Zend_Search_Lucene index file formats are binary compatible with Java Lucene version 1.4 and greater. A detailed description of this format is available here: The currently supported Lucene index file format version is 2.3 (starting from ZF 1.6).. After index creation, the index directory will contain several files: The segments file is a list of index segments. The *.cfs files contain index segments. Note! An optimized index always has only one segment. The deletable file is a list of files that are no longer used by the index, but which could not be deleted. The Java program listing below provides an example of how to index a file using Java Lucene: