Tathagata Das created SPARK-17372:
-------------------------------------
Summary: 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
Here is the result of my investigation. 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
5000 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.
The right solution is to convert the seq to an array before writing to the log.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
