code: func (db *Database) Dereference(root common.Hash) {
  	// Sanity check to ensure that the meta-root is not removed
  	if root == (common.Hash{}) {
  		log.Error("Attempted to dereference the trie cache meta root")
  		return
  	}
  	db.lock.Lock()
  	defer db.lock.Unlock()
  
  	nodes, storage, start := len(db.dirties), db.dirtiesSize, time.Now()
  	db.dereference(root, common.Hash{})
  
  	db.gcnodes += uint64(nodes - len(db.dirties))
  	db.gcsize += storage - db.dirtiesSize
  	db.gctime += time.Since(start)
  
  	memcacheGCTimeTimer.Update(time.Since(start))
  	memcacheGCSizeMeter.Mark(int64(storage - db.dirtiesSize))
  	memcacheGCNodesMeter.Mark(int64(nodes - len(db.dirties)))
  
  	log.Debug("Dereferenced trie from memory database", "nodes", nodes-len(db.dirties), "size", storage-db.dirtiesSize, "time", time.Since(start),
  		"gcnodes", db.gcnodes, "gcsize", db.gcsize, "gctime", db.gctime, "livenodes", len(db.dirties), "livesize", db.dirtiesSize)
  }
docs: // Dereference removes an existing reference from a root node.