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The Oracle Wait Interface provides insight and quantification to the causes of latency experienced when executing SQL.
The 10046 trace event is the primary mechanism for studying wait events at a statement level. The Blackboard Performance Engineering team uses 10046 tracing to investigate the causes of latency combined with 10053 tracing to understand the characteristics of the Oracle Cost-Based Optimizer.
The following two books are excellent resources for learning about wait events and 10046 tracing: