Cory G Watson > Osgood-Server > Osgood::Server

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NAME ^

Osgood::Server - Event Repository

SYNOPSIS ^

    create a database (mysql in our example)
    mysql -u root your_database < sql/schema.sql
    edit osgood_server.yml
    script/osgood_server_server.pl

DESCRIPTION ^

Osgood is a passive, persistent, stateless event repository.

* Passive: Osgood doesn't seek out events, it only waits for notification of them.

* Persistent: Events are durable, they do not disappear if the server goes offline.

* Stateless: Events in Osgood are read-only. You cannot change them.

What's all that fancy talk mean? Osgood is a system wherein you record the fact that something happened. A client library (Osgood::Client that allows you to send events to Osgood and to later retrieve them.

Effectively we are talking about an implementation of the Publisher / Subscriber model. This implementation is built using HTTP as the medium and a relational database as the backing store.

An example may help to illustrate the usefulness.

Imagine a company that sells widgets. Sometimes, customers are unhappy and cancel the widgets. When a customer calls to do so, the call center dutifully cancels the order. This works fine and the world is a happy place.

One day a new marketing employee decides to try and woo these customers back. She asks you to build a system to send an email to a customer that cancels, promising a $5 coupon to come back for more widgets! This is a great idea, and it is a great chance to use Osgood.

When the cancellation happens, you add a smidge of code that uses Osgood::Client to send an event. You might use descriptions like:

  my $event = Osgood::Event->new(
      object    => 'Order',
      action    => 'canceled',
      params    => {
          id    => 12345
      }
  );
  my $list = Osgood::EventList->new(events => [ $event ]);
  $client->send($list);

Meaning that Order #12345 was canceled.

Later, you whip up a job that runs every hour that queries Osgood for all the orders that have been canceled.

  $client->query({
      object    => 'Order',
      action    => 'canceled',
  });

Now you have a list! But every call returns ALL the Order canceled events that happened, ever! The query method provides a bunch of constraints to fix that. The most useful of which is 'id'. Providing query with an id limits the returned events to all the events that have an ID GREATER THAN THE ONE PROVIDED.

There are other constraints provided in Osgood::Server::Controller::Event such as date_before and date_after.

The advantage of this implementation is that you can create subscribers to an event without adding any new code to your cancellation process. State is maintained by the jobs that do the querying, however you choose to implement it. We use ids, you might use dates.

IMPORTANT:

PERFORMANCE ^

Note: See the accompanying section of Osgood::Client as well.

Osgood uses some DBIx::Class shortcuts to pull results faster. Depending on database hardware, small numbers of events (hundreds) should be really fast. Tests have been conducted on lists of 10_000 events and the response time still falls within ::Client's default 30 second timeout on modern hardware.

SEE ALSO ^

Osgood::Server::Controller::Root, Catalyst, Osgood::Client

AUTHORS ^

Lauren O'Meara

Cory 'G' Watson <gphat@cpan.org>

CONTRIBUTORS ^

Guillermo Roditi (groditi) Mike Eldridge (diz)

COPYRIGHT AND LICENSE ^

Copyright 2008 by Magazines.com, LLC

You can redistribute and/or modify this code under the same terms as Perl itself.

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