private ValueWithTimestamp getLocalValue(Column col,long start_ts,long end_ts,boolean hasEnd){
		ValueWithTimestamp data=localData.get(col);
		if(data==null)
			return null;
		if(hasEnd){
			if(data.timestamp>=start_ts && data.timestamp<=end_ts)
				return data;
			return null;
		}else{
			if(data.timestamp>=start_ts)
				return data;
			return null;
		}
		
	}