[Dovecot] keeping indexes in tmpfs

[Justin McAleer]

While doing some testing with converting accounts while simulating 
incoming mail load (no other pop/imap processes going but 4 processes 
converting users), we found that we were maxing out the local disk in 
the server with the index activity. To find out that it was the index 
activity, I mounted a tmpfs for dovecot to keep indexes on, and the 
system load dropped from 70 to 3 :)

Anyway, Timo and others, do you have any thoughts about keeping indexes 
on a tmpfs partition? I realize the obvious issues with this: running 
out of space, and the fact that the partition is lost on reboot. 
However, we plan to run a cluster of these servers anyway, where we will 
keep domains/accounts going to a particular server but fail over to one 
of the others in case of an outage. Recreating the indexes seems pretty 
trivial when writing to tmpfs anyway, plus we could copy the indexes to 
disk (restore after reboot) in the case of planned outages... unplanned 
outages result in another server rebuilding them all anyway.


So, I'm looking for non-obvious issues we may have with this approach. I 
need to do more testing to see how much memory we would actually need to 
feasibly keep the indexes there, but otherwise is there a good reason 
not to do this?