之前服务器要加竹mod的时候提示forge版本过低，于是升级了mcpc，同时看到mcmmo也发布了新版，于是就打算顺手升个级。
但是不料升级后我登陆正常，部分其他用户登陆后无法加载mcmmo等级，后台的log显示
[08:52:11] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] Location: sun.reflect.NativeConstructorAccessorImpl newInstance0 -2
[08:52:11] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] SQLException: Duplicate entry 'Bond_Girl' for key 'user'
[08:52:11] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] SQLState: 23000
[08:52:11] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] VendorError: 1062
[08:52:16] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] Location: sun.reflect.NativeConstructorAccessorImpl newInstance0 -2
[08:52:16] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] SQLException: Duplicate entry 'Bond_Girl' for key 'user'
[08:52:16] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] SQLState: 23000
[08:52:16] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] VendorError: 1062
[08:52:26] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] Location: sun.reflect.NativeConstructorAccessorImpl newInstance0 -2
[08:52:26] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] SQLException: Duplicate entry 'Bond_Girl' for key 'user'
[08:52:26] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] SQLState: 23000
[08:52:26] [Craft Scheduler Thread - 1482/ERROR]: [mcMMO] VendorError: 1062
[08:52:41] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] Location: sun.reflect.NativeConstructorAccessorImpl newInstance0 -2
[08:52:41] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] SQLException: Duplicate entry 'Bond_Girl' for key 'user'
[08:52:41] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] SQLState: 23000
[08:52:41] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] VendorError: 1062
[08:53:01] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] Location: sun.reflect.NativeConstructorAccessorImpl newInstance0 -2
[08:53:01] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] SQLException: Duplicate entry 'Bond_Girl' for key 'user'
[08:53:01] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] SQLState: 23000
[08:53:01] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] VendorError: 1062
[08:53:01] [Craft Scheduler Thread - 1481/ERROR]: [mcMMO] Giving up on attempting to load the PlayerProfile for Bond_Girl
去数据一看，数据库里记录的uuid和用户现在使用的uuid不同。导致mcmmo找不见用户，而要插入新数据的时候则user字段上的unique索引冲突。
最初以为是个例，因为我是能够正常使用的。于是帮着上线了的几个用户修改了数据库，不过随着发现这个问题的玩家越来越多，这么下去也不是办法，于是看了一下mcmmo的源码，
com.gmail.nossr50.database.SQLDatabaseManager#newUser(java.sql.Connection, java.lang.String, java.util.UUID)
这个方法里的sql语句使用的是INSERT INTO，会导致插入时报错，于是干脆改成REPLACE INTO，让MySQL自行处理冲突去。
不过使用了主从同步的服务器请谨慎使用REPLACE INTO，请使用 ON DUPLICATE KEY方法进行处理，比如
"INSERT INTO " + tablePrefix + "users (user, uuid, lastlogin) VALUES (?, ?, UNIX_TIMESTAMP()) ON DUPLICATE KEY UPDATE uuid=?"
然后在
statement.setString(2, uuid != null ? uuid.toString() : null);
之后添加一行
statement.setString(3, uuid != null ? uuid.toString() : null);