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

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## 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 <seanzhong@databricks.com>

Closes #14915 from clockfly/json_oom.
This commit is contained in:
Sean Zhong 2016-09-06 16:05:50 +08:00 committed by Wenchen Fan
parent c0ae6bc6ea
commit 6f13aa7dfe
2 changed files with 12 additions and 2 deletions
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4
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala
View file

@ -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)

10
sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala
View file

@ -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