[SPARK-17549][SQL] Only collect table size stat in driver for cached relation.

This reverts commit 9ac68dbc5720026ea92acc61d295ca64d0d3d132. Turns out
the original fix was correct.

Original change description:
The existing code caches all stats for all columns for each partition
in the driver; for a large relation, this causes extreme memory usage,
which leads to gc hell and application failures.

It seems that only the size in bytes of the data is actually used in the
driver, so instead just colllect that. In executors, the full stats are
still kept, but that's not a big problem; we expect the data to be distributed
and thus not really incur in too much memory pressure in each individual
executor.

There are also potential improvements on the executor side, since the data
being stored currently is very wasteful (e.g. storing boxed types vs.
primitive types for stats). But that's a separate issue.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #15304 from vanzin/SPARK-17549.2.

1 files changed, 14 insertions, 0 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/columnar/InMemoryColumnarQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/columnar/InMemoryColumnarQuerySuite.scala
index 937839644a..0daa29b666 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/columnar/InMemoryColumnarQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/columnar/InMemoryColumnarQuerySuite.scala
@@ -232,4 +232,18 @@ class InMemoryColumnarQuerySuite extends QueryTest with SharedSQLContext {
     val columnTypes2 = List.fill(length2)(IntegerType)
     val columnarIterator2 = GenerateColumnAccessor.generate(columnTypes2)
   }
+
+  test("SPARK-17549: cached table size should be correctly calculated") {
+    val data = spark.sparkContext.parallelize(1 to 10, 5).toDF()
+    val plan = spark.sessionState.executePlan(data.logicalPlan).sparkPlan
+    val cached = InMemoryRelation(true, 5, MEMORY_ONLY, plan, None)
+
+    // Materialize the data.
+    val expectedAnswer = data.collect()
+    checkAnswer(cached, expectedAnswer)
+
+    // Check that the right size was calculated.
+    assert(cached.batchStats.value === expectedAnswer.size * INT.defaultSize)
+  }
+
 }