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Figure 10-6.
Sample query profile
Explain Plan
Evaluating queries before execution is another invaluable tool when performance tuning
code. An explain plan shows the sequential steps performed by the optimizer when
running the SQL statement. You can use an explain plan to evaluate the compile-time
query plan, but note that an explain plan cannot expose runtime optimizations applied
by the execution engine. These optimizations may occur due to prefiltered data from
earlier processing, data distribution patterns, and automatic data skew optimizations.
ChapTer 10
OpTimizing perfOrmanCe