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From "Justin Erenkrantz" <jus...@erenkrantz.com>
Subject Re: mod_cache and its ilk
Date Mon, 30 Oct 2006 18:33:29 GMT
On 10/30/06, Joe Orton <jorton@redhat.com> wrote:
> On Mon, Oct 30, 2006 at 10:26:18AM -0700, Justin Erenkrantz wrote:
> > My concern with this is we should be careful not to teach the
> > providers about the fact that it is sitting in an output filter chain.
>
> This is solvable if desired, but I'd like to address it separately to
> keep this thread under control.

Sure.

> > >2) avoids writing a given URL/variant to the cache more than once
> > >simultaneously using open/O_EXCL
> >
> > There's problems with relying upon O_EXCL.  mod_disk_cache
> > purposefully lets the race condition happen as without inter-process
> > sync, it's not really easy to know who is actually around and is
> > likely to finish.
>
> Are you talking issues with O_EXCL not being reliable on e.g. NFS, or
> just about the fact that the partial file left by a dead/hung process
> subsequently prevents any chance to write to that cache file?

The latter.  (NFS is a lower priority - I'd like to see it work, but
if it can't no biggie, IMO.)

> This is a tricky trade-off; I can go either way.  I would say it would
> be OK to rely on htcacheclean having heuristics to expire (prematurely
> if necessary) such partial files.

Hmm.  Maybe, but that's a bit more complex than I'd like to see.
*shrug*  -- justin

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