Hi,
from experience: commit/apply_latency are not good metrics, the only good
thing about them is that they are really easy to track.
But we have found them to be almost completely useless in the real world.
We track the op_*_latency metrics from perf dump and found them to be very
helpful, they are more annoying to track due to their
format. The median OSD is a good indicator and so is the slowest OSD.
Paul
2018-07-11 17:50 GMT+02:00 Marc Schöchlin <m...@256bit.org>:
> Hello ceph-users and ceph-devel list,
>
> we got in production with our new shiny luminous (12.2.5) cluster.
> This cluster runs SSD and HDD based OSD pools.
>
> To ensure the service quality of the cluster and to have a baseline for
> client latency optimization (i.e. in the area of deepscrub optimization)
> we would like to have statistics about the client interaction latency of
> our cluster.
>
> Which measures can be suitable to get such a "aggregated by
> device_class" average latency KPI?
> Also a percentile rank would be great (% amount of requests serviced by
> < 5ms, % amount of requests serviced by < 20ms, % amount of requests
> serviced by < 50ms, ...)
>
> The following command provides a overview over the commit latency of the
> osds but no average latency and no information about the device_class.
>
> ceph osd perf -f json-pretty
>
> {
> "osd_perf_infos": [
> {
> "id": 71,
> "perf_stats": {
> "commit_latency_ms": 2,
> "apply_latency_ms": 0
> }
> },
> {
> "id": 70,
> "perf_stats": {
> "commit_latency_ms": 3,
> "apply_latency_ms": 0
> }
>
> Device class information can be extracted of "ceph df -f json-pretty".
>
> But building averages of averages not seems to be a good thing .... :-)
>
> It seems that i can get more detailed information using the "ceph daemon
> osd.<nr> perf histogram dump" command.
> This seems to deliver the percentile rank information in a good detail
> level.
> (http://docs.ceph.com/docs/luminous/dev/perf_histograms/)
>
> My questions:
>
> Are there tools to analyze and aggregate these measures for a group of
> OSDs?
>
> Which measures should i use as a baseline for client latency optimization?
>
> What is the time horizon of these measures?
>
> I sometimes see messages like this in my log.
> This seems to be sourced in deep scrubbing. How can find the
> source/solution of this problem?
>
> 2018-07-11 16:58:55.064497 mon.ceph-mon-s43 [INF] Cluster is now healthy
> 2018-07-11 16:59:15.141214 mon.ceph-mon-s43 [WRN] Health check failed: 4
> slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 16:59:25.037707 mon.ceph-mon-s43 [WRN] Health check update: 9
> slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 16:59:30.038001 mon.ceph-mon-s43 [WRN] Health check update:
> 23 slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 16:59:35.210900 mon.ceph-mon-s43 [WRN] Health check update:
> 27 slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 16:59:45.038718 mon.ceph-mon-s43 [WRN] Health check update:
> 29 slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 16:59:50.038955 mon.ceph-mon-s43 [WRN] Health check update:
> 39 slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 16:59:55.281279 mon.ceph-mon-s43 [WRN] Health check update:
> 44 slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 17:00:00.000121 mon.ceph-mon-s43 [WRN] overall HEALTH_WARN 12
> slow requests are blocked > 32 sec
> 2018-07-11 17:00:05.039677 mon.ceph-mon-s43 [WRN] Health check update:
> 12 slow requests are blocked > 32 sec (REQUEST_SLOW)
> 2018-07-11 17:00:09.329897 mon.ceph-mon-s43 [INF] Health check cleared:
> REQUEST_SLOW (was: 12 slow requests are blocked > 32 sec)
> 2018-07-11 17:00:09.329919 mon.ceph-mon-s43 [INF] Cluster is now healthy
>
> Regards
> Marc
>
>
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>
--
Paul Emmerich
Looking for help with your Ceph cluster? Contact us at https://croit.io
croit GmbH
Freseniusstr. 31h
81247 München
www.croit.io
Tel: +49 89 1896585 90
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