困惑解决msyql主从同步问题

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目前从库不同步，
查看状态：
mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State:
                  Master_Host: xxxx
                  Master_User: xxx
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: xxx-bin.000001
          Read_Master_Log_Pos: 1440046
               Relay_Log_File: host-relay-bin.000001
                Relay_Log_Pos: 4
        Relay_Master_Log_File:xxx-bin.000001
             Slave_IO_Running: No
            Slave_SQL_Running: Yes
              Replicate_Do_DB: xxx
          Replicate_Ignore_DB: mysql
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 1440046
              Relay_Log_Space: 106
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 1236
                Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'Could not find first log file name in binary log index file'
               Last_SQL_Errno: 0
               Last_SQL_Error:
1 row in set (0.00 sec)

从服务器大量错误日志：
101027 16:50:58 [Note] Slave I/O thread: connected to master 'xxx@xxxxxx:3306',replication started in log 'xxx-bin.000001' at position 1440046
101027 16:50:58 [ERROR] Error reading packet from server: Could not find first log file name in binary log index file ( server_errno=1236)
101027 16:50:58 [ERROR] Slave I/O: Got fatal error 1236 from master when reading data from binary log: 'Could not find first log file name in binary log index file', Error_code: 1236
101027 16:50:58 [Note] Slave I/O thread exiting, read up to log 'xxx-bin.000001', position 1440046
主状态：

mysql> show master status\G
*************************** 1. row ***************************
            File: mysql-bin.000001
        Position: 1440046
    Binlog_Do_DB:
Binlog_Ignore_DB:
1 row in set (0.00 sec)

按照正常流程解决，应该是：
slave stop;
CHANGE MASTER TO MASTER_HOST='xxx',MASTER_USER='xx',MASTER_PASSWORD='xx',MASTER_PORT=3306,MASTER_LOG_FILE='xxx-bin.000001',MASTER_LOG_POS=1440046;
slave start;

问题依然存在，

后来经过以下步骤解决，不过有点困惑：
1、重启主库
2、给从库重新授权
3、执行以下命令
slave stop;
reset slave;
slave start;