From 3b62d33f884b8886124009abb8870f39a25a380b Mon Sep 17 00:00:00 2001
From: disksing <i@disksing.com>
Date: Fri, 1 Sep 2017 13:54:30 +0800
Subject: [PATCH] *: extract replica selector. (#717)

---
 server/balancer.go | 55 ++++++++++------------------------------------
 server/selector.go | 54 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+), 44 deletions(-)

diff --git a/server/balancer.go b/server/balancer.go
index 9014f026417..9285399a179 100644
--- a/server/balancer.go
+++ b/server/balancer.go
@@ -288,57 +288,24 @@ func (r *replicaChecker) SelectBestStoreToAddReplica(region *RegionInfo, filters
 	}
 	filters = append(filters, newFilters...)
 
-	var (
-		bestStore *StoreInfo
-		bestScore float64
-	)
-
-	// Select the store with best distinct score.
-	// If the scores are the same, select the store with minimal region score.
-	stores := r.cluster.getRegionStores(region)
-	for _, store := range r.cluster.getStores() {
-		if filterTarget(store, filters) {
-			continue
-		}
-		score := r.rep.GetDistinctScore(stores, store)
-		if bestStore == nil || compareStoreScore(store, score, bestStore, bestScore) > 0 {
-			bestStore = store
-			bestScore = score
-		}
-	}
-
-	if bestStore == nil || filterTarget(bestStore, r.filters) {
+	regionStores := r.cluster.getRegionStores(region)
+	selector := newReplicaSelector(regionStores, r.rep, r.filters...)
+	target := selector.SelectTarget(r.cluster.getStores(), filters...)
+	if target == nil {
 		return 0, 0
 	}
-
-	return bestStore.GetId(), bestScore
+	return target.GetId(), r.rep.GetDistinctScore(regionStores, target)
 }
 
 // selectWorstPeer returns the worst peer in the region.
-func (r *replicaChecker) selectWorstPeer(region *RegionInfo, filters ...Filter) (*metapb.Peer, float64) {
-	var (
-		worstStore *StoreInfo
-		worstScore float64
-	)
-
-	// Select the store with lowest distinct score.
-	// If the scores are the same, select the store with maximal region score.
-	stores := r.cluster.getRegionStores(region)
-	for _, store := range stores {
-		if filterSource(store, filters) {
-			continue
-		}
-		score := r.rep.GetDistinctScore(stores, store)
-		if worstStore == nil || compareStoreScore(store, score, worstStore, worstScore) < 0 {
-			worstStore = store
-			worstScore = score
-		}
-	}
-
-	if worstStore == nil || filterSource(worstStore, r.filters) {
+func (r *replicaChecker) selectWorstPeer(region *RegionInfo) (*metapb.Peer, float64) {
+	regionStores := r.cluster.getRegionStores(region)
+	selector := newReplicaSelector(regionStores, r.rep, r.filters...)
+	worstStore := selector.SelectSource(regionStores)
+	if worstStore == nil {
 		return nil, 0
 	}
-	return region.GetStorePeer(worstStore.GetId()), worstScore
+	return region.GetStorePeer(worstStore.GetId()), r.rep.GetDistinctScore(regionStores, worstStore)
 }
 
 // selectBestReplacement returns the best store to replace the region peer.
diff --git a/server/selector.go b/server/selector.go
index 19372ccec1e..a6f32d57539 100644
--- a/server/selector.go
+++ b/server/selector.go
@@ -63,6 +63,60 @@ func (s *balanceSelector) SelectTarget(stores []*StoreInfo, filters ...Filter) *
 	return result
 }
 
+type replicaSelector struct {
+	regionStores []*StoreInfo
+	rep          *Replication
+	filters      []Filter
+}
+
+func newReplicaSelector(regionStores []*StoreInfo, rep *Replication, filters ...Filter) Selector {
+	return &replicaSelector{
+		regionStores: regionStores,
+		rep:          rep,
+		filters:      filters,
+	}
+}
+
+func (s *replicaSelector) SelectSource(stores []*StoreInfo, filters ...Filter) *StoreInfo {
+	var (
+		best      *StoreInfo
+		bestScore float64
+	)
+	for _, store := range stores {
+		if filterSource(store, filters) {
+			continue
+		}
+		score := s.rep.GetDistinctScore(s.regionStores, store)
+		if best == nil || compareStoreScore(store, score, best, bestScore) < 0 {
+			best, bestScore = store, score
+		}
+	}
+	if best == nil || filterSource(best, s.filters) {
+		return nil
+	}
+	return best
+}
+
+func (s *replicaSelector) SelectTarget(stores []*StoreInfo, filters ...Filter) *StoreInfo {
+	var (
+		best      *StoreInfo
+		bestScore float64
+	)
+	for _, store := range stores {
+		if filterTarget(store, filters) {
+			continue
+		}
+		score := s.rep.GetDistinctScore(s.regionStores, store)
+		if best == nil || compareStoreScore(store, score, best, bestScore) > 0 {
+			best, bestScore = store, score
+		}
+	}
+	if best == nil || filterTarget(best, s.filters) {
+		return nil
+	}
+	return best
+}
+
 type randomSelector struct {
 	filters []Filter
 }