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Oct 24, 2016 · Databases

Why Oracle’s AUTO_SAMPLE_SIZE Misses Skewed Data and How to Fix It

The article explains how Oracle’s default DBMS_STATS.AUTO_SAMPLE_SIZE can produce wildly inaccurate cardinality estimates on highly skewed columns, examines the NewDensity and OldDensity algorithms, demonstrates the problem with real‑world examples, and offers practical solutions such as forcing estimate_percent or disabling NewDensity.