search in all fields

[David]

Hi all:
    I study Lucene and I want build search on all the fields, I find
MultiFieldQueryParser can search on multiple fields, but we must specify
fields. maybe we can add a field named all_field that contain all the fields
when indexing, but it make the index file larger.
   so how to make search on all fields without specify any fields ?
Appreciate your help!
--
David