Re: Algorithm for calculating extent size in LMT

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

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"damorgan" <dan.morgan_at_ci.seattle.wa.us> wrote in message
news:3C829FD7.51727A5B_at_ci.seattle.wa.us...


> There is no such thing. Extent sizes are determined by developers and DBAs

> that do their homework and determine the idea size for a class of tables.

> Often ... creating multiple tablespaces with different extent sizes to

avoid


> both fragmentation and keep the number of segments small.

>

> Daniel Morgan

>

>

>

> EP wrote:

>

> > Hi

> >

> > Does anybody know the algorithm used by Oracle when calculating the

extent


> > size for LMT when autoallocate option is specified ???

> >

> > TIA

> > EP

>