core: adjust capacity to fit for more cases (tikv#1035)

conf/config.toml

@@ -62,8 +62,6 @@ region-schedule-limit = 4
 replica-schedule-limit = 8
 merge-schedule-limit = 8
 tolerant-size-ratio = 5
-high-space-reatio = 0.8
-low-space-ratio = 0.6
 
 # customized schedulers, the format is as below
 # if empty, it will use balance-leader, balance-region, hot-region as default

server/core/store.go

@@ -113,17 +113,18 @@ func (s *StoreInfo) LeaderScore(delta int64) float64 {
 
 // RegionScore returns the store's region score.
 func (s *StoreInfo) RegionScore(highSpaceRatio, lowSpaceRatio float64, delta int64) float64 {
-	if s.RegionSize == 0 {
-		return float64(delta)
-	}
-
-	capacity := float64(s.Stats.GetCapacity()) / (1 << 20)
-	available := float64(s.Stats.GetAvailable()) / (1 << 20)
-
 	var score float64
+	var amplification float64
+	available := float64(s.Stats.GetAvailable()) / (1 << 20)
+	used := float64(s.Stats.GetUsedSize()) / (1 << 20)
+	capacity := float64(s.Stats.GetCapacity()) / (1 << 20)
 
-	// because of rocksdb compression, region size is larger than actual used size
-	amplification := float64(s.RegionSize) / (float64(s.Stats.GetUsedSize()) / (1 << 20))
+	if s.RegionSize == 0 {
+		amplification = 1
+	} else {
+		// because of rocksdb compression, region size is larger than actual used size
+		amplification = float64(s.RegionSize) / used
+	}
 
 	if available-float64(delta)/amplification >= (1-highSpaceRatio)*capacity {
 		score = float64(s.RegionSize + delta)
@@ -132,11 +133,17 @@ func (s *StoreInfo) RegionScore(highSpaceRatio, lowSpaceRatio float64, delta int
 	} else {
 		// to make the score function continuous, we use linear function y = k * x + b as transition period
 		// from above we know that there are two points must on the function image
-		// p1(highSpaceRatio*capacity*amplification, highSpaceRatio*capacity*amplification) and
-		// p2(lowSpaceRatio*capacity*amplification, maxScore-(1-lowSpaceRatio)*capacity)
-		// so k = (y2 - y1) / (x2 - x1)
-		x1, y1 := highSpaceRatio*capacity*amplification, highSpaceRatio*capacity*amplification
-		x2, y2 := lowSpaceRatio*capacity*amplification, maxScore-(1-lowSpaceRatio)*capacity
+		// note that it is possible that other irrelative files occupy a lot of storage, so capacity == available + used + irrelative
+		// and we regarded as irrelative as fixed value.
+		// Then amp = size / used = size / (capacity - irrelative - available)
+		//
+		// when available == (1 - highSpaceRatio) * capacity
+		// we can conclude that size = (capacity - irrelative - (1 - highSpaceRatio) * capacity) * amp = (used+available-(1-highSpaceRatio)*capacity)*amp
+		// Similarly, when available == (1 - lowSpaceRatio) * capacity
+		// we can conclude that size = (capacity - irrelative - (1 - highSpaceRatio) * capacity) * amp = (used+available-(1-lowSpaceRatio)*capacity)*amp
+		// These are the two fixed points' x-coordinates, and y-coordinates can easily get from the above two functions.
+		x1, y1 := (used+available-(1-highSpaceRatio)*capacity)*amplification, (used+available-(1-highSpaceRatio)*capacity)*amplification
+		x2, y2 := (used+available-(1-lowSpaceRatio)*capacity)*amplification, maxScore-(1-lowSpaceRatio)*capacity
 
 		k := (y2 - y1) / (x2 - x1)
 		b := y1 - k*x1

server/store_statistics.go

@@ -80,10 +80,9 @@ func (s *storeStatistics) Observe(store *core.StoreInfo) {
 	storeStatusGauge.WithLabelValues(s.namespace, id, "region_count").Set(float64(store.RegionCount))
 	storeStatusGauge.WithLabelValues(s.namespace, id, "leader_size").Set(float64(store.LeaderSize))
 	storeStatusGauge.WithLabelValues(s.namespace, id, "leader_count").Set(float64(store.LeaderCount))
-	storeStatusGauge.WithLabelValues(s.namespace, id, "storage_available").Set(float64(store.Stats.GetAvailable()))
-	storeStatusGauge.WithLabelValues(s.namespace, id, "storage_capacity").Set(float64(store.Stats.GetCapacity()))
-	storeStatusGauge.WithLabelValues(s.namespace, id, "storage_used").Set(float64(store.Stats.GetUsedSize()))
-	storeStatusGauge.WithLabelValues(s.namespace, id, "score_amplify").Set(float64(store.RegionSize) / float64(store.Stats.GetUsedSize()) * (1 << 20))
+	storeStatusGauge.WithLabelValues(s.namespace, id, "store_available").Set(float64(store.Stats.GetAvailable()))
+	storeStatusGauge.WithLabelValues(s.namespace, id, "store_used").Set(float64(store.Stats.GetUsedSize()))
+	storeStatusGauge.WithLabelValues(s.namespace, id, "store_capacity").Set(float64(store.Stats.GetCapacity()))
 }
 
 func (s *storeStatistics) Collect() {