Date: Tue, 19 Dec 1995 11:25:28 GMT From: Chris Coleman <chrisc@MAIL.bbcc.ctc.edu> To: Peter Wemm <peter@haywire.dialix.com> Cc: <freebsd-hackers@freebsd.org> Subject: Re: mail storm Message-ID: <XFMail.951219112528.chrisc@bbcc.ctc.edu> In-Reply-To: <4akk79$89r$1@haywire.DIALix.COM>
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On Wed Dec 13 03:12:41 1995 Peter Wemm wrote: >>wosch@cs.tu-berlin.de (Wolfram Schneider) writes: > >>Jonathan M. Bresler writes: >>>On Sun, 10 Dec 1995, Wolfram Schneider wrote: >>> >>>> Christoph P. Kukulies writes: >>>> >Overnight I had received 650 mails or so (instead of 120 - my >>>> >normal daily load) and many of these are deja-vu mails. >>>> >>>> Me too. I detect funny ``Received: '' lines, 550 mails via ra.dkuug.dk >>>> and 100 mails via th-darmstadt.de. >>> >>> send me one, including headers please, if you have any that you >>>have not deleted > >>I received 2760 Mails since november 29. 83 Mails are dups, mostly >>cross postings (cc: hackers, current). 10 Mails seems really dups, but >>10 Mails is not a problem for me ... > >>Wolfram > >I have an explaination for the volume and a theory about the duplicates.. > >The basic problem was that due to bad connectivity from freefall to >europe and other places, there was a MAJOR pileup of queued mail on >freefall. There were nearly 1000 emails to *.de sites that had been >sitting there for 5 days, and were just about to be bounced to the >postmaster on freefall (5 day timeout). > >I split the mail queue from one "deferred" queue on freefall to 5 >queues, one for each day of backlog. > >After making arrangements with a FreeBSD core member in Denmark >(Poul-Henning Kamp), *all* of the backlogged mail was sent to a >machine under his control for exploding and delivery to the *.de and >other north-eastern european sites. This would account for the >massive flood of email. You could have receieved as many as 900 to >1000 emails over a few hours. > >Also, there is an race condition in the SMTP protocol that is >tickled on bad internet links. Picture this: The originator >(freefall) writes out the message and the trailing "." to end the >body, and waits for the response for a few minutes. If it doesn't get >a response, it times out and requeues the message... *however*, the >network may be slow, and the final 10 or 20K of data including the "." >may take a few minutes to arrive, and the numberic response code may >be delayed due to the pathological TCP retransmit backoff.. But in >reality, the remote machine receieved the mail via SMTP and responded, >but freefall had given up waiting. At this point, there is now a >duplicate mail in the system..... > >Considering the sheer volume of mail sent, and the current extreme >packet losses across international links, I suspect it is most likely >a manifestation of the SMTP race condition. We can only fix that by >lengthening the SMTP transaction timeouts, which will cause freefall's >mail queue to suffer even more in the face of the numerous genuine >broken mailers out there, that genuinely timeout. If the problem >persists, we may have to try something... > >-Peter
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