spark技术分享BroadcastNestedLoopJoinExec Binary Physical Operator
BroadcastNestedLoopJoinExec is a binary physical operator (with two child left and right physical operators) that is created (and converted to) when JoinSelection physical plan strategy finds a Join logical operator that meets either case:
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canBuildRight join type and
rightphysical operator broadcastable -
canBuildLeft join type and
leftbroadcastable -
non-
InnerLikejoin type
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Note
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BroadcastNestedLoopJoinExec is the default physical operator when no other operators have matched selection requirements.
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Note
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canBuildRight join types are:
canBuildLeft join types are:
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val nums = spark.range(2) val letters = ('a' to 'c').map(_.toString).toDF("letter") val q = nums.crossJoin(letters) scala> q.explain == Physical Plan == BroadcastNestedLoopJoin BuildRight, Cross :- *Range (0, 2, step=1, splits=Some(8)) +- BroadcastExchange IdentityBroadcastMode +- LocalTableScan [letter#69] |
| Key | Name (in web UI) | Description |
|---|---|---|
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number of output rows |
| BuildSide | Left Child | Right Child |
|---|---|---|
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BroadcastDistribution (uses |
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BroadcastDistribution (uses |
Creating BroadcastNestedLoopJoinExec Instance
BroadcastNestedLoopJoinExec takes the following when created:
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Left physical operator
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Right physical operator
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Optional join condition expressions
