mcs/tso: add log to show the progress of group cleaning up

pkg/tso/keyspace_group_manager.go

@@ -137,6 +137,13 @@ func (s *state) getDeletedGroups() []uint32 {
 	return groups
 }
 
+// getDeletedGroupNum returns the number of the deleted keyspace groups.
+func (s *state) getDeletedGroupNum() int {
+	s.RLock()
+	defer s.RUnlock()
+	return len(s.deletedGroups)
+}
+
 func (s *state) checkTSOSplit(
 	targetGroupID uint32,
 ) (splitTargetAM, splitSourceAM *AllocatorManager, err error) {
@@ -1391,6 +1398,11 @@ func (kgm *KeyspaceGroupManager) deletedGroupCleaner() {
 	defer ticker.Stop()
 	log.Info("deleted group cleaner is started",
 		zap.Duration("patrol-interval", patrolInterval))
+	var (
+		empty               = true
+		lastDeletedGroupID  uint32
+		lastDeletedGroupNum int
+	)
 	for {
 		select {
 		case <-kgm.ctx.Done():
@@ -1403,6 +1415,7 @@ func (kgm *KeyspaceGroupManager) deletedGroupCleaner() {
 			if groupID == mcsutils.DefaultKeyspaceGroupID {
 				continue
 			}
+			empty = false
 			// Make sure the allocator and group meta are not in use anymore.
 			am, _ := kgm.getKeyspaceGroupMeta(groupID)
 			if am != nil {
@@ -1428,6 +1441,18 @@ func (kgm *KeyspaceGroupManager) deletedGroupCleaner() {
 			kgm.Lock()
 			delete(kgm.deletedGroups, groupID)
 			kgm.Unlock()
+			lastDeletedGroupID = groupID
+			lastDeletedGroupNum += 1
+		}
+		// This log would be helpful to check if the deleted groups are all gone.
+		if !empty && kgm.getDeletedGroupNum() == 0 {
+			log.Info("all the deleted keyspace groups have been cleaned up",
+				zap.Uint32("last-deleted-group-id", lastDeletedGroupID),
+				zap.Int("last-deleted-group-num", lastDeletedGroupNum))
+			// Reset the state to make sure the log won't be printed again
+			// until we have new deleted groups.
+			empty = true
+			lastDeletedGroupNum = 0
 		}
 	}
 }