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https://issues.apache.org/jira/browse/HADOOP-12956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15209219#comment-15209219
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Chris Nauroth commented on HADOOP-12956:
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A few more notes from my stab at this in ZooKeeper:
# The actual code changes for the logging are the trivial part, even if
somewhat time-consuming. ZooKeeper had already completed an almost full
migration to the SLF4J API, so that helped.
# Tests that rely on log capture and inspection of messages needed changes to
hook into the new Log4J 2 classes.
# There is no option for backwards-compatibility with the Log4J 1 configuration
format.
# I couldn't figure out a way to preserve our trick of passing JVM arguments to
tweak the log level, i.e. {{-Dhadoop.security.logger=INFO,DRFAS}}. The Log4J 2
configuration format is much more complex, so there isn't a simple place to do
a token replacement of the "INFO,DRFAS". From a brief chat on the Log4J user
list, that community had some ideas about coding some Log4J 2 customizations
that migh help me achieve that, but I didn't get a chance to explore that.
# What happens when something tries to use a mix of Log4J 1 and Log4J 2? Does
it bomb? Does it work, but split the messages between different files
controlled by the 2 different frameworks? Does this need to be handled as a
massive full ecosystem upgrade, a la Protobuf?
> Inevitable Log4j2 migration via slf4j
> -------------------------------------
>
> Key: HADOOP-12956
> URL: https://issues.apache.org/jira/browse/HADOOP-12956
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Gopal V
>
> {{5 August 2015 --The Apache Logging Services™ Project Management Committee
> (PMC) has announced that the Log4j™ 1.x logging framework has reached its end
> of life (EOL) and is no longer officially supported.}}
> https://blogs.apache.org/foundation/entry/apache_logging_services_project_announces
> A whole framework log4j2 upgrade has to be synchronized, partly for improved
> performance brought about by log4j2.
> https://logging.apache.org/log4j/2.x/manual/async.html#Performance
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