在使用org.apache.spark.sql.functions中的Window functions过程中，遇到了几个棘手的问题，经过不断搜寻和多次试验，终于找到了解决方法。
首先看例子：
import org.apache.spark.rdd.RDD import org.apache.spark.sql.{SaveMode, Row} import org.apache.spark.sql.types._ import org.apache.spark.sql.hive.HiveContext import org.apache.spark.{SparkConf, SparkContext}object WindowQueryTest {def main(args: Array[String]) {val sc = new SparkContext(new SparkConf().setAppName("WndFnc_demo").setMaster("local"))val hiveContext = new HiveContext(sc)val data = Seq(("A", 4), ("C", 1), ("D", 1), ("B", 2), ("B", 2), ("D", 4), ("A", 1), ("B", 4))val withRowNumbers: Seq[(String, Int, Int)] = data.zipWithIndex.map(e => (e._1._1, e._1._2, e._2))val rdd: RDD[Row] = sc.parallelize(withRowNumbers).map(triplet => Row(triplet._1, triplet._2, triplet._3))hiveContext.sql("DROP TABLE IF EXISTS delme") hiveContext.sql( """CREATE TABLE `delme`( `key` string,`val` int,`ord` int)""")val schema = StructType(Seq(StructField("key", StringType),StructField("val", IntegerType), StructField("ord", IntegerType)))hiveContext.createDataFrame(rdd, schema).write.mode(SaveMode.Append).saveAsTable("delme")val qRes = hiveContext.sql("""SELECT key, val ,MAX(val)OVER(PARTITION BY key) mx,MIN(val)OVER(PARTITION BY key) mn,row_number() OVER(ORDER BY ord desc) revord,rank() OVER(ORDER BY val) rnkFROM delme""") qRes.collect().foreach(println)} }
一、初始化必需使用HiveContext
如果初始化的是SQLContext实例：
val sqlContext = new SQLContext(sc) 则会报错，提示必需使用HiveContext：
Exception in thread "main" org.apache.spark.sql.AnalysisException: Could not resolve window function 'row_number'. Note that, using window functions currently requires a HiveContext; …… HiveContext继承自SQLContext。
class HiveContext(sc : org.apache.spark.SparkContext) extends org.apache.spark.sql.SQLContext with org.apache.spark.Logging
二、外部库需要添加spark/lib中的三个jar文件依赖
External Libraies必需包含以下三个jar文件，datanucleus-api-jdo, datanucleus-core和datanucleus-rdbms:
工程编译时将自动生成metastore_db文件夹和derby.log文件。
否则，出现如下错误信息：
16/01/18 15:40:07 WARN Persistence: Error creating validator of type org.datanucleus.properties.CorePropertyValidator ClassLoaderResolver for class "" gave error on creation : {1} org.datanucleus.exceptions.NucleusUserException: ClassLoaderResolver for class "" gave error on creation : {1} …… 16/01/18 15:40:07 WARN HiveMetaStore: Retrying creating default database after error: Unexpected exception caught. javax.jdo.JDOFatalInternalException: Unexpected exception caught. …… 16/01/18 15:40:07 INFO HiveMetaStore: 0: Opening raw store with implemenation class:org.apache.hadoop.hive.metastore.ObjectStore 16/01/18 15:40:07 INFO ObjectStore: ObjectStore, initialize called 16/01/18 15:40:07 WARN Persistence: Error creating validator of type org.datanucleus.properties.CorePropertyValidator ClassLoaderResolver for class "" gave error on creation : {1} org.datanucleus.exceptions.NucleusUserException: ClassLoaderResolver for class "" gave error on creation : {1} …… 16/01/18 15:40:07 WARN Hive: Failed to access metastore. This class should not accessed in runtime. org.apache.hadoop.hive.ql.metadata.HiveException: java.lang.RuntimeException: Unable to instantiate org.apache.hadoop.hive.ql.metadata.SessionHiveMetaStoreClient …… 16/01/18 15:40:07 INFO HiveMetaStore: 0: Opening raw store with implemenation class:org.apache.hadoop.hive.metastore.ObjectStore 16/01/18 15:40:07 INFO ObjectStore: ObjectStore, initialize called 16/01/18 15:40:07 WARN Persistence: Error creating validator of type org.datanucleus.properties.CorePropertyValidator ClassLoaderResolver for class "" gave error on creation : {1} org.datanucleus.exceptions.NucleusUserException: ClassLoaderResolver for class "" gave error on creation : {1} …… 16/01/18 15:40:07 WARN HiveMetaStore: Retrying creating default database after error: Unexpected exception caught. javax.jdo.JDOFatalInternalException: Unexpected exception caught. …… 16/01/18 15:40:07 INFO HiveMetaStore: 0: Opening raw store with implemenation class:org.apache.hadoop.hive.metastore.ObjectStore 16/01/18 15:40:07 INFO ObjectStore: ObjectStore, initialize called 16/01/18 15:40:07 WARN Persistence: Error creating validator of type org.datanucleus.properties.CorePropertyValidator ClassLoaderResolver for class "" gave error on creation : {1} org.datanucleus.exceptions.NucleusUserException: ClassLoaderResolver for class "" gave error on creation : {1} …… Exception in thread "main" java.lang.RuntimeException: java.lang.RuntimeException: Unable to instantiate org.apache.hadoop.hive.ql.metadata.SessionHiveMetaStoreClient ……
这三个文件存在于spark/lib中。
三、运行配置JVM参数JAVA_OPTS （FATAL!）
看起来Everything is OK。编译执行程序，却发生异常退出，而且只在最后报出main进程异常，没有任何ERROR，很难发现到底是什么原因。
…… Exception in thread "main" Process finished with exit code 1
多次执行，会出现如下异常信息，重点在PermGen Space（持久加载区空间大小）。
Exception in thread "main" java.lang.reflect.InvocationTargetExceptionat sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)at java.lang.reflect.Constructor.newInstance(Constructor.java:526)at org.apache.spark.sql.hive.client.IsolatedClientLoader.liftedTree1$1(IsolatedClientLoader.scala:183)at org.apache.spark.sql.hive.client.IsolatedClientLoader.<init>(IsolatedClientLoader.scala:179)at org.apache.spark.sql.hive.HiveContext.metadataHive$lzycompute(HiveContext.scala:226)at org.apache.spark.sql.hive.HiveContext.metadataHive(HiveContext.scala:185)at org.apache.spark.sql.hive.HiveContext.setConf(HiveContext.scala:392)at org.apache.spark.sql.hive.HiveContext.defaultOverrides(HiveContext.scala:174)at org.apache.spark.sql.hive.HiveContext.<init>(HiveContext.scala:177)at WindowQueryTest$.main(WindowQueryTest.scala:14)at WindowQueryTest.main(WindowQueryTest.scala)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:606)at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140) Caused by: java.lang.OutOfMemoryError: PermGen spaceat org.apache.hadoop.hive.ql.metadata.Hive.getAllDatabases(Hive.java:1236)at org.apache.hadoop.hive.ql.metadata.Hive.reloadFunctions(Hive.java:174)at org.apache.hadoop.hive.ql.metadata.Hive.<clinit>(Hive.java:166)at org.apache.hadoop.hive.ql.session.SessionState.start(SessionState.java:503)at org.apache.spark.sql.hive.client.ClientWrapper.<init>(ClientWrapper.scala:171)... 18 moreProcess finished with exit code 1
再次编译执行，还可能出现更长的异常信息，错误可能会变化，但万变不离其宗，症结依旧是PermGen Space的大小！
解决方法：在Run Configuration中添加JVM options：-server -Xms512M -Xmx1024M -XX:PermSize=256M -XX:MaxNewSize=512M -XX:MaxPermSize=512M
各个参数可以根据具体机器配置调整。
四、WindowSpec指定窗口设置
再看这个列子：
import org.apache.spark.sql.expressions.Window import org.apache.spark.sql.functions._ import org.apache.spark.sql.hive.HiveContext import org.apache.spark.{SparkConf, SparkContext}object WindowFunctions {def main(args: Array[String]) {val conf = new SparkConf().setAppName("Window Functions").setMaster("local")val sc = new SparkContext(conf)val hiveContext = new HiveContext(sc)import hiveContext.implicits._val l = (1997, 1) :: (1997, 4) :: (1998, 2) :: (1998, 3) :: (1999, 9) :: Nilval df = sc.parallelize(l).toDF("k", "v")val w = Window.orderBy($"k")val df1 = df.withColumn("No", rowNumber().over(w))val rowW = w.rowsBetween(-2, 0)val rangeW = w.rangeBetween(-1, 0)df1.withColumn("row", avg($"v").over(rowW)).withColumn("range", avg($"v").over(rangeW)).showsc.stop()} }
得到结果：
org.apache.spark.sql.expressions.Window定义WindowSpec，并指定分组或者排序。
@org.apache.spark.annotation.Experimental object Window extends scala.AnyRef {@scala.annotation.varargsdef partitionBy(colName : scala.Predef.String, colNames : scala.Predef.String*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }@scala.annotation.varargsdef partitionBy(cols : org.apache.spark.sql.Column*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }@scala.annotation.varargsdef orderBy(colName : scala.Predef.String, colNames : scala.Predef.String*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }@scala.annotation.varargsdef orderBy(cols : org.apache.spark.sql.Column*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ } }
定义的WindowSpec可以调用rowsBetween或者rangeBetween设置偏移量，定义窗口的区间范围；甚至也可以重置分组和排序。
@org.apache.spark.annotation.Experimental class WindowSpec private[sql] (partitionSpec : scala.Seq[org.apache.spark.sql.catalyst.expressions.Expression], orderSpec : scala.Seq[org.apache.spark.sql.catalyst.expressions.SortOrder], frame : org.apache.spark.sql.catalyst.expressions.WindowFrame) extends scala.AnyRef {@scala.annotation.varargsdef partitionBy(colName : scala.Predef.String, colNames : scala.Predef.String*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }@scala.annotation.varargsdef partitionBy(cols : org.apache.spark.sql.Column*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }@scala.annotation.varargsdef orderBy(colName : scala.Predef.String, colNames : scala.Predef.String*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }@scala.annotation.varargsdef orderBy(cols : org.apache.spark.sql.Column*) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }def rowsBetween(start : scala.Long, end : scala.Long) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }def rangeBetween(start : scala.Long, end : scala.Long) : org.apache.spark.sql.expressions.WindowSpec = { /* compiled code */ }private[sql] def withAggregate(aggregate : org.apache.spark.sql.Column) : org.apache.spark.sql.Column = { /* compiled code */ } }
最后通过具体的窗口函数计算得到需要的列。
References:
[1] https://databricks.com/blog/2015/07/15/introducing-window-functions-in-spark-sql.html
[2] http://www.cnblogs.com/mingforyou/archive/2012/03/03/2378143.html
[3] http://sonra.io/window-functions-aka-analytic-functions-in-spark/
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