Appenders

Appenders are destinations where logging information is sent. Typically logging configs send results to the console and a file. Optionally you can send logs to Syslog, email, sockets, databases and more. Each appender section defines a destination, a format and an optional trigger. Read about appenders in the Logback Manual.

Loggers

Loggers determine what data and what level of data is routed to the appenders. Loggers can match a particular Java class namespace and affect all messages emitted from that space. The default OpenTSDB config explicitly lists some loggers for Zookeeper, AsyncHBase and the Async libraries to set their levels to INFO so as to avoid chatty outputs that are not relevant most of the time. If you enable a plugin and start seeing a lot of messages that you don't care about, add a logger entry to suppress the messages.

Query Log To enable the Query log, find the following section:

<logger name="QueryLog" level="OFF" additivity="false">
  <appender-ref ref="QUERY_LOG"/>
</logger>

and set the level to INFO.

Log File To enable the main log file, find the following section:

<!--<appender-ref ref="FILE"/>-->

and remove the comments so it appears as <appender-ref ref="FILE"/>.

Root

The root section is the catch-all logger that determines that default logging level for all messages that don't match an explicit logger. It also handles routing to the different appenders.

Log to Rotating File

<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
  <file>/var/log/opentsdb/opentsdb.log</file>
  <append>true</append>

  <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
  <fileNamePattern>/var/log/opentsdb/opentsdb.log.%i</fileNamePattern>
  <minIndex>1</minIndex>
  <maxIndex>3</maxIndex>
  </rollingPolicy>

  <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
  <maxFileSize>128MB</maxFileSize>
  </triggeringPolicy>

  <!-- encoders are assigned the type
     ch.qos.logback.classic.encoder.PatternLayoutEncoder by default -->
  <encoder>
  <pattern>%d{HH:mm:ss.SSS} %-5level [%logger{0}.%M] - %msg%n</pattern>
  </encoder>
</appender>

This appender will write to a log file called /var/log/opentsdb/opentsdb.log. When the file reaches 128MB in size, it will rotate the log to opentsdb.log.1 and start a new opentsdb.log file. Once the new log fills up, it bumps .1 to .2, .log to .1 and creates a new one. It repeats this until there are four log files in total. The next time the log fills up, the last log is deleted. This way you are gauranteed to only use up to 512MB of disk space. Many other appenders are available so see what fits your needs the best.