Sometimes it’s more than just ‘search’. We may want it ‘faster’, and many times we want it ‘smaller’.
(And for the case of database/index size, smaller one is probably the faster one — less things to looking for.)
Managing Gigabytes: Compressing and Indexing Documents and Images by Ian H. Witten, Alistair Moffat, and Timothy C. Bell. (read reviews)
From the authors of the book, MG, an open-source indexing and retrieval system for text, images, and textual images.