[Dovecot] index IO patterns

[Stan Hoeppner]

On 5/12/2012 2:32 AM, Cor Bosman wrote:
>> 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. 

I don't see how this is relevant to designing an index storage system.
Whether index file updates are sequential or random, they become random
at the 2nd user and more so from there.  So either way, your storage
system will see a random IO pattern, and that's what you need to
engineer the system for, not the single user index file update pattern.
 You've already expressed interest in SSD, which takes care of this concern.

-- 
Stan