[Dovecot] When are search indexes updated?

[David Abrahams]

I noticed that occasionally searching in my huge archive mailbox can be
really slow, so I tried doveadm index on it and it seemed to do a lot of
work, which seemed strange given, for example, that dovecot-lda says it
keeps Dovecot index files up-to-date.  Then I thought, "maybe these are
different files than the search indices."  If so, that's not entirely
clear from the docs and Wiki.  So, questions:

* When are search indexes updated?
* Are they updated incrementally?
* If not, why not?
* If so, why would a mailbox's index drift out-of-date, as mine had?

BTW, I'm using the clucene search backend.

-- 
Dave Abrahams
BoostPro Computing                  Software Development        Training
http://www.boostpro.com             Clang/LLVM/EDG Compilers  C++  Boost