Originally posted by abhaysk
i love Jmodic to throw more light on this.
ALthough there is not much to be added to slimdave's explanation, you have chalanged me directly, so I will throw just one small comment....
so now with equaility predicate search for particular id wud be faster than any other indx...
No, the index serach in this case will actually be a bit slower compared to normal btree index (the difference will be minimal though). The actual index tree traversing is identical in both cases, but there is a tiny overhead of CPU time with RK indexes as Oracle has first to reverse the order of bytes of the searched values to make it the same as it is stored in the index.

And as slimdave said, you (generaly) can't use RK indexes for range searches, they can only be used for equality based predicates.

Their main (and only?) purpose is to avoid "hot index blocks" when inserting rows with sequence-generated key values. So they were not invented to speed-up queries but to speed-up inserts....