Hi Venky, maybe you can help me clarifying the situation a bit. I don't understand the difference between the two pinning implementations you describe in your reply and I also don't see any difference in meaning in the documentation between octopus and quicy, the difference is just in wording. Both texts state that "all of a directory’s immediate children should be ephemerally pinned" (octopus) and "This has the effect of distributing immediate children across a range of MDS ranks" (quincy).
To me, both mean that, if I enable distributed ephemeral pinning on /home, then for every child /home/X of home it follows that /home/X and any directory under /home/X/ are pinned to the same MDS rank. Meaning their information in cache exists on this rank only and no other MDS is serving requests for any of these directories. Is there something wrong with this interpretation? I tried it with octopus and the cache for directories under /home/X/ was all over the place. Nothing was pinned to a single rank and on top of that the number of sub-trees was extremely unevenly assigned and excessively large. After I set an explicit pin on every child /home/X of /home, only then was all cache information about all subdirs of /home/X/ handled by the MDS I pinned it to. What should the result of distributed ephemeral pinning actually be when set on /home? What would be different between octopus and quincy? Is the documentation (for octopus) misleading or does the implementation not match documentation? Thanks for any insight! Best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14 ________________________________________ From: Venky Shankar <vshan...@redhat.com> Sent: 29 November 2022 10:09:21 To: Frank Schilder Cc: Reed Dier; ceph-users Subject: Re: [ceph-users] Re: MDS stuck ops On Tue, Nov 29, 2022 at 1:42 PM Frank Schilder <fr...@dtu.dk> wrote: > > Hi Venky. > > > You most likely ran into performance issues with distributed ephemeral > > pins with octopus. It'd be nice to try out one of the latest releases > > for this. > > I run into the problem that distributed ephemeral pinning seems not actually > implemented in octopus. This mode didn't pin anything, see also the recent > conversation with Patrick: Distributed ephemeral pins used to distribute inodes under a directory mongst MDSs which had scalability issues due to the sheer number of subtrees. This was changed to distribute dirfrags and I think those changes were not in octopus. > > https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/YEB34F5SREAOOMATOKC6NO3G2GVCSOOZ > > I sent him a couple of dumps, but am not sure if he is doing anything with > it. I wrote a small script to do the distributed pinning by hand and it > solved all sorts of problems. Distributing dirfrags solved a lot of scalability issues and those changes are available in pacific and beyond. We aren't backporting to octopus anymore, so the options are limited. > > Best regards, > ================= > Frank Schilder > AIT Risø Campus > Bygning 109, rum S14 > -- Cheers, Venky _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io
