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 3.1 to 3.2

- Since Spark 3.2, `spark.hadoopRDD.ignoreEmptySplits` is set to `true` by default which means Spark will not create empty partitions for empty input splits. To restore the behavior before Spark 3.2, you can set `spark.hadoopRDD.ignoreEmptySplits` to `false`.

- Since Spark 3.2, `spark.eventLog.compression.codec` is set to `zstd` by default which means Spark will not fallback to use `spark.io.compression.codec` anymore.

- Since Spark 3.2, `spark.storage.replication.proactive` is enabled by default which means Spark tries to replenish in case of the loss of cached RDD block replicas due to executor failures. To restore the behavior before Spark 3.2, you can set `spark.storage.replication.proactive` to `false`.

- In Spark 3.2, `spark.launcher.childConectionTimeout` is deprecated (typo) though still works. Use `spark.launcher.childConnectionTimeout` instead.

## 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](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.

- 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.