Re: [squid-users] few questions around multiple cache_dirs

On tor, 2007-08-09 at 14:08 -0700, Neil Harkins wrote:

> * "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?

It's not a bug, it's a design artefact. The stub and the object is
separate from each other, so there is only 1/N probability they will end
up on the same cache_dir just as for any other two objects (assuming
none of the max-/min-size options is used).

The risk of loosing the object due to loss of another cache_dir is not
considered important.

> * how does squid determine which of several cache_dirs has an object
> after a restart...

By reading the swap.state files, these contains the per-cache_dir object
indexes + transaction log.

> 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,

varies.

> Also, if entirely in memory, is it exempt from cache_mem limits?

cache_mem is only object storage in memory, not the meta data.

> * 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?

Most likely the client forced a refresh of the object using
Control-Reload or similar.

Regards
Henrik