Could it fail fast on the propose dropping while leader changed

[absolute8511]

While leader is transferred, the proposal may be dropped. But we can not get the notify so we can do some retry work.
For example, as below

https://github.com/coreos/etcd/blob/b041ce5d514a4b4aaeefbffb008f0c7570a18986/etcdserver/v3_server.go#L572

	cctx, cancel := context.WithTimeout(ctx, s.Cfg.ReqTimeout())
	defer cancel()

	start := time.Now()
	s.r.Propose(cctx, data)
	proposalsPending.Inc()
	defer proposalsPending.Dec()

	select {
	case x := <-ch:
		return x.(*applyResult), nil
	case <-cctx.Done():
		proposalsFailed.Inc()
		s.w.Trigger(id, nil) // GC wait
		return nil, s.parseProposeCtxErr(cctx.Err(), start)
	case <-s.done:
		return nil, ErrStopped
	}

We just wait context timeout to get to know we failed to propose which is blocking too long. I think we should handle the proposal dropping event to fail fast. One possible way is to wake up the cctx.Done while dropping proposal.

[xiang90]

We could be smarter about this. However, the raft library does not return an error for dropping messages right now. Do you want to help on this one?

[absolute8511]

Yeah, I am looking into this.

[wenjiaswe]

@absolute8511 Vincent, I saw that you have a coupled of PR merged, thanks! I am closing this issue. Please feel free to reopen it if it's not fixed and need further action here.