updateDocuments
Atomically deletes documents matching the provided delTerm and adds a block of documents with sequentially assigned document IDs, such that an external reader will see all or none of the documents.
See .addDocuments.
Return
The #sequence_number for this operation
Throws
if the index is corrupt
IOException
if there is a low-level IO error
Similar to .updateDocuments, but take a query instead of a term to identify the documents to be updated