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.