guy keren wrote:
>
> On Sun, 30 Jan 2000, Omer Efraim wrote:
>
> if you want to check on improving a situation, you first need to check
> exactly what is the situation - i'm not suer that the current method, of
> forking off a process for each connection, is very problematic - the life
> time of the process is much larger then the ammount of time it takes to
> fork it off (i.e. you often take a minute or a few minutes to download
> email - the fork operation takes less then one 10th of a second - now, is
> _this_ where you should optimize??).
Don't forget that on large corporate mail systems quite a lot
of the cpu load comes from people _checking_ for mail.
Imagine 10k users, each checking for mail every 5 minutes.
Each one of those requires a fork even if the user has no (new?) mail.
>
> it sounds to me like a better place for optimization is storing compressed
> email messages - it'll take more CPU power when storing the email, but you
> could set up a capabilities system in which the client will speicy if it
> can handle compressed email or not, and if it can, the decompression can
> be done on the client side. this compress could make download time
> smaller, and thus allow the server to support more clients. ofcourse,
> there's a need to check which part takes longer - downloading the letters,
> or compressing and decompressing them.. also note that this compressiong
> will save up on I/O operations needed to save/load the letters, so it
> might be that the compression itself is usefull even if the letters are
> still sent to the clients in a non-compressed format... measurements are
> needed here....
Well, I agree - but this is a whole other symphony and requires much more
work, and it works on a much larger scale. I myself download mail tunneled
through ssh so it's compressed anyhow, but I guess it would be nice to
have clients supporting it out of the box.
>
> > I'm thinking about a qmail specific scenario (as this is the
> > MTA I'm most familier with), but I'm sure this applies to
> > other MTAs as well.
>
> well, with qmail you got one advantage that you don't have with sendmail
> (for instalce) - the usage of mail dirs. when you have all mail stored in
> one large file, the pop server needs to copy this email folder back and
> forth when servicing the client. when using mail directories - this
> copying operation is not required (unless a letter is not downloaded, and
> rather has its UIDL data updated - anyone can tell if in qmail the header
> and the letter's contents are stored in a single file, or in two seperate
> files?)
Single file.
The reasoning behind Maildirs was not really performance but rather
robustness.
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