[jira] [Resolved] (SPARK-17372) Running a file stream on a directory with partitioned subdirs throw NotSerializableException/StackOverflowError

["Tathagata Das (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-17372?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tathagata Das resolved SPARK-17372.
-----------------------------------
       Resolution: Fixed
    Fix Version/s: 2.1.0
                   2.0.1

Issue resolved by pull request 14987
[https://github.com/apache/spark/pull/14987]

> Running a file stream on a directory with partitioned subdirs throw NotSerializableException/StackOverflowError
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-17372
>                 URL: https://issues.apache.org/jira/browse/SPARK-17372
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL, Streaming
>    Affects Versions: 2.0.0
>            Reporter: Tathagata Das
>            Assignee: Tathagata Das
>             Fix For: 2.0.1, 2.1.0
>
>
> When we create a filestream on a directory that has partitioned subdirs (i.e. dir/x=y/), then ListingFileCatalog.allFiles returns the files in the dir as Seq[String] which internally is a Stream[String]. This is because of this [line|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/PartitioningAwareFileCatalog.scala#L93], where a LinkedHashSet.values.toSeq returns Stream. Then when the [FileStreamSource|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala#L79] filters this Stream[String] to remove the seen files, it creates a new Stream[String], which has a filter function that has a $outer reference to the FileStreamSource (in Scala 2.10). Trying to serialize this Stream[String] causes NotSerializableException. This will happened even if there is just one file in the dir.
> Its important to note that this behavior is different in Scala 2.11. There is no $outer reference to FileStreamSource, so it does not throw NotSerializableException. However, with a large sequence of files (tested with 10000 files), it throws StackOverflowError. This is because how Stream class is implemented. Its basically like a linked list, and attempting to serialize a long Stream requires *recursively* going through linked list, thus resulting in StackOverflowError.
> In short, across both Scala 2.10 and 2.11, serialization fails when both the following conditions are true. 
> - file stream defined on a partitioned directory  
> - directory has 10k+ files
> The right solution is to convert the seq to an array before writing to the log.



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