So I finally got the new mail caching code fully working in normal conditions. Index rebuilding and some error correction still needs a bit work. mbox is also still broken. Anyway, I was mostly interested how fast Dovecot now works with my 367000 LKML mails, but thought I'd have to get something to compare the results against, so here's Dovecot vs. Courier.
Results against older Dovecot would have been pretty boring, the older Dovecot could never perform threading without opening all the files and reading References-headers from them. Sorting would could have been done from cache if IMAP ENVELOPEs were cached, I'd estimate maybe 2-3x larger user CPU usage with it and a _lot_ larger cache file since it would have stored from, to, etc. fields in it.
Results against Cyrus would be interesting. I'll probably do those sometimes later too.. Last I checked, Cyrus was very slow at inserting the mails into it's database, it took .. was it 1-3 hours to insert all those mails, while a simple copying took maybe 20 mins. Anyway, Cyrus's caching is pretty dummy as well so I'd expect Dovecot to be many times faster in threading and likely somewhat faster in sorting.