spark-scheduler-listeners-eventlogginglistener.adoc

EventLoggingListener — Spark Listener for Persisting Events

EventLoggingListener is a SparkListener that persists JSON-encoded events to a file.

When event logging is enabled, EventLoggingListener writes events to a log file under spark.eventLog.dir directory. All Spark events are logged (except SparkListenerBlockUpdated and SparkListenerExecutorMetricsUpdate).

Tip	Use Spark History Server to view the event logs in a browser.

Events can optionally be compressed.

In-flight log files are with .inprogress extension.

EventLoggingListener is a private[spark] class in org.apache.spark.scheduler package.

Tip	Enable INFO logging level for org.apache.spark.scheduler.EventLoggingListener logger to see what happens inside EventLoggingListener. Add the following line to conf/log4j.properties: log4j.logger.org.apache.spark.scheduler.EventLoggingListener=INFO Refer to Logging.

Creating EventLoggingListener Instance

EventLoggingListener requires an application id (appId), the application’s optional attempt id (appAttemptId), logBaseDir, a SparkConf (as sparkConf) and Hadoop’s Configuration (as hadoopConf).

Note	When initialized with no Hadoop’s Configuration it calls SparkHadoopUtil.get.newConfiguration(sparkConf).

Starting EventLoggingListener — start method

start(): Unit

start checks whether logBaseDir is really a directory, and if it is not, it throws a IllegalArgumentException with the following message:

Log directory [logBaseDir] does not exist.

The log file’s working name is created based on appId with or without the compression codec used and appAttemptId, i.e. local-1461696754069. It also uses .inprogress extension.

If overwrite is enabled, you should see the WARN message:

WARN EventLoggingListener: Event log [path] already exists. Overwriting...

The working log .inprogress is attempted to be deleted. In case it could not be deleted, the following WARN message is printed out to the logs:

WARN EventLoggingListener: Error deleting [path]

The buffered output stream is created with metadata with Spark’s version and SparkListenerLogStart class' name as the first line.

{"Event":"SparkListenerLogStart","Spark Version":"2.0.0-SNAPSHOT"}

At this point, EventLoggingListener is ready for event logging and you should see the following INFO message in the logs:

INFO EventLoggingListener: Logging events to [logPath]

Note	start is executed while SparkContext is created.

Logging Event as JSON — logEvent method

logEvent(event: SparkListenerEvent, flushLogger: Boolean = false)

logEvent logs event as JSON.

Caution

FIXME

Stopping EventLoggingListener — stop method

stop(): Unit

stop closes PrintWriter for the log file and renames the file to be without .inprogress extension.

If the target log file exists (one without .inprogress extension), it overwrites the file if spark.eventLog.overwrite is enabled. You should see the following WARN message in the logs:

WARN EventLoggingListener: Event log [target] already exists. Overwriting...

If the target log file exists and overwrite is disabled, an java.io.IOException is thrown with the following message:

Target log file already exists ([logPath])

Note	stop is executed while SparkContext is stopped.

Compressing Logged Events

If event compression is enabled, events are compressed using CompressionCodec.

Tip	Refer to CompressionCodec to learn about the available compression codecs.

Settings

Table 1. Spark Properties

Spark Property	Default Value	Description
spark.eventLog.enabled	false	Enables (true) or disables (false) persisting Spark events.
spark.eventLog.dir	/tmp/spark-events	Directory where events are logged, e.g. hdfs://namenode:8021/directory. The directory must exist before Spark starts up.
spark.eventLog.buffer.kb	100	Size of the buffer to use when writing to output streams.
spark.eventLog.overwrite	false	Enables (true) or disables (false) deleting (or at least overwriting) an existing .inprogress log file.
spark.eventLog.compress	false	Enables (true) or disables (false) event compression.
spark.eventLog.testing	false	Internal flag for testing purposes that enables adding JSON events to the internal loggedEvents array.