[GitHub] [spark] Ngone51 commented on a change in pull request #31763: [SPARK-33114][CORE] Add metadata in MapStatus to support custom shuffle manager

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Ngone51 commented on a change in pull request #31763:
URL: https://github.com/apache/spark/pull/31763#discussion_r589007510



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File path: core/src/main/scala/org/apache/spark/scheduler/MapStatus.scala
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@@ -52,6 +52,13 @@ private[spark] sealed trait MapStatus {
    * partitionId of the task or taskContext.taskAttemptId is used.
    */
   def mapId: Long
+
+  /**
+   * Extra metadata for map status. This could be used by different ShuffleManager implementation
+   * to store information they need. For example, a Remote Shuffle Service ShuffleManager could
+   * store shuffle server information and let reducer task know where to fetch shuffle data.
+   */
+  def metadata: Option[Serializable]

Review comment:
       hmm...what's the relationship between SPARK-33114 and SPARK-25299? According to the JIRA description, SPARK-33114 seems to enhance the support for custom shuffle manager while SPARK-25299 only customize the storage with the default  `SortShuffleManager`.
   
   So if we are only talking about SPARK-33114, adding `metadata` may be a good choice according to its own scenario. But if we bring in SPARK-25299 together (IIUC, what this PR is doing would also benefit SPARK-25299), I personally think we need a more general design here. For example, I'd prefer to redesign the `location` of `MapStatus` to make it be able to support different scenarios (e.g., Spark BlockManager, Spark external shuffle service, custom remote storage, etc. ) mentioned in SPARK-25299. And in this way, different scenarios would be able to reuse the existing features, e.g., decommission(which may update mapstatus location during runtime) and reuse the existing code paths, e.g., we don't need the extra `getAllMapOutputStatuses` and everything should be the same as what we already did during shuffle reading.
   
   WDYT?




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