CREATE TABLE `SEQUENCE` (
  `name` varchar(30) NOT NULL COMMENT '分表的表名',
  `gid` bigint(20) NOT NULL COMMENT '最大全局id',
  PRIMARY KEY (`name`)
) ENGINE=innodb 

update sequence set gid = 203 where name = 'users' and gid < 203; 

//$name 表名
function next_id_db($name){
  //获取数据库全局sequence对象
  $seq_dao = Wk_Sequence_Dao_Sequence::getInstance();
  $threshold = 100; //最大尝试次数
  for($i = 0; $i < $threshold; $i++){
    $last_id = $seq_dao->get_seq_id($name);//从数据库获取全局id
    $id = $last_id +1;
    $ret = $seq_dao->set_seq_id($name, $id);
    if($ret){
      return $id;
      break;
    }
  }
  return false;
}

//使用redis实现
//$name 为 逻辑表名
function next_id_redis($name){
  $redis = Wk_Redis_Util::getRedis();//获取redis对象
  $seq_dao = Wk_Sequence_Dao_Sequence::getInstance();//获取存储全局id数据表对象
  if(!is_object($redis)){
    throw new Exception("fail to create redis object");
  }
  $max_times = 10; //最大执行次数 避免redis不可用的时候 进入死循环
  while(1){
    $i++;
    //检测key是否存在，相当于检测锁是否存在
    $ret = $redis->setnx("sequence_{$name}_flag",time());
    if($ret){
      break;
    }
    if($i > $max_times){
      break;
    }
    $time = $redis->get("sequence_{$name}_flag");
    if(is_numeric($time) && time() - $time > 1){//如果循环等待时间大于1秒，则不再等待。
      break;
    }
  }
  $id = $redis->incr("sequence_{$name}");
  //如果操作失败，则从sequence表中获取全局id并加载到redis
  if (intval($id) === 1 or $id === false) {
    $last_id = $seq_dao->get_seq_id($name);//从数据库获取全局id
    if(!is_numeric($last_id)){
      throw new Exception("fail to get id from db");
    }
    $ret = $redis->set("sequence_{$name}",$last_id);
    if($ret == false){
      throw new Exception("fail to set redis key [ sequence_{$name} ]");
    }
    $id = $redis->incr("sequence_{$name}");
    if(!is_numeric($id)){
      throw new Exception("fail to incr redis key [ sequence_{$name} ]");
    }
  }
  $seq_dao->set_seq_id($name, $id);//把生成的全局id写入数据表sequence
  $redis->delete("sequence_{$name}_flag");//删除key，相当于释放锁
  $db = null;
  return $id;
} 

function next_id($name){
  try{
    return $this->next_id_redis($name);
  }
  catch(Exception $e){
    return $this->next_id_db($name);
  }
} 

CREATE TABLE Tickets64 (
      id bigint(20) unsigned NOT NULL auto_increment,
      stub char(1) NOT NULL default '',
      PRIMARY KEY (id),
      UNIQUE KEY stub (stub)
  ) ENGINE=MyISAM 

REPLACE INTO Tickets64 (stub) VALUES ('a');
SELECT LAST_INSERT_ID(); 

TicketServer1:
auto-increment-increment = 2
auto-increment-offset = 1
TicketServer2:
auto-increment-increment = 2
auto-increment-offset = 2