Logging

= Logging

Delta Lake uses http://logging.apache.org/log4j[log4j] for logging (as does Apache Spark itself).

== [[levels]] Logging Levels

The valid logging levels are http://logging.apache.org/log4j/2.x/log4j-api/apidocs/index.html[log4j's Levels] (from most specific to least):

• OFF (most specific, no logging)
• FATAL (most specific, little data)
• ERROR
• WARN
• INFO
• DEBUG
• TRACE (least specific, a lot of data)
• ALL (least specific, all data)

== [[log4j-properties]] conf/log4j.properties

You can set up the default logging for Delta applications in conf/log4j.properties of the Spark installation. Use Spark's conf/log4j.properties.template as a starting point.

== [[sbt]] sbt

When running a Delta application from within sbt using run task, you can use the following build.sbt to configure logging levels:

[source, scala]¶

fork in run := true javaOptions in run ++= Seq( "-Dlog4j.debug=true", "-Dlog4j.configuration=log4j.properties") outputStrategy := Some(StdoutOutput)

With the above configuration log4j.properties file should be on CLASSPATH which can be in src/main/resources directory (that is included in CLASSPATH by default).

When run starts, you should see the following output in sbt:

[spark-activator]> run
[info] Running StreamingApp
log4j: Trying to find [log4j.properties] using context classloader sun.misc.Launcher$AppClassLoader@1b6d3586.
log4j: Using URL [file:.../classes/log4j.properties] for automatic log4j configuration.
log4j: Reading configuration from URL file:.../classes/log4j.properties