spark的动态分区裁剪下物理计划怎么实现

override def apply(plan: SparkPlan): SparkPlan = {
    if (!SQLConf.get.dynamicPartitionPruningEnabled) {
      return plan
    }

    plan transformAllExpressions {
      case DynamicPruningSubquery(
          value, buildPlan, buildKeys, broadcastKeyIndex, onlyInBroadcast, exprId) =>
        val sparkPlan = QueryExecution.createSparkPlan(
          sparkSession, sparkSession.sessionState.planner, buildPlan)
        // Using `sparkPlan` is a little hacky as it is based on the assumption that this rule is
        // the first to be applied (apart from `InsertAdaptiveSparkPlan`).
        val canReuseExchange = SQLConf.get.exchangeReuseEnabled && buildKeys.nonEmpty &&
          plan.find {
            case BroadcastHashJoinExec(_, _, _, BuildLeft, _, left, _) =>
              left.sameResult(sparkPlan)
            case BroadcastHashJoinExec(_, _, _, BuildRight, _, _, right) =>
              right.sameResult(sparkPlan)
            case _ => false
          }.isDefined

        if (canReuseExchange) {
          val mode = broadcastMode(buildKeys, buildPlan)
          val executedPlan = QueryExecution.prepareExecutedPlan(sparkSession, sparkPlan)
          // plan a broadcast exchange of the build side of the join
          val exchange = BroadcastExchangeExec(mode, executedPlan)
          val name = s"dynamicpruning#${exprId.id}"
          // place the broadcast adaptor for reusing the broadcast results on the probe side
          val broadcastValues =
            SubqueryBroadcastExec(name, broadcastKeyIndex, buildKeys, exchange)
          DynamicPruningExpression(InSubqueryExec(value, broadcastValues, exprId))
        } else if (onlyInBroadcast) {
          // it is not worthwhile to execute the query, so we fall-back to a true literal
          DynamicPruningExpression(Literal.TrueLiteral)
        } else {
          // we need to apply an aggregate on the buildPlan in order to be column pruned
          val alias = Alias(buildKeys(broadcastKeyIndex), buildKeys(broadcastKeyIndex).toString)()
          val aggregate = Aggregate(Seq(alias), Seq(alias), buildPlan)
          DynamicPruningExpression(expressions.InSubquery(
            Seq(value), ListQuery(aggregate, childOutputs = aggregate.output)))
        }
    }
  }