You’ll need Thinking Sphinx 1.3.0 or later.

gem install ts-datetime-delta --source http://gemcutter.org

In your environment.rb file, with the rest of your gem dependencies:

config.gem 'ts-datetime-delta',
  :lib     => 'thinking_sphinx/deltas/datetime_delta'
  :version => '>= 1.0.0',
  :source  => 'http://gemcutter.org'

And add the following line to the bottom of your Rakefile:

require 'thinking_sphinx/deltas/datetime_delta/tasks'

For the indexes you want to use this delta approach, make sure you set that up in their define_index blocks.

define_index do
  # ...

  set_property :delta => :datetime
end

If you want to use a column other than updated_at, you can specify it using the :delta_column option. The same goes for the threshold, which defaults to one day.

set_property :delta => :datetime,
  :threshold    => 1.hour,
  :delta_column => :changed_at

Then, while your Rails application is running, you’ll need to run the delta indexing rake task regularly – as often as your threshold, allowing for some time for the indexing to actually happen.

For example, if you’re going to run the delta indexing task every hour, I would recommend setting your threshold to 70 minutes.

To ensure this rake task is called regularly, it’s best to set it up as a recurring task via cron or similar tools.

rake thinking_sphinx:index:delta

The shorthand version is:

rake ts:in:delta

• W. Andrew Loe III – Environment variable for disabling merging.

Copyright © 2009 Pat Allan, and released under an MIT Licence.