How are JAR files added to a Spark job using Spark-Submit, and what are the different options and considerations for doing so?

Adding JAR Files to a Spark Job with Spark-Submit

When using Spark-Submit, there are several options for adding JAR files to a Spark job, each with its own implications for classpath, file distribution, and priority.

ClassPath Effects

Spark-Submit influences ClassPaths through these options:

• spark.driver.extraClassPath or --driver-class-path: Specifies extra classpaths for the driver node.
• spark.executor.extraClassPath: Specifies extra classpaths for worker nodes.

For a file to be included on both ClassPaths, it needs to be specified in both flags.

File Distribution

File distribution depends on the execution mode:

• Client mode: Spark distributes files to worker nodes via an HTTP server.
• Cluster mode: Spark does not distribute files, and you must manually make them available to all worker nodes through HDFS or other shared storage.

Accepted URI Formats

Spark-Submit supports the following URI prefixes for file distribution:

• file:: Served by the driver HTTP server.
• hdfs:, http:, https:, ftp:: Pulled from the specified URI.
• local:: Must be a local file on each worker node.

Affected Options

The options mentioned in the question affect JAR file handling as follows:

• --jars and SparkContext.addJar: Equivalent options that do not add JARs to ClassPaths.
• SparkContext.addFile: Used for arbitrary files that are not runtime dependencies.
• --conf spark.driver.extraClassPath or --driver-class-path: Aliases for driver ClassPath modifications.
• --conf spark.driver.extraLibraryPath or --driver-library-path: Aliases for driver library paths.
• --conf spark.executor.extraClassPath: Used for runtime dependencies that cannot be included in an über JAR.
• --conf spark.executor.extraLibraryPath: Specifies the JVM's java.library.path option.

Priority

Properties set directly on SparkConf have the highest precedence, followed by Spark-Submit flags and then options in spark-defaults.conf. Therefore, any values set in code will override corresponding flags or options.

Adding JAR Files Simultaneously

In client mode, it's safe to add JAR files using all three main options:

spark-submit --jars additional1.jar,additional2.jar \
  --driver-class-path additional1.jar:additional2.jar \
  --conf spark.executor.extraClassPath=additional1.jar:additional2.jar \
  --class MyClass main-application.jar

However, in cluster mode, you should only add files using --jars, and manually distribute them to the worker nodes yourself. Redundant arguments like passing JAR files to --driver-library-path should be avoided.

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