Apache Spark logging within Scala

Solution 1:

You can use Akhil's solution proposed in
https://www.mail-archive.com/[email protected]/msg29010.html. I have used by myself and it works.

Akhil Das Mon, 25 May 2015 08:20:40 -0700
Try this way:

object Holder extends Serializable {      
   @transient lazy val log = Logger.getLogger(getClass.getName)    
}


val someRdd = spark.parallelize(List(1, 2, 3)).foreach { element =>
   Holder.log.info(element)
}

Solution 2:

Use Log4j 2.x. The core logger has been made serializable. Problem solved.

Jira discussion: https://issues.apache.org/jira/browse/LOG4J2-801

"org.apache.logging.log4j" % "log4j-api" % "2.x.x"

"org.apache.logging.log4j" % "log4j-core" % "2.x.x"

"org.apache.logging.log4j" %% "log4j-api-scala" % "2.x.x"

Solution 3:

If you need some code to be executed before and after a map, filter or other RDD function, try to use mapPartition, where the underlying iterator is passed explicitely.

Example:

val log = ??? // this gets captured and produced serialization error
rdd.map { x =>
  log.info(x)
  x+1
}

Becomes:

rdd.mapPartition { it =>
  val log = ??? // this is freshly initialized in worker nodes
  it.map { x =>
    log.info(x)
    x + 1
  }
}

Every basic RDD function is always implemented with a mapPartition.

Make sure to handle the partitioner explicitly and not to loose it: see Scaladoc, preservesPartitioning parameter, this is critical for performances.

Solution 4:

This is an old post but I want to provide my working solution which I just got after struggling a lot and still can be useful for others:

I want to print rdd contents inside rdd.map function but getting Task Not Serializalable Error. This is my solution for this problem using scala static object which is extending java.io.Serializable:

import org.apache.log4j.Level

object MyClass extends Serializable{

val log = org.apache.log4j.LogManager.getLogger("name of my spark log")

log.setLevel(Level.INFO)

def main(args:Array[String])
{

rdd.map(t=>

//Using object's logger here

val log =MyClass.log

log.INFO("count"+rdd.count)
)
}

}

Solution 5:

val log = Logger.getLogger(getClass.getName),

You can use "log" to write logs . Also if you need change logger properties you need to have log4j.properties in /conf folder. By default we will have a template in that location.