MySQL斷電，出現 Error 1236

今天幾臺MySQL伺服器突然停電，重啟後複製無法啟動，總是報如下錯誤：

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@]

為什麼會報impossible position呢？開啟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*/

最後一個position是2871574，而從庫要從2874108開始，難怪報impossible position，難道是斷電時有部分log在快取中還沒來得及寫入binglog？無論如何先恢復再說吧

stop slave;

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

start slave;

show slave statusG

同步正常。。

後來檢視主庫的啟動日誌中這樣一段

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.

這裡Last MySQL binlog file position 0 2874108也是錯誤的，這個資訊到底是哪裡來的呢？為什麼會這樣呢？不明白。

為了保證以後binglog及時寫入，將主庫sync_binlog變數設定1。