code: @Override
      public Set getDepIdsByRangeDisk(int index, int length) {
          final String methodName = "getDepIdsByRangeDisk()";
          Set ids = new HashSet();
          if (this.swapToDisk) {
              // TODO write code to support getDepIdsByRangeDisk function
              if (tc.isDebugEnabled()) {
                  Tr.debug(tc, methodName + " cacheName=" + cacheName + " ERROR because it is not implemented yet");
              }
          } else {
              if (this.featureSupport.isDiskCacheSupported() == false) {
                  Tr.error(tc, "DYNA1064E", new Object[] { methodName, cacheName, this.cacheProviderName });
              } else {
                  if (tc.isDebugEnabled()) {
                      Tr.debug(tc, methodName + " cacheName=" + cacheName + " no operation is done because the disk cache offload is not enabled");
                  }
              }
          }
          return ids;
      }
docs: Returns a set of dependency IDs based on the range and size.
  WARNING: If index = 1 or -1, the set might contain "DISKCACHE_MORE" to indicate there are more dep ids on the disk cache.
  The caller need to remove DISKCACHE_MORE" from the set before it is being used.
  The "DISKCACHE_MORE" key is defined as HTODDynacache.DISKCACHE_MORE.
  
  @param index If index = 0, it starts the beginning. If index = 1, it means "next". If Index = -1, it means "previous".
  @param length The max number of dependency ids to be read. If length = -1, it reads all dependency ids until the end.
  @return The Set of dependency ids.