On Wed, 4 Jun 2014, Dan Van Der Ster wrote: > On 04 Jun 2014, at 16:06, Sage Weil <[email protected]> wrote: > > > On Wed, 4 Jun 2014, Dan Van Der Ster wrote: > >> Hi Sage, all, > >> > >> On 21 May 2014, at 22:02, Sage Weil <[email protected]> wrote: > >> > >>> * osd: allow snap trim throttling with simple delay (#6278, Sage Weil) > >> > >> Do you have some advice about how to use the snap trim throttle? I saw > >> osd_snap_trim_sleep, which is still 0 by default. But I didn't manage to > >> follow the original ticket, since it started out as a question about > >> deep scrub contending with client IOs, but then at some point you > >> renamed the ticket to throttling snap trim. What exactly does snap trim > >> do in the context of RBD client? And can you suggest a good starting > >> point for osd_snap_trim_sleep = ? ? > > > > This is a coarse hack to make the snap trimming slow down and let client > > IO run by simply sleeping between work. I would start with something > > smallish (.01 = 10ms) after deleting some snapshots and see what effect it > > has on request latency. Unfortunately it's not a very intuitive knob to > > adjust, but it is an interim solution until we figure out how to better > > prioritize this (and other) background work. > > > > Thanks Sage. Is this delay applied per object being removed or at some > higher granularity?
Per object. > And BTW, I was also curious why you?ve only added a throttle to the snap > trim ops. Are object/rbd/pg/pool deletions somehow less disruptive to > client IOs? Other deletions are client IOs. Snap deletions are one of the few operations that are driven by the OSD and thus need their own throttling. FWIW, I think the plan going forward is to create ops for these internally so that the go through the same queues and prioritization as client requests. sage > > Cheers, Dan > > > In short, if you do see a performance degradation after removing snaps, > > adjust this up or down and see how it changes that. If you don't see a > > degradation, then you're lucky and don't need to do anything. :) > > > > You can adjust this on running OSDs with something like 'ceph daemon > > osd.NN config set osd_snap_trim_sleep .01' or with 'ceph tell osd.* > > injectargs -- --osd-snap-trim-sleep .01'. > > > > sage > > > > _______________________________________________ ceph-users mailing list [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
