Log::Fast(3) Fast and flexible logger


This document describes Log::Fast version v2.0.0


use Log::Fast;
$LOG = Log::Fast->global();
$LOG = Log::Fast->new({
level => 'WARN',
prefix => '%D %T [%L] ',
type => 'fh',
fh => \*STDOUT,
use Sys::Syslog qw( LOG_DAEMON );
prefix => '',
type => 'unix',
path => '/dev/log',
facility => LOG_DAEMON,
add_timestamp => 1,
add_hostname => 1,
hostname => 'somehost',
ident => 'someapp',
add_pid => 1,
pid => $$,
$LOG->ERR('Some error');
$LOG->WARN('Some warning');
$LOG->NOTICE('user %s logged in', $user);
$LOG->INFO('data loaded');
$LOG->DEBUG('user %s have %d things', $user, sub {
return SlowOperation_GetAmountOfThingsFor($user);


This is very fast logger, designed for use in applications with thousands high-level events/operations per second (like network servers with thousands clients or web spiders which download hundreds url per second).

For example, on Core2Duo sending about 5000 messages to log on enabled log levels or 20000 messages on disabled log levels in one second will slow down your application only by 2-3%.

Comparing to some other CPAN modules, this one (in average): faster than Log::Dispatch in about 45 times, faster than Log::Handler in about 15 times, faster than Sys::Syslog in about 7 times, and slower than Log::Syslog::Fast in about 2 times.


  • Global and local logger objects
  • Output to any open filehandle or local syslog
  • 5 log levels: ERR, WARN, NOTICE, INFO, DEBUG
  • Configurable prefix (log level, date/time, caller function name)
  • sprintf() support
  • Unicode support (UTF8)
  • Can avoid calculating log message content on disabled log levels


When called first time will create global log object using default options (you can reconfigure it using "config()" later).

Global log object is useful if your application consists of several independent modules which should share same logging options configured outside of these modules. In this case all these modules should use same "global()" log object instead of creating "new()" independent log objects in each module.

Return global log object.

Log::Fast->new( [\%opt] )
Create new log object, configured using defaults and user-provided options, if any.

Return created log object.

$LOG->config( \%opt )
Reconfigure log object. Any options (see ``OPTIONS'') can be changed at any time, including changing output {type} or setting options useless with current output type (new values for these options will be used later, if output type will be changed).

If you need to change only log {level} or syslog's {ident} you should use "level()" or "ident()" methods because they are much faster than more general "config()".

Return nothing. Throw exception if unable to connect to syslog.

$LOG->level( [$level] )
If $level given will change current log level. This is same as call "config({ level=>$level })" but much faster.

Return previous log level.

$LOG->ident( [$ident] )
If $ident given will change current syslog's ident. This is same as call "config({ ident=>$ident })" but much faster.

Return previous syslog's ident.

$LOG->ERR( $message )
$LOG->ERR( $format, @list )
$LOG->WARN( $message )
$LOG->WARN( $format, @list )
$LOG->NOTICE( $message )
$LOG->NOTICE( $format, @list )
$LOG->INFO( $message )
$LOG->INFO( $format, @list )
$LOG->DEBUG( $message )
$LOG->DEBUG( $format, @list )
Output $message to log using different log levels.

If $format, @list used instead of $message, then use "sprintf($format, @list)" to calculate log message.

If @list will contain CODEREF, they will be called (in LIST context) and returned values will be placed inside @list inplace of CODEREF. This can be used to avoid calculating log message (or it part) on disabled log levels - these CODEREFs will be executed only on enabled log levels. Example available in ``SYNOPSIS''.

If $message or items in @list will be Unicode strings, they will be converted to UTF8 before sending to log.

Return nothing. Throw exception if fail to write message to log.


Defaults for all options are:

    level           => 'DEBUG',
    prefix          => q{},
    type            => 'fh',
    fh              => \*STDERR,
    # these will be used if you will call config({ type=>'unix' })
    path            => Sys::Syslog::_PATH_LOG() || '/dev/log',
    facility        => LOG_USER,
    add_timestamp   => 1,
    add_hostname    => 0,
    hostname        => Sys::Hostname::hostname(),
    ident           => ..., # calculated from $0
    add_pid         => 1,
    pid             => $$,
Current log level. Possible values are: 'ERR', 'WARN', 'NOTICE', 'INFO', 'DEBUG'.

Only messages on current or higher levels will be sent to log.

String, which will be output at beginning of each log message. May contain these placeholders:

    %L - log level of current message
    %S - hi-resolution time (seconds.microseconds)
    %D - current date in format YYYY-MM-DD
    %T - current time in format HH:MM:SS
    %P - caller's function package ('main' or 'My::Module')
    %F - caller's function name
    %_ - X spaces, where X is current stack depth
    %% - % character

Example output with prefix '%D %T [%L]%_%P::%F() ':

    2010-11-17 18:06:20 [INFO] main::() something from main script
    2010-11-17 18:06:53 [INFO]  main::a() something from a
    2010-11-17 18:09:09 [INFO]   main::b2() something from b1->b2
    2010-11-17 18:06:56 [INFO]  main::c() something from c

If it will be Unicode string, it will be converted to UTF8.

Output type. Possible values are: 'fh' (output to any already open filehandle) and 'unix' (output to syslog using UNIX socket).

When {type} set to 'fh' you have to also set {fh} to any open filehandle (like "\*STDERR").

When {type} set to 'unix' you have to also set {path} to path to existing unix socket (typically it's '/dev/log').

Luckily, default values for both {fh} and {path} are already provided, so usually it's enough to just set {type}.

File handle to write log messages if {type} set to 'fh'.
Syslog's UNIX socket path to write log messages if {type} set to 'unix'.
Syslog's facility (see ``Facilities'' in Sys::Syslog for a list of well-known facilities).

This module doesn't export any constants, so if you wanna change it from default LOG_USER value, you should import facility constants from Sys::Syslog module. Example available in ``SYNOPSIS''.

If TRUE will include timestamp in syslog messages.
If TRUE will include hostname in syslog messages.
Host name which will be included in syslog messages if {add_hostname} is TRUE.
Syslog's ident (application name) field.

If it will be Unicode string, it will be converted to UTF8. Using non-ASCII ALPHANUMERIC ident isn't allowed by RFC, but usually works.

If TRUE will include PID in syslog messages.
PID which will be included in syslog messages if {add_pid} is TRUE.


Empty prefix is fastest. Prefixes %L, %P and "%%" are fast enough, %D and %T has average speed, %S, %F and %_ are slowest.

Output to file is about 4 times faster than to syslog.

Calling log with single parameter is faster than with many parameters (because in second case sprintf() have to be used).


Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker at <https://github.com/powerman/perl-Log-Fast/issues>. You will be notified automatically of any progress on your issue.

Source Code

This is open source software. The code repository is available for public review and contribution under the terms of the license. Feel free to fork the repository and submit pull requests.


    git clone https://github.com/powerman/perl-Log-Fast.git



Alex Efros <[email protected]>


This software is Copyright (c) 2010-2012 by Alex Efros <[email protected]>.

This is free software, licensed under:

  The MIT (X11) License