Generate correct estimation details in an execution plan using GATHER PLAN STATISTICS hint in Oracle
Video where I tried to show how the gather_plan_statistics hint is a great way to diagnose cardinality errors. The GATHER_PLAN_STATISTICS hint allows for the collection of extra metrics during the execution of the query. Specifically, it shows us the Optimizer's estimated number of rows (E-Rows) and the actual number of rows (A-Rows) for each row source. If the estimates are vastly different from the actual, one probably needs to investigate why.
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