On Fri, 25 Dec 2015, Ning Yao wrote:
> Hi, Dong Wu,
> 1. As I currently work for other things, this proposal is abandon for
> a long time
> 2. This is a complicated task as we need to consider a lots such as
> (not just for writeOp, as well as truncate, delete) and also need to
> consider the different affects for different backends(Replicated, EC).
> 3. I don't think it is good time to redo this patch now, since the
> BlueStore and Kstore  is inprogress, and I'm afraid to bring some
> side-effect.  We may prepare and propose the whole design in next CDS.
> 4. Currently, we already have some tricks to deal with recovery (like
> throttle the max recovery op, set the priority for recovery and so
> on). So this kind of patch may not solve the critical problem but just
> make things better, and I am not quite sure that this will really
> bring a big improvement. Based on my previous test, it works
> excellently on slow disk (say hdd), and also for a short-time
> maintaining. Otherwise, it will trigger the backfill process.  So wait
> for Sage's opinion @sage
> If you are interest on this, we may cooperate to do this.

I think it's a great idea.  We didn't do it before only because it is 
complicated.  The good news is that if we can't conclusively infer exactly 
which parts of hte object need to be recovered from the log entry we can 
always just fall back to recovering the whole thing.  Also, the place 
where this is currently most visible is RBD small writes:

 - osd goes down
 - client sends a 4k overwrite and modifies an object
 - osd comes back up
 - client sends another 4k overwrite
 - client io blocks while osd recovers 4mb

So even if we initially ignore truncate and omap and EC and clones and 
anything else complicated I suspect we'll get a nice benefit.

I haven't thought about this too much, but my guess is that the hard part 
is making the primary's missing set representation include a partial delta 
(say, an interval_set<> indicating which ranges of the file have changed) 
in a way that gracefully degrades to recovering the whole object if we're 
not sure.

In any case, we should definitely have the design conversation!


> Regards
> Ning Yao
> 2015-12-25 14:23 GMT+08:00 Dong Wu <archer.wud...@gmail.com>:
> > Thanks, from this pull request I learned that this issue is not
> > completed, is there any new progress of this issue?
> >
> > 2015-12-25 12:30 GMT+08:00 Xinze Chi (??) <xmdx...@gmail.com>:
> >> Yeah, This is good idea for recovery, but not for backfill.
> >> @YaoNing have pull a request about this
> >> https://github.com/ceph/ceph/pull/3837 this year.
> >>
> >> 2015-12-25 11:16 GMT+08:00 Dong Wu <archer.wud...@gmail.com>:
> >>> Hi,
> >>> I have doubt about pglog, the pglog contains (op,object,version) etc.
> >>> when peering, use pglog to construct missing list,then recover the
> >>> whole object in missing list even if different data among replicas is
> >>> less then a whole object data(eg,4MB).
> >>> why not add (offset,len) to pglog? If so, the missing list can contain
> >>> (object, offset, len), then we can reduce recover data.
> >>> _______________________________________________
> >>> ceph-users mailing list
> >>> ceph-us...@lists.ceph.com
> >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >>
> >>
> >>
> >> --
> >> Regards,
> >> Xinze Chi
> > _______________________________________________
> > ceph-users mailing list
> > ceph-us...@lists.ceph.com
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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