[log4perl-devel] Log::Log4perl Recipe of the Week (#14)

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

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

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Log::Log4perl Recipe of the Week (#14):

How can I drill down on references before logging them?
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If you've got a reference to a nested structure or object,
then you probably don't want to log it as "HASH(0x81141d4)"
but rather dump it as something like

    $VAR1 = {
              'a' => 'b',
              'd' => 'e'
            };

via a module like Data::Dumper. While it's syntactically
correct to say

    $logger->debug(Data::Dumper::Dumper($ref));

this call imposes a huge performance penalty on your
application if the message is suppressed by Log::Log4perl,
because Data::Dumper will perform its expensive operations
in any case, because it doesn't know that its output will be
thrown away immediately.

As of Log::Log4perl 0.28, there's a better way: Use the
message output filter format as in

    $logger->debug( {filter => \&Data::Dumper::Dumper,
                     value  => $ref} );

and Log::Log4perl won't call the filter function unless the
message really gets written out to an appender. Just make
sure to pass the whole slew as a reference to a hash
specifying a filter function (as a sub reference) under the
key "filter" and the value to be passed to the filter
function in "value"). When it comes to logging,
Log::Log4perl will call the filter function, pass the
"value" as an argument and log the return value. Saves you
serious cycles.


Have fun! Until next week.

-- Mike

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