Re: Er.... for Sendmail users......enough

On Tue, 12 Sep 2006, Christopher E. Brown wrote:

> I have only seen the "twice native maildir" performance on an otherwise
> unloaded system. Once the systems were going IO or CPU bound (my
> benchmarks were run with 25, 50 and 100 IMAP clients hitting the systems,
> listing messages, moving blocks of messages from folder to folder, etc)
> the faster lookups remained, but message access itself was the delay. On
> deliver/move the indexing was just more file ops to be done, and more CPU
> cycles.

I think the one thing missing from this is what the normal user interactions
are. The cost of maintaining that index was more than compensated by the fact
that the average user did more listing/subject searches, and message
retrievals than moves. There is a threshold, of course, where enough
concurrent moves, etc., will compound CPU & I/O usage, and you do have to
scale in anticipation.

It's common sense that *not* maintaining that db is cheaper than doing so.
Even so, given the predominant activity of users I'm still inclined to go
Cyrus' route if I have to do maildir at all.

> I do want to note that both system had enough memory allocated to fs
> data/metadata buffer cache that the entire active directory structure was
> more or less in memory. This would tend to make the directory walks in
> straight maildir less expensive than an untuned system since 95% or the
> required info would normally be in cache.

With good write caching you can get a lot of the same performance benefits.
And that can be said for *all* mail systems. You can speed them all up with
a good caching strategy.

In LISA 2003 a analysis of db-driven mail servers was given that included
Cyrus, UW, and Courier. It used three different sizes of user box sizes
(~1k, ~9k, ~21k messages @ 5MB, 30MB, 100MB respectively). In it they
concluded that Courier's pure maildir "scale terribly compared to the
storage mechanisms of Cyrus and UW."

   http://www.usenix.org/events/lisa03/tech/full_papers/elprin/elprin_html/index.html

         --Arthur Corliss
           Bolverk's Lair -- http://arthur.corlissfamily.org/
           Digital Mages -- http://www.digitalmages.com/
           "Live Free or Die, the Only Way to Live" -- NH State Motto
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Received on Tue Sep 12 08:55:27 2006