场景大概是：需要记录大量用户的操作Action，需要查询用户最新的行为

采用数据库设计有类似的SQL

SELECT id, name, stamp FROM actions WHERE userid = 1
ORDER BY stamp DESC LIMIT 10 OFFSET 20;
NSERT INTO actions (id, userid, name, stamp) VALUES (newid(), 1, 'Joe User', epoch());

如果采用HBASE设计，ROW设计为<userid><reverse_order_stamp><actionid>
之所以采用row-per-action而不是row-per-user,主要考虑采用row自身的索引进行查询

public static byte [] makeActionRow(int userid, long stamp, int actionid)
throws Exception {
  byte [] useridBytes = Bytes.toBytes(userid);
  byte [] stampBytes = Bytes.toBytes(stamp);
  byte [] actionidBytes = Bytes.toBytes(actionid);
  return Bytes.add(useridBytes, stampBytes, actionidBytes);
}

public static Action readActionRow(byte [] row)
throws Exception {
  // Bytes.toInt(byte [] buf, int offset, int length)
  int userid = Bytes.toInt(row,0,4);
  long stamp = Long.MAX_VALUE - Bytes.toLong(row,4,8);
  int actionid = Bytes.toInt(row,12,4);
  return new Action(userid,stamp,actionid);
}

插入操作

public static void putUserAction(Action action) throws Exception {
  // Get the fields from the Action object
  int userid = action.getUserID();
  long stamp = Long.MAX_VALUE - action.getStamp();
  int actionid = action.getID();
  String name = action.getName();
 
  // Build the composite row, column, and value
  byte [] row = makeActionRow(userid,stamp,actionid);
  byte [] column = Bytes.toBytes("content:name");
  byte [] value = Bytes.toBytes(name);
 
  // Insert to HBase
  HTable ht = new HTable("useractions");
  BatchUpdate bu = new BatchUpdate(row);
  bu.put(column,value)
  ht.commit(bu);
}

进行分页查询

public static List<Action> getUserActions(int userid, int offset, int limit)
throws Exception {
  // Initialize counter and List to return
  int count = 0;
  List<Action> actions = new ArrayList<Action>(limit);
 
  // Initialize startRow, stopRow, and columns to match
  byte [] startRow = makeActionRow(userid,0,0);
  byte [] stopRow = makeActionRow(userid,Long.MAX_VALUE,Integer.MAX_VALUE);
  byte [][] columns = {Bytes.toBytes("content:name")};
 
  // Open Scanner
  HTable ht = new HTable("useractions");
  Scanner s = ht.getScanner(columns,startRow,stopRow);
  RowResult res = null;
 
  // Iterate over Scanner
  while((res = s.next()) != null) {
    // Check if past offset
    if(++count <= offset) continue;
 
    // Get data from RowResult
    byte [] row = res.getRow();
    byte [] value = res.get(columns[0]).getValue();
 
    // Build Action
    Action action = readActionRow(row);
    String name = Bytes.toString(value);
    action.setName(name);
    actions.add(action);
 
    // Check limit
    if(count == offset + limit) break;
  }
  // Cleanup and return
  s.close();
  return actions;
}