Midnight Oil

I recently downloaded and installed acts_as_solr, and I must say that I am quite impressed. I was dreading trying to include any sort of search service, but acts_as_solr made it a snap. As always with Rails plugins, there were a few snafus along the way, but I’ll try to help people get over them.

Note: This writeup deals with acts_as_solr 0.7, so be wary if you’re using a different version.

Config/Setup

Get the plugin

As always, the first step is to get the plugin. You can use the built in plugin installation scripts like so:

script/plugin install svn://svn.railsfreaks.com/projects/acts_as_solr/trunk

However, I will urge you to use a vendor drop instead. This plugin is unstable enough that you will probably want to edit the source, and a vendor drop will allow you to do it a little easier. Instructions for performing a vendor drop in Rails can be found in one of my earlier posts.

If you do a vendor drop, it will skip one small installation step, so you’ll have to manually copy the lib/solr.yml file in the acts_as_solr plugin into your main config directory. No big deal.

Get Solr

Solr is a Java app that is deployed inside a servlet container, for example, Tomcat. If you’re like me, that fact brings an unhappy frown to your face. One of the main reasons I switched to Rails was because I was tired of editing arcane servlet config files. Still, over the years, there have been a lot of great projects written as servlets, so sometimes we just have to grin and bear it.

Anyways, to get started fastest, just grab the latest Solr distribution from the Solr homepage. This will come with an embedded Jetty servlet container which will get you going super fast.

After you unzip the Solr distribution somewhere, you’ll need to copy the schema.xml file into the right place:

cp myrailsproject/vendor/plugins/acts_as_solr/schema.xml apache_solr_directory/example/solr/conf/

At this point, you’re ready to rock.

cd apache_solr_directory/example
java -jar start.jar


Test it out

The basic installation given in the acts_as_solr documentation have you using Jetty on port 8983. So, to test it out, point your browser to http://localhost:8983/solr/admin If that brings up the Solr admin interface, you’re 99% home. If not, it’s time to start debugging your servlet container. Good luck

Using it in a model

There’s really no point to me explaining this part, as there is an excellent tutorial movie on the acts_as_solr homepage. Just look for Up and running in less than 5 minutes.

Still, there’s one special point I want to make at this stage. After everything is set up and you have Solr running, you might find that you cannot use it to find any of your model objects. This is because, by default, acts_as_solr only indexes your objects on save. This makes good sense, but it also means that all objects currently in your database will have to be loaded and re-saved in order to show up in the index. There is probably an easier way to do it, but as of right now, I don’t know what it is.

Update: In the comments section, Jason posted a great way to get all your model objects into Solr quickly using rebuild_solr_index. Assuming your model is called Book, you can index all the Book objects in your database with the following call:

Book.rebuild_solr_index

Note, however, that with the current behavior, acts_as_solr calls a commit after indexing each object, which can be a costly operation, according to the Solr docs. I will see if I can find a way to modify rebuild_solr_index to only call commit after all objects are committed, or perhaps at user-specified intervals along the way.

To verify that objects are being indexed, watch the output from Jetty in the terminal window where you started it from. As soon as an object is indexed, Jetty should scroll some output about it. At that point, use the find_by_solr command to see if it was successfully placed in the index.

Single Table Inheritance

Because of the way that acts_as_solr names the indices, version 0.7 is incompatible with single table inheritance (STI), and therefore does not work with model object heirarchies. However, it’s a very small bug, and I am guessing that it was simply an oversight on the part of the author. I looked into it and was able to create a fix in about 10 minutes.

Attached is my acts_as_solr STI patch to enable indexing of STI models. (see update)

Update: This patch has been merged into the trunk as part of acts_as_solr 0.8. So, if you’re using 0.8 or higher, the patch is unnecessary.

Development vs Production environment - Howto

WARNING! Do not have your development and production environments pointing to the same Solr installation. They will step all over each other, and find_by_solr will return incorrect results. It is roughly equivalent to using the same database for production and development. So, a general rule of thumb is that each separate database needs its own Solr index.

The easiest way to do this is to set up multiple servet containers on different ports. You can have Jetty for production on 8983 and Jetty for development on 8984, for example. To enable this, you will want two separate copies of the Solr distribution. To change the port Jetty is listening on, edit the jetty.xml file at apache_solr_directory/example/etc/jetty.xml. Look for the line that says:

<Set name="Port"><SystemProperty name="jetty.port" default="8983"/></Set>

Even though it’s easy, just adding more servlet containers is usually not the best solution, due to memory and sysadmin overhead. Instead, it’s probably a better idea to deploy multiple Solr servlets to the same container. Heck, it may even be possible to have a single Solr instance handle multiple distinct indices.

Update: I have found a way to deploy multiple Solr instances inside a single Tomcat container. The details are available in another blog post.

An example in the wild

I have acts_as_solr up and running on my site, Obsidian Portal. For a good example of it in action, Take a look at the characters list page and search for ‘Nent’. If you look at the individual characters, you’ll see that each of them has ‘Nent’ in their content somewhere. This is the sort of functionality that acts_as_solr gives out of the box.

Gotchas

Coming soon…
Until then: did you forget to copy schema.xml into the Solr conf directory?