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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Maximum height of an Oracle B-tree index
what type of algorithm do you run to increase the height of a b-tree index? My understanding is that oracle dynamically increases the number of pointers each block can have(which is different than other b-trees) in order to keep the height low? am I correct in this assumption?
Why isn't it good to rebuild an index when the height increases? The formula for calculating I/O of an index is as follows
LOG_height(blocks) = estimated I/O
That is LOG of the height of an index to the base of its total number of blocks. Now I think there is a fudge factor based on the size of your blocks, because larger blocks incur more LIOs.
This is not oracle specific. Its general tree theory.
>
> From: "Richard Foote" <richard.foote_at_bigpond.com>
> Date: 2004/03/09 Tue AM 09:18:59 EST
> To: <oracle-l_at_freelists.org>
> Subject: Maximum height of an Oracle B-tree index
>
> Hi All,
>
> I'm currently writing a rather detailed paper for our local user group on
> Index Internals, tentatively titled "Index Internals - Rebuilding The
> Truth". I haven't had this much fun with tree and block dumps for quite a
> while ;)
>
> One of the many myths I'm exposing is the "rebuild if index has more than 2,
> 3, 4, 42, whatever levels". Now to get an honary mention in the paper (what
> more reward can one wish for !!), I would love to know who on the list has
> created an index with the greatest height and perhaps a little info on it's
> circumstance.
>
> Steve Adams once mentioned to me creating an index with 20+ levels, can
> anyone else come close ?
>
> Thanks for any replies.
>
> Richard
>
>
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-- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Tue Mar 09 2004 - 07:17:02 CST
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