Just documenting what all we could use if we decide to move away from Xapian.
Full Text Indexing Solutions
The project seems kind of dead.
Another option is to build our own full text indexing solution. We don't want to do all the hard work of the lower level file access, concurrency, paging, etc. It makes more sense to build it on top of some existing btree solution.
Offers both persistent hash tables and btrees.