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When and how do you use Broadcast Join in Spark?

Spark/Big Datamedium0.6 min readPremium
Frequency
Low
Asked at 2 companies
Category
452
questions in Spark/Big Data
Difficulty Split
88E|81M|283H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Delivery HeroFragma Data Systems
Key Concepts Tested
joinsparksql
Expert AnswerPremium
113 wordsInterview-ready
Broadcast join sends the small table to every executor; join happens locally without shuffle. **Trigger**: broadcast(df) hint or spark.sql.autoBroadcastJoinThreshold (default 10MB). **Why use it**: Avoids shuffling the large table—the dominant cost in sort-merge join. **When**: One table fits in executor memory (typically < 100MB after serialization). **Scalability trade-off**: Driver fetches and distributes; oversized broadcast causes driver OOM....
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