[WIP]broadcast region when we use etcdBaseKV to saveRegion

[bradyjoestar]

I am reading the core/kv.go and found the following code

// SaveRegion saves one region to KV.
func (kv *KV) SaveRegion(region *metapb.Region) error {
	if atomic.LoadInt32(&kv.useRegionKV) > 0 {
		return kv.regionKV.SaveRegion(region)
	}
	return saveProto(kv.KVBase, regionPath(region.GetId()), region)
}

If useRegionKV=0, we will use kv.KVBase to saveRegion, but at the same time region_syncer is still runing in the
https://github.com/pingcap/pd/blob/59968e186cf23bdc172cd7be3c3c7e22aeb600f0/server/cluster.go#L128

And the leader will broadcast the region to member due to
https://github.com/pingcap/pd/blob/59968e186cf23bdc172cd7be3c3c7e22aeb600f0/server/cluster_info.go#L563

Maybe it could be skipped when we dont use leveldb as kvstore to decrease the network flow?

[nolouch]

@bradyjoestar It's not always broadcast the changed, only if the client has established the stream with the leader. and if not use leveldb, it will not establish stream with the leader.

[nolouch]

But there is a problem that the config change only know if PD restart or leader changed, maybe you can help us to improve it.

[bradyjoestar]

@nolouch my pleasure if it is not hurry . 😁

[nolouch]

@bradyjoestar Thanks, you can have a try. Now, the config of the follower only reload when the lead changed, what we want is when the config of the leader changed, we can also apply the change to the follower server. and now the related code is here:
https://github.com/pingcap/pd/blob/59968e186cf23bdc172cd7be3c3c7e22aeb600f0/server/leader.go#L298-L307

[bradyjoestar]

@nolunch I will try to handle it. 👌