code: private List getBlockKeys(QueryConditonDatakey qcdk) {
  		List keys = blockCacheManager.getBlockKeysFromCache(qcdk);
  		if ((keys == null)) {
  			keys = blockQueryJDBC.fetchDatas(qcdk);
  			if (keys != null && keys.size() != 0)
  				blockCacheManager.saveBlockKeys(qcdk, keys);
  		}
  		Debug.logVerbose("[JdonFramework] getBlockKeys, size=" + keys.size(), module);
  		return keys;
  	}
docs: get a Block that begin at the start
  
  @param qcdk
  QueryConditonDatakey
  @return return the collection fit for start value and count value.