diff --git a/pkg/services/ngalert/state/cache.go b/pkg/services/ngalert/state/cache.go
index 6d480bf3917..d48c19c5eab 100644
--- a/pkg/services/ngalert/state/cache.go
+++ b/pkg/services/ngalert/state/cache.go
@@ -92,8 +92,8 @@ func (c *cache) set(entry *State) {
 }
 
 func (c *cache) get(orgID int64, alertRuleUID, stateId string) (*State, error) {
-	c.mtxStates.Lock()
-	defer c.mtxStates.Unlock()
+	c.mtxStates.RLock()
+	defer c.mtxStates.RUnlock()
 	if state, ok := c.states[orgID][alertRuleUID][stateId]; ok {
 		return state, nil
 	}
@@ -102,8 +102,8 @@ func (c *cache) get(orgID int64, alertRuleUID, stateId string) (*State, error) {
 
 func (c *cache) getAll(orgID int64) []*State {
 	var states []*State
-	c.mtxStates.Lock()
-	defer c.mtxStates.Unlock()
+	c.mtxStates.RLock()
+	defer c.mtxStates.RUnlock()
 	for _, v1 := range c.states[orgID] {
 		for _, v2 := range v1 {
 			states = append(states, v2)
@@ -114,8 +114,8 @@ func (c *cache) getAll(orgID int64) []*State {
 
 func (c *cache) getStatesForRuleUID(orgID int64, alertRuleUID string) []*State {
 	var ruleStates []*State
-	c.mtxStates.Lock()
-	defer c.mtxStates.Unlock()
+	c.mtxStates.RLock()
+	defer c.mtxStates.RUnlock()
 	for _, state := range c.states[orgID][alertRuleUID] {
 		ruleStates = append(ruleStates, state)
 	}
@@ -135,9 +135,9 @@ func (c *cache) reset() {
 	c.states = make(map[int64]map[string]map[string]*State)
 }
 
-func (c *cache) trim() {
-	c.mtxStates.Lock()
-	defer c.mtxStates.Unlock()
+func (c *cache) recordMetrics() {
+	c.mtxStates.RLock()
+	defer c.mtxStates.RUnlock()
 
 	// Set default values to zero such that gauges are reset
 	// after all values from a single state disappear.
@@ -153,13 +153,6 @@ func (c *cache) trim() {
 		c.metrics.GroupRules.WithLabelValues(fmt.Sprint(org)).Set(float64(len(orgMap)))
 		for _, rule := range orgMap {
 			for _, state := range rule {
-				if len(state.Results) > 100 {
-					newResults := make([]Evaluation, 100)
-					// Keep last 100 results
-					copy(newResults, state.Results[len(state.Results)-100:])
-					state.Results = newResults
-				}
-
 				n := ct[state.State]
 				ct[state.State] = n + 1
 			}
diff --git a/pkg/services/ngalert/state/manager.go b/pkg/services/ngalert/state/manager.go
index 49210de5bd3..3c7259143fa 100644
--- a/pkg/services/ngalert/state/manager.go
+++ b/pkg/services/ngalert/state/manager.go
@@ -1,7 +1,6 @@
 package state
 
 import (
-	"fmt"
 	"time"
 
 	"github.com/grafana/grafana/pkg/infra/log"
@@ -25,7 +24,7 @@ func NewManager(logger log.Logger, metrics *metrics.Metrics) *Manager {
 		Log:     logger,
 		metrics: metrics,
 	}
-	go manager.cleanUp()
+	go manager.recordMetrics()
 	return manager
 }
 
@@ -78,6 +77,7 @@ func (st *Manager) setNextState(alertRule *ngModels.AlertRule, result eval.Resul
 		EvaluationState:  result.State,
 		EvaluationString: result.EvaluationString,
 	})
+	currentState.TrimResults(alertRule)
 
 	st.Log.Debug("setting alert state", "uid", alertRule.UID)
 	switch result.State {
@@ -104,19 +104,18 @@ func (st *Manager) GetStatesForRuleUID(orgID int64, alertRuleUID string) []*Stat
 	return st.cache.getStatesForRuleUID(orgID, alertRuleUID)
 }
 
-func (st *Manager) cleanUp() {
+func (st *Manager) recordMetrics() {
 	// TODO: parameterize?
 	// Setting to a reasonable default scrape interval for Prometheus.
 	dur := time.Duration(15) * time.Second
 	ticker := time.NewTicker(dur)
-	st.Log.Debug("starting cleanup process", "dur", fmt.Sprint(dur))
 	for {
 		select {
 		case <-ticker.C:
-			st.Log.Info("trimming alert state cache", "now", time.Now())
-			st.cache.trim()
+			st.Log.Info("recording state cache metrics", "now", time.Now())
+			st.cache.recordMetrics()
 		case <-st.quit:
-			st.Log.Debug("stopping cleanup process", "now", time.Now())
+			st.Log.Debug("stopping state cache metrics recording", "now", time.Now())
 			ticker.Stop()
 			return
 		}
diff --git a/pkg/services/ngalert/state/state.go b/pkg/services/ngalert/state/state.go
index 3b535ccdc70..dc11b6a4a7e 100644
--- a/pkg/services/ngalert/state/state.go
+++ b/pkg/services/ngalert/state/state.go
@@ -123,3 +123,17 @@ func (a *State) Equals(b *State) bool {
 		a.LastEvaluationTime == b.LastEvaluationTime &&
 		data.Labels(a.Annotations).String() == data.Labels(b.Annotations).String()
 }
+
+func (a *State) TrimResults(alertRule *ngModels.AlertRule) {
+	numBuckets := 2 * (int64(alertRule.For.Seconds()) / alertRule.IntervalSeconds)
+	if numBuckets == 0 {
+		numBuckets = 10 // keep at least 10 evaluations in the event For is set to 0
+	}
+
+	if len(a.Results) < int(numBuckets) {
+		return
+	}
+	newResults := make([]Evaluation, numBuckets)
+	copy(newResults, a.Results[len(a.Results)-int(numBuckets):])
+	a.Results = newResults
+}