[jira] [Created] (SPARK-4835) Streaming saveAs*HadoopFiles() methods may throw FileAlreadyExistsException during checkpoint recovery

["Josh Rosen (JIRA)" <ji...@apache.org>]

Josh Rosen created SPARK-4835:
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             Summary: Streaming saveAs*HadoopFiles() methods may throw FileAlreadyExistsException during checkpoint recovery
                 Key: SPARK-4835
                 URL: https://issues.apache.org/jira/browse/SPARK-4835
             Project: Spark
          Issue Type: Bug
          Components: Streaming
    Affects Versions: 1.3.0
            Reporter: Josh Rosen
            Assignee: Tathagata Das
            Priority: Critical


While running (a slightly modified version of) the "recovery with saveAsHadoopFiles operation" test in the streaming CheckpointSuite, I noticed the following error message in the streaming driver log:

{code}
14/12/12 17:42:50.687 pool-1-thread-1-ScalaTest-running-CheckpointSuite INFO JobScheduler: Added jobs for time 1500 ms
14/12/12 17:42:50.687 pool-1-thread-1-ScalaTest-running-CheckpointSuite INFO RecurringTimer: Started timer for JobGenerator at time 2000
14/12/12 17:42:50.688 sparkDriver-akka.actor.default-dispatcher-3 INFO JobScheduler: Starting job streaming job 1500 ms.0 from job set of time 1500 ms
14/12/12 17:42:50.688 pool-1-thread-1-ScalaTest-running-CheckpointSuite INFO JobGenerator: Restarted JobGenerator at 2000 ms
14/12/12 17:42:50.688 pool-1-thread-1-ScalaTest-running-CheckpointSuite INFO JobScheduler: Started JobScheduler
14/12/12 17:42:50.689 sparkDriver-akka.actor.default-dispatcher-3 INFO JobScheduler: Starting job streaming job 1500 ms.1 from job set of time 1500 ms
14/12/12 17:42:50.689 sparkDriver-akka.actor.default-dispatcher-3 ERROR JobScheduler: Error running job streaming job 1500 ms.0
org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory file:/var/folders/0k/2qp2p2vs7bv033vljnb8nk1c0000gn/T/1418434967213-0/-1500.result already exists
	at org.apache.hadoop.mapred.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:121)
	at org.apache.spark.rdd.PairRDDFunctions.saveAsHadoopDataset(PairRDDFunctions.scala:1045)
	at org.apache.spark.rdd.PairRDDFunctions.saveAsHadoopFile(PairRDDFunctions.scala:944)
	at org.apache.spark.streaming.dstream.PairDStreamFunctions$$anonfun$9.apply(PairDStreamFunctions.scala:677)
	at org.apache.spark.streaming.dstream.PairDStreamFunctions$$anonfun$9.apply(PairDStreamFunctions.scala:675)
	at org.apache.spark.streaming.dstream.ForEachDStream$$anonfun$1.apply$mcV$sp(ForEachDStream.scala:42)
	at org.apache.spark.streaming.dstream.ForEachDStream$$anonfun$1.apply(ForEachDStream.scala:40)
	at org.apache.spark.streaming.dstream.ForEachDStream$$anonfun$1.apply(ForEachDStream.scala:40)
	at scala.util.Try$.apply(Try.scala:161)
	at org.apache.spark.streaming.scheduler.Job.run(Job.scala:32)
	at org.apache.spark.streaming.scheduler.JobScheduler$JobHandler.run(JobScheduler.scala:171)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)
14/12/12 17:42:50.691 pool-12-thread-1 INFO SparkContext: Starting job: apply at Transformer.scala:22
{code}

Spark Streaming's {{saveAsHadoopFiles}} method calls Spark's {{rdd.saveAsHadoopFile}} method.  The Spark method, in turn, called {{PairRDDFunctions.saveAsHadoopDataset()}}, which has error-checking to ensure that the output directory does not already exist:

{code}
    if (self.conf.getBoolean("spark.hadoop.validateOutputSpecs", true)) {
      // FileOutputFormat ignores the filesystem parameter
      val ignoredFs = FileSystem.get(hadoopConf)
      hadoopConf.getOutputFormat.checkOutputSpecs(ignoredFs, hadoopConf)
    }
{code}

If Spark Streaming recovers from a checkpoint and re-runs the last batch in the checkpoint, then {{saveAsHadoopDataset}} will have been called twice with the same output path.  If the output path exists from the first, pre-recovery run, then the recovery will fail.

This seems like it could be a pretty serious issue: imagine that a streaming job fails partway through a save() operation, then recovers: in this case, the existing directory will prevent us from ever recovering and finishing the save().

Fortunately, this should be simple to fix: we should disable the existing directory checks for output operations called by streaming jobs.



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