He's changed his mind.
Regards
HJR
"DA Morgan" <damorgan_at_exesolutions.com> wrote in message
news:3E3B0D3F.9916449D_at_exesolutions.com...
> "Howard J. Rogers" wrote:
>
> > "DA Morgan" <damorgan_at_exesolutions.com> wrote in message
> > > I never thought I'd ever try to correct you but I believe (sticking it
> > > way out there on ths one) it is possible for there to be four on one
and
> > > three on the other from time-to-time as Oracle doesn't rebalance
every
> > > time someone performs a single insert or delete. Isn't it more a case
of
> > > never having 5 and 3?
> >
> > Jonathan can answer for himself, of course. But I'll take a stab at it
> > too... no, it's not possible for a single insert to result in an
unbalanced
> > index. Oracle's indexes are *always* balanced. That's why you really
don't
> > want to create indexes unnecessarily, because they can slow down simple
DML
> > on the table dramatically. Your simple insert that threatens to
unbalance an
> > index will cause a whole raft of cascading adjustments to the index
> > structure precisely to avoid imbalance.
> >
> > I don't know whether it's just a myth or not, but Oracle refers to its
> > indexes as "B*Tree" structures, not 'b-tree' ones. And that's because
the
> > 'b' doesn't stand for 'binary', but 'balanced'.
> >
> > Whether that bit of apocrypha is true or not, Oracle index structures
are
> > always re-balanced.
> >
> > Regards
> > HJR
>
> Just went through my files and found a posting by Jonathan from 23 May,
2002
> subject title "unbalance indexes --common widsom?". And I quote:
>
> "No matter how perfectly an index is maintained, it will always be
possible to
> ensure that you can get it to a state where either just one 3rd level node
has
> split to produce an "imbalance" or (the only possible alternative) every
3rd
> level node has to split to leave the index half-populated if you want
"balance"
> - i.e. every leaf has to be at the fourth level.
>
> The important point about balance b-trees is that no leaf is MORE THAN ONE
level
> deeper that every other leaf."
>
> (even the above misspelling accurately copied).
>
> So unless Jonathan has changed his mind ... my recollection is correct.
>
> Jonathan?
>
> Daniel Morgan
>
Received on Fri Jan 31 2003 - 18:59:39 CST
