Thread_pools increase value

Hello!

I am getting an errors:
Caused by: org.elasticsearch.common.util.concurrent.EsRejectedExecutionException: rejected execution of org.elasticsearch.transport.TcpTransport$RequestHandler@670e2606 on EsThreadPoolExecutor[search, queue capacity = 1000, org.elasticsearch.common.util.concurrent.EsThreadPoolExecutor@71540818[Running, pool size = 13, active threads = 13, queued tasks = 1000, completed tasks = 5097151]]

Also i have a lot of "rejected" bulk and search operations in _cat/thread_pool?v:

bulk 244
fetch_shard_started 0
fetch_shard_store 0
flush 0
force_merge 0
generic 0
get 0
index 0
listener 0
management 0
refresh 0
search 11373
snapshot 0
warmer 0

We have a cluster with 7 nodes:
8 cpu
30 RAM

Elasticsearch v5.1

I found that i can increase number of threadpool.search.queue_size, but i think that i should increase the number of threads and pool size, but i am not really sure which number should be there.
Probably i should increase something else.
I am hoping for your support.

Best regards.

See my previous comments on this subject.

Thank you, for fast reply, yeah it's definitely make sense.

You're welcome.