public static Map<FIndexKey, Double > buildGlobalFIndexTermFreMap() {
		
		Map<FIndexKey, Double > fIndexTermFreMap = new HashMap<FIndexKey, Double >(NUM_FORWARD_INDEX);
		
		try{
			conn = DBConnection.getConnectionInstance();
			String sql = "select docid, word, termfre from forward_index";
			PreparedStatement preparedStatement = conn.prepareStatement(sql);
			ResultSet rs = preparedStatement.executeQuery();
			int cnt = 0;
			while(rs.next()) {
				
				FIndexKey fKey = new FIndexKey();
				fKey.setDocId(rs.getInt(1));
				fKey.setWord(rs.getString(2));
				
				if(++cnt%1000 == 0)
					System.out.println(cnt);
				
				fIndexTermFreMap.put(fKey, rs.getDouble(3));
			}
			
		}
		catch(Exception e) {
			
			System.out.println("get failure !");
			e.printStackTrace();
		}

		return fIndexTermFreMap;
	}