Github user JoshRosen commented on the pull request:
https://github.com/apache/spark/pull/4021#issuecomment-76511660
I think that this patch may have introduced a bug that may cause
accumulator updates to be lost:
https://issues.apache.org/jira/browse/SPARK-6075
I'm still trying to see if I can spot the problem, but my hunch is that
maybe the `localAccums` thread-local maps should not hold weak references.
When deserializing an accumulator in an executor and registering it with
`localAccums`, is there ever a moment in which the accumulator has no strong
references pointing to it? Does someone object hold a strong reference to an
accumulator while it's being deserialized? If not, this could lead to it being
dropped from the `localAccums` map, causing that task's accumulator updates to
be lost.
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