Logging

Delta Lake uses log4j for logging (as does Apache Spark itself).

Logging Levels

The valid logging levels are 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)

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

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

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