Spark Optimization

Spark run faster and faster

• Cluster Optimization
• Parameters Optimization
• Code Optimization

Cluster Optimization

Locality Level

Data locality is how close data is to the code processing it. There are several levels of locality based on the data’s current location. In order from closest to farthest:

• PROCESS_LOCAL data is in the same JVM as the running code. This is the best locality possible
• NODE_LOCAL data is on the same node. Examples might be in HDFS on the same node, or in another executor on the same node. This is a little slower than PROCESS_LOCAL because the data has to travel between processes
• NO_PREF data is accessed equally quickly from anywhere and has no locality preference
• RACK_LOCAL data is on the same rack of servers. Data is on a different server on the same rack so needs to be sent over the network, typically through a single switch
• ANY data is elsewhere on the network and not in the same rack

Performance: PROCESS_LOCAL > NODE_LOCAL > NO_PREF > RACK_LOCAL

Locality settting

• spark.locality.wait.process
• spark.locality.wait.node
• spark.locality.wait.rack

Data Format

• text
• orc
• parquet
• avro

format setting

• spark.sql.hive.convertCTAS
• spark.sql.sources.default

parallelising

• spark.sql.shuffle.partitions : default is 200

computing

• —executor-memory : default is 1G
• —executor-cores : default is 1 if large memory cause resource throtle in cluster, if small memory cause task termination if more cores cause IO issue, if less cores slow dow computing

memory

• spark.executor.overhead.memory

table join

• spark.sql.autoBroadcastJoinThreshold : default 10M

predicate push down in Spark SQL queries

• spark.sql.parquet.filterPushdown : default True
• spark.sql.orc.filterPushdown=true : default False

reuse RDD

    df.persist(pyspark.StorageLevel.MEMORY_ONLY)

Spark operators

• shuffle operators

  • avoid using reduceByKey, join, distinct, repartition etc
  • Broadcast small dataset

• High performance operator

  • reduceByKey > groupByKey (reduceByKey works at map side)
  • mapPartitions > map (reduce function calls)
  • treeReduce > reduce (treeReduce works at executor not driver)
    • treeReduce & reduce return some result to driver
    • treeReduce does more work on the executors while reduce bring everything back to the driver.
  • foreachPartitions > foreach (reduce function calls)
  • filter -> coalesce (reduce number of partitions and reduce tasks)
  • repartitionAndSortWithinPartitions > repartition & sort
  • broadcast (100M)

shuffle

• spark.shuffle.sort.bypassMergeThreshold
• spark.shuffle.io.retryWait
• spark.shuffle.io.maxRetries

TBC