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What is Broadcast Join and Why is It Required?

Spark/Big Datamedium0.5 min readPremium
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Asked at 1 company
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Nagarro
Key Concepts Tested
joinsparksql
Expert AnswerPremium
91 wordsInterview-ready
**Broadcast Join**: Small table sent to all executors; each does local hash join. No shuffle of large table. **Why Required**: Shuffle join on 100GB + 1GB = shuffle 100GB. Broadcast 1GB = each executor gets 1GB; no shuffle. 10–100x faster. **When**: Small table < ~100MB (configurable via spark.sql.autoBroadcastJoinThreshold). Manual: `broadcast(df)`. **Trade-offs**: Broadcast table must fit in executor memory. Oversized = OOM....
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