memcached got a high cpu in couchbase4.0

[yqy...@gmail.com]

Hi all.

       I use couchbase4.0's Counter to count sum of some data.Here is my enviroment:

       These is 5 machine in the couchbase cluster and I create a couchbase bucket with 2 replica. the bucket is 20GB RAM per node.

       My app is about 15000qps - 20000qps Counter write to couchbase. 

       When it runs. the couchbase has a very high cpu cost ( 500% for memcached and 150% for beam.smp). It shouldn't be so high for memcached. How can I figure it out ?