Sitecore has a flexible search framework that allows the development of plugins to integrate any search engine, and have them behave the same way
Sitecore’s default search engine is Lucene, but you can also download a plugin for Solr, which is a better solution for large installations.
The FXM component was shipped with some missing settings in the SOLR configuration file. A corrected file is located at https://kb.sitecore.net/articles/227897.
Note: For SOLR version 4.9 or higher, schema.xml requires modification to make it compatible with Sitecore. For more information, go to https://kb.sitecore.net/articles/227897.
The Sitecore documentation for setting up Solr is located at: http://sdn.sitecore.net/Reference/Sitecore%207/Sitecore%20Search%20and%20CMS%20Scaling%20Guide.aspx
The binary files required to set up Solr are located at: https://dev.sitecore.net/Downloads/Sitecore_Experience_Platform/8_0.aspx