Ngone51 commented on a change in pull request #32287:
URL: https://github.com/apache/spark/pull/32287#discussion_r618553230



##########
File path: 
core/src/main/scala/org/apache/spark/storage/ShuffleBlockFetcherIterator.scala
##########
@@ -683,7 +694,28 @@ final class ShuffleBlockFetcherIterator(
             }
           }
 
-        case FailureFetchResult(blockId, mapIndex, address, e) =>
+        // Catching OOM and do something based on it is only a workaround for 
handling the
+        // Netty OOM issue, which is not the best way towards memory 
management. We can
+        // get rid of it when we find a way to manage Netty's memory precisely.
+        case FailureFetchResult(blockId, mapIndex, address, size, 
isNetworkReqDone, e)
+            if e.isInstanceOf[OutOfDirectMemoryError] || 
e.isInstanceOf[NettyOutOfMemoryError] =>
+          assert(address != blockManager.blockManagerId &&
+            !hostLocalBlocks.contains(blockId -> mapIndex),
+            "Netty OOM error should only happen on remote fetch requests")
+          logWarning(s"Failed to fetch block $blockId due to Netty OOM, will 
retry", e)
+          NettyUtils.isNettyOOMOnShuffle = true
+          numBlocksInFlightPerAddress(address) = 
numBlocksInFlightPerAddress(address) - 1
+          bytesInFlight -= size
+          if (isNetworkReqDone) {
+            reqsInFlight -= 1
+            logDebug("Number of requests in flight " + reqsInFlight)
+          }
+          val defReqQueue =
+            deferredFetchRequests.getOrElseUpdate(address, new 
Queue[FetchRequest]())
+          defReqQueue.enqueue(FetchRequest(address, 
Array(FetchBlockInfo(blockId, size, mapIndex))))

Review comment:
       It will keep retry until succeeds. So in the worst case, it will retry 
for the times of the number of total requests, which would fetch one by one. 
Theoretically, it should succeed in the end (unless that netty is even not able 
to serve one request at a time) and won't be an endless retry.




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