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30 May 2011

Searching with Sphinx on Heroku

Just over two weeks ago, I released Flying Sphinx – which provides Sphinx search capability for Heroku apps. I’ll talk more about how I built it and the challenges faced at some point, but right now I just want to introduce the service and how you may go about using it.

Why Sphinx?

Perhaps you’re not familiar with Sphinx and how it can be useful. For those who are new to Sphinx, it’s a full-text search tool – think of your own personal Google for within your website. It comes with two main moving parts – the indexer tool for interpreting and storing your search data (indices), and the searchd tool, which runs as a daemon accepting search requests, and returns the most appropriate matches for a given search query.

In most situations, Sphinx is very fast at indexing your data, and connects directly to MySQL and PostgreSQL databases – so it’s quite a good fit for a lot of Rails applications.

Using Sphinx in Rails

I’ve written a gem, Thinking Sphinx, which integrates Sphinx neatly with ActiveRecord. It allows you to define indices in your models, and then use rake tasks to handle the processing of these indices, along with managing the searchd daemon.

If you want to install Sphinx, have a read through of this guide from the Thinking Sphinx documentation – in most cases it should be reasonably painless.

Installing Thinking Sphinx in a Rails 3 application is quite simple – just add the gem to your Gemfile:

gem 'thinking-sphinx', '2.0.5'

For older versions of Rails, the Thinking Sphinx docs have more details.

I’m not going to get too caught up in the details of how to structure indices – this is also covered within the Thinking Sphinx documentation – but here’s a quick example, for user account:

class User < ActiveRecord::Base
  # ...
  
  define_index do
    indexes name, :sortable => true
    indexes location
    
    has admin, created_at
  end
  
  # ...
end

The indexes method defines fields – which are the textual data that people can search for. In this case, we’ve got the user names and locations covered. The has method is for attributes – which are used for filtering and sorting (fields can’t be used for sorting by default). The distinction of fields and attributes is quite important – make sure you understand the difference.

Now that we have our index defined, we can have Sphinx grab the required data from our database, which is done via a rake task:

rake ts:index

What Sphinx does here is grab all the required data from the database, inteprets it and stores it in a custom format. This allows Sphinx to be smarter about ranking search results and matching words within your fields.

Once that’s done, we next start up the Sphinx daemon:

rake ts:start

And now we can search! Either in script/console or in an appropriate action, just use the search method on your model:

User.search 'pat'

This returns the first page of users that match your search query. Sphinx always paginates results – though you can set the page size to be quite large if you wish – and Thinking Sphinx search results can be used by both WillPaginate and Kaminari pagination view helpers.

Instead of sorting by the most relevant matches, here’s examples where we sort by name and created_at:

User.search 'pat', :order => :name
User.search 'pat', :order => :created_at

And if we only want admin users returned in our search, we can filter on the admin attribute:

User.search 'pat', :with => {:admin => true}

There’s many more options for search calls – the documentation (yet again) covers most of them quite well.

One more thing to remember – if you change your index structures, or add/remove index defintions, then you should restart and reindex Sphinx. This can be done in a single rake task:

rake ts:rebuild

If you just want the latest data to be processed into your indices, there’s no need to restart Sphinx – a normal ts:index call is fine.

Using Thinking Sphinx with Heroku

Now that we’ve got a basic search setup working quite nicely, let’s get it sorted out on Heroku as well. Firstly, let’s add the flying-sphinx gem to our Gemfile (below our thinking-sphinx reference):

gem 'flying-sphinx', '0.5.0'

Get that change (along with your indexed model setup) deployed to Heroku, then inform Heroku you’d like to use the Flying Sphinx add-on (the entry level plan costs $12 USD per month):

heroku addons:add flying_sphinx:wooden

And finally, let’s get our data on the site indexed and the daemon running:

heroku rake fs:index
heroku rake fs:start

Note the fs prefix instead of the ts prefix in those rake calls – the normal Thinking Sphinx tasks are only useful on your local machine (or on servers that aren’t Heroku).

When you run those rake tasks, you will probably see the following output:

Sphinx cannot be found on your system. You may need to configure the
following settings in your config/sphinx.yml file:
  * bin_path
  * searchd_binary_name
  * indexer_binary_name

For more information, read the documentation:
http://freelancing-god.github.com/ts/en/advanced_config.html

This is because Thinking Sphinx doesn’t have access to Sphinx locally, and isn’t sure which version of Sphinx is available. To have these warnings silenced, you should add a config/sphinx.yml file to your project, with the version set for the production environment:

production:
  version: 1.10-beta

Push that change up to Heroku, and you won’t see the warnings again.

For the more curious of you: the Sphinx daemon is located on a Flying Sphinx server, also located within the Amazon cloud (just like Heroku) to keep things fast and cheap. This is all managed by the flying-sphinx gem, though – you don’t need to worry about IP addresses or port numbers.

Also: the same rules apply with Flying Sphinx for modifying index structures or adding/removing index definitions – make sure you restart Sphinx so it’s aware of the changes:

heroku rake fs:rebuild

The final thing to note is that you’ll want the data in your Sphinx indices updated regularly – perhaps every day or every hour. This is best done on Heroku via their Cron add-on – since that’s just a rake task as well.

If you don’t have a cron task already, the following (perhaps in lib/tasks/cron.rake) will do the job:

desc 'Have cron index the Sphinx search indices'
task :cron => 'fs:index'

Otherwise, maybe something more like the following suits:

desc 'Have cron index the Sphinx search indices'
task :cron => 'fs:index' do
  # Other things to do when Cron comes calling
end

If you’d like your search data to have your latest changes, then I recommend you read up on delta indexing – both for Thinking Sphinx and for Flying Sphinx.

Further Sources

Keep in mind this is just an introduction – the documentation for Thinking Sphinx is pretty good, and Flying Sphinx is improving regularly. There’s also the Thinking Sphinx google group and the Flying Sphinx support site if you have questions about either, along with numerous blog posts (though the older they are, the more likely they’ll be out of date). And finally – I’m always happy to answer questions about this, so don’t hesitate to get in touch.

Comments

5 responses to this article

30 May 2011
iGEL said:

Does thinking sphinx work well with utf8 encoded asian (Chinese, Korean) text?

30 May 2011
pat said:

I know people have got Sphinx working decently with Chinese and Japanese characters – though I’m not sure of the best place to start with that. I think there is a fork of Sphinx with improved Chinese charset dictionary support… though maybe this has been made better in recent releases of Sphinx as well?

If there’s something in that fork that could be used in my build of Sphinx for Flying Sphinx that improves Chinese/Korean/etc support, I’d definitely be open to merging it in.

08 Jul 2011
DmitriG said:

Size “of indexed data” is a bit confusing. Is it the size on index, or total size of a database? What if I only have a handful of fields to index while my DB contains a lot of other columns?

08 Jul 2011
pat said:

Hi Dmitri

I’m referring to the size of all Sphinx indices – so in a default setup, whatever’s in db/sphinx/RAILS_ENV. In other words: all the data for the fields and attributes you’ve defined.

29 May 2014
Luka said:

Hi, great post! Thank you… One question though… If I run the re-indexing every hour and running a service such as ebay what happens to newly added things within that hour? What I want to say is there a possibility of fallback to query the DB directly? Also, would you say that re-indexing is costly in terms of performance (every 20min)?
Again, great tool!!!

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