[squid-users] few questions around multiple cache_dirs

Hi. I'm in the early stages of designing and testing a config with
multiple aufs cache_dirs on squid-2.6.STABLE3 as httpd accel for a lot
of content, and have a few questions based on what I've observed thus
far:

* "x-squid-internal/vary" stubs appear to be able to wind up on a
different cache_dir than the object itself. Is this a bug? Or a
tradeoff in favor of performance in the cache_dir being available 99%
of the time case, rather than storing the stubs on the same cache_dir
so a failure of a disk containing one or the other doesn't invalidate
the object? (note: I'm using max-size, which may have contributed to
the splitting, as the stubs are small and the objects large).

* how does squid determine which of several cache_dirs has an object
after a restart... is the complete url->cachefile mapping stored in
swap.state and each completely loaded into memory at startup, or are N
lookups performed, where N is the # of cache_dirs? Does an unclean
shutdown/interrupted flush to swap.state completely invalidate all
objects in a cache_dir, or does it attempt to "fsck" the objects?
Also, if entirely in memory, is it exempt from cache_mem limits?

* although i admittedly can't reproduce now, i earlier saw object
files in the aufs cache_dir occasionally getting renamed(rewritten?)
in the same cache_dir, incrementing the filename by 1 on each of
multiple successive identical requests (same client). any idea what
could account for this behavior?

thanks,
-neil
Received on Thu Aug 09 2007 - 15:08:55 MDT