Re: TCP_SWAPFAIL_MISS and asyncufs/2.3

Franklin R. Jones wrote:
>
> On Wed, Apr 05, 2000 at 07:20:21PM +0200, Henrik Nordstrom wrote:
>
> > > Q's:
> > > 1. TCP_SWAPFAIL_MISS means squid thought it had the object but cannot
> > > retrieve it from the cache. Why would this be happening (especially on a
> > > fresh cache)?
> >
> > Some might happen, but you should not see a lot of them.
>
> define "some", just this morning I flushed my cache on a Solaris 2.7
> system, running 2.3 stable2. system was built and cache init on 2.2,
> (~3 months ago?) then upgraded to 2.3 about 2+ weeks ago. response
> through this cache dropped dramaticly, noticed that almost all
> accesses were either swapfail_miss or tcp_miss. seemed almost that i
> was getting swapfails instead of hits, but haven't gone log file
> diving to find out yet. since this was a production cache I flushed it
> (nulled out swap.state) and things seem normal again. No disk problems
> or other untoward errors logged in cache or system logs that I can
> find.
>
> an oddment, any ideas, insights similar occurrences out there?

I can't remember whether it was early 2.1 or early 2.2 when it happened, but
I recall there were some changes to the cache metadata in order to overcome
(I think) a "big-endian" versus "little-endian" problem in data contributing
to cache digests - or something like that. I don't have the relevant source
code lying around, so can't check the changelogs to confirm vague
recollections of the details or timing, but I think that meant that old
cache entries wouldn't be recognised, except for a temporary fixup that was
included for a while (with a fixed time after which it wouldn't be used)
that allowed old entries to be recognised.

I may be muddling the details a little (or a lot), and it may pre-date the
version you started off with, but it sounds like that sort of problem. Our
hit-rates certainly didn't suffer when switching from 2.2.STABLE5 to
2.1.STABLE1 (with Henrik's patch set, in both cases).

                                John Line

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