private void upgrade() throws IllegalPathException {
    // upgrade from old database-level ttl to new device-level ttl
    if (configManager.getTTLManager().getTTLCount() == 1) {
      configManager
          .getTTLManager()
          .setTTL(configManager.getClusterSchemaManager().getTTLInfoForUpgrading());
    }
  }
During the reboot, perform some upgrade works to adapt to the optimizations in the new version.
iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/service/ConfigNode.java