Elasticsearch High CPU when searching using Kibana

Hi All,

I am indexing 5000 Docs/sec.
I've a problem with search query that it consumes 100% of CPU when I do search with Kibana. its size 30 GB and have more that 1 Billion docs inside.
System Configuration: 16 GB RAM
ES_HEAP_SIZE=3g
ES_MIN_MEM=3g
ES_MAX_MEM=3g

Index Setting:

index.number_of_shards: 8
index.number_of_replicas: 1

I do some experiment with Segment also but i am still stuck.
Please suggest me i need to do something with Segment.

Thanks,
Sumit Gupta