Re: OCP - Performance Tuning

From: Don Burleson <don_at_burleson.cc>
Date: 28 Jan 2003 11:45:35 -0800
Message-ID: <998d28f7.0301281145.4a901fce@posting.google.com>

It sounds like the question is about why Oracle chooses a nested-loop(index access) over a full-table scan access (e.g. sort-merge join).

To me, a or b are not correct as there are no absolutes with the CBO!

C - The sort parameters CAN influence this decision because is the CBO knows that a disk sort is involved, when he will favor index access.

D - The number of rows in the table also influences the CBO. For example, even with optimizer_index_cost_adj=1 and first_rows, Oracle will do a sort-merge join on a small table, and an index access on a large table.

Hence I vote for C and D. . . . Received on Tue Jan 28 2003 - 13:45:35 CST