Date: Mon, 25 Mar 2002 04:58:30 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Dag-Erling Smorgrav <des@ofug.org> Cc: Taylor Dondich <thexder@lvcm.com>, chat@freebsd.org Subject: Re: qmail (Was: Maintaining Access Control Lists ) Message-ID: <3C9F1EF6.CB28EDD7@mindspring.com> References: <F61GQUEYvZmDvHbYxPo0000a6bd@hotmail.com> <20020323002608.B20699@rain.macguire.net> <3C9C84CF.2090300@flash.net> <20020323084327.A354@rain.macguire.net> <3C9DF87D.5050306@cream.org> <p05101505b8c430e28572@[10.0.1.9]> <000c01c1d3ab$6d2c6960$6600a8c0@penguin> <xzp3cyo7rbu.fsf@flood.ping.uio.no>
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Dag-Erling Smorgrav wrote: > You can't have looked very hard at Postfix. Wedging per domain mail queues into Postfix is much harder than wedging them into sendmail. They are almost natural in sendmail (well, older versions of sendmail; the newer stuff breaks a lot of intersting things by putting security barriers in the way). If you do wedge them in, then on an ETRN/ATRN, you are guaranteed a 100% hit rate on queue messages, instead of just the percentage of the main queue of the messages for a particular domain. Yeah, it's an "abuse of the file system", but with the qmail or postfix file format, there's no way to key on the file name for this sort order, even if you were guaranteed a btree directory structure, since you have to traverse all entries and post-compare them for a match, even if you could jam it into the name. Actually, Windows has an advantage here: the Windows directory searching code is passed a globbing pattern, and does the globbing for you. That way, only files matching the pattern have their directory information copied back from kernel to user space. Doing globbing in the kernel is a *significant* performance win. A hack for this for Samba shows about a 30% performance inprovement in directory operations (Ed Lane did this work) due to reduced directory iteration overhead. Unfortunately, UNIX is pretty set in concrete in this regard (shells do globbing expansion of argument lists prior to pasing them to programs), and changing this would be really hard at this point (you can't just expand in main(), because you don't know if the paremeters passed were unquoted before they got to your main(); you'd have to screw with all sorts of semantics to make it work out "magically". And you'd need to be able to turn it off on a per program basis, if a program understood how to handle globbing by itself. It's a mess. 8-(. Even kernel globbing means you have to traverse twice the average directory length than you would for a specific file (average for an exact match is 50% of the directory; globbing requires doing the whole directory, since you can't just stop after the first match). So you might get 30% out of it for SAMBA, which is emulating the Windows globbing behaviour anyway, but the win for a mail server will be much less. And for domains, in sendmail you have to open the present before you can see who it's for (the domain name is not part of the file name, because of multiple recipients). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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