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Posted to issues@spark.apache.org by "Josh Rosen (JIRA)" <ji...@apache.org> on 2015/01/22 02:05:35 UTC
[jira] [Updated] (SPARK-5063) Display more helpful error messages
for several invalid operations
[ https://issues.apache.org/jira/browse/SPARK-5063?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Josh Rosen updated SPARK-5063:
------------------------------
Summary: Display more helpful error messages for several invalid operations (was: Raise more helpful errors when RDD actions or transformations are called inside of transformations)
> Display more helpful error messages for several invalid operations
> ------------------------------------------------------------------
>
> Key: SPARK-5063
> URL: https://issues.apache.org/jira/browse/SPARK-5063
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Reporter: Josh Rosen
> Assignee: Josh Rosen
>
> Spark does not support nested RDDs or performing Spark actions inside of transformations; this usually leads to NullPointerExceptions (see SPARK-718 as one example). The confusing NPE is one of the most common sources of Spark questions on StackOverflow:
> - https://stackoverflow.com/questions/13770218/call-of-distinct-and-map-together-throws-npe-in-spark-library/14130534#14130534
> - https://stackoverflow.com/questions/23793117/nullpointerexception-in-scala-spark-appears-to-be-caused-be-collection-type/23793399#23793399
> - https://stackoverflow.com/questions/25997558/graphx-ive-got-nullpointerexception-inside-mapvertices/26003674#26003674
> (those are just a sample of the ones that I've answered personally; there are many others).
> I think we can detect these errors by adding logic to {{RDD}} to check whether {{sc}} is null (e.g. turn {{sc}} into a getter function); we can use this to add a better error message.
> In PySpark, these errors manifest themselves slightly differently. Attempting to nest RDDs or perform actions inside of transformations results in pickle-time errors:
> {code}
> rdd1 = sc.parallelize(range(100))
> rdd2 = sc.parallelize(range(100))
> rdd1.mapPartitions(lambda x: [rdd2.map(lambda x: x)])
> {code}
> produces
> {code}
> [...]
> File "/Users/joshrosen/anaconda/lib/python2.7/pickle.py", line 306, in save
> rv = reduce(self.proto)
> File "/Users/joshrosen/Documents/Spark/python/lib/py4j-0.8.2.1-src.zip/py4j/java_gateway.py", line 538, in __call__
> File "/Users/joshrosen/Documents/Spark/python/lib/py4j-0.8.2.1-src.zip/py4j/protocol.py", line 304, in get_return_value
> py4j.protocol.Py4JError: An error occurred while calling o21.__getnewargs__. Trace:
> py4j.Py4JException: Method __getnewargs__([]) does not exist
> at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:333)
> at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:342)
> at py4j.Gateway.invoke(Gateway.java:252)
> at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
> at py4j.commands.CallCommand.execute(CallCommand.java:79)
> at py4j.GatewayConnection.run(GatewayConnection.java:207)
> at java.lang.Thread.run(Thread.java:745)
> {code}
> We get the same error when attempting to broadcast an RDD in PySpark. For Python, improved error reporting could be as simple as overriding the {{getnewargs}} method to throw a more useful UnsupportedOperation exception with a more helpful error message.
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