[KUDU-2211] improve the thread pool for rpc service

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Won't Fix
• Affects Version/s: 1.5.0
• Component/s: rpc
• Assignee: Unassigned
• Reporter: LiFu He
• Created: 08/Nov/17 07:37
• Updated: 13/Apr/18 02:39
• Resolved: 13/Apr/18 02:39

Description

in user mail list, Lee King modified his config of 'rpc_num_threads' to 128 for consensus stability, but it will waste too much resource. maybe we could do some improvement:
1) different rpc service use different config of 'rpc_num_thread';
2) use 'threadpool' instead of 'std::vector<scoped_refptr<kudu::Thread> > threads_', just like negotiation pool does;