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From Vicky Kak <vicky....@gmail.com>
Subject Re: Write performance with 1.2.12
Date Fri, 06 Dec 2013 17:05:07 GMT
Can you set the memtable_total_space_in_mb value, it is defaulting to 1/3
which is 8/3 ~ 2.6 gb in capacity
http://www.datastax.com/dev/blog/whats-new-in-cassandra-1-0-improved-memory-and-disk-space-management

The flushing of 2.6 gb to the disk might slow the performance if frequently
called, may be you have lots of write operations going on.



On Fri, Dec 6, 2013 at 10:06 PM, srmore <comomore@gmail.com> wrote:

>
>
>
> On Fri, Dec 6, 2013 at 9:59 AM, Vicky Kak <vicky.kak@gmail.com> wrote:
>
>> You have passed the JVM configurations and not the cassandra
>> configurations which is in cassandra.yaml.
>>
>
> Apologies, was tuning JVM and that's what was in my mind.
> Here are the cassandra settings http://pastebin.com/uN42GgYT
>
>
>
>> 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?
>>
>
> There are no big spikes, the overall performance seems to be about 40% low.
>
>
>>
>>
>>
>>
>> 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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