add region cache state test & fix some issues of replica selector (ti…

…kv#910)

Signed-off-by: you06 <[email protected]>

internal/locate/region_cache.go

@@ -534,10 +534,12 @@ func (c *RegionCache) Close() {
 	c.cancelFunc()
 }
 
+var reloadRegionInterval = int64(10 * time.Second)
+
 // asyncCheckAndResolveLoop with
 func (c *RegionCache) asyncCheckAndResolveLoop(interval time.Duration) {
 	ticker := time.NewTicker(interval)
-	reloadRegionTicker := time.NewTicker(10 * time.Second)
+	reloadRegionTicker := time.NewTicker(time.Duration(atomic.LoadInt64(&reloadRegionInterval)))
 	defer func() {
 		ticker.Stop()
 		reloadRegionTicker.Stop()

internal/locate/region_request.go

@@ -2012,6 +2012,7 @@ func (s *RegionRequestSender) onRegionError(
 	}
 
 	// This peer is removed from the region. Invalidate the region since it's too stale.
+	// if the region error is from follower, can we mark the peer unavailable and reload region asynchronously?
 	if regionErr.GetRegionNotFound() != nil {
 		s.regionCache.InvalidateCachedRegion(ctx.Region)
 		return false, nil
@@ -2041,6 +2042,10 @@ func (s *RegionRequestSender) onRegionError(
 			s.replicaSelector.onDeadlineExceeded()
 			return true, nil
 		}
+		if s.replicaSelector.canFallback2Follower() {
+			// immediately retry on followers.
+			return true, nil
+		}
 		if s.replicaSelector != nil {
 			return s.replicaSelector.onServerIsBusy(bo, ctx, req, serverIsBusy)
 		}