My initial tests for CLucene were that it would take 30% of mailbox size (compared to 50% for Xapian). But this was before I actually implemented it to Dovecot.. I haven't really looked at how large the indexes actually are.
Did you ever make an fts_xapian plugin, Timo? I've looked into Xapian as an alternative to the solr codebase, mainly out of a dislike of java and its downstream technologies.
=R=
