[GitHub] [spark] squito commented on a change in pull request #25856: [SPARK-29182][Core] Cache preferred locations of checkpointed RDD

[GitBox <gi...@apache.org>]

squito commented on a change in pull request #25856: [SPARK-29182][Core] Cache preferred locations of checkpointed RDD
URL: https://github.com/apache/spark/pull/25856#discussion_r334679728
 
 

 ##########
 File path: core/src/main/scala/org/apache/spark/rdd/ReliableCheckpointRDD.scala
 ##########
 @@ -82,16 +84,38 @@ private[spark] class ReliableCheckpointRDD[T: ClassTag](
     Array.tabulate(inputFiles.length)(i => new CheckpointRDDPartition(i))
   }
 
-  /**
-   * Return the locations of the checkpoint file associated with the given partition.
-   */
-  protected override def getPreferredLocations(split: Partition): Seq[String] = {
+  // Cache of preferred locations of checkpointed files.
+  @transient private[spark] lazy val cachedPreferredLocations = CacheBuilder.newBuilder()
+    .expireAfterWrite(
+      SparkEnv.get.conf.get(CACHE_CHECKPOINT_PREFERRED_LOCS_EXPIRE_TIME).get,
+      TimeUnit.MINUTES)
+    .build(
+      new CacheLoader[Partition, Seq[String]]() {
+        override def load(split: Partition): Seq[String] = {
+          getPartitionBlockLocations(split)
+        }
+      })
+
+  // Returns the block locations of given partition on file system.
+  private def getPartitionBlockLocations(split: Partition): Seq[String] = {
     val status = fs.getFileStatus(
       new Path(checkpointPath, ReliableCheckpointRDD.checkpointFileName(split.index)))
     val locations = fs.getFileBlockLocations(status, 0, status.getLen)
     locations.headOption.toList.flatMap(_.getHosts).filter(_ != "localhost")
   }
 
+  /**
+   * Return the locations of the checkpoint file associated with the given partition.
+   */
+  protected override def getPreferredLocations(split: Partition): Seq[String] = {
+    val cachedExpireTime = SparkEnv.get.conf.get(CACHE_CHECKPOINT_PREFERRED_LOCS_EXPIRE_TIME)
 
 Review comment:
   minor -- reading confs is a bit expensive, you should do this once for the rdd, rather than once per call

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