druid/docs/content/Logging.md

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Logging

Druid nodes will emit logs that are useful for debugging to the console. Druid nodes also emit periodic metrics about their state. For more about metrics, see Configuration. Metric logs are printed to the console by default, and can be disabled with -Ddruid.emitter.logging.logLevel=debug.

Druid uses log4j for logging, and console logs can be configured by adding a log4j.xml file. Add this xml file to your classpath if you want to override default Druid log configuration.

An example log4j.xml file is shown below:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

  <appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%d{ISO8601} %-5p [%t] %c - %m%n"/>
    </layout>
  </appender>

  <!-- ServerView-related stuff is way too chatty -->
  <logger name="io.druid.client.BatchServerInventoryView">
    <level value="warn"/>
  </logger>
  <logger name="io.druid.curator.inventory.CuratorInventoryManager">
    <level value="warn"/>
  </logger>

  <root>
    <priority value="info" />
    <appender-ref ref="ConsoleAppender"/>
  </root>

</log4j:configuration>