spark技术分享spark-class shell script
spark-class shell script is the Spark application command-line launcher that is responsible for setting up JVM environment and executing a Spark application.
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Note
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Ultimately, any shell script in Spark, e.g. spark-submit, calls spark-class script.
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You can find spark-class script in bin directory of the Spark distribution.
When started, spark-class first loads $SPARK_HOME/bin/load-spark-env.sh, collects the Spark assembly jars, and executes org.apache.spark.launcher.Main.
Depending on the Spark distribution (or rather lack thereof), i.e. whether RELEASE file exists or not, it sets SPARK_JARS_DIR environment variable to [SPARK_HOME]/jars or [SPARK_HOME]/assembly/target/scala-[SPARK_SCALA_VERSION]/jars, respectively (with the latter being a local build).
If SPARK_JARS_DIR does not exist, spark-class prints the following error message and exits with the code 1.
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Failed to find Spark jars directory ([SPARK_JARS_DIR]). You need to build Spark with the target "package" before running this program. |
spark-class sets LAUNCH_CLASSPATH environment variable to include all the jars under SPARK_JARS_DIR.
If SPARK_PREPEND_CLASSES is enabled, [SPARK_HOME]/launcher/target/scala-[SPARK_SCALA_VERSION]/classes directory is added to LAUNCH_CLASSPATH as the first entry.
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Note
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Use SPARK_PREPEND_CLASSES to have the Spark launcher classes (from [SPARK_HOME]/launcher/target/scala-[SPARK_SCALA_VERSION]/classes) to appear before the other Spark assembly jars. It is useful for development so your changes don’t require rebuilding Spark again.
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SPARK_TESTING and SPARK_SQL_TESTING environment variables enable test special mode.
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Caution
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FIXME What’s so special about the env vars? |
spark-class uses org.apache.spark.launcher.Main command-line application to compute the Spark command to launch. The Main class programmatically computes the command that spark-class executes afterwards.
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Tip
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Use JAVA_HOME to point at the JVM to use.
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Launching org.apache.spark.launcher.Main Standalone Application
org.apache.spark.launcher.Main is a Scala standalone application used in spark-class to prepare the Spark command to execute.
Main expects that the first parameter is the class name that is the “operation mode”:
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org.apache.spark.deploy.SparkSubmit—Mainuses SparkSubmitCommandBuilder to parse command-line arguments. This is the mode spark-submit uses. -
anything —
MainusesSparkClassCommandBuilderto parse command-line arguments.
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$ ./bin/spark-class org.apache.spark.launcher.Main Exception in thread "main" java.lang.IllegalArgumentException: Not enough arguments: missing class name. at org.apache.spark.launcher.CommandBuilderUtils.checkArgument(CommandBuilderUtils.java:241) at org.apache.spark.launcher.Main.main(Main.java:51) |
Main uses buildCommand method on the builder to build a Spark command.
If SPARK_PRINT_LAUNCH_COMMAND environment variable is enabled, Main prints the final Spark command to standard error.
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Spark Command: [cmd] ======================================== |
If on Windows it calls prepareWindowsCommand while on non-Windows OSes prepareBashCommand with tokens separated by
