[GitHub] [spark] JoshRosen commented on a change in pull request #24672: [SPARK-27801][SQL] Improve performance of InMemoryFileIndex.listLeafFiles for HDFS directories with many files

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JoshRosen commented on a change in pull request #24672: [SPARK-27801][SQL] Improve performance of InMemoryFileIndex.listLeafFiles for HDFS directories with many files
URL: https://github.com/apache/spark/pull/24672#discussion_r287652831
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryFileIndex.scala
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 @@ -274,7 +275,21 @@ object InMemoryFileIndex extends Logging {
     // [SPARK-17599] Prevent InMemoryFileIndex from failing if path doesn't exist
     // Note that statuses only include FileStatus for the files and dirs directly under path,
     // and does not include anything else recursively.
-    val statuses = try fs.listStatus(path) catch {
+    val statuses: Array[FileStatus] = try {
+      fs match {
+        // DistributedFileSystem overrides listLocatedStatus to make 1 single call to namenode
+        // to retrieve the file status with the file block location. The reason to still fallback
+        // to listStatus is because the default implementation would potentially throw a
+        // FileNotFoundException which is better handled by doing the lookups manually below.
+        case _: DistributedFileSystem =>
 
 Review comment:
   Unless I'm misunderstanding something, I don't think that @melin's posted benchmark is an apples-to-apples comparison: `listLocatedStatus` is going to be slower than `listStatus` because it's doing more work in order to get location information. In order for this to be a fair performance comparison you'd want to compare `listStatus + getBlockLocations` to `listLocatedStatus`.
   
   The direct comparison is only useful in cases where we're never going to make use of the location information and to my knowledge we currently do not have a flag to bypass locality fetching in `InMemoryFileIndex` (so the location-free performance isn't relevant).

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