[GitHub] [spark] xkrogen commented on a diff in pull request #38832: [WIP] SPARK-41313 Combine fixes for SPARK-3900 and SPARK-21138

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

xkrogen commented on code in PR #38832:
URL: https://github.com/apache/spark/pull/38832#discussion_r1038612370


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resource-managers/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala:
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@@ -240,6 +240,9 @@ private[spark] class ApplicationMaster(
 
       logInfo("ApplicationAttemptId: " + appAttemptId)
 
+      // During shutdown, we may not be able to create an FileSystem object. So, pre-create here.
+      val stagingDirPath = new Path(System.getenv("SPARK_YARN_STAGING_DIR"))
+      val stagingDirFs = stagingDirPath.getFileSystem(yarnConf)

Review Comment:
   > Is it safe to hold on to the FS object like this in the hook?
   
   I don't see why this would be an issue. It adds one additional reference to the state required for the hook, but this is negligible. FS objects are already globally cached, so in a typical case there is no new/additional FS instance being held onto by the hook; just a reference to the same FS object which would be used elsewhere throughout the driver. If `SPARK_YARN_STAGING_DIR` happens to be on a different file system than everything else, you'll end up with an additional FS reference, but most FS implementations (including HDFS) initialize all of their external connections lazily (upon the time of the first RPC) so you're just talking about a small amount of in-memory state.
   
   > But that does not seem to be the case right now.
   
   Can you elaborate @xinglin?



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