[Dovecot] Design: Asynchronous I/O for single/multi-dbox

Timo Sirainen tss at iki.fi
Sun Mar 14 04:48:10 EET 2010

On 14.3.2010, at 4.40, Frank Cusack wrote:

> Just playing devil's advocate since you haven't presented the advantage
> of async I/O.  I don't want to guess at the reasoning, but e.g. I hope
> you're not planning to return success results before I/O actually
> completes.

The idea was that a single process could handle tons of connections. Maybe in the end the number of IMAP processes you'd have would be about 1-2 x the number of CPU cores.

And not just that. Also parallelism. Dovecot could issue a lot of I/O requests in parallel and OS can reorder those so that it gives the best performance by reading them from disk in the right order. And the higher the latency to disks is, the higher benefits there comes from parallelism (NFS, NoSQL).

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