Re: how Oracle processes index scans

Steve Perry wrote:

> Does anyone know how Oracle processes a range scan on an index? Does it
> find the high and low values in the index and work toward the center
> or???
> What about other types of index access?
>
> Thanks,
> steve

As far as I know Oracle uses B++ tree indexing mechanism in general if you donot specify. Well in a range scan, the problem is that the address on the file will not be continous. So oracle will probably recursively descend down the B++ index and get all the file address (rowids). From thereon, I donot know whether it does an internal sort of rowid so that it doesnot have to access a single block multiple times ? Therefore, a range scan isnot a fast method of searching data unless your data is sorted on the disk and you can do a single sweep with one disk access and read the stuff.

Dogan

PS. This is highly guesswork... Received on Fri Aug 20 1999 - 20:53:50 CDT