Redis and key tracking

Redis is a bit different than a lot of other "data stores". This also means that thinking about ownership management is a little bit different in redis.

Typically one domain "concept" will have different relationships with multiple keys.

Take Resque for example. A individual worker in Resque interacts with the following keys:

• The worker id is a member of resque:workers
• It creates resque:worker:<id> and resque:worker:<id>:started

When the worker shuts down it must remove its id from resque:workers and delete the other two keys.

With breadcrumbs you could describe those relationships thusly:

class WorkerBreadcrumb < Redis::Breadcrumb
  owns 'resque:worker:<id>'
  owns 'resque:worker:<id>:started'

  member_of_set '<id>' => 'resque:workers'
end

Installation

Either

gem install redis-breadcrumbs

or add the following to your Gemfile

gem "redis-breadcrumbs", "~> 0.0.3"

Usage

Create your breadcrumb; we'll continue with the Resque example:

class WorkerBreadcrumb < Redis::Breadcrumb
  owns 'resque:worker:<id>'
  owns 'resque:worker:<id>:started'

  member_of_set '<id>' => 'resque:workers'
end

Keys that have <...> snippets in them are templates. When you call track! or clean!, the Breadcrumb will expect an object that responds to symbols in between the brackets.

You can also specify a key to track keys in with tracked_in 'resque:worker:<id>:tracking'

Using tracked_in will let your breadcrumb remember how to clean up keys that are not currently defined in the class (because of code changes, etc).

Breadcrumb also needs to be told about a redis connection:

# Breadcrumb always operates on the 'raw' client,
# so it will 'unwrap' Redis::Namespace

Redis::Breadcrumb.redis = Resque.redis

When you're ready to start tracking keys (say after the worker finished booting) you can do:

WorkerBreadcrumb.track!(self)

And when you're ready to clean up keys (say when working is shutting down, or in a clean up rake task)

WorkerBreadcrumb.clean!(self)

Contributing

1. Fork it.
2. Create a branch (git checkout -b my_awesome_branch)
3. Commit your changes (git commit -am "Added some magic")
4. Push to the branch (git push origin my_awesome_branch)
5. Send pull request