I am trying to filter a collection of objects, that are in a RDD, based on a field of these objects being in a list.
The approach I am trying the same as here: Filter based on another RDD in Spark
val namesToFilterOn = sc.textFile("/names_to_filter_on.txt").collect.toSet
val usersRDD = userContext.loadUsers("/user.parquet")
This works:
usersRDD.filter(user => Set("Pete","John" ).contains( user.firstName )).first
When I try
usersRDD.filter(user => namesToFilterOn.contains( user.firstName )).first
I get this error
org.apache.spark.SparkException: Task not serializable
Caused by: java.io.NotSerializableException: org.apache.spark.SparkContext
The same error I get when I try this
val shortTestList = Set("Pete","John" )
usersRDD.filter(user => shortTestList .contains( user.firstName )).first
Why do I get this errer when specifying a Set of names/String in these filter statements?
As far as I can see this should work, I a not specifying the SparkContext anywhere in the filter statements. So why the error? And how not to get the error?
The version of Spark that I am using is 1.5.2.
I also tried to first broadcast the Set of names.
val namesToFilterOnBC = sc.broadcast(namesToFilterOn)
usersRDD.filter(user => namesToFilterOnBC.value.contains( user.firstName )).first
This leads again to the same error
org.apache.spark.SparkException: Task not serializable
Caused by: java.io.NotSerializableException: org.apache.spark.SparkContext
The reason is that val namesToFilterOn = sc.textFile("/names_to_filter_on.txt").collect.toSet
belongs to an object that contains unserializable vals and hence the error.
When user => namesToFilterOn.contains( user.firstName )
is transformed into a byte format to send to executors over the wire, Spark checks whether there are any references to unserializable objects and SparkContext is among them.
It appears that Spark found a place where you reference a non-serializable SparkContext and threw the exception.
A solution is to wrap val namesToFilterOn = sc.textFile("/names_to_filter_on.txt").collect.toSet
or val shortTestList = Set("Pete","John" )
as separate methods of an object
in Scala. You can also use the other val shortTestList
inside the closure (as described in Job aborted due to stage failure: Task not serializable ) or broadcast it.
You may find the document SIP-21 - Spores quite informatory for the case.
Asked the developers of userContext and solved the issue by not explicitly instantiating userContext but by just importing its functions.
import userContext._
sc.loadUsers("/user.parquet")
usersRDD.filter(user => namesToFilterOn.contains( user.firstName )).first
instead of
val userContext = new UserContext(sc)
userContext.loadUsers("/user.parquet")
usersRDD.filter(user => namesToFilterOn.contains( user.firstName )).first
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