On Wed, 4 Jun 2014, Andrey Korolyov wrote: > On 06/04/2014 06:06 PM, Sage Weil 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. > > > > 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 > > > > Hi, > > we had the same mechanism for almost a half of year and it working nice > except cases when multiple background snap deletions are hitting their > ends - latencies may spike not regarding very large sleep gap for snap > operations. Do you have any thoughts on reducing this particular impact?
This isn't ringing any bells. If this is somethign you can reproduce with osd logging enabled we should be able to tell what is causing the spike, though... sage _______________________________________________ ceph-users mailing list [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
