spark-instrumented-optimizer/docs/core-migration-guide.md

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title: "Migration Guide: Spark Core"
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* Table of contents
{:toc}

## Upgrading from Core 2.4 to 3.0

- The `org.apache.spark.ExecutorPlugin` interface and related configuration has been replaced with
  `org.apache.spark.plugin.SparkPlugin`, which adds new functionality. Plugins using the old
  interface need to be modified to extend the new interfaces. Check the
  [Monitoring](monitoring.html) 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.

- 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 writes 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. Old external shuffle services can still be used by setting the configuration `spark.shuffle.useOldFetchProtocol` to `true`. Otherwise, Spark may run into errors with messages like `IllegalArgumentException: Unexpected message type: <number>`.