Re: index node split autonomy

"Richard Foote" <richard.foote_at_bigpond.com> wrote:
> >
> > If an DML statement causes a index block to split, and then
> > that statement rolls back, is the split also rolled back, or does
> > it persist?
> >
> >
> Hi Xho,
>
> It persists.
>
> Much in the same way that a bunch of inserts increments the HWM only to
> be rolled back. The new HWM persists..
>
> The issue to remember here is that Oracle is a multi-user database and if
> an index node splits, it's quite plausible that another transaction has
> inserted an entry into a split node as well. If Oracle could be bothered
> to redo all the work involved in the split, what of the effects of other
> transactions ?

Hi Richard,

Thanks you (and the others who responded) for the answer. I thought that this must be the case, based on pretty much the same reasoning, but I wanted to make sure before wading in farther.

So this must make the undo for indices especially complex, as a failed transaction may need to roll data back into blocks other than the ones they originally came from, and a transaction making a read-consistent view may need to look for undo which came from blocks other than the one it is rolling back.

Since the API for extensible indexing doesn't seem to allow this kind of intimate interaction with the rollback mechanism, I'm thinking that any domain index requiring special node-split logic is going to be very, very hard to make "long trousers", as Paul would say.

Regards,

Xho

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