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From fathersson <...@git.apache.org>
Subject [GitHub] spark pull request #15923: [SPARK-4105] retry the fetch or stage if shuffle ...
Date Thu, 22 Dec 2016 16:21:00 GMT
Github user fathersson commented on a diff in the pull request:

    https://github.com/apache/spark/pull/15923#discussion_r93652448
  
    --- Diff: core/src/main/scala/org/apache/spark/storage/ShuffleBlockFetcherIterator.scala
---
    @@ -305,40 +316,84 @@ final class ShuffleBlockFetcherIterator(
        */
       override def next(): (BlockId, InputStream) = {
         numBlocksProcessed += 1
    -    val startFetchWait = System.currentTimeMillis()
    -    currentResult = results.take()
    -    val result = currentResult
    -    val stopFetchWait = System.currentTimeMillis()
    -    shuffleMetrics.incFetchWaitTime(stopFetchWait - startFetchWait)
    -
    -    result match {
    -      case SuccessFetchResult(_, address, size, buf, isNetworkReqDone) =>
    -        if (address != blockManager.blockManagerId) {
    -          shuffleMetrics.incRemoteBytesRead(buf.size)
    -          shuffleMetrics.incRemoteBlocksFetched(1)
    -        }
    -        bytesInFlight -= size
    -        if (isNetworkReqDone) {
    -          reqsInFlight -= 1
    -          logDebug("Number of requests in flight " + reqsInFlight)
    -        }
    -      case _ =>
    -    }
    -    // Send fetch requests up to maxBytesInFlight
    -    fetchUpToMaxBytes()
     
    -    result match {
    -      case FailureFetchResult(blockId, address, e) =>
    -        throwFetchFailedException(blockId, address, e)
    +    var result: FetchResult = null
    +    var input: InputStream = null
    +    // Take the next fetched result and try to decompress it to detect data corruption,
    +    // then fetch it one more time if it's corrupt, throw FailureFetchResult if the second
fetch
    --- End diff --
    
    Could you elaborate a bit here. In my mind TCP provides pretty robust data transfer, which
means that if there is an error, then it's been written to disk corrupted and fetch it one
more time won't help.


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