It should be clear that
Zend_Search_Lucene as well as any other
Lucene implementation does not comprise a "database".
Indexes should not be used for data storage. They do not provide partial backup/restore functionality, journaling, logging, transactions and many other features associated with database management systems.
Zend_Search_Lucene attempts to keep indexes in a
consistent state at all times.
Index backup and restoration should be performed by copying the contents of the index folder.
If index corruption occurs for any reason, the corrupted index should be restored or completely rebuilt.
So it's a good idea to backup large indexes and store changelogs to perform manual restoration and roll-forward operations if necessary. This practice dramatically reduces index restoration time.