[SPARK-13071] Coalescing HadoopRDD overwrites existing input metrics

This issue is causing tests to fail consistently in master with Hadoop 2.6 / 2.7. This is because for Hadoop 2.5+ we overwrite existing values of `InputMetrics#bytesRead` in each call to `HadoopRDD#compute`. In the case of coalesce, e.g.
```
sc.textFile(..., 4).coalesce(2).count()
```
we will call `compute` multiple times in the same task, overwriting `bytesRead` values from previous calls to `compute`.

For a regression test, see `InputOutputMetricsSuite.input metrics for old hadoop with coalesce`. I did not add a new regression test because it's impossible without significant refactoring; there's a lot of existing duplicate code in this corner of Spark.

This was caused by #10835.

Author: Andrew Or <andrew@databricks.com>

Closes #10973 from andrewor14/fix-input-metrics-coalesce.

core/src/main/scala/org/apache/spark/rdd/HadoopRDD.scala

@@ -215,6 +215,7 @@ class HadoopRDD[K, V](
       // TODO: there is a lot of duplicate code between this and NewHadoopRDD and SqlNewHadoopRDD
 
       val inputMetrics = context.taskMetrics().registerInputMetrics(DataReadMethod.Hadoop)
+      val existingBytesRead = inputMetrics.bytesRead
 
       // Sets the thread local variable for the file's name
       split.inputSplit.value match {
@@ -230,9 +231,13 @@ class HadoopRDD[K, V](
         case _ => None
       }
 
+      // For Hadoop 2.5+, we get our input bytes from thread-local Hadoop FileSystem statistics.
+      // If we do a coalesce, however, we are likely to compute multiple partitions in the same
+      // task and in the same thread, in which case we need to avoid override values written by
+      // previous partitions (SPARK-13071).
       def updateBytesRead(): Unit = {
         getBytesReadCallback.foreach { getBytesRead =>
-          inputMetrics.setBytesRead(getBytesRead())
+          inputMetrics.setBytesRead(existingBytesRead + getBytesRead())
         }
       }
 

core/src/main/scala/org/apache/spark/rdd/NewHadoopRDD.scala

@@ -130,6 +130,7 @@ class NewHadoopRDD[K, V](
       val conf = getConf
 
       val inputMetrics = context.taskMetrics().registerInputMetrics(DataReadMethod.Hadoop)
+      val existingBytesRead = inputMetrics.bytesRead
 
       // Find a function that will return the FileSystem bytes read by this thread. Do this before
       // creating RecordReader, because RecordReader's constructor might read some bytes
@@ -139,9 +140,13 @@ class NewHadoopRDD[K, V](
         case _ => None
       }
 
+      // For Hadoop 2.5+, we get our input bytes from thread-local Hadoop FileSystem statistics.
+      // If we do a coalesce, however, we are likely to compute multiple partitions in the same
+      // task and in the same thread, in which case we need to avoid override values written by
+      // previous partitions (SPARK-13071).
       def updateBytesRead(): Unit = {
         getBytesReadCallback.foreach { getBytesRead =>
-          inputMetrics.setBytesRead(getBytesRead())
+          inputMetrics.setBytesRead(existingBytesRead + getBytesRead())
         }
       }
 

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/SqlNewHadoopRDD.scala

@@ -127,6 +127,7 @@ private[spark] class SqlNewHadoopRDD[V: ClassTag](
       val conf = getConf(isDriverSide = false)
 
       val inputMetrics = context.taskMetrics().registerInputMetrics(DataReadMethod.Hadoop)
+      val existingBytesRead = inputMetrics.bytesRead
 
       // Sets the thread local variable for the file's name
       split.serializableHadoopSplit.value match {
@@ -142,9 +143,13 @@ private[spark] class SqlNewHadoopRDD[V: ClassTag](
         case _ => None
       }
 
+      // For Hadoop 2.5+, we get our input bytes from thread-local Hadoop FileSystem statistics.
+      // If we do a coalesce, however, we are likely to compute multiple partitions in the same
+      // task and in the same thread, in which case we need to avoid override values written by
+      // previous partitions (SPARK-13071).
       def updateBytesRead(): Unit = {
         getBytesReadCallback.foreach { getBytesRead =>
-          inputMetrics.setBytesRead(getBytesRead())
+          inputMetrics.setBytesRead(existingBytesRead + getBytesRead())
         }
       }