*: get nil in the LFU's onEvict (#45949)

close pingcap/tidb#45946

planner/core/plan_stats_test.go

@@ -296,8 +296,7 @@ func TestPlanStatsLoadTimeout(t *testing.T) {
 }
 
 func TestPlanStatsStatusRecord(t *testing.T) {
-	restore := config.RestoreFunc()
-	defer restore()
+	defer config.RestoreFunc()()
 	config.UpdateGlobal(func(conf *config.Config) {
 		conf.Performance.EnableStatsCacheMemQuota = true
 	})

statistics/handle/cache/internal/lfu/lfu_cache.go

@@ -117,6 +117,11 @@ func DropEvicted(item statistics.TableCacheItem) {
 }
 
 func (s *LFU) onEvict(item *ristretto.Item) {
+	if item.Value == nil {
+		// Sometimes the same key may be passed to the "onEvict/onExit" function twice,
+		// and in the second invocation, the value is empty, so it should not be processed.
+		return
+	}
 	// We do not need to calculate the cost during onEvict, because the onexit function
 	// is also called when the evict event occurs.
 	metrics.EvictCounter.Inc()
@@ -135,6 +140,11 @@ func (s *LFU) onEvict(item *ristretto.Item) {
 }
 
 func (s *LFU) onExit(val interface{}) {
+	if val == nil {
+		// Sometimes the same key may be passed to the "onEvict/onExit" function twice,
+		// and in the second invocation, the value is empty, so it should not be processed.
+		return
+	}
 	s.cost.Add(-1 * val.(*statistics.Table).MemoryUsage().TotalTrackingMemUsage())
 	metrics.CostGauge.Set(float64(s.cost.Load()))
 }

statistics/handle/cache/statscacheinner.go

@@ -161,6 +161,7 @@ func (sc *StatsCache) SetCapacity(c int64) {
 // Close stops the cache.
 func (sc *StatsCache) Close() {
 	sc.c.Close()
+	logutil.BgLogger().Info("closed LFU cache")
 }
 
 // Version returns the version of the current cache, which is defined as