update all region stats

Close #3286, close #3558, close #3199

Signed-off-by: Ryan Leung <rleungx@gmail.com>

server/cluster/cluster.go

@@ -660,6 +660,7 @@ func (c *RaftCluster) processRegionHeartbeat(region *core.RegionInfo) error {
 		hotStat.CheckWriteAsync(statistics.NewCheckPeerTask(peerInfo, region))
 	}
 
+	statsJobs := []func(){func() { c.updateStats(region) }}
 	// Save to storage if meta is updated.
 	// Save to cache if meta or leader is updated, or contains any down/pending peer.
 	// Mark isNew if the region in cache does not have leader.
@@ -707,11 +708,10 @@ func (c *RaftCluster) processRegionHeartbeat(region *core.RegionInfo) error {
 	changedRegions := c.changedRegions
 	c.Unlock()
 
-	var statsJobs []func()
 	for _, item := range overlaps {
-		statsJobs = append(statsJobs, func() { c.clearStats(item) })
+		statsJobs = append([]func(){func() { c.clearStats(item) }}, statsJobs...)
 	}
-	c.statsJobCh <- append(statsJobs, func() { c.updateStats(region) })
+	c.statsJobCh <- statsJobs
 
 	if storage != nil {
 		// If there are concurrent heartbeats from the same region, the last write will win even if