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Home -> Community -> Mailing Lists -> Oracle-L -> Re: RE: How does Oracle keep B-tree indexes to 3 levels?
so nodes can be as sparse as having 1-2 pointers in them? Doesnt this increase the size of the tree and decrease performance?
also, does oracle use 'sparse' indexes. With standard dense indexes there is a pointer to every record in the table. With sparse indexes you get pointers to a range of records.
For example.
You have a column with
1
2
3
4
5
You might have a pointer to '1' and a pointer to '5'. Does oracle use this?
>
> From: "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk>
> Date: 2004/02/06 Fri AM 08:43:28 EST
> To: <oracle-l_at_freelists.org>
> Subject: Re: RE: How does Oracle keep B-tree indexes to 3 levels?
>
>
> Oracle doesn't do it.
>
> I think the merge and re-distribute features
> are part of the definition of B*trees, and
> although Oracle claims (at some points in
> the manual) to do B*, it's really only doing
> a variant of B+ (which I think is when there
> are forward and backward pointers between
> adjacent leaf blocks).
>
> (I should probably have used the word NODE
> rather than block, because I think that Oracle
> uses blocks as nodes)
>
>
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> The educated person is not the person
> who can answer the questions, but the
> person who can question the answers -- T. Schick Jr
>
>
> Next public appearances:
> March 2004 Hotsos Symposium - The Burden of Proof
> March 2004 Charlotte NC OUG - CBO Tutorial
> April 2004 Iceland
>
>
> One-day tutorials:
> http://www.jlcomp.demon.co.uk/tutorial.html
>
>
> Three-day seminar:
> see http://www.jlcomp.demon.co.uk/seminar.html
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> ____UK___June
>
>
> The Co-operative Oracle Users' FAQ
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
>
>
> ----- Original Message -----
> From: <ryan.gaffuri_at_cox.net>
> To: <oracle-l_at_freelists.org>
> Sent: Friday, February 06, 2004 1:34 PM
> Subject: Re: RE: How does Oracle keep B-tree indexes to 3 levels?
>
>
> how does oracle determine underflow? In class the professor said that if =
> a block is less than 1/2 full the block is either merged with another blo=
> ck if it can fit, or the data is redistributed amongst multiple blocks. =
>
>
> Oracle doesn't have a pctused for indexes. The pctfree is the overflow. D=
> oes oracle use the 1/2 full line for underflow? =
>
> > =
>
>
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