Cassandra high cpu load issues with 3.11.1

We have a 12 node Cassandra cluster with below specs 8 cores 16GB HEAP/32GB RAM with G1GC

Java version : openjdk version “1.8.0_151”

All of a sudden we started seeing some high cpu load (which is around 18-24 on 8 core nodes)

When I tried to get cassandra stack trace, it was showing lot of runnable threads like below. Method)  MessagingService-Incoming-/10.xx.xx.xx  MessagingService-Incoming-/10.xx.xx.xx at Method) at at at at at at at at at at 


"epollEventLoopGroup-2-9": running at Method) at at at at io.netty.util.concurrent.SingleThreadEventExecutor$ at io.netty.util.concurrent.DefaultThreadFactory$ at 

First thread mentioned above has 35 occurrences and 24 occurrences for 2nd thread.

Can any one figure out what is wrong here ??

From the cluster side, **

  • Don’t have any pending compactions/tasks.
  • GC pauses are below 100ms