Github user tgravescs commented on a diff in the pull request:
https://github.com/apache/spark/pull/12113#discussion_r58698221
--- Diff: core/src/main/scala/org/apache/spark/MapOutputTracker.scala ---
@@ -492,16 +624,51 @@ private[spark] object MapOutputTracker extends
Logging {
} {
objOut.close()
}
- out.toByteArray
+ val arr = out.toByteArray
+ if (minBroadcastSize >= 0 && arr.length >= minBroadcastSize) {
+ // Use broadcast instead.
+ // Important arr(0) is the tag == DIRECT, ignore that while
deserializing !
+ val bcast = broadcastManager.newBroadcast(arr, isLocal)
+ // toByteArray creates copy, so we can reuse out
+ out.reset()
+ out.write(BROADCAST)
+ val oos = new ObjectOutputStream(new GZIPOutputStream(out))
+ oos.writeObject(bcast)
+ oos.close()
+ val outArr = out.toByteArray
+ logInfo("Broadcast mapstatuses size = " + outArr.length + ", actual
size = " + arr.length)
+ (outArr, bcast)
+ } else {
+ (arr, null)
+ }
}
// Opposite of serializeMapStatuses.
def deserializeMapStatuses(bytes: Array[Byte]): Array[MapStatus] = {
- val objIn = new ObjectInputStream(new GZIPInputStream(new
ByteArrayInputStream(bytes)))
- Utils.tryWithSafeFinally {
- objIn.readObject().asInstanceOf[Array[MapStatus]]
- } {
- objIn.close()
+ assert (bytes.length > 0)
+
+ def deserializeObject(arr: Array[Byte], off: Int, len: Int): AnyRef = {
+ val objIn = new ObjectInputStream(new GZIPInputStream(
+ new ByteArrayInputStream(arr, off, len)))
+ Utils.tryWithSafeFinally {
+ objIn.readObject()
+ } {
+ objIn.close()
+ }
+ }
+
+ bytes(0) match {
+ case DIRECT =>
+ deserializeObject(bytes, 1, bytes.length -
1).asInstanceOf[Array[MapStatus]]
+ case BROADCAST =>
+ // deserialize the Broadcast, pull .value array out of it, and
then deserialize that
+ val bcast = deserializeObject(bytes, 1, bytes.length - 1).
+ asInstanceOf[Broadcast[Array[Byte]]]
+ logInfo("Broadcast mapstatuses size = " + bytes.length +
+ ", actual size = " + bcast.value.length)
+ // Important - ignore the DIRECT tag ! Start from offset 1
+ deserializeObject(bcast.value, 1, bcast.value.length -
1).asInstanceOf[Array[MapStatus]]
--- End diff --
sorry not sure I follow the question?
The deserialize is getting the small message, which will indicate its a
broadcast and then each executor will get the broadcast variable just like any
other broadcast variable (done by the user). Multiple executors can fetch at
the same time and it uses the torrent broadcast which will share the load as
other executors get parts.
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