Apache Spark - Best Practices and Tuning
  • Introduction
  • RDD
    • Don’t collect large RDDs
    • Don't use count() when you don't need to return the exact number of rows
    • Avoiding Shuffle "Less stage, run faster"
    • Picking the Right Operators
      • Avoid List of Iterators
      • Avoid groupByKey when performing a group of multiple items by key
      • Avoid groupByKey when performing an associative reductive operation
      • Avoid reduceByKey when the input and output value types are different
      • Avoid the flatMap-join-groupBy pattern
      • Use TreeReduce/TreeAggregate instead of Reduce/Aggregate
      • Hash-partition before transformation over pair RDD
      • Use coalesce to repartition in decrease number of partition
    • TreeReduce and TreeAggregate Demystified
    • When to use Broadcast variable
    • Joining a large and a small RDD
    • Joining a large and a medium size RDD
  • Dataframe
    • Joining a large and a small Dataset
    • Joining a large and a medium size Dataset
  • Storage
    • Use the Best Data Format
    • Cache Judiciously and use Checkpointing
  • Parallelism
    • Use the right level of parallelism
    • How to estimate the size of a Dataset
    • How to estimate the number of partitions, executor's and driver's params (YARN Cluster Mode)
  • Serialization and GC
    • Tuning Java Garbage Collection
    • Serialization
  • References
    • References
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  1. RDD

Don't use count() when you don't need to return the exact number of rows

PreviousDon’t collect large RDDsNextAvoiding Shuffle "Less stage, run faster"

Last updated 2 years ago

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When you don't need to return the exact number of rows use:

DataFrame inputJson = sqlContext.read().json(...);
if (inputJson.takeAsList(1).size() == 0) {...}

or

if (inputJson.queryExecution.toRdd.isEmpty()) {...}

instead of:

if (inputJson.count() == 0) {...}

In RDD you can use isEmpty() because if you see the code: 

def isEmpty(): Boolean = withScope { 
    partitions.length == 0 || take(1).length == 0 
}
https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/rdd/RDD.scala