The need to resolve the problems of enterprise search has triggered interest in many IT companies to come up with an enterprise search solution. This includes companies such as Oracle, Microsoft, and Google who sell their solutions to customers. Doug Cutting created the open source information retrieval library called Apache Lucene during 1997. It became part of sourceforge.net (one of the sites hosting open source projects and their development). Lucene was capable of providing powerful full text search, and indexing capabilities on Java. Later in 2001, the Lucene project became a member of the Apache software foundation. The open source community contributed significantly to the development of Apache Lucene, which has led to exponential growth until this point in time. Apache Lucene is widely used in many organizations for information retrieval and search.

Since Apache Solr uses Apache Lucene for indexing and searching, Solr and Lucene index are the same. That means Apache Solr can access indexes generated using Lucene; although, we may just need to modify the Solr schema file to accommodate all the attributes of the Lucene index. Additionally, if Apache Solr is using a different Lucene library, we need to change <luceneMatchVersion> in solrconfig.xml. This is particularly useful when the client would like to upgrade his custom Lucene search engine to Solr without losing data.