Hi, Andy!

> The real problem here is that the person is using a backdoor to modify
> the file. Had the user modified the file on the disk cache and let it
> migrate back down, there would not be a problem. Using backdoors opens
> a whole range of problems, only one of which the user experienced.

It should not be called a back door, it's a perfectly valid situation of
separation production from analysis. We do this all the time at SLAC. The
only difference is that we have read-only files, and this simplifies our
life a lot. Whether D0 user can do it our way really depends on how they
do their production. But I think that such function Jean-Yves described
should exists and be configurable for those who find it necessary.


> I'm not opposed to putting in an option to do the check but I think
> serious consideration needs to be given whether this is *really* the
> mode of operation you want or will be happy with.
> Andy
> On Wed, 2 Mar 2005, Jean-Yves Nief wrote:
> > hello all,
> >
> >           one of the D0 user accessing files via xrootd encountered the
> > following issue: after having accessed a file via xrootd (so after being
> > staged from the "master" copy stored in HPSS), he modified the master
> > copy in HPSS and wanted to access the modified file via xrootd: but as
> > the old version of the file was already on the disk cache, no staging
> > occured of course (but that is the expected behavior obviously) and he
> > grabbed the old one version, which is not what he wanted. Well as an
> > emergency solution and as it was the first time it happened, I've
> > deleted the old version on the disk cache so he could proceed.
> > However, I think it would be nice to have some control on the validity
> > of the cache: one solution would be to add the following test: in case
> > the file is already in the cache, compare the creation time on the cache
> > disk (t1) with the last modified time of the file stored in HPSS (t2):
> > if t1<t2 then restage the file.
> > it will be a very small overhead to the mechanism, each time a file is
> > accessed: it have just to issue a "statx" request to the MSS.
> > or maybe there is a more simple solution.
> > cheers,
> > JY
> >
> >