Solr is a open source standalone enterprise search server. It comes with great features like full-text search, auto suggest, faceted search, database integration and many more. To know more you can visit http://lucene.apache.org/solr/.
Solr extension is a light-weight, very fast and feature-rich library which allows to communicate with the Apache Solr Server in PHP. To know more solr-php methods visit http://php.net/manual/en/book.solr.php
We have been using Apache Solr in one of our service project. The project is a website which is basically collection of artefacts, posters and other memorabilia from across the globe, importantly India. It currently has about 75,000 objects in our database. In addition, there are roughly 100,000 items in ‘masterlists’. Within the masterlists we have the list of people, films etc, which are the related data for the objects.