log4r

Original manual provided here: http://log4r.sourceforge.net/

== Enhancements

We have added support for an Nested Diagnostic Context, or NDC and GDC.

=== NDC

NDCs are per thread, and can be set by:

Log4r::Logger::NDC.push('something')

Then in the configuration xml it can be used:

pattern="%x"

Which will output the top most diagnostic message on the NDC stack.

Based on the log4j NDC implementation: http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/NDC.html

=== GDC

We also added a Global Diagnostic Context for per application diagnostic messages.

Log4r::Logger.GDC = "app1"

Then in the configuration xml it can be used:

pattern="%g"

log4_logging.rb uses this to set the message to be the name of the rails application.
This can be useful for sorting messages if logs for multiple applications are aggregated at a single point, for example in something like Splunk.