In article <3842ac32.11741392_at_read.news.globalnet.co.uk>,
boulke_at_globalnet.co.uk (Keith Boulton) wrote:
> On 29 Nov 1999 12:46:39 +0000, Robin Smith
> <smithrc_at_zdbaora.nat.bt.com> wrote:
>
> >records will always be added to the right hand side of the index so
it
> >will become skewed. If you reverse the key then entries will also go
> >into the middle of the index so will become self balancing.
>
> A b*tree index cannot become skewed.
>
I believe that your comment that a b*tree index cannot become skewed is
only true in theory. Depending on how the b*tree is implemented in
code, activity unbalances the tree. In theory it should be rebalanced
as activity takes place but there is a cost to doing so. This cost is
highest for deletes and if my memory is correct the version 7
documentation claimed that Oracle rebalanced for inserts but it
deferred much of the work for deletes. I have read some posts in the
past questioning how good a job Oracle did rebalancing for inserts in
the case of sequential keys. I can not remember the ver 8
documentation on this topic but I have not noticed any growth behavior
changes on our indexes so I suspect there has been no major changes to
the implementation of b*trees with Oracle.
--
Mark D. Powell -- The only advice that counts is the advice that
you follow so follow your own advice --
Sent via Deja.com http://www.deja.com/
Before you buy.
Received on Mon Nov 29 1999 - 14:07:24 CST
