[GitHub] [spark] dbtsai commented on a change in pull request #26085: [SPARK-29434][Core] Improve the MapStatuses Serialization Performance

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dbtsai commented on a change in pull request #26085: [SPARK-29434][Core] Improve the MapStatuses Serialization Performance
URL: https://github.com/apache/spark/pull/26085#discussion_r336689651
 
 

 ##########
 File path: core/src/main/scala/org/apache/spark/MapOutputTracker.scala
 ##########
 @@ -822,18 +830,42 @@ private[spark] object MapOutputTracker extends Logging {
     } {
       objOut.close()
     }
-    val arr = out.toByteArray
+
+    val arr: Array[Byte] = {
+      val zos = new ZstdOutputStream(compressedOut)
+      Utils.tryWithSafeFinally {
+        compressedOut.write(DIRECT)
+        // `out.writeTo(zos)` will write the uncompressed data from `out` to `zos`
+        //  without copying to avoid unnecessary allocation and copy of byte[].
+        out.writeTo(zos)
+      } {
+        zos.close()
+      }
+      compressedOut.toByteArray
+    }
     if (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
 
 Review comment:
   We are still calling toByteArray; thus, compressedOut can be reused.

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