I have used Log::Log4perl is production with Apache and mod_perl2, although not in very high traffic applications. So what are the performance impacts of (log4perl) logging in a high traffic web application? The answer is, as always, it depends.

Running in DEBUG mode (full detail) can seriously slow down performance, so you should be careful when setting up your loggers, appenders and levels. Also, very verbose logging can make the logs hard to read, and you can keep less history than if you were less verbose.

Benchmarking your application with different log4perl settings is important to understand how it affects you in your environment. Perhaps you should experiment with different disk setups, such as having /var/log/ on a separate disk system? Your I/O performance will most likely be one of the most important factors.

Do also keep an eye on the is_level functions in order to minimize impact of suppressed messages:

    if($logger->is_error()) {
        $logger->error("Erroneous array: @super_long_array");
    }
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