log4perl mike schilli, yahoo! oscon, 07/24/2008. logging – why? debug during development go back...

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

Loggers

Layouts

Appenders

Locate it in the system

Format it

Write it out

Levels Log/Suppress Priority/Level

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()

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

use strict;

Easy Log4perl

$ ./hello

Easy Log4perl

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

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

Easy Log4perl

$ ./hello

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

Easy Log4perl

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

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

WARNING

Chatty configuration

Log LevelConfigured

MessagePriority

WARNING

TRACE TRACE

Silent configuration

Log LevelConfigured

MessagePriority

WARNING

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;

sub foo {

Location-Awareness

package Foo;

sub foo {

$ ./hello

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

Location-Awareness

package Foo;

sub foo {

$ ./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

Net::Amazon

Script

Modules

Using Categories

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

Modules

Script

Net::Amazon

Categories

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

Net::Amazon

Category Inheritance

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

Net::Google

Net::Amazon

Remote Control #5: Appenders

Root Logger

#l4p.confl4p.logger = DEBUG, Screen

Net::Google

Net::Amazon

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

Multiple Appenders (different log levels)

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

Net::Amazon

main Screen

Multiple Appenders

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

Net::Amazon

main Screen

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’ );

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

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

Log4perl-enable a CPAN Module

package Foo;

sub foo {

# … do something

DEBUG “Fooing $bar”;

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

Be Open

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

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;

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

• 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.

• Appender Additivity (with dupes)

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

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

DEBUG - Debugging! DEBUG - Debugging!

Appender Additivity

Net::Amazon

Screen Appender

File Appender

• Appender Additivity (no dupes)

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

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

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

do_something or

LOGDIE “Horrible error!”;

• LOGCARP, LOGCLUCK, LOGCONFESS etc. also available.

Best Practices

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

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

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!

Java / log4j Program

Log::Log4perl enabled Perl Script

Log::Log4perl::Layout::XML

Log::Log4perl::Appender::Socket

log4perl mike schilli, yahoo! oscon, 07/24/2008. logging – why? debug during development go back...

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