Log4perl

Mike Schilli, Yahoo!

OSCON, 07/24/2008

Logging – why?

• Debug during development

• Go back in time and figure out what happened.

• Measure performance

• Trace activity on live systems

Why Log4perl and not one of the 20 Logging modules on CPAN?

• No CPAN dependencies

• Easy to use, but scales with complexity

• Unique Features

Log::Log4perl Availability

• cpan> install Log::Log4perl(Only requires core modules)

• Included in major Linux distrossudo apt-get install liblog-log4perl

• Requires Perl 5.00503 or better

• Windows: ppm package available in ActiveState archives or from log4perl.com

Use Log4perl as a Remote Control to your System.

Log::Log4perl Remote Controls

Loggers

Layouts

Appenders

Levels

Log::Log4perl Remote Controls

Loggers

Layouts

Appenders

Locate it in the system

Format it

Write it out

Levels Log/Suppress Priority/Level

Log::Log4perl Remote Controls

Loggers

Layouts

Appenders

DEBUG “Starting up”; ERROR “Cannot open $file”;

“Starting up” =>2007-06-21 07:30:33 Foo.pm-123 Starting up

DatabaseLog File …

Levels

Turn logging on in main or Net::Amazon

Sounds complicated?

Actually, it’s easy …

Easy Log4perl

#!/usr/bin/perl –w

use strict;

use Log::Log4perl qw(:easy);

DEBUG “Starting up”;

Don’t like macros? Use get_logger()

#!/usr/bin/perl –w

use strict;

use Log::Log4perl qw(get_logger);

my $logger = get_logger();

$logger->debug(“Starting up”);

Like it clean? Use Moose!

package Ferrari;use Moose;with “MooseX::Log::Log4perl”;

sub drive { my($self) = @_; $self->log->debug(“Wroom!!”);}

Easy Log4perl

#!/usr/bin/perl –w

use strict;

use Log::Log4perl qw(:easy);

DEBUG “Starting up”;

Easy Log4perl

$ ./hello

$

Easy Log4perl

#!/usr/bin/perl –wuse strict;use Log::Log4perl qw(:easy);

Log::Log4perl->easy_init( $DEBUG );

DEBUG “Starting up”;

Easy Log4perl

$ ./hello

2008/07/08 18:37:12 Starting up

$

Easy Log4perl

#!/usr/bin/perl –wuse strict;use Log::Log4perl qw(:easy);

Log::Log4perl->easy_init( $DEBUG );

DEBUG “Starting up”; # … something happensERROR “Horrible error!”;

Easy Log4perl

$ ./hello

2008/07/08 18:37:12 Starting up

2008/07/08 18:37:12 Horrible error!

$

Easy Log4perl

#!/usr/bin/perl –wuse strict;use Log::Log4perl qw(:easy);

Log::Log4perl->easy_init( $ERROR );

DEBUG “Starting up”;ERROR “Horrible error!”;

Easy Log4perl

$ ./hello

2008/07/08 18:37:12 Horrible error!

$

Remote Control #1: Levels

You get the concept:

Log LevelConfigured

MessagePriority

FATAL

ERROR

WARNING

INFO

DEBUG

TRACE

FATAL

ERROR

WARNING

INFO

DEBUG

TRACE

Chatty configuration

Log LevelConfigured

MessagePriority

FATAL

ERROR

WARNING

INFO

DEBUG

TRACE TRACE

Silent configuration

ERROR

Log LevelConfigured

MessagePriority

FATAL

ERROR

WARNING

INFO

DEBUG

TRACE

Log Levels

• Choose them wisely– TRACE(“$bytes bytes transferred”);– DEBUG(“HTTP get OK”);– INFO(“Starting up”);– WARN(“HTTP get failed, retrying”);– ERROR(“Out of retries!”);– FATAL(“Panic! Shutting down.”);

Remote Control #2: Layouts

Location-Awareness

• Log4perl’s Loggers are aware of their location:

package Foo;

use Log::Log4perl qw(:easy);

sub foo {

DEBUG “Starting up”;

}

Location-Awareness

package Foo;

use Log::Log4perl qw(:easy);

sub foo {

DEBUG “Starting up”;

}

$ ./hello

2008/07/13 19:32:39 Starting up

Location-Awareness

package Foo;

use Log::Log4perl qw(:easy);

sub foo {

DEBUG “Starting up”;

}

$ ./hello

637 Foo::foo ./Foo.pm-4> Starting up

Location-Awareness

package main;use Log::Log4perl (:easy);Log::Log4perl->easy_init({ level => $DEBUG, layout => “%r %M %F-%L> %m%n”,});

Foo::foo(); # unchanged!

$ ./hello637 Foo::foo ./Foo.pm-4> Starting up

Configuration Files

If this becomes unwieldy:

Log::Log4perl->easy_init({ level => $DEBUG, layout => “%r %M %F-%L>%m%n”,});

Configuration Files

#l4p.confl4p.logger = DEBUG, Screen

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = PatternLayoutl4p.appender.Screen.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Log::Log4perl->init( “l4p.conf” );

Advantages of Config Files

• Can be edited– indepentently of the script– while the script runs– by people without access to the code

Remote Control #3: Categories (Loggers)

Turn on Logging EverywhereScript

Modulesl4p.logger = DEBUG, Screen

Using Categories

l4p.logger.Net.Amazon = \ DEBUG, Screen

Net::Amazon

Script

Modules

Using Categories

l4p.logger.main = \ DEBUG, Screen

main

Net::Amazon

Script

Modules

Using Categories

l4p.logger.main = DEBUG, Screenl4p.logger.Net.Amazon = \ DEBUG, Screen

Modules

Script

Net::Amazon

main

Categories

#l4p.confl4p.logger.main = DEBUG, Screenl4p.logger.Net.Amazon = DEBUG, Screen

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = PatternLayoutl4p.appender.Screen.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Net::Amazon

main

Category Inheritance

#l4p.confl4p.logger.Net = DEBUG, Screen

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = PatternLayoutl4p.appender.Screen.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Net::Google

Net::Amazon

main

Remote Control #5: Appenders

Root Logger

#l4p.confl4p.logger = DEBUG, Screen

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = PatternLayoutl4p.appender.Screen.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Net::Google

Net::Amazon

main

Multiple Appenders

#l4p.confl4p.logger.main = DEBUG, Screenl4p.logger.Net.Amazon = DEBUG, File

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = SimpleLayout

l4p.appender.File = Log::Log4perl::Appender::Filel4p.appender.File.filename = /var/log/myapp.logl4p.appender.File.Layout = PatternLayoutl4p.appender.File.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Net::Amazon

main Screen

File

Multiple Appenders (different log levels)

#l4p.confl4p.logger.main = DEBUG, Screenl4p.logger.Net.Amazon = ERROR, File

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = SimpleLayout

l4p.appender.File = Log::Log4perl::Appender::Filel4p.appender.File.filename = /var/log/myapp.logl4p.appender.File.Layout = PatternLayoutl4p.appender.File.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Net::Amazon

main Screen

File

Multiple Appenders

#l4p.confl4p.logger.main = DEBUG, Screen, File

l4p.appender.Screen = Log::Log4perl::Appender::Screenl4p.appender.Screen.Layout = SimpleLayout

l4p.appender.File = Log::Log4perl::Appender::Filel4p.appender.File.filename = /var/log/myapp.logl4p.appender.File.Layout = PatternLayoutl4p.appender.File.Layout.ConversionPattern = \ %r %M %F-%L> %m%n

Net::Amazon

main Screen

File

Log4perl Flow

Application sends a log message (Category, Priority)

Log4perl Configuration decides go/no go, based on Category and Priority

Appender Appender Appender

Layout

?

Log4perl and Log4j

• Log::Log4perl ports Log4j to Perl

• Log4j: de facto Java logging standard, by Ceki Gülcü– Latest development: ‘logback’

• http://logging.apache.org/log4j

• Log::Log4perl adds perlisms demanded by users

Log4perl History

• 0.01 release 2002• Current release 1.17 (07/2008)• Authors: Mike Schilli, Kevin Goess• Used by major banks, target.com,

fedex.com, Yahoo!, Google, …• Several CPAN modules support it (e.g.

Catalyst, Net::Amazon, …)• Every major Linux distro has it (Ubuntu,

Suse, Fedora …)

Log4perl Release History

Design Goals

• Easy to use in small scripts

• Scales easily with growing architecture

• Log4perl-enabled CPAN modules can be used with and without Log4perl initialization

• Optimized for Speed

• Open Architecture, extensible

Combine Remote Controls

• Write code once, and L4p-enabled scripts/modules can be used– with any logging configuration you desire– by changing loggers, appenders and layouts

independently– similar to dtrace probes

• No need to change your source code to change the logging behavior

Init and Watch

• Log::Log4perl->init(“l4p.conf”);• Log::Log4perl->init(\$conf_string);

• Log::Log4perl->init_and_watch(“l4p.conf”, 30);• Log::Log4perl->init_and_watch(“l4p.conf”, ‘HUP’ );

Demo

Appenders

• Appenders are output sinks

• Get called if a message passes category and level hurdles

Appenders

• Log::Log4perl::Appender::Screen Log::Log4perl::Appender::File Log::Log4perl::Appender::Socket Log::Log4perl::Appender::DBI Log::Log4perl::Appender::Synchronized Log::Log4perl::Appender::RRDs

• Log::Dispatch provides even more:

Log::Dispatch Appenders

• Log::Dispatch::ApacheLog Log::Dispatch::DBI, Log::Dispatch::Email, Log::Dispatch::Email::MIMELite Log::Dispatch::File Log::Dispatch::FileRotate Log::Dispatch::Screen Log::Dispatch::Syslog, Log::Dispatch::Tk

Example: Rotating Log File Appender

• Keep 5 days of logfiles, then delete:

log4perl.category = WARN, Logfile log4perl.appender.Logfile = Log::Dispatch::FileRotate log4perl.appender.Logfile.filename = test.log log4perl.appender.Logfile.max = 5 log4perl.appender.Logfile.DatePattern = yyyy-MM-dd log4perl.appender.Logfile.TZ = PST log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::SimpleLayout

Rotating Files

• Rotating File Appender:– Log::Dispatch::FileRotate– Single request pays for rotation– Rotation runs as particular user

• External Rotators (e.g. newsyslog):– recreate flag makes sure file appender adjusts– recreate_check_interval saves on stat() calls

Layouts

• SimpleLayout

$log->debug(“Sending Mail”);

DEBUG – Sending Mail

log4perl.appender.Screen = \ Log::Log4perl::Appender::Screenlog4perl.appender.Screen.layout = SimpleLayout

Layouts

• PatternLayout

$log->debug(“Sending Mail”);

2004/10/17 18:47:25 l4ptest.pl:25> Sending Mail

log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::PatternLayout log4perl.appender.Logfile.layout.ConversionPattern = \ %d %F{1}:%L> %m %n

Layouts

• PatternLayout%T stack trace%c Category of the logging event. %C Fully qualified package (or class) name of the caller %d Current date in yyyy/MM/dd hh:mm:ss format %F File where the logging event occurred %H Hostname %l calling method + file + line %L Line number within the file where the log statement was issued %m The message to be logged %M Method or function where the logging request was issued %n Newline (OS-independent) %p Priority of the logging event %P pid of the current process %r Number of milliseconds elapsed from program start %x The elements of the NDC stack%X{key} The entry 'key' of the MDC%% A literal percent (%) sign

Layouts

• Still not enough? Write your own:

log4perl.PatternLayout.cspec.U = sub { return "UID $<" } …log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::PatternLayout log4perl.appender.Logfile.layout.ConversionPattern = \ %d %U> %m %n

Speed

Benchmarks

• 1M/sec suppressed calls

• 50k/sec logged messages (memory appender)

• No degradation with subcategories

Avoid Wasting Cycles

for (@super_long_array) {

$logger->debug("Element: $_\n");

}

if($logger->is_debug()) {

for (@super_long_array) {

$logger->debug("Element: $_\n");

}

}

Dirty Tricks

Resurrect in a Single File

• The :resurrect target uncomments lines starting with ###l4p:

use Log4perl qw(:easy :resurrect);

sub foo {

# …

###l4p DEBUG “foo was here”;

}

Resurrect L4p in all Modules

• The Log::Log4perl::Resurrector touches all subsequently loaded modules (experimental!):

use Log4perl qw(:easy);

use Log::Log4perl::Resurrector;

use Foo::Bar;

# Deploy a module without requiring L4p at all!

package Foo::Bar;

###l4p use Log4perl qw(:easy);

sub foo {

###l4p DEBUG “This will be resurrected!”;

}

The Future

Wouldn’t it be nice …

• … if all modules on CPAN had a standard logging interface?

Log4perl-enable a CPAN Module

package Foo;

sub foo {

# … do something

}

1;

Log4perl-enable a CPAN Module

package Foo;

use Log::Log4perl qw(:easy);

sub foo {

# … do something

DEBUG “Fooing $bar”;

}

1;

… and voila, your CPAN module has a built-in remote.

Be Open

• Let other people debug your module in a standard way.

Q & A

Q & A

Thank You!

Log::Log4perl Project Page (includes slides of this talk):

http:/log4perl.com

Email me:Mike Schilli mschilli@yahoo-inc.com

Don’t forget to submit a Review!

• Go to the OSCON schedule, click on this talk and then ‘rate this talk’

• Thanks!

Bonus Slides

Advanced Trickery

Infiltrating LWP

• Ever wondered what LWP is doing behind the scenes?

use LWP::UserAgent;use HTTP::Request::Common;

use Log::Log4perl qw(:easy);

Log::Log4perl->easy_init($DEBUG);Log::Log4perl->infiltrate_lwp();

my $ua = LWP::UserAgent->new();my $resp = $ua->request(GET "http://www.yahoo.com");

Infiltrating LWP

• Getting LWP to use Log4perl for logging:

2004/10/20 18:36:43 ()2004/10/20 18:36:43 ()2004/10/20 18:36:43 GET http://www.yahoo.com2004/10/20 18:36:43 Not proxied2004/10/20 18:36:43 ()2004/10/20 18:36:43 read 634 bytes2004/10/20 18:36:43 read 4096 bytes…2004/10/20 18:36:43 read 2488 bytes2004/10/20 18:36:43 Simple response: OK

Pitfalls

Beginner’s Pitfalls

Beginner’s Pitfalls

• Appender Additivity:– Once a lower level logger decides to fire, it will

forward the message to its appenders.– It will also forward the message

unconditionally to all of its parent logger’s appenders.

Beginner’s Pitfalls

• Appender Additivity (with dupes)

package Net::Amazon;DEBUG(“Debugging!”);

log4perl.category = FATAL, Screenlog4perl.category.Net.Amazon = DEBUG, Screen

log4perl.appender.Screen = \ Log::Log4perl::Appender::Screenlog4perl.appender.Screen.layout = SimpleLayout

DEBUG - Debugging! DEBUG - Debugging!

Appender Additivity

Net::Amazon

Net

root

DEBUG

FATAL

Screen Appender

File Appender

Beginner’s Pitfalls

• Appender Additivity (no dupes)

package Net::Amazon;DEBUG(“Debugging!”); Q

log4perl.category = ERROR, Screenlog4perl.category.Net.Amazon = DEBUG, Screenlog4perl.additivity.Net.Amazon = 0

log4perl.appender.Screen = \ Log::Log4perl::Appender::Screenlog4perl.appender.Screen.layout = SimpleLayout

DEBUG – Debugging!

Write Your Own Appender (1)

package ColorScreenAppender;our @ISA = qw(Log::Log4perl::Appender);use Term::ANSIColor;

sub new { my($class, %options) = @_; my $self = {%options, …}; bless $self, $class;}

sub log { my($self, %params) = @_; print colored($params{message}, $self->{color});}

Write Your Own Appender (2)

log4perl.logger = INFO, ColorApp log4perl.appender.ColorApp=ColorScreenAppender log4perl.appender.ColorApp.color = red log4perl.appender.ColorApp.layout = SimpleLayout

Filters

• Last minute chance for Appenders to block

• More expensive than Level/Category blocking

• Text/Level Match comes with L4p

• Write your own custom filters

Filters

log4perl.category = INFO, Screen log4perl.filter.MyFilter = \ Log::Log4perl::Filter::StringMatchlog4perl.filter.M1.StringToMatch = let this through

log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen log4perl.appender.Screen.Filter = MyFilter log4perl.appender.Screen.layout = \ Log::Log4perl::Layout::SimpleLayout

Filters

log4perl.filter.M1 = Log::Log4perl::Filter::StringMatch log4perl.filter.M1.StringToMatch = let this through log4perl.filter.M1.AcceptOnMatch = true

log4perl.filter.M1 = Log::Log4perl::Filter::LevelMatch log4perl.filter.M1.LevelToMatch = INFO log4perl.filter.M1.AcceptOnMatch = true

Best Practices

• Don’t provide program name, function name in the message. Use Layouts instead.

• Log plenty. Don’t worry about space, use rotating log files for chatty output.

What you should log

• Program starting up, shutting down

• Function parameters

• Milestones in request processing

• Start/end of lenghty operations (e.g. DB access)

• result of called function (logged in calling function)

What you shouldn’t log

• Function/method names (although you want parameters)

• Date

• Process ID

• … everything else provided by the layout

Error Handling

use Log::Log4perl qw(:easy);

do_something or

LOGDIE “Horrible error!”;

• LOGCARP, LOGCLUCK, LOGCONFESS etc. also available.

Best Practices

• Rolling out new L4p-enabled Modulespackage My::Module;

use Log::Log4perl qw(:easy);

sub new { # … }sub foo { DEBUG “I’m here”; # … }sub bar { INFO “Now I’m here”; # … }

# Use w/o Log4perluse My::Module;

$o = My::Module->new();$o->foo();

# Log4perl enableduse My::Module;use Log::Log4perl qw(:easy);Log::Log4perl->easy_init($DEBUG);$o = My::Module->new();$o->foo();

Gotchas

• Avoid ‘append’ on NFS (creating lots of ‘read’ traffic)

• Don’t put expensive operations into the logger call which are executed before the logger decides

• Permission issues with rotating file appenders

mod_perl

• Init() in startup handler

• Current limitation: One init().

• Use init_once() if you’re not sure who inits first.

Combat overlapping Messages

• Either live with it or– Use the Synchronized appender– Use Appender.File.syswrite=1

Driving Log::Log4perl further

• Bug Fixes: Submit to log4perl-devel@sourceforge.net

• New Features: Propose features or send patches

• New Appenders: Release separately as a module in the

Log::Log4perl::Appender::xx namespace on CPAN

• … or contact me: mschilli@yahoo-inc.com

Easy Mode Init with Files

use Log::Log4perl qw(:easy);

Log::Log4perl->easy_init({

level => $DEBUG,

file => “>file.log”,

category => “Bar::Twix”,

});

Multiline Layout

Instead of2007/04/04 23:59:01 This isa message withmultiple lines

get this:2007/04/04 23:59:01 This is2007/04/04 23:59:01 a message with2007/04/04 23:59:01 multiple lines

with PatternLayout::Multiline:log4perl.appender.Logfile. layout = \ Log::Log4perl::Layout::PatternLayout::Multilinelog4perl.appender.Logfile.layout.ConversionPattern = %d %m %n

Perl Hooks

• Add parameters known at init() time

log4perl.appender.Logfile.filename = sub { \

“mylog.$$.log” }

Loggers

• Have a– category (e.g. “Net::Amazon” )– priority (e.g. $DEBUG )

• Take a message (e.g. “Starting” )

Loggers

• Pass on their message if– logging has been configured for

• their category ( “Net::Amazon”) or• a parent category ( “Net”, “” )

– and (!) the message priority (e.g. $DEBUG) is greater or equal than the configured log level (e.g. $DEBUG) for the category

Limit Throughput: Levels and Categories

• Categories determine which parts of the system are addressed.my $log = get_logger(“Net::Amazon”);

or simplypackage Net::Amazon;

DEBUG “…”;

• Levels indicate the message priority.$log->debug(“Request sent ($bytes bytes)”;

Displaying Logs with Chainsaw

• Log4j features an XML layout and a socket appender

• XML output is displayed in a nice GUI called Chainsaw

• Log::Log4perl also features an XML layout and a socket appender

• … XML output is also displayed in a nice GUI called Chainsaw!

Displaying Logs with Chainsaw

Java / log4j Program

Java / log4j Program

Log::Log4perl enabled Perl Script

Log::Log4perl::Layout::XML

Log::Log4perl::Appender::Socket

Displaying Logs with Chainsaw