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
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
This wait can have an impact to production and deteriorate performance on a DB, so lets investigate… Lets see the output from a AWR report where this event is 23% of the total wait time: As per “Analyzing ‘enq: HW – contention’ Wait Event (Doc ID 740075.1)”, this can be generated by multiple sessions fighting... » read more