Github user pwendell commented on the pull request:
https://github.com/apache/spark/pull/1481#issuecomment-50935680
I'm not totally finished with this but a couple high level comments:
1. I think this entirely subsumes some existing code that tracks timing
only in order to bubble it up to the write metrics, so if that code could be
removed it would be great (it will simplify things and maybe this patch can
even net remove code).
2. The fields in `ShuffleWriteMetrics` should be made `volatile` in order
to ensure that they are visible when heartbeats happen. I think this should be
fine from a performance perspective because at run-time the writer threads are
really active and the reader threads just come by infrequently to hearbeat.
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