[GitHub] incubator-spark pull request: Default log4j initialization causes ...

[pwendell]

Github user pwendell commented on the pull request:

    https://github.com/apache/incubator-spark/pull/573#issuecomment-34698102
  
    The issue is a user reported problems when they were writing from slf4j to 
Logback, they had log4j-over-slf4j on the classpath, and this initialization 
code kicked in when they never intended to output to log4j. I'm proposing this 
as a defensive check to fix this problem in the 0.9 branch with a minimal 
modification. If the user has log4j-over-slf4j enabled and someone manually 
creates a properties configuration it's been known to cause problems. Checkout 
the section here "When does this not work":
    
    http://www.slf4j.org/legacy.html#losFail