[GitHub] [spark] tgravescs commented on a change in pull request #23695: [SPARK-26780][CORE]Improve shuffle read using ReadAheadInputStream

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tgravescs commented on a change in pull request #23695: [SPARK-26780][CORE]Improve shuffle read using ReadAheadInputStream 
URL: https://github.com/apache/spark/pull/23695#discussion_r280150222
 
 

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 File path: core/src/main/scala/org/apache/spark/storage/ShuffleBlockFetcherIterator.scala
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 @@ -474,6 +475,12 @@ final class ShuffleBlockFetcherIterator(
               // TODO: manage the memory used here, and spill it into disk in case of OOM.
               Utils.copyStream(input, out, closeStreams = true)
               input = out.toChunkedByteBuffer.toInputStream(dispose = true)
+            } else {
+              val readAheadEnabled = SparkEnv.get != null &&
+                SparkEnv.get.conf.get(config.SHUFFLE_READ_AHEAD)
+              if (readAheadEnabled) {
+                input = new ReadAheadInputStream(input, 1024 * 1024)
 
 Review comment:
   yes I think we should document this behavior, also agree with some of the other comments not sure we need the enabled config, perhaps the buffer size one and if its set to 0 then disabled.  How did you choose the buffer size, just take it from the existing spill reader config? did you try different buffer sizes?

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