No more struggles with Apache Spark workloads in production
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Paris Scala Group Event May 2019, No more struggles with Apache Spark workloads in production. Apache Spark Primary data structures (RDD, DataSet, Dataframe) Pragmatic explanation - executors, cores, containers, stage, job, a task in Spark. Parallel read from JDBC: Challenges and best practices. Bulk Load API vs JDBC write An optimization strategy for Joins: SortMergeJoin vs BroadcastHashJoin Avoid unnecessary shuffle Alternative to spark default sort Why dropDuplicates() doesn’t result consistency, What is alternative Optimize Spark stage generation plan Predicate pushdown with partitioning and bucketing Why not to use Scala Concurrent ‘Future’ explicitly!
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No more struggles with Apache Spark workloads in production
- 1. Chetan Khatri, Lead - Data Science. Accionlabs India. Paris Scala User Group (PSUG), Paris - France. 23rd May, 2019. Twitter: @khatri_chetan, Email: chetan.khatri@live.com chetan.khatri@accionlabs.com LinkedIn: https://www.linkedin.com/in/chetkhatri Github: chetkhatri
- 2. Lead - Data Science, Technology Evangelist @ Accion labs India Pvt. Ltd. Contributor @ Apache Spark, Apache HBase, Elixir Lang. Co-Authored University Curriculum @ University of Kachchh, India. Data Engineering @: Nazara Games, Eccella Corporation. M.Sc. - Computer Science from University of Kachchh, India.
- 3. ● Apache Spark ● Primary data structures (RDD, DataSet, Dataframe) ● Pragmatic explanation - executors, cores, containers, stage, job, a task in Spark. ● Parallel read from JDBC: Challenges and best practices. ● Bulk Load API vs JDBC write ● An optimization strategy for Joins: SortMergeJoin vs BroadcastHashJoin ● Avoid unnecessary shuffle ● Alternative to spark default sort ● Why dropDuplicates() doesn’t result consistency, What is alternative ● Optimize Spark stage generation plan ● Predicate pushdown with partitioning and bucketing ● Why not to use Scala Concurrent ‘Future’ explicitly!
- 4. ● Apache Spark is a fast and general-purpose cluster computing system / Unified Engine for massive data processing. ● It provides high level API for Scala, Java, Python and R and optimized engine that supports general execution graphs. Structured Data / SQL - Spark SQL Graph Processing - GraphX Machine Learning - MLlib Streaming - Spark Streaming, Structured Streaming
- 6. RDD RDD RDD RDD Logical Model Across Distributed Storage on Cluster HDFS, S3
- 7. RDD RDD RDD T T RDD -> T -> RDD -> T -> RDD T = Transformation
- 8. Integer RDD String or Text RDD Double or Binary RDD
- 9. RDD RDD RDD T T RDD RDD RDD T A RDD - T - RDD - T - RDD - T - RDD - A - RDD T = Transformation A = Action
- 11. TRANSFORMATIONSACTIONS General Math / Statistical Set Theory / Relational Data Structure / I/O map gilter flatMap mapPartitions mapPartitionsWithIndex groupBy sortBy sample randomSplit union intersection subtract distinct cartesian zip keyBy zipWithIndex zipWithUniqueID zipPartitions coalesce repartition repartitionAndSortWithinPartitions pipe reduce collect aggregate fold first take forEach top treeAggregate treeReduce forEachPartition collectAsMap count takeSample max min sum histogram mean variance stdev sampleVariance countApprox countApproxDistinct takeOrdered saveAsTextFile saveAsSequenceFile saveAsObjectFile saveAsHadoopDataset saveAsHadoopFile saveAsNewAPIHadoopDataset saveAsNewAPIHadoopFile
- 12. You care about control of dataset and knows how data looks like, you care about low level API. Don’t care about lot’s of lambda functions than DSL. Don’t care about Schema or Structure of Data. Don’t care about optimization, performance & inefficiencies! Very slow for non-JVM languages like Python, R. Don’t care about Inadvertent inefficiencies.
- 13. parsedRDD.filter { case (project, sprint, numStories) => project == "finance" }. map { case (_, sprint, numStories) => (sprint, numStories) }. reduceByKey(_ + _). filter { case (sprint, _) => !isSpecialSprint(sprint) }. take(100).foreach { case (project, stories) => println(s"project: $stories") }
- 14. val employeesDF = spark.read.json("employees.json") // Convert data to domain objects. case class Employee(name: String, age: Int) val employeesDS: Dataset[Employee] = employeesDF.as[Employee] val filterDS = employeesDS.filter(p => p.age > 3) Type-safe: operate on domain objects with compiled lambda functions.
- 16. Strongly Typing Ability to use powerful lambda functions. Spark SQL’s optimized execution engine (catalyst, tungsten) Can be constructed from JVM objects & manipulated using Functional transformations (map, filter, flatMap etc) A DataFrame is a Dataset organized into named columns DataFrame is simply a type alias of Dataset[Row]
- 17. SQL DataFrames Datasets Syntax Errors Runtime Compile Time Compile Time Analysis Errors Runtime Runtime Compile Time Analysis errors are caught before a job runs on cluster
- 18. DataFrame Dataset Untyped API Typed API Dataset (2016) DataFrame = Dataset [Row] Alias Dataset [T]
- 19. // convert RDD -> DF with column names val parsedDF = parsedRDD.toDF("project", "sprint", "numStories") //filter, groupBy, sum, and then agg() parsedDF.filter($"project" === "finance"). groupBy($"sprint"). agg(sum($"numStories").as("count")). limit(100). show(100) project sprint numStories finance 3 20 finance 4 22
- 20. parsedDF.createOrReplaceTempView("audits") val results = spark.sql( """SELECT sprint, sum(numStories) AS count FROM audits WHERE project = 'finance' GROUP BY sprint LIMIT 100""") results.show(100) project sprint numStories finance 3 20 finance 4 22
- 21. // DataFrame data.groupBy("dept").avg("age") // SQL select dept, avg(age) from data group by 1 // RDD data.map { case (dept, age) => dept -> (age, 1) } .reduceByKey { case ((a1, c1), (a2, c2)) => (a1 + a2, c1 + c2) } .map { case (dept, (age, c)) => dept -> age / c }
- 22. SQL AST DataFrame Datasets Unresolved Logical Plan Logical Plan Optimized Logical Plan Physical Plans CostModel Selected Physical Plan RDD
- 23. employees.join(events, employees("id") === events("eid")) .filter(events("date") > "2015-01-01") events file employees table join filter Logical Plan scan (employees) filter Scan (events) join Physical Plan Optimized scan (events) Optimized scan (employees) join Physical Plan With Predicate Pushdown and Column Pruning
- 28. Job - Each transformation and action mapping in Spark would create a separate jobs. Stage - A Set of task in each job which can run parallel using ThreadPoolExecutor. Task - Lowest level of Concurrent and Parallel execution Unit. Each stage is split into #number-of-partitions tasks, i.e Number of Tasks = stage * number of partitions in the stage
- 33. yarn.scheduler.minimum-allocation-vcores = 1 Yarn.scheduler.maximum-allocation-vcores = 6 Yarn.scheduler.minimum-allocation-mb = 4096 Yarn.scheduler.maximum-allocation-mb = 28832 Yarn.nodemanager.resource.memory-mb = 54000 Number of max containers you can run = (Yarn.nodemanager.resource.memory-mb = 54000 / Yarn.scheduler.minimum-allocation-mb = 4096) = 13
- 41. What happens when you run this code? What would be the impact at Database engine side?
- 51. JoinSelection execution planning strategy uses spark.sql.autoBroadcastJoinThreshold property (default: 10M) to control the size of a dataset before broadcasting it to all worker nodes when performing a join. val threshold = spark.conf.get("spark.sql.autoBroadcastJoinThreshold").toInt scala> threshold / 1024 / 1024 res0: Int = 10 // logical plan with tree numbered sampleDF.queryExecution.logical.numberedTreeString // Query plan sampleDF.explain
- 52. Repartition: Boost the Parallelism, by increasing the number of Partitions. Partition on Joins, to get same key joins faster. // Reduce number of partitions without shuffling, where repartition does equal data shuffling across the cluster. employeeDF.coalesce(10).bulkCopyToSqlDB(bulkWriteConfig("EMPLOYEE_CLIENT")) For example, In case of bulk JDBC write. Parameter "bulkCopyBatchSize" -> "2500", means Dataframe has 10 partitions and each partition will write 2500 records Parallely. Reduce: Impact on Network Communication, File I/O, Network I/O, Bandwidth I/O etc.
- 53. 1. // disable autoBroadcastJoin spark.conf.set("spark.sql.autoBroadcastJoinThreshold", -1) 2. // Order doesn't matter table1.leftjoin(table2) or table2.leftjoin(table1) 3. force broadcast, if one DataFrame is not small! 4. Minimize shuffling & Boost Parallism, Partitioning, Bucketing, coalesce, repartition, HashPartitioner
- 64. Code!