Enterprise scalability

Julian Field mailscanner at ecs.soton.ac.uk
Thu Feb 26 19:28:20 GMT 2004

At 19:12 26/02/2004, you wrote:
>On Thu, Feb 26, 2004 at 03:27:01PM +0000, Julian Field wrote:
> > I would advise against Qmail and Postfix. They both only have 1 file per
> > message, which results in far more I/O being done than for systems with 2
> > files per message (such as sendmail and Exim).
>Can you elaborate on that? How does the 2 file method save I/O?

Most of the time, MailScanner doesn't want to modify the body of the
message at all. So if the body is held in a separate file, then it just
takes a link and an unlink operation to move the message body from the
incoming queue to the outgoing queue. This is totally independent of the
file size, and is *very* fast as it is no more than 2 very simple
filesystem changes.

If the body is held in the same file as the headers, then the message has
to be read in from the in queue, and written to the out queue. The time
this takes is proportional to the size of the message as it entails I/O on
the entire message body. This is noticeably slower, as you can imagine.
Julian Field
Professional Support Services at www.MailScanner.biz
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