wangshuo128 commented on a change in pull request #31968:
URL: https://github.com/apache/spark/pull/31968#discussion_r607812378
##########
File path:
sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLDriver.scala
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@@ -64,9 +65,15 @@ private[hive] class SparkSQLDriver(val context: SQLContext =
SparkSQLEnv.sqlCont
new VariableSubstitution().substitute(command)
}
context.sparkContext.setJobDescription(substitutorCommand)
- val execution =
context.sessionState.executePlan(context.sql(command).logicalPlan)
- hiveResponse = SQLExecution.withNewExecutionId(execution) {
Review comment:
`toDF` only produces a `executionId` by
`SQLExecution.withNewExecutionId`, but the `command` with side effects would
run only once. It happens as below:
1. when run `sql("show tables")`, Spark generates a `QueryExecution` object.
The `QueryExecution`'s `LogicalPlan` is eagerly executed when we pass the
`QueryExecution` to a Dataset and initialize `Dataset.logicalPlan`
2. when run `show`, the code goes to
`Dataset.showString`https://github.com/apache/spark/blob/3b634f66c3e4a942178a1e322ae65ce82779625d/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala#L340
and then call `Dataset.getRows`
https://github.com/apache/spark/blob/3b634f66c3e4a942178a1e322ae65ce82779625d/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala#L291
we new a `Dataset` with the same `QueryExecution` object in _**step1**_
https://github.com/apache/spark/blob/3b634f66c3e4a942178a1e322ae65ce82779625d/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala#L454
thus, the `command` would be wrapped in `SQLExecution.withNewExecutionId`
when initializing the `df.logicalPlan` , however, the `QueryExecution` has
already been optimized and planned, won't execute the underlying command any
more, see `ExecutedCommandExec.sideEffectResult`
https://github.com/apache/spark/blob/3b634f66c3e4a942178a1e322ae65ce82779625d/sql/core/src/main/scala/org/apache/spark/sql/execution/command/commands.scala#L68
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