CountedCache

The counted_cache gem. A cache for use in cases where data is mostly only read and where the cost of rebuilding that data is high, and yet, the size of the data is too large to keep all of it in RAM all of the time.

Add this line to your application's Gemfile:

gem 'counted_cache'

And then execute:

$ bundle

Or install it yourself as:

$ gem install counted_cache

Creating a counted cache is as simple as:

cache_on_hand = CountedCache.new(10) {|key| retrieve_data_for(key) }

Where:

• The argument is the optional cache depth, which is the number of data items kept in the cache.
• The required block is used to fetch the data associated with the key when that data is needed, but not currently in the cache.

So how do we use a counted cache to get at our data? That is really simple:

data = cache_on_hand[key]

That's it! And that is the complete essentials guide. There are a very few extras to determine how well the cache is working. The hits and misses properties record how many times the data was found in the cache (a hit) and how many times it had to be retrieved (a miss).

At some point, data items will need to be removed from the cache to make room for newer data requests.

Normally when this happens, the old data can go away and no further action needs to be taken. In some cases however, modified data will need to be written out to save any changes that may have been made to that data. This is done by giving the cache a block that does the work of saving the data into wherever is identified by the key.

cache_on_hand.set_save_block do |key, data|
  # Code to save data at key goes here.
end

Consider the case of an application that uses embedded ruby (erb) files. This could look like:

erb_cache = CountedCache.new {|name| ERB.new(IO.read(name))}

# Other code omitted.

view_text = erb_cache["home_page/my_file.html.erb"].result(a_binding)

The benchmark in the demo folder examines just such a scenario.

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

OR...

• Make a suggestion by raising an issue . All ideas and comments are welcome.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the counted_cache project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.