[SPARK-16238] Metrics for generated method and class bytecode size

## What changes were proposed in this pull request?

This extends SPARK-15860 to include metrics for the actual bytecode size of janino-generated methods. They can be accessed in the same way as any other codahale metric, e.g.

```
scala> org.apache.spark.metrics.source.CodegenMetrics.METRIC_GENERATED_CLASS_BYTECODE_SIZE.getSnapshot().getValues()
res7: Array[Long] = Array(532, 532, 532, 542, 1479, 2670, 3585, 3585)

scala> org.apache.spark.metrics.source.CodegenMetrics.METRIC_GENERATED_METHOD_BYTECODE_SIZE.getSnapshot().getValues()
res8: Array[Long] = Array(5, 5, 5, 5, 10, 10, 10, 10, 15, 15, 15, 38, 63, 79, 88, 94, 94, 94, 132, 132, 165, 165, 220, 220)
```

## How was this patch tested?

Small unit test, also verified manually that the performance impact is minimal (<10%). hvanhovell

Author: Eric Liang <ekl@databricks.com>

Closes #13934 from ericl/spark-16238.

1 files changed, 12 insertions, 0 deletions

diff --git a/core/src/main/scala/org/apache/spark/metrics/source/StaticSources.scala b/core/src/main/scala/org/apache/spark/metrics/source/StaticSources.scala
index 6819222e15..6bba259acc 100644
--- a/core/src/main/scala/org/apache/spark/metrics/source/StaticSources.scala
+++ b/core/src/main/scala/org/apache/spark/metrics/source/StaticSources.scala
@@ -47,4 +47,16 @@ object CodegenMetrics extends Source {
    * Histogram of the time it took to compile source code text (in milliseconds).
    */
   val METRIC_COMPILATION_TIME = metricRegistry.histogram(MetricRegistry.name("compilationTime"))
+
+  /**
+   * Histogram of the bytecode size of each class generated by CodeGenerator.
+   */
+  val METRIC_GENERATED_CLASS_BYTECODE_SIZE =
+    metricRegistry.histogram(MetricRegistry.name("generatedClassSize"))
+
+  /**
+   * Histogram of the bytecode size of each method in classes generated by CodeGenerator.
+   */
+  val METRIC_GENERATED_METHOD_BYTECODE_SIZE =
+    metricRegistry.histogram(MetricRegistry.name("generatedMethodSize"))
 }