今天几台MySQL服务器突然停电，重启后复制无法启动，总是报如下错误：

080922 10:29:01 [Note] Slave SQL thread initialized, starting replication in log 'mysql-bin.000778' at position 2874108, relay log '
./relay-bin.003287' position: 2874245
080922 10:29:01 [Note] Slave I/O thread: connected to master 'replication@192.168.0.10:3306',  replication started in log 'mysql-b
in.000778' at position 2874108
080922 10:29:01 [ERROR] Error reading packet from server: Client requested master to start replication from impossible position ( se
rver_errno=1236)
080922 10:29:01 [ERROR] Got fatal error 1236: 'Client requested master to start replication from impossible position' from master wh
en reading data from binary log

[@more@]

为什么会报impossible position呢？打开mysql-bin.000778看看。

mysqlbinlog mysql-bin.000778 > log.sql

tail -f log.sql

# at 2871574
#080922 10:20:27 server id 2  end_log_pos 2871601       Xid = 2516638
COMMIT/*!*/;
DELIMITER ;
# End of log file
ROLLBACK /* added by mysqlbinlog */;
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/

最后一个position是2871574，而从库要从2874108开始，难怪报impossible position，难道是断电时有部分log在缓存中还没来得及写入binglog？无论如何先恢复再说吧

stop slave;

CHANGE MASTER TO
MASTER_LOG_FILE='mysql-bin.000778',
MASTER_LOG_POS=2871574;

start slave;

show slave statusG

同步正常。。

后来查看主库的启动日志中这样一段

InnoDB: Last MySQL binlog file position 0 2874108, file name ./mysql-bin.000778
080922 10:22:09  InnoDB: Started; log sequence number 6 2534366248
080922 10:22:09 [Note] Recovering after a crash using mysql-bin
080922 10:22:09 [Note] Starting crash recovery...
080922 10:22:09 [Note] Crash recovery finished.
080922 10:22:09 [Note] /usr/sbin/mysqld: ready for connections.

这里Last MySQL binlog file position 0 2874108也是错误的，这个信息到底是哪里来的呢？为什么会这样呢？不明白。

为了保证以后binglog及时写入，将主库sync_binlog变量设置1。