address comment

Signed-off-by: bufferflies <1045931706@qq.com>

pkg/schedule/scatter/region_scatterer.go

@@ -318,6 +318,7 @@ func (r *RegionScatterer) scatterRegion(region *core.RegionInfo, group string, s
 		for i, filterFunc := range context.filterFuncs {
 			filters[i] = filterFunc()
 		}
+		filters[filterLen-2] = filter.NewExcludedFilter(r.name, nil, selectedStores)
 		for _, peer := range peers {
 			if _, ok := selectedStores[peer.GetStoreId()]; ok {
 				if allowLeader(oldFit, peer) {
@@ -333,7 +334,6 @@ func (r *RegionScatterer) scatterRegion(region *core.RegionInfo, group string, s
 			}
 			filters[filterLen-1] = filter.NewPlacementSafeguard(r.name, r.cluster.GetSharedConfig(), r.cluster.GetBasicCluster(), r.cluster.GetRuleManager(), region, sourceStore, oldFit)
 			for {
-				filters[filterLen-2] = filter.NewExcludedFilter(r.name, nil, selectedStores)
 				newPeer := r.selectNewPeer(context, group, peer, filters)
 				targetPeers[newPeer.GetStoreId()] = newPeer
 				selectedStores[newPeer.GetStoreId()] = struct{}{}
@@ -355,7 +355,7 @@ func (r *RegionScatterer) scatterRegion(region *core.RegionInfo, group string, s
 	// FIXME: target leader only considers the ordinary stores, maybe we need to consider the
 	// special engine stores if the engine supports to become a leader. But now there is only
 	// one engine, tiflash, which does not support the leader, so don't consider it for now.
-	targetLeader, leaderHit := r.selectAvailableLeaderStore(group, region, leaderCandidateStores, r.ordinaryEngine)
+	targetLeader, leaderStorePickedCount := r.selectAvailableLeaderStore(group, region, leaderCandidateStores, r.ordinaryEngine)
 	if targetLeader == 0 {
 		scatterSkipNoLeaderCounter.Inc()
 		return nil
@@ -391,7 +391,7 @@ func (r *RegionScatterer) scatterRegion(region *core.RegionInfo, group string, s
 		scatterSuccessCounter.Inc()
 		r.Put(targetPeers, targetLeader, group)
 		op.AdditionalInfos["group"] = group
-		op.AdditionalInfos["leader-hit"] = strconv.FormatUint(leaderHit, 10)
+		op.AdditionalInfos["leader-picked-count"] = strconv.FormatUint(leaderStorePickedCount, 10)
 		op.SetPriorityLevel(constant.High)
 	}
 	return op
@@ -426,6 +426,12 @@ func isSameDistribution(region *core.RegionInfo, targetPeers map[uint64]*metapb.
 	return region.GetLeader().GetStoreId() == targetLeader
 }
 
+// selectNewPeer return the new peer which pick the fewest picked count.
+// it keeps the origin peer if the origin store's pick count is equal the fewest pick.
+// it can be diveded into three steps:
+// 1. found the max pick count and the min pick count.
+// 2. if max pick count equals min pick count, it means all store picked count are some, return the origin peer.
+// 3. otherwise, select the store which pick count is the min pick count and pass all filter.
 func (r *RegionScatterer) selectNewPeer(context engineContext, group string, peer *metapb.Peer, filters []filter.Filter) *metapb.Peer {
 	stores := r.cluster.GetStores()
 	maxStoreTotalCount := uint64(0)
@@ -442,11 +448,11 @@ func (r *RegionScatterer) selectNewPeer(context engineContext, group string, pee
 
 	var newPeer *metapb.Peer
 	minCount := uint64(math.MaxUint64)
-	sourceHit := uint64(math.MaxUint64)
+	originStorePickedCount := uint64(math.MaxUint64)
 	for _, store := range stores {
 		storeCount := context.selectedPeer.Get(store.GetID(), group)
 		if store.GetID() == peer.GetId() {
-			sourceHit = storeCount
+			originStorePickedCount = storeCount
 		}
 		// If storeCount is equal to the maxStoreTotalCount, we should skip this store as candidate.
 		// If the storeCount are all the same for the whole cluster(maxStoreTotalCount == minStoreTotalCount), any store
@@ -463,7 +469,7 @@ func (r *RegionScatterer) selectNewPeer(context engineContext, group string, pee
 			}
 		}
 	}
-	if sourceHit <= minCount {
+	if originStorePickedCount <= minCount {
 		return peer
 	}
 	if newPeer == nil {
@@ -475,7 +481,7 @@ func (r *RegionScatterer) selectNewPeer(context engineContext, group string, pee
 // selectAvailableLeaderStore select the target leader store from the candidates. The candidates would be collected by
 // the existed peers store depended on the leader counts in the group level. Please use this func before scatter spacial engines.
 func (r *RegionScatterer) selectAvailableLeaderStore(group string, region *core.RegionInfo,
-	leaderCandidateStores []uint64, context engineContext) (leaderID uint64, hit uint64) {
+	leaderCandidateStores []uint64, context engineContext) (leaderID uint64, leaderStorePickedCount uint64) {
 	sourceStore := r.cluster.GetStore(region.GetLeader().GetStoreId())
 	if sourceStore == nil {
 		log.Error("failed to get the store", zap.Uint64("store-id", region.GetLeader().GetStoreId()), errs.ZapError(errs.ErrGetSourceStore))