Look for the "Statistics Feedback" section. If you see "This plan was re-optimized," the optimizer learned from its mistake—but this adds a hard parse overhead.
Stop using static snapshots. Use that shift with workload patterns. Look for the "Statistics Feedback" section
Before diving into syntax and parameters, one must understand the Oracle Press methodology: tuning is a systematic process, not a reactive guessing game. In 12c Release 2, this process begins with defining the baseline. You cannot improve what you cannot measure. 1% error but .
Replace COUNT(DISTINCT column) with APPROX_COUNT_DISTINCT . In 12.2, this uses a HyperLogLog algorithm with <1% error but . Look for the "Statistics Feedback" section