Rewind after cacheGC reaches the end (tikv#678)

Signed-off-by: Yilin Chen <sticnarf@gmail.com>

internal/locate/region_cache.go

@@ -1924,7 +1924,8 @@ func (c *RegionCache) cacheGC() {
 	ticker := time.NewTicker(cleanCacheInterval)
 	defer ticker.Stop()
 
-	iterItem := newBtreeSearchItem([]byte(""))
+	beginning := newBtreeSearchItem([]byte(""))
+	iterItem := beginning
 	expired := make([]*btreeItem, cleanRegionNumPerRound)
 	for {
 		select {
@@ -1950,6 +1951,11 @@ func (c *RegionCache) cacheGC() {
 			})
 			c.mu.RUnlock()
 
+			// Reach the end of the region cache, start from the beginning
+			if count <= cleanRegionNumPerRound {
+				iterItem = beginning
+			}
+
 			if len(expired) > 0 {
 				c.mu.Lock()
 				for _, item := range expired {

internal/locate/region_cache_test.go

@@ -1611,8 +1611,8 @@ func (s *testRegionCacheSuite) TestShouldNotRetryFlashback() {
 }
 
 func (s *testRegionCacheSuite) TestBackgroundCacheGC() {
-	// Prepare 50 regions
-	regionCnt := 50
+	// Prepare 100 regions
+	regionCnt := 100
 	regions := s.cluster.AllocIDs(regionCnt)
 	regions = append([]uint64{s.region1}, regions...)
 	peers := [][]uint64{{s.peer1, s.peer2}}
@@ -1642,6 +1642,26 @@ func (s *testRegionCacheSuite) TestBackgroundCacheGC() {
 		s.cache.mu.RLock()
 		defer s.cache.mu.RUnlock()
 		return len(s.cache.mu.regions) == remaining
-	}, 2*time.Second, 200*time.Millisecond)
+	}, 3*time.Second, 200*time.Millisecond)
+	s.checkCache(remaining)
+
+	// Make another part of the regions stale
+	remaining = 0
+	s.cache.mu.Lock()
+	now = time.Now().Unix()
+	for verID, r := range s.cache.mu.regions {
+		if verID.id%3 == 1 {
+			atomic.StoreInt64(&r.lastAccess, now-regionCacheTTLSec-10)
+		} else {
+			remaining++
+		}
+	}
+	s.cache.mu.Unlock()
+
+	s.Eventually(func() bool {
+		s.cache.mu.RLock()
+		defer s.cache.mu.RUnlock()
+		return len(s.cache.mu.regions) == remaining
+	}, 3*time.Second, 200*time.Millisecond)
 	s.checkCache(remaining)
 }