Why it matters

Optimization needs plan understanding. Reading EXPLAIN is core Impala skill.

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The architecture

Levels: SUMMARY (high-level), STANDARD (per-operator), VERBOSE (all details), EXTENDED (physical).

Impala EXPLAINEXPLAIN levelssummary → extendedOperatorsscan / join / aggDistributionbroadcast / partitionLook for full scans + skew warnings + wrong join strategies
Plan analysis.
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How it works end to end

Scan strategies: partition pruning, predicate pushdown, column pruning.

Joins: broadcast (small side to all), partitioned (shuffle both sides by join key).

Aggregations: pre-aggregate (per-node) + finalize.