Re: RE: How does Oracle keep B-tree indexes to 3 levels?

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Fri, 6 Feb 2004 13:43:28 -0000
Message-ID: <01ae01c3ecb7$35c1a7c0$6702a8c0@Primary>

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
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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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Received on Fri Feb 06 2004 - 07:43:28 CST