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

How To Analyze wait: ‘enq: HW – contention’

This wait can have an impact to production and deteriorate performance on a DB, so lets investigateā€¦ 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