Github user CodingCat commented on a diff in the pull request:
https://github.com/apache/spark/pull/2490#discussion_r17949828
--- Diff: docs/programming-guide.md ---
@@ -1183,6 +1188,10 @@ running on the cluster can then add to it using the
`add` method or the `+=` ope
However, they cannot read its value.
Only the driver program can read the accumulator's value, using its
`value` method.
+The same task may run multiple times, either when its output data becomes
lost or when multiple
+actions make use of the same stage. In these cases, only the additions
reported by the first
+successful task contribute to the accumulator's value.
--- End diff --
@sryza Actually this is not true....
scala> val acc = sc.accumulator(0)
scala> val data = sc.parallelize(List(1, 2, 3))
data: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[0] at
parallelize at <console>:12
scala> val a = data.map(x => acc += 1)
scala> a.count
scala> acc.value
res5: Int = 3
scala> a.count
scala> acc.value
res7: Int = 6
I will resubmit https://github.com/apache/spark/pull/228 tonight or
tomorrow,
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