Lucene vs Solr

1) Solr uses Lucene under the hood. Lucene has no clue about the Solr API.

2) Lucene is a powerful search engine framework that lets us add search capability to our application. It exposes an easy-to-use API while hiding all the search-related complex operations. Any application can use this library, not just Solr.

3) Solr is built around Lucene. It is not just an http-wrapper around Lucene but has been known to add more arsenal to Lucene. Solr is ready-to-use out of box. It is a web application that offers related infrastructure and a lot more features in addition to what Lucene offers.

4) Lucene doesn't just create the Index for the consumption by Solr. Lucene handles all the search related operations. Any application can use the Lucene framework.

When to use Lucene?

• You are a search engineer AND
• You are a programmer AND
• You want full control over almost all the internals of Lucene AND
• Your requirements demand you to do all sorts of geeky customization to Lucene AND
• You are willing to take care of infrastructure elements of your search like scaling, distribution, etc.

When to use Solr?

• At least one of the above didn't make sense. OR
• You want something that is ready to use out-of-the-box (even without knowledge of Java) OR Your infrastructure requirements outweigh search customization requirements.