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Module Version: 0.2.0   Source   Latest Release: POE-Component-MessageQueue-0.3004

NAME ^

POE::Component::MessageQueue - A POE message queue that uses STOMP for its communication protocol

USAGE ^

If you are only interested in running with the recommended storage backend and some predetermined defaults, you can use the included command line script:

  POE::Component::MessageQueue version 0.2.0
  Copyright 2007, 2008 David Snopek (http://www.hackyourlife.org)
  Copyright 2007, 2008 Paul Driver <frodwith@gmail.com>
  Copyright 2007 Daisuke Maki <daisuke@endeworks.jp>
  
  mq.pl [--port|-p <num>]               [--hostname|-h <host>]
        [--front-store <str>]           [--front-max <size>] 
        [--granularity <seconds>]       [--nouuids]
        [--timeout|-i <seconds>]        [--throttle|-T <count>]
        [--data-dir <path_to_dir>]      [--log-conf <path_to_file>]
        [--stats-interval|-i <seconds>] [--stats]
        [--pidfile|-p <path_to_file>]   [--background|-b]
        [--crash-cmd <path_to_script>]
        [--debug-shell] [--version|-v]  [--help|-h]
  
  SERVER OPTIONS:
    --port     -p <num>     The port number to listen on (Default: 61613)
    --hostname -h <host>    The hostname of the interface to listen on 
                            (Default: localhost)
  
  STORAGE OPTIONS:
    --front-store -f <str>  Specify which in-memory storage engine to use for
                            the front-store (can be memory or bigmemory).
    --front-max <size>      How much message body the front-store should cache.
                            This size is specified in "human-readable" format
                            as per the -h option of ls, du, etc. (ex. 2.5M)
    --timeout  -i <secs>    The number of seconds to keep messages in the 
                            front-store (Default: 4)
    --granularity <secs>    How often (in seconds) Complex should check for
                            messages that have passed the timeout.  
    --[no]uuids             Use (or do not use) UUIDs instead of incrementing
                            integers for message IDs.  Default: uuids 
    --throttle -T <count>   The number of messages that can be stored at once 
                            before throttling (Default: 2)
    --data-dir <path>       The path to the directory to store data 
                            (Default: /var/lib/perl_mq)
    --log-conf <path>       The path to the log configuration file 
                            (Default: /etc/perl_mq/log.conf
  
  STATISTICS OPTIONS:
    --stats                 If specified the, statistics information will be 
                            written to $DATA_DIR/stats.yml
    --stats-interval <secs> Specifies the number of seconds to wait before 
                            dumping statistics (Default: 10)
  
  DAEMON OPTIONS:
    --background -b         If specified the script will daemonize and run in the
                            background
    --pidfile    -p <path>  The path to a file to store the PID of the process
  
    --crash-cmd  <path>     The path to a script to call when crashing.
                            A stacktrace will be printed to the script's STDIN.
                            (ex. 'mail root@localhost')
  
  OTHER OPTIONS:
    --debug-shell           Run with POE::Component::DebugShell
    --version    -v         Show the current version.
    --help       -h         Show this usage message

SYNOPSIS ^

Subscriber

  use Net::Stomp;
  
  my $stomp = Net::Stomp->new({
    hostname => 'localhost',
    port     => 61613
  });
  
  # Currently, PoCo::MQ doesn't do any authentication, so you can put
  # whatever you want as the login and passcode.
  $stomp->connect({ login => $USERNAME, passcode => $PASSWORD });
  
  $stomp->subscribe({
    destination => '/queue/my_queue.sub_queue',
    ack         => 'client'
  });
  
  while (1)
  {
    my $frame = $stomp->receive_frame;
    print $frame->body . "\n";
    $stomp->ack({ frame => $frame });
  }
  
  $stomp->disconnect();

Producer

  use Net::Stomp;
  
  my $stomp = Net::Stomp->new({
    hostname => 'localhost',
    port     => 61613
  });
  
  # Currently, PoCo::MQ doesn't do any authentication, so you can put
  # whatever you want as the login and passcode.
  $stomp->connect({ login => $USERNAME, passcode => $PASSWORD });
  
  $stomp->send({
    destination => '/queue/my_queue.sub_queue',
    body        => 'I am a message',
    persistent  => 'true',
  });
  
  $stomp->disconnect();

Server

If you want to use a different arrangement of storage engines or to embed PoCo::MQ inside another application, the following synopsis may be useful to you:

  use POE;
  use POE::Component::Logger;
  use POE::Component::MessageQueue;
  use POE::Component::MessageQueue::Storage::Default;
  use strict;

  my $DATA_DIR = '/tmp/perl_mq';

  # we create a logger, because a production message queue would
  # really need one.
  POE::Component::Logger->spawn(
    ConfigFile => 'log.conf',
    Alias      => 'mq_logger'
  );

  POE::Component::MessageQueue->new({
    port     => 61613,            # Optional.
    address  => '127.0.0.1',      # Optional.
    hostname => 'localhost',      # Optional.
    domain   => AF_INET,          # Optional.
    
    logger_alias => 'mq_logger',  # Optional.

    # Required!!
    storage => POE::Component::MessageQueue::Storage::Default->new({
      data_dir     => $DATA_DIR,
      timeout      => 2,
      throttle_max => 2
    })
  });

  POE::Kernel->run();
  exit;

DESCRIPTION ^

This module implements a message queue [1] on top of POE that communicates via the STOMP protocol [2].

There exist a few good Open Source message queues, most notably ActiveMQ [3] which is written in Java. It provides more features and flexibility than this one (while still implementing the STOMP protocol), however, it was (at the time I last used it) very unstable. With every version there was a different mix of memory leaks, persistence problems, STOMP bugs, and file descriptor leaks. Due to its complexity I was unable to be very helpful in fixing any of these problems, so I wrote this module!

This component distinguishes itself in a number of ways:

Special STOMP headers

You can see the main STOMP documentation here: http://stomp.codehaus.org/Protocol

PoCo::MQ implements a number of non-standard STOMP headers:

persistent

Set to the string "true" to request that a message be persisted. Not setting this header or setting it to any other value, means that a message is non-persistent.

Many storage engines ignore the "persistent" header, either persisting all messages or no messages, so be sure to check the documentation for your storage engine.

Using the Complex or Default storage engines, persistent messages will always be sent to the back store and non-persistent messages will be discarded eventually.

expire-after

For non-persistent messages, you can set this header to the number of seconds this message must be kept before being discarded. This is ignored for persistent messages.

Many storage engines ignore the "expire-after" header, so be sure to check the documentation for your storage engine.

Using the Complex or Default storage engines, this header will be honored. If it isn't specified, non-persistent messages are discarded when pushed out of the front store.

Queues and Topics

In PoCo::MQ there are two types of destinations: queues and topics

queue

Each message is only delivered to a single subscriber (not counting messages that were delivered but not ACK'd). If there are multiple subscribers on a single queue, the messages will be divided amoung them, roughly equally.

topic

Each message is delivered to every subscriber. Topics don't support any kind of persistence, so to get a message, a subscriber must be connected at the time it was sent.

All destination names start with either "/queue/" or "/topic/" to distinguish between queues and topics.

Tips and Tricks

Logging! Use it.

PoCo::MQ uses POE::Component::Logger for logging which is based on Log::Dispatch. By default mq.pl looks for a log file at: "/etc/perl_mq/log.conf". Or you can specify an alternate location with the --log-conf command line argument.

Using the login/passcode to track clients in the log.

Currently the login and passcode aren't used by PoCo::MQ for auth, but they are written to the log file. In the log file clients are only identified by the client id. But if you put information identifying the client in the login/passcode you can connect that to a client id by finding it in the log.

STORAGE ^

When creating an instance of this component you must pass in a storage object so that the message queue knows how to store its messages. There are some storage backends provided with this distribution. See their individual documentation for usage information. Here is a quick break down:

CONSTRUCTOR PARAMETERS ^

storage => SCALAR

The only required parameter. Sets the object that the message queue should use for message storage. This must be an object that follows the interface of POE::Component::MessageQueue::Storage but doesn't necessarily need to be a child of that class.

alias => SCALAR

The session alias to use.

port => SCALAR

The optional port to listen on. If none is given, we use 61613 by default.

address => SCALAR

The option interface address to bind to. It defaults to INADDR_ANY or INADDR6_ANY when using IPv4 or IPv6, respectively.

hostname => SCALAR

The optional name of the interface to bind to. This will be converted to the IP and used as if you set address instead. If you set both hostname and address, address will override this value.

domain => SCALAR

Optionally specifies the domain within which communication will take place. Defaults to AF_INET.

logger_alias => SCALAR

Opitionally set the alias of the POE::Component::Logger object that you want the message queue to log to. If no value is given, log information is simply printed to STDERR.

observers => ARRAYREF

Optionally pass in a number of objects that will receive information about events inside of the message queue.

Currently, only one observer is provided with the PoCo::MQ distribution: POE::Component::MessageQueue::Statistics. Please see its documentation for more information.

REFERENCES ^

[1]

http://en.wikipedia.org/Message_Queue -- General information about message queues

[2]

http://stomp.codehaus.org/Protocol -- The informal "spec" for the STOMP protocol

[3]

http://www.activemq.org/ -- ActiveMQ is a popular Java-based message queue

UPGRADING FROM OLDER VERSIONS ^

If you used any of the following storage engines with PoCo::MQ 0.1.7 or older:

The database format has changed.

Note: When using POE::Component::MessageQueue::Storage::Default (meaning mq.pl) the database will be automatically updated in place, so you don't need to worry about this.

Included in the distribution, is a schema/ directory with a few SQL scripts for upgrading:

CONTACT ^

Please check out the Google Group at:

http://groups.google.com/group/pocomq

Or just send an e-mail to: pocomq@googlegroups.com

DEVELOPMENT ^

If you find any bugs, have feature requests, or wish to contribute, please contact us at our Google Group mentioned above. We'll do our best to help you out!

Development is coordinated via Bazaar (See http://bazaar-vcs.org). The main Bazaar branch can be found here:

http://code.hackyourlife.org/bzr/dsnopek/perl_mq

We prefer that contributions come in the form of a published Bazaar branch with the changes. This helps facilitate the back-and-forth in the review process to get any new code merged into the main branch.

FUTURE ^

The goal of this module is not to support every possible feature but rather to be small, simple, efficient and robust. For the most part expect incremental changes to address those areas.

There is one remaining big feature coming soon and that is the ability to run PoCo::MQ clustered accross multiple servers with some kind of fail-over.

Beyond that we have a TODO list (shown below) called "The Long Road To 1.0". This is a list of things we feel we need to have inorder to call the product complete. That includes management and monitoring tools for sysadmins as well as documentation for developers.

SEE ALSO ^

External modules:

POE, POE::Component::Server::Stomp, POE::Component::Client::Stomp, Net::Stomp, POE::Filter::Stomp, POE::Component::Logger, DBD::SQLite, POE::Component::Generic

Storage modules:

POE::Component::MessageQueue::Storage, POE::Component::MessageQueue::Storage::Memory, POE::Component::MessageQueue::Storage::BigMemory, POE::Component::MessageQueue::Storage::DBI, POE::Component::MessageQueue::Storage::FileSystem, POE::Component::MessageQueue::Storage::Generic, POE::Component::MessageQueue::Storage::Generic::DBI, POE::Component::MessageQueue::Storage::Double, POE::Component::MessageQueue::Storage::Throttled, POE::Component::MessageQueue::Storage::Complex, POE::Component::MessageQueue::Storage::Default

Statistics modules:

POE::Component::MessageQueue::Statistics, POE::Component::MessageQueue::Statistics::Publish, POE::Component::MessageQueue::Statistics::Publish::YAML

ID generatior modules:

POE::Component::MessageQueue::IDGenerator, POE::Component::MessageQueue::IDGenerator::SimpleInt, POE::Component::MessageQueue::IDGenerator::UUID

BUGS ^

We are serious about squashing bugs! Currently, there are no known bugs, but some probably do exist. If you find any, please let us know at the Google group.

That said, we are using this in production in a commercial application for thousands of large messages daily and we experience very few issues.

AUTHORS ^

Copyright 2007, 2008 David Snopek (http://www.hackyourlife.org)

Copyright 2007, 2008 Paul Driver <frodwith@gmail.com>

Copyright 2007 Daisuke Maki <daisuke@endeworks.jp>

LICENSE ^

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.

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