public long getDatabaseMaxTTL(final String database) {
    lock.readLock().lock();
    try {
      return ttlCache.getDatabaseMaxTTL(database);
    } finally {
      lock.readLock().unlock();
    }
  }
Get the maximum ttl of the subtree of the corresponding database.

@param database the path of the database.
@return the maximum ttl of the subtree of the corresponding database. return NULL_TTL if the
    TTL is not set or the database does not exist.
iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/persistence/TTLInfo.java