When you have TombstoneOverwhelmingExceptions occuring in queries, this will cause the query to be simply dropped on every data-node, but no response is sent back to the coordinator. Instead the coordinator waits for the specified read_request_timeout_in_ms.
On the application side this can cause memory issues, since the application is waiting for the timeout interval for every request.Therefore, if our application runs into TombstoneOverwhelmingExceptions, then (sooner or later) our entire application cluster goes down
I think the data nodes should send a error message to the coordinator when they run into a TombstoneOverwhelmingException. Then the coordinator does not have to wait for the timeout-interval.