statistics,metrics: allow stats health to have finer granularity (#56475)

close pingcap/tidb#56498

pkg/statistics/handle/cache/statscache.go

@@ -258,7 +258,7 @@ func (s *StatsCacheImpl) SetStatsCacheCapacity(c int64) {
 
 // UpdateStatsHealthyMetrics updates stats healthy distribution metrics according to stats cache.
 func (s *StatsCacheImpl) UpdateStatsHealthyMetrics() {
-	distribution := make([]int64, 5)
+	distribution := make([]int64, 9)
 	uneligibleAnalyze := 0
 	for _, tbl := range s.Values() {
 		distribution[4]++ // total table count
@@ -273,16 +273,22 @@ func (s *StatsCacheImpl) UpdateStatsHealthyMetrics() {
 		}
 		if healthy < 50 {
 			distribution[0]++
-		} else if healthy < 80 {
+		} else if healthy < 55 {
 			distribution[1]++
-		} else if healthy < 100 {
+		} else if healthy < 60 {
 			distribution[2]++
-		} else {
+		} else if healthy < 70 {
 			distribution[3]++
+		} else if healthy < 80 {
+			distribution[4]++
+		} else if healthy < 100 {
+			distribution[5]++
+		} else {
+			distribution[6]++
 		}
 	}
 	for i, val := range distribution {
 		handle_metrics.StatsHealthyGauges[i].Set(float64(val))
 	}
-	handle_metrics.StatsHealthyGauges[5].Set(float64(uneligibleAnalyze))
+	handle_metrics.StatsHealthyGauges[8].Set(float64(uneligibleAnalyze))
 }

pkg/statistics/handle/metrics/metrics.go

@@ -35,7 +35,10 @@ func init() {
 func InitMetricsVars() {
 	StatsHealthyGauges = []prometheus.Gauge{
 		metrics.StatsHealthyGauge.WithLabelValues("[0,50)"),
-		metrics.StatsHealthyGauge.WithLabelValues("[50,80)"),
+		metrics.StatsHealthyGauge.WithLabelValues("[50,55)"),
+		metrics.StatsHealthyGauge.WithLabelValues("[55,60)"),
+		metrics.StatsHealthyGauge.WithLabelValues("[60,70)"),
+		metrics.StatsHealthyGauge.WithLabelValues("[70,80)"),
 		metrics.StatsHealthyGauge.WithLabelValues("[80,100)"),
 		metrics.StatsHealthyGauge.WithLabelValues("[100,100]"),
 		// [0,100] should always be the last