剛剛接到報警短信，從庫宕機，馬上通知機房重啓，在檢查MySQL時，發現同步掛了，報主鍵衝突，詢問開發是不是有往裏面寫數據，回答沒有。
這就奇怪了，怎麼會無緣無故報錯呢？在檢查了my.cnf配置文件，發現有個參數沒有配置：
innodb_overwrite_relay_log_info = 1
當從庫宕機後，重新開啓主從複製同步，它可以重新執行已提交事務，這樣就會造成同步失敗，而這個參數就會避免這個問題的出現。
當開啓了這個參數後
.... + InnoDB: Warning: innodb_overwrite_relay_log_info is enabled. Updates of other storage engines may have problem of consistency. + InnoDB: relay-log.info is detected. + InnoDB: relay log: position 429, file name ./gauntlet3-relay-bin.000111 + InnoDB: master log: position 280, file name gauntlet3-bin.000015 .... InnoDB: Starting crash recovery. .... InnoDB: Apply batch completed + InnoDB: In a MySQL replication slave the last master binlog file + InnoDB: position 0 468, file name gauntlet3-bin.000015 + InnoDB: and relay log file + InnoDB: position 0 617, file name ./gauntlet3-relay-bin.000111 090205 17:41:31 InnoDB Plugin 1.0.2-3 started; log sequence number 57933 + InnoDB: relay-log.info have been overwritten. .... 090205 17:41:31 [Note] Slave SQL thread initialized, starting replication in log ``gauntlet3-bin.000015`` at position 468, relay log ``./gauntlet3-relay-bin.000111`` position: 617
已經執行完的Position點：
master log: position 280, file name gauntlet3-bin.000015
在恢復時它內部會檢測到280這個點已經執行完畢，從下一個點468開始同步，並且重寫relay.info文件，確保了主從同步正確。
建議在從庫上添加，如果是官方MySQL，參數是relay_log_recovery=1
具體請參考：http://www.percona.com/doc/percona-server/5.5/reliability/crash_resistant_replication.html