Scatter peer should consider the group

[rleungx]

Bug Report

Right now, the scatter region consists of two parts: peer and leader. But the behavior is different. The scatter peer is according to the count of all groups, however, the scatter leader will use the count of a single group. It might cause the leader to be not balanced due to the wrong usage of TiDB. See pingcap/tidb#46135.

pd/pkg/schedule/scatter/region_scatterer.go

Lines 453 to 461 in 70e9ffc

	for _, store := range stores {
	count := context.selectedPeer.TotalCountByStore(store.GetID())
	if count > maxStoreTotalCount {
	maxStoreTotalCount = count
	}
	if count < minStoreTotalCount {
	minStoreTotalCount = count
	}
	}

pd/pkg/schedule/scatter/region_scatterer.go

Lines 514 to 524 in 70e9ffc

	for _, storeID := range leaderCandidateStores {
	store := r.cluster.GetStore(storeID)
	if store == nil {
	continue
	}
	storeGroupLeaderCount := context.selectedLeader.Get(storeID, group)
	if minStoreGroupLeader > storeGroupLeaderCount {
	minStoreGroupLeader = storeGroupLeaderCount
	id = storeID
	}
	}