents = 1M (128 blocks of 8K apiece)
    next ? extents = 8M (1024 blocks of 8K apiece)

In my tablespaces, I haven't seen more than 16 extents of 64K for any segment, and I haven't seen more than 63 extents of 1M for any segment. I
don't have any objects big enough (yet) to probe the upper reaches of the 8M
extent range...

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Author: Jonathan Lewis
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