@TestOnly
  public void remove(K key) {
    V value = keyValueMap.remove(key);
    if (value != null) {
      Set<K> keysSet = valueKeysMap.get(value);
      keysSet.remove(key);
      if (keysSet.isEmpty()) {
        valueKeysMap.remove(value);
      }
    }
  }
Get key with minimum value.

@return Key with minimum value
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/structure/BalanceTreeMap.java