Github user sryza commented on a diff in the pull request:
https://github.com/apache/spark/pull/4020#discussion_r23057341
--- Diff: core/src/main/scala/org/apache/spark/executor/TaskMetrics.scala
---
@@ -240,10 +284,18 @@ class ShuffleWriteMetrics extends Serializable {
/**
* Number of bytes written for the shuffle by this task
*/
- @volatile var shuffleBytesWritten: Long = _
-
+ @volatile private var _shuffleBytesWritten: Long = _
+ def shuffleBytesWritten = _shuffleBytesWritten
+ private[spark] def incShuffleBytesWritten(value: Long) =
_shuffleBytesWritten += value
+ private[spark] def decShuffleBytesWritten(value: Long) =
_shuffleBytesWritten -= value
+
/**
* Time the task spent blocking on writes to disk or buffer cache, in
nanoseconds
*/
- @volatile var shuffleWriteTime: Long = _
--- End diff --
`_shuffleWriteTime` can only get incremented from a single thread. It's
marked volatile so that other threads can read from it. Using an `AtomicLong`
would unnecessarily bloat the size of the task results. I probably should have
documented this access pattern better.
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