Hmmm, it works out in practice that checking for the file every time in
HPSS significantly slows down the open process. That also would mean that
if HPSS is down, the disk cache becomes inaccessible since xrootd
can't check the hpss copy. Something we've decided to avoid here for
robustness reasons (there is already an option to check during file
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.
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.
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.