Re: [PR] [SPARK-39771][CORE] Add a warning msg in `Dependency` when a too large number of shuffle blocks is to be created. [spark]

["mridulm (via GitHub)" <gi...@apache.org>]

mridulm commented on code in PR #45266:
URL: https://github.com/apache/spark/pull/45266#discussion_r1508350378


##########
core/src/main/scala/org/apache/spark/Dependency.scala:
##########
@@ -206,6 +206,21 @@ class ShuffleDependency[K: ClassTag, V: ClassTag, C: ClassTag](
     finalizeTask = Option(task)
   }
 
+  // Set the threshold to 1 billion which leads to an 128MB bitmap and
+  // the actual size of `HighlyCompressedMapStatus` can be much larger than 128MB.
+  // This may crash the driver with an OOM error.
+  private val SHUFFLE_BLOCK_NUMBER_WARNING_THRESHOLD: Long = 1L << 30
+  private val numberOfShuffleBlocks = numPartitions.toLong * partitioner.numPartitions.toLong
+
+  if (numberOfShuffleBlocks > SHUFFLE_BLOCK_NUMBER_WARNING_THRESHOLD) {
+    logWarning(
+      s"The number of shuffle blocks (${numberOfShuffleBlocks}) for shuffleId ${shuffleId} " +
+        s"for ${_rdd} with ${numPartitions} partitions is possibly too large, " +
+        "which could cause the driver to crash with an out-of-memory error. " +
+        "Consider decreasing the number of partitions in this shuffle stage."
+    )
+  }
+

Review Comment:
   
   We can avoid the instance variables here.
   Move `SHUFFLE_BLOCK_NUMBER_WARNING_THRESHOLD` to the companion object, and
   
   ```suggestion
     {
       val numberOfShuffleBlocks = numPartitions.toLong * partitioner.numPartitions.toLong
   
       if (numberOfShuffleBlocks > SHUFFLE_BLOCK_NUMBER_WARNING_THRESHOLD) {
         logWarning(
           s"The number of shuffle blocks (${numberOfShuffleBlocks}) for shuffleId ${shuffleId} " +
             s"for ${_rdd} with ${numPartitions} partitions is possibly too large, " +
             "which could cause the driver to crash with an out-of-memory error. " +
             "Consider decreasing the number of partitions in this shuffle stage."
         )
       }
     }
   ```



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