MySQL主从复制中断，绝大多数的情况是SQL线程应用错误。有时我们会选择跳过这个事务来恢复主从复制，事后再分析主从复制中断的原因。

选择跳过指定事务常见的情况如下：

1. 从库中对象已经存在；
2. 从库中对象已经不存在；
3. 主键重复；
4. 其他。

以上情况的直接原因是主从数据不一致，跳过只是临时的解决办法，最保险的方式是重建复制。

对于主键重复的情况，需要格外注意，一定不能轻易跳过，需要确认：

• 这条记录主库从库是否只是主键相同，其他字段不完全相同；
• 此事务可能包含多个操作。

如果是以上情况，不能通过跳过事务恢复。可行方案是从库删除这条记录，然后重启复制。

下面分享一个案例：

1 查看复制状态

mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for source to send event
                  Master_Host: 192.168.131.99
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: binlog.000068
          Read_Master_Log_Pos: 586
               Relay_Log_File: mysql002-relay-bin.000010
                Relay_Log_Pos: 672
        Relay_Master_Log_File: binlog.000061
             Slave_IO_Running: Yes
            Slave_SQL_Running: No
              Replicate_Do_DB:
          Replicate_Ignore_DB:
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 1410
                   Last_Error: Coordinator stopped because there were error(s) in the worker(s). The most recent failure being: Worker 1 failed                       executing transaction 'bd4b724b-ab29-11ee-826f-000c294bd026:424255' at source log binlog.000061, end_log_pos 2765. See error log and/or perfor                      mance_schema.replication_applier_status_by_worker table for more details about this failure or others, if any.
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 1766
              Relay_Log_Space: 9989536
              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: 0
                Last_IO_Error:
               Last_SQL_Errno: 1410
               Last_SQL_Error: Coordinator stopped because there were error(s) in the worker(s). The most recent failure being: Worker 1 failed                       executing transaction 'bd4b724b-ab29-11ee-826f-000c294bd026:424255' at source log binlog.000061, end_log_pos 2765. See error log and/or perfor                      mance_schema.replication_applier_status_by_worker table for more details about this failure or others, if any.
  Replicate_Ignore_Server_Ids:
             Master_Server_Id: 1
                  Master_UUID: bd4b724b-ab29-11ee-826f-000c294bd026
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State:
           Master_Retry_Count: 86400
                  Master_Bind:
      Last_IO_Error_Timestamp:
     Last_SQL_Error_Timestamp: 240302 23:30:53
               Master_SSL_Crl:
           Master_SSL_Crlpath:
           Retrieved_Gtid_Set: bd4b724b-ab29-11ee-826f-000c294bd026:424253-426568
            Executed_Gtid_Set: 2218063c-aef7-11ee-9e40-000c29f059d3:1-6,
bd4b724b-ab29-11ee-826f-000c294bd026:1-424254
                Auto_Position: 1
         Replicate_Rewrite_DB:
                 Channel_Name:
           Master_TLS_Version:
       Master_public_key_path:
        Get_master_public_key: 1
            Network_Namespace:
1 row in set, 1 warning (0.00 sec)

2 错误分析

根据复制状态，可以看到 Slave_SQL_Running: No，此时sql线程已经停止，错误信息为：

Last_SQL_Error: Coordinator stopped because there were error(s) in the worker(s). The most recent failure being: Worker 1 failed executing transaction'bd4b724b-ab29-11ee-826f-000c294bd026:424255' at source log binlog.000061, end_log_pos 2765. See error log and/or perfor mance_schema.replication_applier_status_by_worker table for more details about this failure or others, if any.

提示 Worker 1 有执行错误的事务，根据提示查看性能视图：

mysql> select * from performance_schema.replication_applier_status_by_worker where LAST_ERROR_MESSAGE <> ''\G
*************************** 1. row ***************************
                                           CHANNEL_NAME:
                                              WORKER_ID: 1
                                              THREAD_ID: NULL
                                          SERVICE_STATE: OFF
                                      LAST_ERROR_NUMBER: 1410
                                     LAST_ERROR_MESSAGE: Worker 1 failed executing transaction 'bd4b724b-ab29-11ee-826f-000c294bd026:424255' at source log binlog.000061, end_log_pos 2765; Error 'You are not allowed to create a user with GRANT' on query. Default database: ''. Query: 'GRANT SELECT, RELOAD, PROCESS, REPLICATION CLIENT, BACKUP_ADMIN ON *.* TO 'pmm'@'192.168.131.99''
                                   LAST_ERROR_TIMESTAMP: 2024-03-02 23:30:53.719870
                               LAST_APPLIED_TRANSACTION: bd4b724b-ab29-11ee-826f-000c294bd026:424254
     LAST_APPLIED_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 2024-01-29 23:25:54.899869
    LAST_APPLIED_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 2024-01-29 23:25:54.899869
         LAST_APPLIED_TRANSACTION_START_APPLY_TIMESTAMP: 2024-03-02 23:30:53.712714
           LAST_APPLIED_TRANSACTION_END_APPLY_TIMESTAMP: 2024-03-02 23:30:53.717294
                                   APPLYING_TRANSACTION: bd4b724b-ab29-11ee-826f-000c294bd026:424255
         APPLYING_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 2024-01-29 23:26:22.316756
        APPLYING_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 2024-01-29 23:26:22.316756
             APPLYING_TRANSACTION_START_APPLY_TIMESTAMP: 2024-03-02 23:30:53.717343
                 LAST_APPLIED_TRANSACTION_RETRIES_COUNT: 0
   LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER: 0
  LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE:
LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000
                     APPLYING_TRANSACTION_RETRIES_COUNT: 0
       APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER: 0
      APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE:
    APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000
1 row in set (0.00 sec)

关键信息为：Error ‘You are not allowed to create a user with GRANT’，可知执行失败的语句是赋权相关的。

从库执行错误的sql为：

GRANT SELECT, RELOAD, PROCESS, REPLICATION CLIENT, BACKUP_ADMIN ON *.* TO 'pmm'@'192.168.131.99'

查看从库’pmm’@'192.168.131.99’用户的权限：

mysql> show grants for 'pmm'@'192.168.131.99';
+------------------------------------------------------------------------------------+
| Grants for pmm@192.168.131.99                                                      |
+------------------------------------------------------------------------------------+
| GRANT SELECT, RELOAD, PROCESS, REPLICATION CLIENT ON *.* TO `pmm`@`192.168.131.99` |
+------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

查看主库’pmm’@'192.168.131.99’用户的权限：

mysql> show grants for 'pmm'@'192.168.131.99';
+------------------------------------------------------------------------------------+
| Grants for pmm@192.168.131.99                                                      |
+------------------------------------------------------------------------------------+
| GRANT SELECT, RELOAD, PROCESS, REPLICATION CLIENT ON *.* TO `pmm`@`192.168.131.99` |
| GRANT BACKUP_ADMIN ON *.* TO `pmm`@`192.168.131.99`                                |
+------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

可知报错的sql语句从库已经应用成功。

3 错误处理方法

根据前面搜集到的信息可知，从库sql进程错误执行的事务为一个赋权语句，且从库已经应用。所以此事务直接跳过即可。

步骤如下：

1）关闭复制

mysql> stop slave;
Query OK, 0 rows affected, 1 warning (0.00 sec)

确认是否关闭：

mysql> show slave status\G
*************************** 1. row ***************************
...
             Slave_IO_Running: No
            Slave_SQL_Running: No
...

2）确定跳过的事务

跳过的事务为Executed_Gtid_Set的最大值加1。

mysql> show slave status\G
*************************** 1. row ***************************
...
           Retrieved_Gtid_Set: bd4b724b-ab29-11ee-826f-000c294bd026:424253-426568
            Executed_Gtid_Set: 2218063c-aef7-11ee-9e40-000c29f059d3:1-6,
bd4b724b-ab29-11ee-826f-000c294bd026:1-424254
...

跳过的事务为：bd4b724b-ab29-11ee-826f-000c294bd026:424255

3）跳过事务

跳过事务的本质是插入一个空的事务，关键步骤是 set session gtid_next。

跳过事务后，需要将gtid_next设置回automatic。

mysql> set session gtid_next='bd4b724b-ab29-11ee-826f-000c294bd026:424255';
Query OK, 0 rows affected (0.00 sec)

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> set session gtid_next='automatic';
Query OK, 0 rows affected (0.00 sec)

4）重启复制

mysql> start slave;
Query OK, 0 rows affected, 1 warning (0.05 sec)

mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for source to send event
                  Master_Host: 192.168.131.99
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: binlog.000068
          Read_Master_Log_Pos: 586
               Relay_Log_File: mysql002-relay-bin.000022
                Relay_Log_Pos: 451
        Relay_Master_Log_File: binlog.000068
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB:
          Replicate_Ignore_DB:
           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: 586
              Relay_Log_Space: 1303
              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: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:
  Replicate_Ignore_Server_Ids:
             Master_Server_Id: 1
                  Master_UUID: bd4b724b-ab29-11ee-826f-000c294bd026
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Replica has read all relay log; waiting for more updates
           Master_Retry_Count: 86400
                  Master_Bind:
      Last_IO_Error_Timestamp:
     Last_SQL_Error_Timestamp:
               Master_SSL_Crl:
           Master_SSL_Crlpath:
           Retrieved_Gtid_Set: bd4b724b-ab29-11ee-826f-000c294bd026:424253-426568
            Executed_Gtid_Set: 2218063c-aef7-11ee-9e40-000c29f059d3:1-6,
bd4b724b-ab29-11ee-826f-000c294bd026:1-426568
                Auto_Position: 1
         Replicate_Rewrite_DB:
                 Channel_Name:
           Master_TLS_Version:
       Master_public_key_path:
        Get_master_public_key: 1
            Network_Namespace:
1 row in set, 1 warning (0.00 sec)

双YES，说明复制已经恢复正常。

4 验证主从是否一致

查看从库数据：

mysql> show grants for 'pmm'@'192.168.131.99';
+------------------------------------------------------------------------------------+
| Grants for pmm@192.168.131.99                                                      |
+------------------------------------------------------------------------------------+
| GRANT SELECT, RELOAD, PROCESS, REPLICATION CLIENT ON *.* TO `pmm`@`192.168.131.99` |
+------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

查看主库数据：

mysql> show grants for 'pmm'@'192.168.131.99';
+------------------------------------------------------------------------------------+
| Grants for pmm@192.168.131.99                                                      |
+------------------------------------------------------------------------------------+
| GRANT SELECT, RELOAD, PROCESS, REPLICATION CLIENT ON *.* TO `pmm`@`192.168.131.99` |
| GRANT BACKUP_ADMIN ON *.* TO `pmm`@`192.168.131.99`                                |
+------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

发现从库pmm@192.168.131.99用户少了BACKUP_ADMIN权限。

把这个缺失的权限补齐：

#主库执行：
mysql> GRANT BACKUP_ADMIN ON *.* TO `pmm`@`192.168.131.99`;
Query OK, 0 rows affected (0.00 sec)