On Sat, Mar 14, 2015 at 7:03 AM, Scottix <scottix@xxxxxxxxx> wrote: > ... > > >> The time variation is caused cache coherence. when client has valid >> information >> in its cache, 'stat' operation will be fast. Otherwise the client need to >> send >> request to MDS and wait for reply, which will be slow. > > > This sounds like the behavior I had with CephFS giving me question marks. > When I had a directory with a large amount of files in it and the first ls > -la took a while to populate and ended with some unknown stats. The second > time I did an ls -la it ran quick with no question marks. My inquiry was if > there is a timeout that could occur? since it has to go ask the mds on a > different machine it seems plausible that the full response is not coming > back in time or fails to get all stats at some point. unknown stats shouldn't happen. which kernel are ypu using? can you reproduce it with ceph-fuse? Regards Yan, Zheng > > I could test this more; is there a command or proccess I can perform to > flush the ceph-fuse cache? > > Thanks, > Scott > > > On Fri, Mar 13, 2015 at 1:49 PM Francois Lafont <flafdivers@xxxxxxx> wrote: >> >> Hi, >> >> Yan, Zheng wrote : >> >> >> http://tracker.ceph.com/issues/11059 >> >> >> > >> > It's a bug in ACL code, I have updated >> > http://tracker.ceph.com/issues/11059 >> >> Ok, thanks. I have seen and I will answer quickly. ;) >> >> >> I'm still surprised by such times. For instance, It seems to me >> >> that, with a mounted nfs share, commands like "ls -la" are very >> >> fast in comparison (with a directory which contains the same number >> >> of files). Can anyone explain to me why there is a such difference >> >> between the nfs case and the cephfs case? This is absolutely not a >> >> criticism but it's just to understand the concepts that come into >> >> play. In the case of "ls -al" ie just reading (it is assumed that >> >> there is no writing on the directory), the nfs and the cephfs cases >> >> seem to me very similar: the client just requests a stat on each file >> >> in the directory. Am I wrong? >> > >> > NFS has no cache coherence mechanism. It can't guarantee one client >> > always >> > see other client's change. >> >> Ah ok, I didn't know that. Indeed, now I understand that can generate >> performance impact. >> >> > The time variation is caused cache coherence. when client has valid >> > information >> > in its cache, 'stat' operation will be fast. Otherwise the client need >> > to send >> > request to MDS and wait for reply, which will be slow. >> >> Ok, thanks a lot for your explanations. >> Regards. >> >> -- >> François Lafont >> _______________________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
 |