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From Vicky Kak <vicky....@gmail.com>
Subject Re: Write performance with 1.2.12
Date Fri, 06 Dec 2013 15:59:54 GMT
You have passed the JVM configurations and not the cassandra configurations
which is in cassandra.yaml.
The spikes are not that significant in our case and we are running the
cluster with 1.7 gb heap.

Are these spikes causing any issue at your end?




On Fri, Dec 6, 2013 at 9:10 PM, srmore <comomore@gmail.com> wrote:

>
>
>
> On Fri, Dec 6, 2013 at 9:32 AM, Vicky Kak <vicky.kak@gmail.com> wrote:
>
>> Hard to say much without knowing about the cassandra configurations.
>>
>
> The cassandra configuration is
> -Xms8G
> -Xmx8G
> -Xmn800m
> -XX:+UseParNewGC
> -XX:+UseConcMarkSweepGC
> -XX:+CMSParallelRemarkEnabled
> -XX:SurvivorRatio=4
> -XX:MaxTenuringThreshold=2
> -XX:CMSInitiatingOccupancyFraction=75
> -XX:+UseCMSInitiatingOccupancyOnly
>
>
>
>> Yes compactions/GC's could skipe the CPU, I had similar behavior with my
>> setup.
>>
>
> Were you able to get around it ?
>
>
>>
>> -VK
>>
>>
>> On Fri, Dec 6, 2013 at 7:40 PM, srmore <comomore@gmail.com> wrote:
>>
>>> We have a 3 node cluster running cassandra 1.2.12, they are pretty big
>>> machines 64G ram with 16 cores, cassandra heap is 8G.
>>>
>>> The interesting observation is that, when I send traffic to one node its
>>> performance is 2x more than when I send traffic to all the nodes. We ran
>>> 1.0.11 on the same box and we observed a slight dip but not half as seen
>>> with 1.2.12. In both the cases we were writing with LOCAL_QUORUM. Changing
>>> CL to ONE make a slight improvement but not much.
>>>
>>> The read_Repair_chance is 0.1. We see some compactions running.
>>>
>>> following is my iostat -x output, sda is the ssd (for commit log) and
>>> sdb is the spinner.
>>>
>>> avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>>>           66.46    0.00    8.95    0.01    0.00   24.58
>>>
>>> Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz
>>> avgqu-sz   await  svctm  %util
>>> sda               0.00    27.60  0.00  4.40     0.00   256.00
>>> 58.18     0.01    2.55   1.32   0.58
>>> sda1              0.00     0.00  0.00  0.00     0.00     0.00
>>> 0.00     0.00    0.00   0.00   0.00
>>> sda2              0.00    27.60  0.00  4.40     0.00   256.00
>>> 58.18     0.01    2.55   1.32   0.58
>>> sdb               0.00     0.00  0.00  0.00     0.00     0.00
>>> 0.00     0.00    0.00   0.00   0.00
>>> sdb1              0.00     0.00  0.00  0.00     0.00     0.00
>>> 0.00     0.00    0.00   0.00   0.00
>>> dm-0              0.00     0.00  0.00  0.00     0.00     0.00
>>> 0.00     0.00    0.00   0.00   0.00
>>> dm-1              0.00     0.00  0.00  0.60     0.00     4.80
>>> 8.00     0.00    5.33   2.67   0.16
>>> dm-2              0.00     0.00  0.00  0.00     0.00     0.00
>>> 0.00     0.00    0.00   0.00   0.00
>>> dm-3              0.00     0.00  0.00 24.80     0.00   198.40
>>> 8.00     0.24    9.80   0.13   0.32
>>> dm-4              0.00     0.00  0.00  6.60     0.00    52.80
>>> 8.00     0.01    1.36   0.55   0.36
>>> dm-5              0.00     0.00  0.00  0.00     0.00     0.00
>>> 0.00     0.00    0.00   0.00   0.00
>>> dm-6              0.00     0.00  0.00 24.80     0.00   198.40
>>> 8.00     0.29   11.60   0.13   0.32
>>>
>>>
>>>
>>> I can see I am cpu bound here but couldn't figure out exactly what is
>>> causing it, is this caused by GC or Compaction ? I am thinking it is
>>> compaction, I see a lot of context switches and interrupts in my vmstat
>>> output.
>>>
>>> I don't see GC activity in the logs but see some compaction activity.
>>> Has anyone seen this ? or know what can be done to free up the CPU.
>>>
>>> Thanks,
>>> Sandeep
>>>
>>>
>>>
>>
>

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