[Dovecot] index IO patterns

[Cor Bosman]

> Mail is always a random IO workload, unless your mailbox count is 1,
> whether accessing indexes or mail files.  Regarding the other two
> questions, you'll likely need to take your own measurements.

Wait, maybe there is a misunderstanding. I mean the IO inside one
index file, not across the different mailboxes. So within 1 index
file that covers a mailbox with say 10.000 emails, how does the IO
occur. I would guess pretty random as well, but on the other hand
i guess in some ways it could be pretty linear too. If dovecot keeps
most changes in memory and writes it all back in 1 go. 

Cor