🚀 go-pugleaf

In article <3hqcv9$qho@bunyip.cc.uq.oz.au> cs307319@student.uq.edu.au (Julian Boot) writes:
> scotta@jolt.mpx.com.au (Scott A Howard) writes:
> 
> >Cacheing of non-local filesystems is basically impossible, as you never 
> >know when the remote files have changed, and thus when you need to 
> >re-read the data.

Sorry, its been done for 10+ years... You do need lome method
of reliably controlling things though.

> So what is the *real* difference between reading a file 1 second before
> it is deleted on a local filesystem, and reading a file 1 second after
> it has been deleted on a remote filesystem, because it is cached?
> 
> Sure, you get data tha may not be quite current, but can happen at
> anytime on a multiuser system.  And althogh I have not had a close
> look at the kernel NFS src, I see to get some caching on my systems.

The difference is in stable, predictable defined semantics of the
opperation. Replace 1 min with 1 day, and ask the question again.

Most systems define deletion to be a deletion request, that happens
when the last user closes (de-accesses ) the file. Many, but not all,
systems will not allow opens after a delete operation. A few systems
treat a delete as a 'de-reference' operation, and only destroy(sic)
the file when its reference count is 0.

Any of them is fine. Win some, lose some. But if the system is properly
done, you can design a reliable race-free system on to of them.
If the system is not predictable, you are in deep smelly brown stuff...

--
~Paul
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