1. Smart Logging With Log4perl Mike Schilli, Yahoo! YAPC, 06/27/2007 Grab A T-Shirt!

2. Smart Logging With Log4perl Mike Schilli, Yahoo! YAPC, 06/27/2007

3. Logging – why? Go back in time and figure out what happened. Measure performance Trace activity on live systems Debug during development

4. 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

5. Log4perl History 0.01 release 2002 Current release 1.11 (06/2007) 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, …)

6. Log4perl Release History

7. 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

8. Why Log4perl and not one of the 20 Logging modules on CPAN? Write once, and L4p-enabled scripts/modules can be used –with any logging configuration you desire –by changing loggers, appenders and layouts independently Target specific areas of your application only No need to change your source code to change the logging behaviour Log4perl is aimed to be the last logging module you’ll ever install

9. Log::Log4perl for Simple Scripts #!/usr/bin/perl –w use strict; use Log::Log4perl qw(:easy); Log::Log4perl->easy_init($INFO); DEBUG "Won't make it"; INFO "Will go through"; ERROR "Will also go through"; $ easy.pl 2004/10/19 10:56:56 Will go through 2004/10/19 10:56:56 Will also go through

10. Log::Log4perl for CPAN Modules package YourCPANModule; use strict; use Log::Log4perl qw(:easy); sub somefunc { DEBUG "Won't make it"; INFO "Will go through"; } use strict; use YourCPANModule; use Log::Log4perl qw(:easy); Log::Log4perl->easy_init( $INFO ); YourCPANModule::somefunc();

11. Log::Log4perl for CPAN Modules package YourCPANModule; use strict; use Log::Log4perl qw(:easy); sub somefunc { DEBUG "Won't make it"; INFO "Won’t make it"; } use strict; use YourCPANModule; YourCPANModule::somefunc();

12. Log::Log4perl Building Blocks Loggers Layouts Appenders

13. Log::Log4perl Building Blocks Loggers Layouts Appenders Log it or suppress it Format it Write it out

14. Log::Log4perl Building Blocks Loggers Layouts Appenders DEBUG “Starting up”); or my $log = get_logger(); $log->debug(“Starting up”); “Starting up” => 2007-06-21 07:30:33 Foo.pm-123 Starting up Database Log File …

15. Easy vs. Standard Mode use Log::Log4perl qw(:easy); sub somefunc { DEBUG “Debug Message”; INFO “Info Message”; } use Log::Log4perl qw(get_logger); sub somefunc { my $logger = get_logger(); $logger->debug(“Debug message”); $logger->info(“Info message”); }

16. Log4perl Operation Initialize once, at startup: –Define which loggers should fire base on message priority (DEBUG, INFO, …) location (Foo::Bar, …) –Define where messages should end up at Loggers planted in program code get activated

17. Easy Init vs. Standard Init use Log::Log4perl qw(:easy); Log::Log4perl->easy_init($INFO); use Log::Log4perl; Log::Log4perl->init(“l4p.conf”); #l4p.conf log4perl.category = INFO, Screen log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen log4perl.appender.Screen.stderr = 1 log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::SimpleLayout

18. Mix&Match: Standard Init with Easy Functions use Log::Log4perl qw(:easy); Log::Log4perl->init(“l4p.conf”); DEBUG “Debug Message”; INFO “Info Message”; #l4p.conf log4perl.category = WARN, Logfile log4perl.appender.Logfile = \ Log::Log4perl::Appender::File log4perl.appender.Logfile.filename = test.log log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::SimpleLayout

19. Mix and Match Easy Mode DEBUG(…) Standard Mode get_logger() easy_init() OK init() OK

20. Categories or: What the hell does this logo mean?

21. Categories: Areas of your App package Bar::Twix; use Log::Log4perl qw(get_logger); sub eat { # Gets a Bar::Twix logger my $logger = get_logger(); $logger->debug(“Debug Message”); } #l4p.conf log4perl.category.Bar.Twix = WARN, Logfile log4perl.appender.Logfile = \ Log::Log4perl::Appender::File log4perl.appender.Logfile.filename = test.log log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::SimpleLayout

22. Categories (Easy Mode) package Bar::Twix; use Log::Log4perl qw(:easy); sub eat { # Has a Bar::Twix logger DEBUG “Debug Message”; } #l4p.conf log4perl.category.Bar.Twix = WARN, Logfile log4perl.appender.Logfile = \ Log::Log4perl::Appender::File log4perl.appender.Logfile.filename = test.log log4perl.appender.Logfile.layout = \ Log::Log4perl::Layout::SimpleLayout

23. Loggers Have a – category (e.g. “Net::Amazon” ) – priority (e.g. $DEBUG ) Take a message (e.g. “Starting” )

24. 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

25. Limit Throughput: Levels and Categories Categories determine which parts of the system are addressed. my $log = get_logger(“Net::Amazon”); or simply package Net::Amazon; DEBUG “…”; Levels indicate the message priority. $log->debug(“Request sent ($bytes bytes)”;

26. Log Levels Levels –$TRACE –$DEBUG –$INFO –$WARN –$ERROR –$FATAL –$OFF

27. Log Levels Methods –$log->trace(“$bytes bytes transferred”); –$log->debug(“HTTP get OK”); –$log->info(“Starting up”); –$log->warn(“HTTP get failed, retrying”); –$log->error(“Out of retries!”); –$log->fatal(“Panic! Shutting down.”);

28. Log Levels Macros –TRACE(“$bytes bytes transferred”); –DEBUG(“HTTP get OK”); –INFO(“Starting up”); –WARN(“HTTP get failed, retrying”); –ERROR(“Out of retries!”); –FATAL(“Panic! Shutting down.”);

29. Remote Control via Categories l4p.conf package Net::Amazon; ERROR “Makes it through!”; DEBUG “Makes it through”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Makes it through!” my $amzn = Net::Amazon->new(); log4perl.category = DEBUG, Screen

30. Remote Control via Categories l4p.conf package Net::Amazon; ERROR “Makes it through!”; DEBUG “Gets blocked”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Gets blocked!” my $amzn = Net::Amazon->new(); Log4perl.category = ERROR, Screen

31. Remote Control via Categories l4p.conf package Net::Amazon; ERROR “Gets blocked!”; DEBUG “Gets blocked”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Gets blocked!” my $amzn = Net::Amazon->new(); Log4perl.category = FATAL, Screen

32. Remote Control via Categories l4p.conf package Net::Amazon; ERROR “Makes it through!”; DEBUG “Gets blocked”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Makes it through!” my $amzn = Net::Amazon->new(); Log4perl.category.main = DEBUG, Screen Log4perl.category.Net.Amazon = ERROR, Screen

33. Remote Control via Categories l4p.conf package Net::Amazon; ERROR “Makes it through!”; DEBUG “Makes it through!”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Gets blocked”; my $amzn = Net::Amazon->new(); Log4perl.category.main = ERROR, Screen Log4perl.category.Net.Amazon = DEBUG, Screen

34. Category Inheritance (1) l4p.conf package Net::Amazon; ERROR “Makes it through!”; DEBUG “Gets blocked”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Makes it through!” my $amzn = Net::Amazon->new(); Log4perl.category.main = DEBUG, Screen Log4perl.category.Net = ERROR, Screen

35. Category Inheritance (2) l4p.conf package Net::Amazon; ERROR “Makes it through!”; DEBUG “Gets blocked”; #!/usr/bin/perl use Net::Amazon; Log::Log4perl->init(“l4p.conf”); DEBUG “Makes it through!” my $amzn = Net::Amazon->new(); Log4perl.category.main = DEBUG, Screen Log4perl.category = ERROR, Screen

36. Log4perl Flow Application sends a log message (Category, Priority) Log4perl Configuration decides go/no go, based on Category and Priority Appender Layout ?

37. l4p.conf: Screen Appender log4perl.category.main = DEBUG, Screen Log4perl.category.Net.Amazon = INFO, Screen log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen …

38. l4p.conf: File Appender log4perl.category.main = DEBUG, Logfile Log4perl.category.Net.Amazon = INFO, Logfile log4perl.appender.Logfile = \ Log::Log4perl::Appender::File log4perl.appender.Logfile.filename = test.log …

39. l4p.conf: Two appenders log4perl.category.main = DEBUG, Logfile Log4perl.category.Net.Amazon = INFO, Screen log4perl.appender.Logfile = \ Log::Log4perl::Appender::File log4perl.appender.Logfile.filename = test.log log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen …

40. 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’ );

41. Demo

42. Appenders Appenders are output sinks Get called if a message passes category and level hurdles

43. 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:

44. 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

45. 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

46. 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

47. 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}); }

48. Write Your Own Appender (2) log4perl.logger = INFO, ColorApp log4perl.appender.ColorApp=ColorScreenAppender log4perl.appender.ColorApp.color = red log4perl.appender.ColorApp.layout = SimpleLayout

49. Layouts SimpleLayout $log->debug(“Sending Mail”); DEBUG – Sending Mail log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen log4perl.appender.Screen.layout = SimpleLayout

50. 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

51. Layouts PatternLayout %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

52. 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

53. 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

54. Filters log4perl.category = INFO, Screen log4perl.filter.MyFilter = \ Log::Log4perl::Filter::StringMatch log4perl.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

55. 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

56. Speed

57. Avoid Wasting Cycles for (@super_long_array) { $logger->debug("Element: $_\n"); } if($logger->is_debug()) { for (@super_long_array) { $logger->debug("Element: $_\n"); }

58. Performance On a Pentium 4 Linux box at 2.4 GHz, you'll get through –500,000 suppressed log statements per second –30,000 logged messages per second (using an in-memory appender) –init_and_watch delay mode: 300,000 suppressed, 30,000 logged. –init_and_watch signal mode: 450,000 suppressed, 30,000 logged.

59. Advanced Trickery

60. 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");

61. Infiltrating LWP Getting LWP to use Log4perl for logging: 2004/10/20 18:36:43 () 2004/10/20 18:36:43 GET http://www.yahoo.com 2004/10/20 18:36:43 Not proxied 2004/10/20 18:36:43 () 2004/10/20 18:36:43 read 634 bytes 2004/10/20 18:36:43 read 4096 bytes … 2004/10/20 18:36:43 read 2488 bytes 2004/10/20 18:36:43 Simple response: OK

62. 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”; }

63. 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!”; }

64. Pitfalls Beginner’s Pitfalls

65. 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.

66. Beginner’s Pitfalls Appender Additivity (with dupes) package Net::Amazon; DEBUG(“Debugging!”); log4perl.category = FATAL, Screen log4perl.category.Net.Amazon = DEBUG, Screen log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen log4perl.appender.Screen.layout = SimpleLayout DEBUG - Debugging!

67. Appender Additivity Net::Amazon Net root DEBUG FATAL Screen Appender File Appender

68. Beginner’s Pitfalls Appender Additivity (no dupes) package Net::Amazon; DEBUG(“Debugging!”); Q log4perl.category = ERROR, Screen log4perl.category.Net.Amazon = DEBUG, Screen log4perl.additivity.Net.Amazon = 0 log4perl.appender.Screen = \ Log::Log4perl::Appender::Screen log4perl.appender.Screen.layout = SimpleLayout DEBUG – Debugging!

69. Log::Log4perl Availability Cpan> install Log::Log4perl –Only requires core modules Requires Perl 5.00503 or better Included in major Linux distros Windows: ppm package available in ActiveState archives or from log4perl.sf.net

70. 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.

71. What you should log Program starting up, shutting down Function parameters Milestones in request processing Start/end of lenghty operations (e.g. DB access)

72. What you shouldn’t log Function/method names (although you want parameters) Date Process ID … everything else provided by the layout

73. Best Practices Rolling out new L4p-enabled Modules package 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 Log4perl use My::Module; $o = My::Module->new(); $o->foo(); # Log4perl enabled use My::Module; use Log::Log4perl qw(:easy); Log::Log4perl->easy_init($DEBUG); $o = My::Module->new(); $o->foo();

74. 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

75. mod_perl Init() in startup handler Current limitation: One init(). Use init_once() if you’re not sure who inits first.

76. Combat overlapping Messages Either live with it or –Use the Synchronized appender –Use Appender.File.syswrite=1

77. Driving Log::Log4perl further Bug Fixes: Submit to log4perl-devel@sourceforge.netlog4perl-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

78. Q & A

79. Thank You! Log::Log4perl Project Page: http://log4perl.sourceforge.net Email me: Mike Schilli mschilli@yahoo-inc.com Post to the List: log4perl-devel@sourceforge.net

80. Bonus Slides

81. Error Handling use Log::Log4perl qw(:easy); do_something or LOGDIE “Horrible error!”; LOGCARP, LOGCLUCK, LOGCONFESS etc. also available.

82. 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!

83. Displaying Logs with Chainsaw Java / log4j Program Log::Log4perl enabled Perl Script Log::Log4perl::Layout::XML Log::Log4perl::Appender::Socket

84. Displaying Logs with Chainsaw

85. The Future Allow multiple configurations within the same process (e.g. for mod_perl)

86. Easy Mode Init with Files use Log::Log4perl qw(:easy); Log::Log4perl->easy_init({ level => $DEBUG, file => “>file.log”, category => “Bar::Twix”, });

87. Multiline Layout Instead of 2007/04/04 23:59:01 This is a message with multiple lines get this: 2007/04/04 23:59:01 This is 2007/04/04 23:59:01 a message with 2007/04/04 23:59:01 multiple lines with PatternLayout::Multiline: log4perl.appender.Logfile. layout = \ Log::Log4perl::Layout::PatternLayout::Multiline log4perl.appender.Logfile.layout.ConversionPattern = %d %m %n

88. Perl Hooks Add parameters known at init() time log4perl.appender.Logfile.filename = sub { \ “mylog.$$.log” }