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Basic Logging

Introduction

This page describes the basic logging function provided by Alluxio server processes (e.g., masters, workers and etc) and application processes utilizing Alluxio clients (e.g., Spark or MapReduce jobs running on Alluxio). Note that there is an experimental feature that streams server-side and client-side logs to separate Alluxio logservers (see remote logging for more details).

Alluxio logging is implemented using log4j and thus most of the configuration is done through modifying log4j.properties.

Log Location

Server Logs

Log files for each individual Alluxio server process (e.g., master, worker, FUSE, proxy) can be found under ${ALLUXIO_HOME}/logs/. Files suffixed with .log like master.log or worker.log are generated by log4j, logging the events that Alluxio system is recording through JVM. These files are typically the main target for users to investigate logs. Files suffixed with .out like master.out or worker.out are the redirection of stdout and stderr of the corresponding process. Fatal error messages (e.g., killed by the OS), will most likely go to these files.

The log location can be customized by setting environment variable ALLUXIO_LOGS_DIR. See the configuration settings page for more information.

By default, the *.log files rotate. For example this is the default log4j configuration for master.log:

# Appender for Master
log4j.appender.MASTER_LOGGER=org.apache.log4j.RollingFileAppender
log4j.appender.MASTER_LOGGER.File=${alluxio.logs.dir}/master.log
log4j.appender.MASTER_LOGGER.MaxFileSize=10MB
log4j.appender.MASTER_LOGGER.MaxBackupIndex=100
log4j.appender.MASTER_LOGGER.layout=org.apache.log4j.PatternLayout
log4j.appender.MASTER_LOGGER.layout.ConversionPattern=%d{ISO8601} %-5p %c{1} - %m%n

However, the *.out files do not rotate. So it makes sense to regularly check the size of these files, and clean them up if necessary.

Application Logs

Log files for the Alluxio client utilized by different applications are located with their respective application logs. Please check out particular compute frameworks on where their logs may be found.

Here are the documentation to configure individual application logs including Apache Hadoop, Apache Hive, Apache Spark.

For the Alluxio command line interface, the user log is located at ${ALLUXIO_HOME}/logs/user/user_${user_name}.log.

Configuring Log Levels

Alluxio uses the following five logging levels:

  • TRACE: verbose information, only useful for debugging a certain method or class

  • DEBUG: fine-grained information, most useful for debugging purposes

  • INFO: messages that highlight the status or progress

  • WARN: potentially harmful events that users may need to know about, but the process will still continue running

  • ERROR: system errors that users should pay attention to

By default, Alluxio server processes write logs at INFO level, which includes all events at INFO, WARN and ERROR levels.

Modifying Logging with log4j.properties

You can modify ${ALLUXIO_HOME}/conf/log4j.properties to customize logging levels and restart corresponding server processes to apply new changes. This is the recommended way to modify logging configurations.

For example, to modify the level for all logs to DEBUG, change the rootLogger level by modifying the first line of log4j.properties as the following:

To modify the logging level for a particular Java class (e.g., set alluxio.client.file.AlluxioFileInStream to DEBUG), add a new line at the end of this file:

To modify the logging level for a package (e.g., set all classes under alluxio to DEBUG), add a new line in the end of this file as below. This can be helpful when you do not know what the target classes are, or many classes are relevant.

Modifying Server Logging at Runtime

An alternative way to modify logging configurations is use the logLevel command. This allows someone to modify the configuration at runtime without needing to restart processes. This is not the recommended way as any modifications will not be persisted across restart, and causes a configuration mismatch between the running process and its log4j.properties file. See the logLevel command documentation for the command options.

For example, the following command sets the logger level of the class alluxio.underfs.hdfs.HdfsUnderFileSystem to DEBUG on master as well as a worker at 192.168.100.100:30000:

And the following command returns the log level of the class alluxio.underfs.hdfs.HdfsUnderFileSystem among all the workers:

You can also update the log level at a package level. For example, you can update the log level of all classes in alluxio.underfs package with the following command:

This works because log4j loggers will inherit the log level from their ancestors. In this case alluxio.underfs.hdfs.HdfsUnderFileSystem inherits the log level if it is set on alluxio.underfs or alluxio.underfs.hdfs.

Furthermore, you can turn on Alluxio debug logging when you are troubleshooting a certain issue in a running cluster, and turn it off when you are done.

Finally, if your Alluxio deployment uses custom web ports (e.g. alluxio.master.web.port is different from 19999, or alluxio.worker.web.port is different from 30000), you can use the format host:port:role for your target. role can be one of master or worker or job_master or job_worker. For example, if your master running on 10.10.10.10 has alluxio.master.web.port=2181 configured, you would use:

If your worker is running on 127.0.0.1 with alluxio.worker.web.port=25252 configured, you would use:

Enabling Advanced Logging

Logging JVM GC (Garbage Collection) events

Add the following line to conf/allulxio-env.sh to enable logging GC events for server processes in log files with .out suffix like master.out and worker.out:

ALLUXIO_JAVA_OPTS is included in Java VM options for all Alluxio server processes. Alternatively, modify ALLUXIO_MASTER_JAVA_OPTS, ALLUXIO_WORKER_JAVA_OPTS to turn on GC for each individual process.

Logging all FUSE API calls

Set in conf/log4j.properties:

You will see debug logs at both the start and end of each FUSE API call with its arguments and result in logs/fuse.log:

Logging RPCs Calls Sent by Client

Add the following to your application-side log4j.properties to capture RPCs between the Alluxio client and FileSystem Master:

Similarly, capture lower-level RPCs between Alluxio client and Block Master:

You will see debug logs at the beginning and end of each RPC with its arguments and result in the client logs like the following:

Logging RPC Calls Received by Masters

On the master, debug-level logging for incoming File System level RPC calls can be turned on (e.g., creating/reading/writing/removing files, updating file attributions) using the logLevel command:

Similarly, turn on the debug-level logging for block related RPC calls (e.g., adding/removing blocks):

Similarly, you can update the log level for these classes in the conf/log4j.properties file. You need to restart the relevant processes for the log4j properties to take effect.

Logging UnderFileSystem Operations

Sometimes it can be useful to log all operations on under storage. On the master, debug-level logging for UnderFileSystem operations can be turned on (e.g., creating/reading/writing/removing files on UFS) using the logLevel command:

One can similarly turn on UFS operations on workers by passing --target workers. You can see operations in corresponding master or worker logs like below:

Similarly, you can update the log level for these classes in the conf/log4j.properties file. You need to restart the relevant processes for the log4j properties to take effect.

Identifying Expensive Calls

When debugging the performance, it is often useful to understand which RPCs take most of the time but without recording all the communication (e.g., enabling all debug logging). Alluxio can record slow calls or RPCs in logs with WARN level by setting the following properties:

  1. Set alluxio.user.logging.threshold to record slow client-side RPCs in application logs.

  2. Set alluxio.fuse.logging.threshold to record slow FUSE API calls in fuse logs (logs/fuse.log).

  3. Set alluxio.underfs.logging.threshold to record slow under storage RPCs (logs/master.log or logs/worker.log).

For example, the following setting in conf/alluxio-site.properties will log each FUSE API call slower than 1s, each UFS call slower than 10s, and each client-side RPC slower than 200ms:

Example results are:

Redirecting debug log for certain classes

Sometimes it is useful to separate the log for certain classes into a separate log. This can be useful for reasons including but not limited to:

  1. Clearly separate the wanted logs for further analysis.

  2. Avoid master.log or worker.log being too big or having too many files created by log rotation.

  3. Use a separate logger to send logs to a remote endpoint like a socket.

This can be achieved by adding a separate logger in the conf/log4j.properties. For example, the below example redirects debug logs of alluxio.master.StateLockManager to a separate set of files, so the master.log will not be full of DEBUG logs created by alluxio.master.StateLockManager.

Disable certain log files

Sometimes it makes sense to disable certain logs files.

One example of use cases is when Alluxio is running in a containerized environment, where logs are written to the writable layer. This has performance penalties and the writable layer may grow indefinitely, causing disk pressure on the host. In that case you can either mount a volume to the log directory so logs are written to the volume, or rely on the Remote Logging and disable local logs.

To disable local log output, you can set the corresponding logger(s) as below:

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