Enterprise scalability

Eric Dantan Rzewnicki rzewnickie at RFA.ORG
Thu Feb 26 19:37:29 GMT 2004

On Thu, Feb 26, 2004 at 07:28:20PM +0000, Julian Field wrote:
> 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.

I see. Thank you very much for taking the time to explain this.

-Eric Rz.

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