TheSchwartz(3)

NAME
TheSchwartz - reliable job queue

SYNOPSIS
    # MyApp.pm
    package MyApp;

    sub work_asynchronously {
        my %args = @_;

        my $client = TheSchwartz->new( databases => $DATABASE_INFO );
        $client->insert('MyWorker', \%args);
    }

    # myworker.pl
    package MyWorker;
    use base qw( TheSchwartz::Worker );

    sub work {
        my $class = shift;
        my TheSchwartz::Job $job = shift;

        print "Workin' hard or hardly workin'? Hyuk!!\n";

        $job->completed();
    }

    package main;

    my $client = TheSchwartz->new( databases => $DATABASE_INFO );
    $client->can_do('MyWorker');
    $client->work();

DESCRIPTION
TheSchwartz is a reliable job queue system. Your application can put jobs into the system, and your worker processes can pull jobs from the queue atomically to perform. Failed jobs can be left in the queue to retry later.

Abilities specify what jobs a worker process can perform. Abilities are the names of "TheSchwartz::Worker" sub-classes, as in the synopsis: the "MyWorker" class name is used to specify that the worker script can perform the job. When using the "TheSchwartz" client's "work" functions, the class-ability duality is used to automatically dispatch to the proper class to do the actual work.

TheSchwartz clients will also prefer to do jobs for unused abilities before reusing a particular ability, to avoid exhausting the supply of one kind of job while jobs of other types stack up.

Some jobs with high setup times can be performed more efficiently if a group of related jobs are performed together. TheSchwartz offers a facility to coalesce jobs into groups, which a properly constructed worker can find and perform at once. For example, if your worker were delivering email, you might store the domain name from the recipient's address as the coalescing value. The worker that grabs that job could then batch deliver all the mail for that domain once it connects to that domain's mail server.

USAGE

  "TheSchwartz->new( %args )"
Optional members of %args are:

•   "databases"

    An arrayref of database information. TheSchwartz workers can use multiple databases, such that if any of them are unavailable, the worker will search for appropriate jobs in the other databases automatically.

    Each member of the "databases" value should be a hashref containing either:

    •   "dsn"

        The database DSN for this database.

    •   "user"

        The user name to use when connecting to this database.

    •   "pass"

        The password to use when connecting to this database.

    or

    •   "driver"

        A "Data::ObjectDriver::Driver::DBI" object.

        See note below.

•   "verbose"

    A value indicating whether to log debug messages. If "verbose" is a coderef, it is called to log debug messages. If "verbose" is not a coderef but is some other true value, debug messages will be sent to "STDERR". Otherwise, debug messages will not be logged.

•   "prioritize"

    A value indicating whether to utilize the job 'priority' field when selecting jobs to be processed. If unspecified, jobs will always be executed in a randomized order.

•   "floor"

    A value indicating the minimum priority a job needs to be for this worker to perform. If unspecified all jobs are considered.

•   "batch_size"

    A value indicating how many jobs should be fetched from the DB for consideration.

•   "driver_cache_expiration"

    Optional value to control how long database connections are cached for in seconds. By default, connections are not cached. To re-use the same database connection for five minutes, pass driver_cache_expiration => 300 to the constructor. Improves job throughput in cases where the work to process a job is small compared to the database connection set-up and tear-down time.

•   "retry_seconds"

    The number of seconds after which to try reconnecting to apparently dead databases. If not given, TheSchwartz will retry connecting to databases after 30 seconds.

•   "strict_remove_ability"

    By default when work_once does not find a job it will reset current_abilities to all_abilities and look for a job. Setting this option will prevent work_once from resetting abilities if it can't find a job for the current capabilities.

  "$client->list_jobs( %args )"
Returns a list of "TheSchwartz::Job" objects matching the given arguments. The required members of %args are:

•   "funcname"

    the name of the function or a reference to an array of functions

•   "run_after"

    the value you want to check <= against on the run_after column

•   "grabbed_until"

    the value you want to check <= against on the grabbed_until column

•   "coalesce_op"

    defaults to '=', set it to whatever you want to compare the coalesce field too if you want to search, you can use 'LIKE'

•   "coalesce"

    coalesce value to search for, if you set op to 'LIKE' you can use '%' here, do remember that '%' searches anchored at the beginning of the string are much faster since it is can do a btree index lookup

•   "want_handle"

    if you want all your jobs to be set up using a handle. defaults to true. this option might be removed, as you should always have this on a Job object.

•   "jobid"

    if you want a specific job you can pass in it's ID and if it's available it will be listed.

It is important to remember that this function does not lock anything, it just returns as many jobs as there is up to amount of databases * $client->{batch_size}

  "$client->lookup_job( $handle_id )"
Returns a "TheSchwartz::Job" corresponding to the given handle ID.

  "$client->set_verbose( $verbose )"
Sets the current logging function to $verbose if it's a coderef. If not a coderef, enables debug logging to "STDERR" if $verbose is true; otherwise, disables logging.

POSTING JOBS
The methods of TheSchwartz clients used by applications posting jobs to the queue are:

  "$client->insert( $job )"
Adds the given "TheSchwartz::Job" to one of the client's job databases.

  "$client->insert( $funcname, $arg )"
Adds a new job with function name $funcname and arguments $arg to the queue.

  "$client->insert_jobs( @jobs )"
Adds the given "TheSchwartz::Job" objects to one of the client's job databases. All the given jobs are recorded in one job database.

  "$client->set_prioritize( $prioritize )"
Set the "prioritize" value as described in the constructor.

  "$client->set_floor( $floor )"
Set the "floor<gt" value as described in the constructor.

  "$client->set_batch_size( $batch_size )"
Set the "batch_size<gt" value as described in the constructor.

  "$client->set_strict_remove_ability( $strict_remove_ability )"
Set the "strict_remove_ability<gt" value as described in the constructor.

WORKING
The methods of TheSchwartz clients for use in worker processes are:

  "$client->can_do( $ability )"
Adds $ability to the list of abilities $client is capable of performing. Subsequent calls to that client's "work" methods will find jobs requiring the given ability.

  "$client->work_once()"
Find and perform one job $client can do.

  "$client->work_until_done()"
Find and perform jobs $client can do until no more such jobs are found in any of the client's job databases.

  "$client->work( [$delay] )"
Find and perform any jobs $client can do, forever. When no job is available, the working process will sleep for $delay seconds (or 5, if not specified) before looking again.

  "$client->work_on($handle)"
Given a job handle (a scalar string) $handle, runs the job, then returns.

  "$client->grab_and_work_on($handle)"
Similar to "$client->work_on($handle)", except that the job will be grabbed before being run. It guarantees that only one worker will work on it (at least in the "grab_for" interval).

Returns false if the worker could not grab the job, and true if the worker worked on it.

  "$client->find_job_for_workers( [$abilities] )"
Returns a "TheSchwartz::Job" for a random job that the client can do. If specified, the job returned matches one of the abilities in the arrayref $abilities, rather than $client's abilities.

  "$client->find_job_with_coalescing_value( $ability, $coval )"
Returns a "TheSchwartz::Job" for a random job for a worker capable of $ability and with a coalescing value of $coval.

  "$client->find_job_with_coalescing_prefix( $ability, $coval )"
Returns a "TheSchwartz::Job" for a random job for a worker capable of $ability and with a coalescing value beginning with $coval.

Note the "TheSchwartz" implementation of this function uses a "LIKE" query to find matching jobs, with all the attendant performance implications for your job databases.

  "$client->get_server_time( $driver )"
Given an open driver $driver to a database, gets the current server time from the database.

THE SCOREBOARD
The scoreboards can be used to monitor what the TheSchwartz::Worker sub-classes are currently working on. Once the scoreboard has been enabled in the workers with "set_scoreboard" method the "thetop" utility (shipped with TheSchwartz distribution in the "extras" directory) can be used to list all current jobs being worked on.

  "$client->set_scoreboard( $dir )"
Enables the scoreboard. Setting this to 1 or "on" will cause TheSchwartz to create a scoreboard file in a location it determines is optimal.

Passing in any other option sets the directory the TheSchwartz scoreboard directory should be created in. For example, if you set this to "/tmp" then this would create a directory called "/tmp/theschwartz" and a scoreboard file "/tmp/theschwartz/scoreboard.pid" in it (where pid is the current process pid.)

  "$client->scoreboard()"
Returns the path to the current scoreboard file.

  "$client->start_scoreboard()"
Writes the current job information to the scoreboard file (called by the worker in work_safely before it actually starts working)

  "$client->end_scoreboard()"
Appends the current job duration to the end of the scoreboard file (called by the worker in work_safely once work has been completed)

  "$client->clean_scoreboard()"
Removes the scoreboard file (but not the scoreboard directory.) Automatically called by TheSchwartz during object destruction (i.e. when the instance goes out of scope)

PASSING IN AN EXISTING DRIVER
You can pass in a existing Data::ObjectDriver object which also allows you to reuse exist Database handles like so:

        my $dbh = DBI->connect( $dsn, "root", "", {
                RaiseError => 1,
                PrintError => 0,
                AutoCommit => 1,
            } ) or die $DBI::errstr;
        my $driver = Data::ObjectDriver::Driver::DBI->new( dbh => $dbh);
        return TheSchwartz->new(databases => [{ driver => $driver }]);

Note: it's important that the "RaiseError" and "AutoCommit" flags are set on the handle for various bits of functionality to work.

COPYRIGHT, LICENSE & WARRANTY
This software is Copyright 2007, Six Apart Ltd, cpan@sixapart.com. All rights reserved.

TheSchwartz is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

TheSchwartz comes with no warranty of any kind.