[SPARK-20283][SQL] Add preOptimizationBatches

## What changes were proposed in this pull request?
We currently have postHocOptimizationBatches, but not preOptimizationBatches. This patch adds preOptimizationBatches so the optimizer debugging extensions are symmetric.

## How was this patch tested?
N/A

Author: Reynold Xin <rxin@databricks.com>

Closes #17595 from rxin/SPARK-20283.

1 files changed, 7 insertions, 1 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkOptimizer.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkOptimizer.scala
index 2cdfb7a782..1de4f508b8 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkOptimizer.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkOptimizer.scala
@@ -30,7 +30,7 @@ class SparkOptimizer(
     experimentalMethods: ExperimentalMethods)
   extends Optimizer(catalog, conf) {
 
-  override def batches: Seq[Batch] = (super.batches :+
+  override def batches: Seq[Batch] = (preOptimizationBatches ++ super.batches :+
     Batch("Optimize Metadata Only Query", Once, OptimizeMetadataOnlyQuery(catalog, conf)) :+
     Batch("Extract Python UDF from Aggregate", Once, ExtractPythonUDFFromAggregate) :+
     Batch("Prune File Source Table Partitions", Once, PruneFileSourcePartitions)) ++
@@ -38,6 +38,12 @@ class SparkOptimizer(
     Batch("User Provided Optimizers", fixedPoint, experimentalMethods.extraOptimizations: _*)
 
   /**
+   * Optimization batches that are executed before the regular optimization batches (also before
+   * the finish analysis batch).
+   */
+  def preOptimizationBatches: Seq[Batch] = Nil
+
+  /**
    * Optimization batches that are executed after the regular optimization batches, but before the
    * batch executing the [[ExperimentalMethods]] optimizer rules. This hook can be used to add
    * custom optimizer batches to the Spark optimizer.