docs: private void init() {
          logger.info("metadata init().");
  
          writeLock.lock();
          try {
          // Required keys
          initCache(CLUSTER_KEY);
  
          // If stores definition storage engine is not null, initialize metadata
          // Add the mapping from key to the storage engine used
          if(this.storeDefinitionsStorageEngine != null) {
              initStoreDefinitions(null);
          } else {
              initCache(STORES_KEY);
          }
  
          // Initialize system store in the metadata cache
          initSystemCache();
          initSystemRoutingStrategies(getCluster());
  
          // Initialize with default if not present
          initCache(SLOP_STREAMING_ENABLED_KEY, true);
          initCache(PARTITION_STREAMING_ENABLED_KEY, true);
          initCache(READONLY_FETCH_ENABLED_KEY, true);
          initCache(QUOTA_ENFORCEMENT_ENABLED_KEY, true);
          initCache(REBALANCING_STEAL_INFO, new RebalancerState(new ArrayList<RebalanceTaskInfo>()));
          initCache(SERVER_STATE_KEY, VoldemortState.NORMAL_SERVER.toString());
          initCache(REBALANCING_SOURCE_CLUSTER_XML, null);
          initCache(REBALANCING_SOURCE_STORES_XML, null);
  
  
          } finally {
              writeLock.unlock();
          }
      }