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From Brooke Jensen <bro...@instaclustr.com>
Subject Re: Troubleshooting random node latency spikes
Date Tue, 24 Jan 2017 02:40:45 GMT
Hi Ted.

How long are the latency spikes when they occur?  Have you investigated
compactions (nodetool compactionstats) during the spike?

Are you also seeing large latency spikes in the p95 (95th percentile)
metrics? p99 catches outliers, which aren't necessarily always cause for
alarm.

Are the nodes showing any other signs of stress? CPU, GC, etc? Is there
anything pending in nodetool tpstats?

Regarding the read repairs, have you tested writing at a higher consistency
to see if that changes the number of RR occurring?


*Brooke Jensen*
VP Technical Operations & Customer Services
www.instaclustr.com | support.instaclustr.com
<https://support.instaclustr.com/hc/en-us>

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On 18 January 2017 at 02:11, <SEAN_R_DURITY@homedepot.com> wrote:

> Is this Java 8 with the G1 garbage collector or CMS? With Java 7 and CMS,
> garbage collection can cause delays like you are seeing. I haven’t seen
> that problem with G1, but garbage collection is where I would start looking.
>
>
>
>
>
> Sean Durity
>
> *From:* Ted Pearson [mailto:ted@tedpearson.com]
> *Sent:* Thursday, January 05, 2017 2:34 PM
> *To:* user@cassandra.apache.org
> *Subject:* Troubleshooting random node latency spikes
>
>
>
> Greetings!
>
> I'm working on setting up a new cassandra cluster with a write-heavy
> workload (50% writes), and I've run into a strange spiky latency problem.
> My application metrics showed random latency spikes. I tracked the latency
> back to spikes on individual cassandra nodes. ClientRequest.Latency.Read/Write.p99
> is occasionally jumping on one node at a time to several seconds, instead
> of its normal value of around 1000 microseconds. I also noticed
> that ReadRepair.RepairedBackground.m1_rate goes from zero to a non-zero
> (around 1-2/sec) during the spike on that node. I'm lost as to why these
> spikes are happening, hope someone can give me ideas.
>
> I attempted to test if the ReadRepair metric is causally linked to the
> latency spikes, but even when I changed dclocal_read_repair_chance to 0 on
> my tables, even though the metrics showed no ReadRepair.Attempted, the
> ReadRepair.RepairedBackground metric still went up during latency spikes.
> Am I misunderstanding what this metric tracks? I don't understand why it
> went up if I turned off read repair.
>
> I'm currently running 2.2.6 in a dual-datacenter setup. It's patched to
> allow metrics to be recency-biased instead of tracking latency over the
> entire running of the java process. I'm using STCS. There is a large amount
> of data per node, about 500GB currently. I expect each row to be less than
> 10KB. It's currently running on way overpowered hardware - 512GB/raid 0 on
> nvme/44 cores on 2 sockets. All of my queries (reads and writes) are
> LOCAL_ONE and I'm using r=3.
>
>
>
> Thanks,
>
> Ted
>
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