High cpu usage on store() , small number of keys

Tony Bussieres t.bussieres at gmail.com
Wed Aug 17 22:05:55 EDT 2011


Hi Ryan,

The cpu usage is mostly constant, on both nodes. I tried to play with my N
but it doesn't make a significant difference.
The 10 writes are happening almost concurrently.

Is there a way to show the impact of the conflict resolutions (stats or
something like it)?

thanks!

-tony

On Mon, Aug 8, 2011 at 10:29 PM, Ryan Zezeski <rzezeski at basho.com> wrote:

> Tony,
>
> Is it a constant 200% usage?  On both nodes in the cluster?  My first
> thought, since your working with a small key-space, would be conflict
> resolution or vclock explosion but you're spacing the writes out by 6s which
> seems like more than enough time.  Are all 10 writes happening at the same
> time concurrently?
>
> I would set your N=2 since you only have two machines, or add a 3rd node.
>
> Perhaps there is some weird behavior in the cache backend, but I would be
> surprised if that was it.
>
> -Ryan
>
> On Wed, Aug 3, 2011 at 11:31 AM, Tony Bussieres <t.bussieres at gmail.com>wrote:
>
>> I'm starting to play with Riak,  so far I am very impressed with the
>> product.
>>
>> I want to use Riak as an highly available distributed cache.
>>
>> I've compiled Erlang R1304 from source (--with-ssl, --enable-smp-support,
>> --enable-kernel-poll)
>> I've compiled riak-0.14.2 from source
>> I use 2 nodes, they are running on two RHEL5 box . (2.6.18.8.el5 #1 SMP).
>> They are clustered.
>> I use HAProxy to load balance the request on the two nodes.
>>
>> I have a test bench that  plays with  80 keys in one bucket (I use
>> riak_kv_cache_backend)
>> I use the java client (riak-client 0.14.1 fetched using a maven repo)
>>
>>
>> I have 10 clients that does something like this :
>> while(true) {
>>    Fetch a key from the bucket
>>    Sleep between 100 and 400ms
>> }
>>
>> I have also 10 servers that updates data in the keys every 6 seconds  (80
>> keys)
>> conceptually they do something like this :
>> while (true) {
>>    Fetch a key from the bucket
>>    Update the data
>>    Store the key in the bucket
>>    Sleep 6000ms
>> }
>>
>> The number of clients have a little impact on the CPU usage of the nodes.
>> However when I start 10 servers, the CPU usage goes very high (I saw one
>> of the node going up to 200%)
>>
>> Is there something I should check or do  to lower the CPU usage on the
>> nodes when I write keys to Riak?
>>
>> Thanks a lot!
>>
>> -tony
>>
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>>
>>
>
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