- From: Alex Rousskov <rousskov@measurement-factory.com>
- Date: Tue, 6 Jul 2004 16:02:50 -0600 (MDT)
- To: Koen Holtman <k.holtman@chello.nl>
- Cc: Greg Robson-Garth <gregrg@optusnet.com.au>, ietf-http-wg@w3.org
On Tue, 6 Jul 2004, Koen Holtman wrote: > On Tue, 6 Jul 2004, Alex Rousskov wrote: > > > The age calculation algorithm in RFC 2616 is indeed buggy, but in > > a different, more subtle, way: > > http://lists.w3.org/Archives/Public/ietf-http-wg/2002JulSep/0048.html > > > > IIRC, nobody commented on that age calculation bug and its > > proposed fix. It is not mentioned in the RFC 2616 errata. I > > suspect it will remain with us forever. > > I recall that this bug (and ways to fix it) did get discussed back > in the late 1990s when the spec was being written. Opinions ranged > from `it is a bug' to `this is a safe way for the calculation to err > on the side of caution'. I recall that the original author of the > calculation (Jeff Mogul) did intend it this way. Consensus back > then was that the bug/feature should be kept in. Thanks for the info! I may have found that e-mail thread: http://www.hpl.hp.com/personal/ange/archives/http-wg-archive/0378.html Jeff Mogul said, "The fact that the response_delay is counted twice in the final result is an attempt to correct for clock skew, since if you can't guarantee that the client and server clocks are synchronized (and we can't!), then the apparent_age could be wrong by a significant amount." The formulas I proposed do not use apparent_age or response_delay, so I cannot apply the above logic directly. Unfortunately, I do not know what Jeff was using to estimate "clock skew" effect on a formula, so I am not sure whether the simpler formulas I came up with suffer from clock skew more than the current complex ones. As of now, I am only sure that the complexity (and unexpected results?) of current formulas lead to implementation bugs. I am not sure whether simpler, natural formulas do not suffer from higher clock skew sensitivity. Thanks, Alex.
Received on Tuesday, 6 July 2004 18:03:04 UTC