spark技术分享ReuseExchange Physical Query Optimization
ReuseExchange is a physical query optimization (aka physical query preparation rule or simply preparation rule) that QueryExecution uses to optimize the physical plan of a structured query by FIXME.
Technically, ReuseExchange is just a Catalyst rule for transforming physical query plans, i.e. Rule[SparkPlan].
ReuseExchange is part of preparations batch of physical query plan rules and is executed when QueryExecution is requested for the optimized physical query plan (i.e. in executedPlan phase of a query execution).
apply Method
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apply(plan: SparkPlan): SparkPlan |
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Note
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apply is part of Rule Contract to apply a rule to a physical plan.
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apply finds all Exchange unary operators and…FIXME
apply does nothing and simply returns the input physical plan if spark.sql.exchange.reuse internal configuration property is off (i.e. false).
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Note
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spark.sql.exchange.reuse internal configuration property is on (i.e. true) by default.
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