What is Cassandra?

1. It has no single point of failure, and
2. Adding nodes to the cluster is as simple as pointing it to any one live node

Cassandra also has built-in multi-master writes, replication, rack awareness, and can handle downed nodes gracefully. Cassandra has a thriving community and is currently being used at companies like Facebook, Digg and Twitter to name a few.

Enter Lucandra

Lucandra is a Cassandra backend for Lucene. Since Cassandra’s original use within Facebook was for search, integrating Lucene with Cassandra seemed like a “no brainer”. Lucene’s core design makes it fairly simple to strip away and plug in custom Analyzer, Writer, Reader, etc. implementations. Rather than trying to build a Lucene Directory interface on top of Lucene as some backends do (DbDirectory for example), our approach was to implement a an IndexReader and IndexWriter directly on top of Cassandra.

      Term Key                    ColumnName   Value
      "indexName/field/term" => { documentId , positionVector }

      Document Key
      "indexName/documentId" => { fieldName , value }

Lucandra in Action

Using Lucandra is extremely simple and switching a regular Lucene search application to use Lucandra is a matter of just several lines of code. Let’s have a look.

First we need to create the connection to Cassandra


import lucandra.CassandraUtils;
import lucandra.IndexReader;
import lucandra.IndexWriter;
...
Cassandra.Client client = CassandraUtils.createConnection();

Next, we create Lucandra’s IndexWriter and IndexReader, and Lucene’s own IndexSearcher.


IndexWriter indexWriter = new IndexWriter("bookmarks", client);
IndexReader indexReader = new IndexReader("bookmarks", client);
IndexSearcher indexSearcher = new IndexSearcher(indexReader);


From here on, you work with IndexWriter and IndexSearcher just like you in vanilla Lucene. Look at the BookmarksDemo for the complete class.

What’s next? Solandra!