mysterious stalls

[me at ibotty.net]

hi,

i have strange not easily reproducible stalls.

on a debian squeeze varnish 3.0.2-1~1squeeze1 runs in front of very slow
php scripts on apache 2.2.16-6+squeeze3. the machine is a virtual
machine with 4gb of ram and 2 cpus.

the vcl w/o comments is below, the varnishlog with maybe too much output
is at [1]. the vcl is at [2].

i hope, i did not forget necessary information.

the problem is the following. sometimes (in this example at about 20:43)
it stalls for about one to three minutes. there are some timeouts in
that timeframe, but i fail to see the reason. without varnish in front,
apache does not show such stalls (but because it has been so extremly
slow, noone really knows). i found one bug (#951, [3]), that described
similar problems, but here, we explicitly return (pass) these urls. so
the workaround mentioned there (req.hash_ignore_busy=true) as expected
does not work.

if you have any pointer on how to proceed, i'd be glad to know.

[1] http://pastebin.com/z78RQwra or
 http://pastebin.com/download.php?i=z78RQwra for download

[2] http://pastebin.com/vGzfHCZC

[3] https://www.varnish-cache.org/trac/ticket/951

thanks in advance,
 tobias florek