code: func (db *DB) releaseSnapshot(se *snapshotElement) {
  	db.snapsMu.Lock()
  	defer db.snapsMu.Unlock()
  
  	se.ref--
  	if se.ref == 0 {
  		db.snapsList.Remove(se.e)
  		se.e = nil
  	} else if se.ref < 0 {
  		panic("leveldb: Snapshot: negative element reference")
  	}
  }
docs: // Releases given snapshot element.