db upgrades in 2.4.x?

[Zachariah Mully]

Howdy all-
	We're prepping for updating from 2.2.13->2.4.12 and I'm attempting to 
figure out some of the database differences between the two to make sure 
things go smoothly.
	We've already uncovered several issues in our testing that I've not 
been able solve searching through the list archives:
1) Seen state updates
2) the purpose of /var/lib/cyrus/db

	First, if I understand correctly, seen flags are now incorporated into 
the cyrus.index file in 2.4.x. What I can't figure out is if there is 
any way to manually trigger the reindexing of a single mailbox 
cyrus.index file. A reconstruct doesn't appear to do it (just using the 
-r flag).
	When we do the cutover over, we've a tight deadline, and what I'd like 
to do is reindex only the hot mailboxes, and then queue the remaining 
ones for later. I don't think my users will tolerate loosing all their 
Seen states, so I want to make sure we're preserving it while reducing 
the re-indexing impact so that the server is still responsive.
	Is it possible to trigger a reindex manually of a single mailbox? How 
are others dealing with this?

	Second, I don't understand the purpose of the /var/lib/cyrus/db in 
2.4.12, it complained when the directory wasn't there, and I'm sure what 
it's storing now that it is. Everything on our 2.4.12 install is either 
skiplist or flat (sub), so what is that /db for?

Thanks,
Z