retry on leader for region not available (#1769)

Signed-off-by: rishabh_mittal <rishabh.mittal@airbnb.com>

Co-authored-by: rishabh_mittal <rishabh.mittal@airbnb.com>

internal/locate/region_cache.go

@@ -1851,6 +1851,14 @@ func (c *RegionCache) BatchLoadRegionsFromKey(bo *retry.Backoffer, startKey []by
 	return regions[len(regions)-1].EndKey(), nil
 }
 
+func (c *RegionCache) AsyncInvalidateCachedRegion(id RegionVerID) {
+	cachedRegion := c.GetCachedRegionWithRLock(id)
+	if cachedRegion == nil {
+		return
+	}
+	cachedRegion.setSyncFlags(needDelayedReloadPending)
+}
+
 // InvalidateCachedRegion removes a cached Region.
 func (c *RegionCache) InvalidateCachedRegion(id RegionVerID) {
 	c.InvalidateCachedRegionWithReason(id, Other)

internal/locate/region_request.go

@@ -1956,8 +1956,12 @@ 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
+		if s.replicaSelector != nil {
+			return s.replicaSelector.onRegionNotFound(bo, ctx, req)
+		} else {
+			s.regionCache.InvalidateCachedRegion(ctx.Region)
+			return false, nil
+		}
 	}
 
 	if regionErr.GetKeyNotInRegion() != nil {

internal/locate/region_request_state_test.go

@@ -303,11 +303,11 @@ func testRegionCacheStaleRead(t *testing.T) {
 			leaderAsyncReload:     util.Some(false),
 			leaderSuccessReplica:  []string{"z1"},
 			leaderSuccessReadType: SuccessStaleRead,
-			followerRegionValid:   false,
-			followerAsyncReload:   util.Some(false),
+			followerRegionValid:   true,
+			followerAsyncReload:   util.Some(true),
 			// may async reload region and access it from leader.
-			followerSuccessReplica:  []string{},
-			followerSuccessReadType: ReadFail,
+			followerSuccessReplica:  []string{"z1"},
+			followerSuccessReadType: SuccessStaleRead,
 		},
 		{
 			do:                evictLeader,

internal/locate/replica_selector.go

@@ -517,6 +517,23 @@ func (s *replicaSelector) onDataIsNotReady() {
 	}
 }
 
+func (s *replicaSelector) onRegionNotFound(
+	bo *retry.Backoffer, ctx *RPCContext, req *tikvrpc.Request,
+) (shouldRetry bool, err error) {
+	leaderIdx := s.region.getStore().workTiKVIdx
+	leader := s.replicas[leaderIdx]
+	if !leader.isExhausted(1, 0) {
+		// if the request is not sent to leader, we can retry it with leader and invalidate the region cache asynchronously. It helps in the scenario
+		// where region is split by the leader but not yet created in replica due to replica down.
+		req.SetReplicaReadType(kv.ReplicaReadLeader)
+		s.replicaReadType = kv.ReplicaReadLeader
+		s.regionCache.AsyncInvalidateCachedRegion(ctx.Region)
+		return true, nil
+	}
+	s.regionCache.InvalidateCachedRegion(ctx.Region)
+	return false, nil
+}
+
 func (s *replicaSelector) onServerIsBusy(
 	bo *retry.Backoffer, ctx *RPCContext, req *tikvrpc.Request, serverIsBusy *errorpb.ServerIsBusy,
 ) (shouldRetry bool, err error) {

internal/locate/replica_selector_test.go

@@ -1149,12 +1149,24 @@ func testReplicaReadAccessPathByBasicCase(s *testReplicaSelectorSuite) {
 						respErr = "region 0 is not prepared for the flashback"
 						respRegionError = nil
 						regionIsValid = true
+					case RegionNotFoundErr:
+						regionIsValid = false
 					}
 					switch readType {
 					case kv.ReplicaReadLeader:
 						accessPath = []string{"{addr: store1, replica-read: false, stale-read: false}"}
 					case kv.ReplicaReadFollower:
-						accessPath = []string{"{addr: store2, replica-read: true, stale-read: false}"}
+						// For RegionNotFoundErr from follower, it will retry on leader
+						if tp == RegionNotFoundErr {
+							accessPath = []string{
+								"{addr: store2, replica-read: true, stale-read: false}",
+								"{addr: store1, replica-read: false, stale-read: false}",
+							}
+							respRegionError = nil
+							regionIsValid = true
+						} else {
+							accessPath = []string{"{addr: store2, replica-read: true, stale-read: false}"}
+						}
 					case kv.ReplicaReadMixed:
 						if staleRead {
 							accessPath = []string{"{addr: store1, replica-read: false, stale-read: true}"}