通过在spark-shell中执行word count的过程,让读者了解到可以使用spark-shell提交Spark作业。现在读者应该很想知道spark-shell究竟做了什么呢?
在Spark安装目录的bin文件夹下可以找到spark-shell,其中有代码清单1-1所示的一段脚本。
代码清单1-1 spark-shell脚本
function main() { if $cygwin; then stty -icanon min 1 -echo > /dev/null 2>&1 export SPARK_SUBMIT_OPTS="$SPARK_SUBMIT_OPTS -Djline.terminal=unix" "${SPARK_HOME}"/bin/spark-submit --class org.apache.spark.repl.Main --name "Spark shell" "$@" stty icanon echo > /dev/null 2>&1 else export SPARK_SUBMIT_OPTS "${SPARK_HOME}"/bin/spark-submit --class org.apache.spark.repl.Main --name "Spark shell" "$@" fi }
我们看到脚本spark-shell里执行了spark-submit脚本,那么打开spark-submit脚本,发现代码清单1-2中所示的脚本。
代码清单1-2 spark-submit脚本
if [ -z "${SPARK_HOME}" ]; then source "$(dirname "$0")"/find-spark-home fi # disable randomized hash for string in Python 3.3+ export PYTHONHASHSEED=0 exec "${SPARK_HOME}"/bin/spark-class org.apache.spark.deploy.SparkSubmit "$@"
可以看到spark-submit中又执行了脚本spark-class。打开脚本spark-class,首先发现以下一段脚本:
# Find the java binary if [ -n "${JAVA_HOME}" ]; then RUNNER="${JAVA_HOME}/bin/java" else if [ "$(command -v java)" ]; then RUNNER="java" else echo "JAVA_HOME is not set" >&2 exit 1 fi fi
上面的脚本是为了找到Java命令。在spark-class脚本中还会找到以下内容:
build_command() { "$RUNNER" -Xmx128m -cp "$LAUNCH_CLASSPATH" org.apache.spark.launcher.Main "$@" printf "%d/0" $? } CMD=() while IFS= read -d '' -r ARG; do CMD+=("$ARG") done < <(build_command "$@")
根据代码清单1-2,脚本spark-submit在执行spark-class脚本时,给它增加了参数SparkSubmit 。所以读到这,应该知道Spark启动了以SparkSubmit为主类的JVM进程。
为便于在本地对Spark进程进行远程监控,在spark-shell脚本中找到以下配置:
SPARK_SUBMIT_OPTS="$SPARK_SUBMIT_OPTS -Dscala.usejavacp=true"
并追加以下jmx配置:
-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=10207 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false
如果Spark安装在其他机器,那么在本地打开jvisualvm后需要添加远程主机,如图1所示:
图1 添加远程主机
右键单击已添加的远程主机,添加JMX连接,如图2:
图2 添加JMX连接
如果Spark安装在本地,那么打开jvisualvm后就会在应用程序窗口看到org.apache.spark.deploy.SparkSubmit进程,只需双击即可。
选择右侧的“线程”选项卡,选择main线程,然后点击“线程Dump”按钮,如图3。
图3 查看Spark线程
从线程Dump的内容中找到线程main的信息如代码清单1-3所示。
代码清单1-3 main线程的Dump信息
"main" #1 prio=5 os_prio=31 tid=0x00007fa012802000 nid=0x1303 runnable [0x000000010d11c000] java.lang.Thread.State: RUNNABLE at java.io.FileInputStream.read0(Native Method) at java.io.FileInputStream.read(FileInputStream.java:207) at jline.internal.NonBlockingInputStream.read(NonBlockingInputStream.java:169) - locked <0x00000007837a8ab8> (a jline.internal.NonBlockingInputStream) at jline.internal.NonBlockingInputStream.read(NonBlockingInputStream.java:137) at jline.internal.NonBlockingInputStream.read(NonBlockingInputStream.java:246) at jline.internal.InputStreamReader.read(InputStreamReader.java:261) - locked <0x00000007837a8ab8> (a jline.internal.NonBlockingInputStream) at jline.internal.InputStreamReader.read(InputStreamReader.java:198) - locked <0x00000007837a8ab8> (a jline.internal.NonBlockingInputStream) at jline.console.ConsoleReader.readCharacter(ConsoleReader.java:2145) at jline.console.ConsoleReader.readLine(ConsoleReader.java:2349) at jline.console.ConsoleReader.readLine(ConsoleReader.java:2269) at scala.tools.nsc.interpreter.jline.InteractiveReader.readOneLine(JLineReader.scala:57) at scala.tools.nsc.interpreter.InteractiveReader$$anonfun$readLine$2.apply(InteractiveReader.scala:37) at scala.tools.nsc.interpreter.InteractiveReader$$anonfun$readLine$2.apply(InteractiveReader.scala:37) at scala.tools.nsc.interpreter.InteractiveReader$.restartSysCalls(InteractiveReader.scala:44) at scala.tools.nsc.interpreter.InteractiveReader$class.readLine(InteractiveReader.scala:37) at scala.tools.nsc.interpreter.jline.InteractiveReader.readLine(JLineReader.scala:28) at scala.tools.nsc.interpreter.ILoop.readOneLine(ILoop.scala:404) at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:413) at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:923) at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:909) at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:909) at scala.reflect.internal.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:97) at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:909) at org.apache.spark.repl.Main$.doMain(Main.scala:68) at org.apache.spark.repl.Main$.main(Main.scala:51) at org.apache.spark.repl.Main.main(Main.scala) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:738) at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:187) at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:212) at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:126) at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
从main线程的栈信息中看出程序的调用顺序:SparkSubmit.main→repl.Main→Iloop.process。
我们根据上面的线索,直接阅读Iloop的process方法的源码(Iloop是Scala语言自身的类库中的用于实现交互式shell的实现类,提供对REPL(Read-eval-print-loop)的实现),见代码清单1-4。
代码清单1-4 process的实现
def process(settings: Settings): Boolean = savingContextLoader { this.settings = settings createInterpreter() // sets in to some kind of reader depending on environmental cues in = in0.fold(chooseReader(settings))(r => SimpleReader(r, out, interactive = true)) globalFuture = future { intp.initializeSynchronous() loopPostInit() !intp.reporter.hasErrors } loadFiles(settings) printWelcome() try loop() match { case LineResults.EOF => out print Properties.shellInterruptedString case _ => } catch AbstractOrMissingHandler() finally closeInterpreter() true }
根据代码清单1-4,Iloop的process方法调用了loadFiles方法。Spark中的SparkILoop继承了Iloop并重写了loadFiles方法,其实现如下:
override def loadFiles(settings: Settings): Unit = { initializeSpark() super.loadFiles(settings) }
根据上面展示的代码,loadFiles方法调用了SparkILoop的initializeSpark方法,initializeSpark的实现见代码清单1-5。
代码清单1-5 initializeSpark的实现
def initializeSpark() { intp.beQuietDuring { processLine(""" @transient val spark = if (org.apache.spark.repl.Main.sparkSession != null) { org.apache.spark.repl.Main.sparkSession } else { org.apache.spark.repl.Main.createSparkSession() } @transient val sc = { val _sc = spark.sparkContext if (_sc.getConf.getBoolean("spark.ui.reverseProxy", false)) { val proxyUrl = _sc.getConf.get("spark.ui.reverseProxyUrl", null) if (proxyUrl != null) { println(s"Spark Context Web UI is available at ${proxyUrl}/proxy/${_sc.applicationId}") } else { println(s"Spark Context Web UI is available at Spark Master Public URL") } } else { _sc.uiWebUrl.foreach { webUrl => println(s"Spark context Web UI available at ${webUrl}") } } println("Spark context available as 'sc' " + s"(master = ${_sc.master}, app id = ${_sc.applicationId}).") println("Spark session available as 'spark'.") _sc } """) processLine("import org.apache.spark.SparkContext._") processLine("import spark.implicits._") processLine("import spark.sql") processLine("import org.apache.spark.sql.functions._") replayCommandStack = Nil // remove above commands from session history. } }
我们看到initializeSpark向交互式shell发送了一大串代码,Scala的交互式shell将调用org.apache.spark.repl.Main的createSparkSession方法(见代码清单1-6)创建SparkSession。我们看到常量spark将持有SparkSession的引用,并且sc持有SparkSession内部初始化好的SparkContext。所以我们才能够在spark-shell的交互式shell中使用sc和spark。
代码清单1-6 createSparkSession的实现
def createSparkSession(): SparkSession = { val execUri = System.getenv("SPARK_EXECUTOR_URI") conf.setIfMissing("spark.app.name", "Spark shell") conf.set("spark.repl.class.outputDir", outputDir.getAbsolutePath()) if (execUri != null) { conf.set("spark.executor.uri", execUri) } if (System.getenv("SPARK_HOME") != null) { conf.setSparkHome(System.getenv("SPARK_HOME")) } val builder = SparkSession.builder.config(conf) if (conf.get(CATALOG_IMPLEMENTATION.key, "hive").toLowerCase == "hive") { if (SparkSession.hiveClassesArePresent) { sparkSession = builder.enableHiveSupport().getOrCreate() logInfo("Created Spark session with Hive support") } else { builder.config(CATALOG_IMPLEMENTATION.key, "in-memory") sparkSession = builder.getOrCreate() logInfo("Created Spark session") } } else { sparkSession = builder.getOrCreate() logInfo("Created Spark session") } sparkContext = sparkSession.sparkContext sparkSession }
根据代码清单1-6,createSparkSession方法通过SparkSession的API创建SparkSession实例。本书将有关SparkSession等API的内容在《Spark内核设计的艺术》一书的第10章讲解,初次接触Spark的读者现在只需要了解即可。
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