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When and how do you use Broadcast Join?

Spark/Big Datamedium0.6 min readPremium
Frequency
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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
AltimetrikInfosys
Key Concepts Tested
joinsparksql
Expert AnswerPremium
115 wordsInterview-ready
**When**: One join side fits in memory across executors (typically < ~100MB, configurable via `spark.sql.autoBroadcastJoinThreshold`). **How**: Use `broadcast(df)` hint or rely on Spark auto-broadcast. Driver sends the small table to all executors; join runs locally without shuffle of the large table. **Why**: Shuffle of a large fact table is expensive (network, disk, serialization); broadcasting the dimension avoids it....
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