spark git commit: [SPARK-17356][SQL] Fix out of memory issue when generating JSON for TreeNode

[we...@apache.org]

Repository: spark
Updated Branches:
  refs/heads/master c0ae6bc6e -> 6f13aa7df


[SPARK-17356][SQL] Fix out of memory issue when generating JSON for TreeNode

## What changes were proposed in this pull request?

class `org.apache.spark.sql.types.Metadata` is widely used in mllib to store some ml attributes. `Metadata` is commonly stored in `Alias` expression.

```
case class Alias(child: Expression, name: String)(
    val exprId: ExprId = NamedExpression.newExprId,
    val qualifier: Option[String] = None,
    val explicitMetadata: Option[Metadata] = None,
    override val isGenerated: java.lang.Boolean = false)
```

The `Metadata` can take a big memory footprint since the number of attributes is big ( in scale of million). When `toJSON` is called on `Alias` expression, the `Metadata` will also be converted to a big JSON string.
If a plan contains many such kind of `Alias` expressions, it may trigger out of memory error when `toJSON` is called, since converting all `Metadata` references to JSON will take huge memory.

With this PR, we will skip scanning Metadata when doing JSON conversion. For a reproducer of the OOM, and analysis, please look at jira https://issues.apache.org/jira/browse/SPARK-17356.

## How was this patch tested?

Existing tests.

Author: Sean Zhong <se...@databricks.com>

Closes #14915 from clockfly/json_oom.


Project: http://git-wip-us.apache.org/repos/asf/spark/repo
Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/6f13aa7d
Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/6f13aa7d
Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/6f13aa7d

Branch: refs/heads/master
Commit: 6f13aa7dfee12b1b301bd10a1050549008ecc67e
Parents: c0ae6bc
Author: Sean Zhong <se...@databricks.com>
Authored: Tue Sep 6 16:05:50 2016 +0800
Committer: Wenchen Fan <we...@databricks.com>
Committed: Tue Sep 6 16:05:50 2016 +0800

----------------------------------------------------------------------
 .../org/apache/spark/sql/catalyst/trees/TreeNode.scala    |  4 +++-
 .../src/test/scala/org/apache/spark/sql/QueryTest.scala   | 10 +++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)
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http://git-wip-us.apache.org/repos/asf/spark/blob/6f13aa7d/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala
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diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala
index 037f8cb..893af51 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala
@@ -618,7 +618,9 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
     case s: String => JString(s)
     case u: UUID => JString(u.toString)
     case dt: DataType => dt.jsonValue
-    case m: Metadata => m.jsonValue
+    // SPARK-17356: In usage of mllib, Metadata may store a huge vector of data, transforming
+    // it to JSON may trigger OutOfMemoryError.
+    case m: Metadata => Metadata.empty.jsonValue
     case s: StorageLevel =>
       ("useDisk" -> s.useDisk) ~ ("useMemory" -> s.useMemory) ~ ("useOffHeap" -> s.useOffHeap) ~
         ("deserialized" -> s.deserialized) ~ ("replication" -> s.replication)

http://git-wip-us.apache.org/repos/asf/spark/blob/6f13aa7d/sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala
----------------------------------------------------------------------
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala b/sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala
index c7af402..d361f61 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala
@@ -33,7 +33,7 @@ import org.apache.spark.sql.execution.aggregate.TypedAggregateExpression
 import org.apache.spark.sql.execution.columnar.InMemoryRelation
 import org.apache.spark.sql.execution.datasources.LogicalRelation
 import org.apache.spark.sql.execution.streaming.MemoryPlan
-import org.apache.spark.sql.types.ObjectType
+import org.apache.spark.sql.types.{Metadata, ObjectType}
 
 
 abstract class QueryTest extends PlanTest {
@@ -274,6 +274,14 @@ abstract class QueryTest extends PlanTest {
     val normalized1 = logicalPlan.transformAllExpressions {
       case udf: ScalaUDF => udf.copy(function = null)
       case gen: UserDefinedGenerator => gen.copy(function = null)
+      // After SPARK-17356: the JSON representation no longer has the Metadata. We need to remove
+      // the Metadata from the normalized plan so that we can compare this plan with the
+      // JSON-deserialzed plan.
+      case a @ Alias(child, name) if a.explicitMetadata.isDefined =>
+        Alias(child, name)(a.exprId, a.qualifier, Some(Metadata.empty), a.isGenerated)
+      case a: AttributeReference if a.metadata != Metadata.empty =>
+        AttributeReference(a.name, a.dataType, a.nullable, Metadata.empty)(a.exprId, a.qualifier,
+          a.isGenerated)
     }
 
     // RDDs/data are not serializable to JSON, so we need to collect LogicalPlans that contains


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