Configuring logging

About Cassandra logging functionality using Simple Logging Facade for Java (SLF4J) with a logback backend.

Cassandra provides logging functionality using Simple Logging Facade for Java (SLF4J) with a logback backend. Logs are written to the system.log file in the Cassandra logging directory. You can configure logging programmatically or manually. Manual ways to configure logging are:

  • Run the nodetool setlogginglevel command
  • Configure the logback-test.xml or logback.xml file installed with Cassandra
  • Use the JConsole tool to configure logging through JMX.

Logback looks for logback-test.xml first, and then for logback.xml. The logback.xml location for different types of installations is listed in the "File locations" section. For example, on tarball and source installations, logback.xml is located in the install_location/conf directory.

The XML configuration files look something like this:
<configuration scan="true">
  <jmxConfigurator />
  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">

    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
      <pattern>%-5level [%thread] %date{ISO8601} %F:%L - %msg%n</pattern>
      <!-- old-style log format
      <pattern>%5level [%thread] %date{ISO8601} %F (line %L) %msg%n</pattern>
  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
      <pattern>%-5level %date{HH:mm:ss,SSS} %msg%n</pattern>
  <root level="INFO">
    <appender-ref ref="FILE" />
    <appender-ref ref="STDOUT" />
  <logger name="com.thinkaurelius.thrift" level="ERROR"/>
The appender configurations specify where to print the log and its configuration. The first appender directs logs to a file. The second appender directs logs to the console. You can change the following logging functionality:
  • Rolling policy
    • The policy for rolling logs over to an archive
    • Location and name of the log file
    • Location and name of the archive
    • Minimum and maximum file size to trigger rolling
  • Format of the message
  • The log level

Log levels

The valid values for setting the log level include ALL for logging information at all levels, TRACE through ERROR, and OFF for no logging. TRACE creates the most verbose log, and ERROR, the least.

  • ALL
  • INFO (Default)
  • WARN
  • OFF
Note: Increasing logging levels can generate heavy logging output on a moderately trafficked cluster.
You can use the nodetool getlogginglevels command to see the current logging configuration.
nodetool getlogginglevels
Logger Name                                        Log Level
ROOT                                                    INFO
com.thinkaurelius.thrift                               ERROR
To add debug logging to a class permanently using the logback framework, use nodetool setlogginglevel to check you have the right class before you set it in the logback.xml file in install_location/conf. Modify to include the following line or similar at the end of the file:
<logger name="org.apache.cassandra.gms.FailureDetector" level="DEBUG"/>
Restart the node to invoke the change.

Migrating to logback from log4j

If you upgrade from a previous version of Cassandra that used log4j, you can convert files to logback.xml using the logback PropertiesTranslator web-application.

Using log file rotation

The default policy rolls the system.log file after the size exceeds 20MB. Archives are compressed in zip format. Logback names the log files,, and so on. For more information, see logback documentation.