Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/11105#discussion_r86486669
--- Diff: core/src/main/scala/org/apache/spark/TaskContext.scala ---
@@ -69,6 +69,20 @@ object TaskContext {
}
}
+/**
+ * Identifies where an update for a data property accumulator update came
from. This is important
+ * to ensure that updates are not double-counted when rdds get recomputed.
When the executors send
+ * back data property acucmualtor updates, they seperate out the updates
per rdd or shuffle output
+ * generated by the task. That gives the driver sufficient info to ensure
that each update is
+ * counted once. The shuffleId is important since two seperate shuffle
actions could happen on the
+ * same RDD and the RDD ID and partition ID with different accumulators.
+ * Any accumulators used inside of `runJob` directly are always counted
because there is no
+ * resubmition of `runJob`/`foreach`.
--- End diff --
Can you add something here about why this is important for tracking
incomplete partitions, eg. with repeatedly partially computing partitions with
`take()`?
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