optimizer

Trace File 10053 to understand the Optimizer (CBO)

The reason to trace the CBO is to understand why the Optimizer made some decisions. In this example we are going to see why same query sometimes uses an index and others it doesn’t, same example was explained HERE It is always useful to have a “GOOD” and “BAD” execution, this way it is easier... » read more

Oracle: When is a full table scan better than index scan?

You might face this question if you are going though job interviews. and these are some cases where the Optimizer thinks going for a full table scan is better than index scan. 1:- The selectivity of the records is very high: We have this table and range of contents: We have an index and it... » read more