Migration Guide: Spark Core

• Upgrading from Core 3.0 to 3.1
• Upgrading from Core 2.4 to 3.0

Upgrading from Core 3.0 to 3.1

• In Spark 3.0 and below, SparkContext can be created in executors. Since Spark 3.1, an exception will be thrown when creating SparkContext in executors. You can allow it by setting the configuration spark.executor.allowSparkContext when creating SparkContext in executors.

• In Spark 3.0 and below, Spark propagated the Hadoop classpath from yarn.application.classpath and mapreduce.application.classpath into the Spark application submitted to YARN when Spark distribution is with the built-in Hadoop. Since Spark 3.1, it does not propagate anymore when the Spark distribution is with the built-in Hadoop in order to prevent the failure from the different transitive dependencies picked up from the Hadoop cluster such as Guava and Jackson. To restore the behavior before Spark 3.1, you can set spark.yarn.populateHadoopClasspath to true.

Upgrading from Core 2.4 to 3.0

• The org.apache.spark.ExecutorPlugin interface and related configuration has been replaced with org.apache.spark.api.plugin.SparkPlugin, which adds new functionality. Plugins using the old interface must be modified to extend the new interfaces. Check the Monitoring guide for more details.

• Deprecated method TaskContext.isRunningLocally has been removed. Local execution was removed and it always has returned false.

• Deprecated method shuffleBytesWritten, shuffleWriteTime and shuffleRecordsWritten in ShuffleWriteMetrics have been removed. Instead, use bytesWritten, writeTime and recordsWritten respectively.

• Deprecated method AccumulableInfo.apply have been removed because creating AccumulableInfo is disallowed.

• Deprecated accumulator v1 APIs have been removed and please use v2 APIs instead.

• Event log file will be written as UTF-8 encoding, and Spark History Server will replay event log files as UTF-8 encoding. Previously Spark wrote the event log file as default charset of driver JVM process, so Spark History Server of Spark 2.x is needed to read the old event log files in case of incompatible encoding.

• A new protocol for fetching shuffle blocks is used. It’s recommended that external shuffle services be upgraded when running Spark 3.0 apps. You can still use old external shuffle services by setting the configuration spark.shuffle.useOldFetchProtocol to true. Otherwise, Spark may run into errors with messages like IllegalArgumentException: Unexpected message type: <number>.

• SPARK_WORKER_INSTANCES is deprecated in Standalone mode. It’s recommended to launch multiple executors in one worker and launch one worker per node instead of launching multiple workers per node and launching one executor per worker.