[log4perl-devel] Log::Log4perl Recipe of the Week (#15)

[<log...@pe...>]

Welcome to the Log::Log4perl recipe of the week. Today:

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Log::Log4perl Recipe of the Week (#15):

How can I collect all FATAL messages in an extra log file?
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Suppose you have employed Log4perl all over your system and
you've already activated logging in various subsystems. On
top of that, without disrupting any other settings, how can
you collect all FATAL messages all over the system and send
them to a separate log file?

If you define a root logger like this:

    log4perl.logger                  = FATAL, File
    log4perl.appender.File           = Log::Dispatch::File
    log4perl.appender.File.filename  = /tmp/fatal.txt
    log4perl.appender.File.layout    = PatternLayout
    log4perl.appender.File.layout.ConversionPattern= %d %m %n
        # !!! Something's missing ...

you'll be surprised to not only receive all FATAL messages
issued anywhere in the system, but also everything else --
gazillions of ERROR, WARN, INFO and even DEBUG messages will
end up in your fatal.txt logfile! Reason for this is
Log4perl's (or better: Log4j's) appender additivity. Once a
lower-level logger decides to fire, the message is going to
be forwarded to all appenders upstream -- without further
priority checks with their attached loggers.

There's a way to prevent this, however: If your appender
defines a minimum threshold, only messages of this priority
or higher are going to be logged. So, just add

    log4perl.appender.File.Threshold = FATAL 

to the configuration above, and you'll get what you wanted
in the first place: An overall system FATAL message
collector.


Have fun! Until next week.

-- Mike

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# Mike Schilli                    #
# log...@pe...        #
# http://perlmeister.com          #
# http://log4perl.sourceforge.net #
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