Hello,
On Wed, 29 Aug 2007 18:10:00 -0700 Tom Bombadil grlists@gmail.com wrote:
of indexing during delivery are negligible for us in general and potentially negative in some scenarios (mass mail to many/all users).
Is this negative hypothetical or have you actually seen load spikes in situations like this?
I actually did see that. In the case of exim, for each piece of mail going to the mailbox, one exim process is spawned, and this exim delivery process spawns the dovecot's LDA. The load pretty much doubles.
There is that little detail of the additional processes spawned, but the overhead for that alone is not so much of an issue here (linux, plenty of CPU and memory to spare). But when you have 80000 emails rushing towards your mailstorage (and yes, of course we have sensible limits on number of process, maximum load before defer, etc) your I/O will be a bottleneck and adding the additional strain of indexing on top of that is not a good idea. It is only at times of mass mails like that I see our mailstorge boxes break into a light sweat and avoiding any additional load then is just the sensible thing to do. The indexing for these mails will be spread out over hours to days (frequency of access by the clients) instead of being lumped on top of the existing peak and I/O saturation.
It all boils down to your hardware and usage patterns. Our systems are plenty fast and any delay by having to (re)build the indexes is hardly noticeable. But if you have a system with less reserves, users that access mail very infrequently but get plenty of mail (so indexing at access time will be an involved process) and no mass mail spikes, dovecot LDA starts to look a lot more promising. ^_^
Regards,
Christian
Christian Balzer Network/Systems Engineer NOC chibi@gol.com Global OnLine Japan/Fusion Network Services http://www.gol.com/