Full-text index content truncate syntax is identical to the table’s truncation command. 

Syntax:  

TRUNCATE TABLE fulltext_index_name

The Lucene full-text index will be re-created and all indexed data lost. From this point, the current DB table’s content will not be found in a full-text search. However, new changes will appear in full-text index. The full-text truncation technique could be applied for performance gain to minimize the size of the index. For example, we truncate old data, which stays in the DB table as so-called archived objects, but is not indexed. Only new/fresh changes are indexed.