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List:       qmail
Subject:    Re: patch for tcpserver
From:       Charles Cazabon <qmail () discworld ! dyndns ! org>
Date:       2007-03-26 14:15:02
Message-ID: 20070326141502.GA10792 () discworld ! dyndns ! org
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Joshua Megerman <qmail@honorablemenschen.com> wrote:
> >
> > > but I would think for that application NFS would be adequate.
> >
> > Agreed.
> >
> Actually, it isn't.  I worked on a cluster of about 10 front-end 
> qmail/vpopmail servers serving ~6000 users and handling ~200K messages/day.  
> At the height of the busy times, with literally 100+ pop/imap 
> connections/second, the tcp.smtp cdb couldn't get rebuilt fast enough to 
> avoid collisions.  Since vpopmail keeps a dynamic list of IP addresses in (in 
> our case) a MySQL DB, and has to combine it with the static list from the FS, 
> it was rebuilding the tcp.smtp.cdb file 100 times/second, which is NOT where 
> CDB excels.

No, of course not.  For fast-changing data like that, skip CDB entirely.  Keep
track with individual (probably 0-length) files that you look up either by
hashing, or by simply converting an address A.B.C.D to path .../A/B/C/D.

> The solution for us was to use the tcpserver MySQL patch which 
> checks checks the MySQL table in a read-only manner, and let vpopmail handle 
> the updates.  Which, incidentally, is what the original patch author wrote it 
> for...

It's still ugly to put a relational database into this path.  All that's
needed is a tiny shim after the checkpassword program that creates the state
file as described above; it'll only be run on successful authentication.  Then
you have a similar tiny shim before qmail-smtpd that checks for the existence
of the file and conditionally sets RELAYCLIENT before execing qmail-smtpd
(optionally checking the timestamp on the file is recent enough), and an
external process removing stale state files.

Charles
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Charles Cazabon                               <qmail@discworld.dyndns.org>
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