早上巡检数据库，发现一个延迟从库的sql_thread中断了。
Last_SQL_Errno: 1755
Last_SQL_Error: Cannot execute the current event group in the parallel mode. Encountered event Gtid, relay-log name ./oracle-relay-bin.000093, position 152912092 which prevents execution of this event group in parallel mode. Reason: The master event is logically timestamped incorrectly..
检查performance_schema下的replication_applier_status_by_worker表，除了GTID之外也没有更具体的信息：
"root@localhost:mysql3308.sock [(none)]>select * from performance_schema.replication_applier_status_by_worker; +--------------+-----------+-----------+---------------+------------------------------------------------+-------------------+--------------------+----------------------+ | CHANNEL_NAME | WORKER_ID | THREAD_ID | SERVICE_STATE | LAST_SEEN_TRANSACTION | LAST_ERROR_NUMBER | LAST_ERROR_MESSAGE | LAST_ERROR_TIMESTAMP | +--------------+-----------+-----------+---------------+------------------------------------------------+-------------------+--------------------+----------------------+ | | 1 | NULL | OFF | 0b961fcc-41c2-11e7-84fd-286ed488c7da:156369774 | 0 | | 0000-00-00 00:00:00 | | | 2 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | | | 3 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | | | 4 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | | | 5 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | | | 6 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | | | 7 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | | | 8 | NULL | OFF | | 0 | | 0000-00-00 00:00:00 | +--------------+-----------+-----------+---------------+------------------------------------------------+-------------------+--------------------+----------------------+
既然relay_log的位置信息都有了，那就去日志里看看吧：
解析Binlog文件：
mysqlbinlog -v --base64-output=decode-rows oracle-relay-bin.000093 >1.sql
找到152912092位置点附近的日志：
检查了一下数据库中这个表ID为14816035的数据确实是不存在的。
另外除了这条日志，其它日志的last_committed和sequence_number都为0，last_committed表示事务提交的时候，上次事务提交的编号。last_committed和sequence_number代表的就是所谓的LOGICAL_CLOCK。
猜测如果手动把这条数据插入延迟从库，并且使用注入一个空事务跳过这个GTID的方法重启sql_thread，相信这个错误也能被解决。
但既然带了LOGICAL_CLOCK的事务就会出错，跳过事务的方法很难保证以后不会出错。
注意到这条日志的last_committed是一个异常大的值，且错误信息中有提到The master event is logically timestamped incorrectly。我怀疑是不是并行配置的问题。
从库配置：
"root@localhost:mysql3308.sock [(none)]>show variables like '%para%'; +------------------------+---------------+ | Variable_name | Value | +------------------------+---------------+ | slave_parallel_type | LOGICAL_CLOCK | | slave_parallel_workers | 8 | +------------------------+---------------+
再检查主库配置：
(root@localhost:mysql.sock) [(none)]>show variables like '%para%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | slave_parallel_workers | 0 | +------------------------+-------+
发现主库根本就没有slave_parallel_type这项配置。想起来主库是mysql5.6了。
(root@localhost:mysql.sock) [(none)]>select version(); +------------+ | version() | +------------+ | 5.6.35-log | +------------+
那么问题基本上就知道了，主库5.6只支持基于DATABASE的并行复制，而5.7的从库配置成LOGICAL_CLOCK导致了异常。
明白了问题所在，那就好解决了，把从库的slave_parallel_type改为DATABASE，再起sql_thread问题应该就解决了：
"root@localhost:mysql3308.sock [none]>set global slave_parallel_type='DATABASE';
Query OK, 0 rows affected (0.00 sec)
"root@localhost:mysql3308.sock [none]>show global variables like '%slave_parallel_type%';
+---------------------+----------+
| Variable_name | Value |
+---------------------+----------+
| slave_parallel_type | DATABASE |
+---------------------+----------+
1 row in set (0.00 sec)
"root@localhost:mysql3308.sock [none]>show slave statusG
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: master
Master_User: rep
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: binlog.000104
Read_Master_Log_Pos: 160115307
Relay_Log_File: oracle-relay-bin.000093
Relay_Log_Pos: 152912092
Relay_Master_Log_File: binlog.000100
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: 1755
Last_Error: Cannot execute the current event group in the parallel mode. Encountered event Gtid, relay-log name ./oracle-relay-bin.000093, position 152912092 which prevents execution of this event group in parallel mode. Reason: The master event is logically timestamped incorrectly..
Skip_Counter: 0
Exec_Master_Log_Pos: 152911925
Relay_Log_Space: 4455094667
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: 1755
Last_SQL_Error: Cannot execute the current event group in the parallel mode. Encountered event Gtid, relay-log name ./oracle-relay-bin.000093, position 152912092 which prevents execution of this event group in parallel mode. Reason: The master event is logically timestamped incorrectly..
Replicate_Ignore_Server_Ids:
Master_Server_Id: 50
Master_UUID: 0b961fcc-41c2-11e7-84fd-286ed488c7da
Master_Info_File: mysql.slave_master_info
SQL_Delay: 3600
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State:
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp: 180716 18:02:56
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: 0b961fcc-41c2-11e7-84fd-286ed488c7da:111060115-163843604
Executed_Gtid_Set: 0b961fcc-41c2-11e7-84fd-286ed488c7da:1-156369774
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
"root@localhost:mysql3308.sock [none]>stop slave sql_thread;
Query OK, 0 rows affected, 1 warning (0.00 sec)
"root@localhost:mysql3308.sock [none]>start slave sql_thread;
Query OK, 0 rows affected (0.01 sec)
"root@localhost:mysql3308.sock [none]>show slave statusG
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: master
Master_User: rep
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: binlog.000104
Read_Master_Log_Pos: 160161836
Relay_Log_File: oracle-relay-bin.000093
Relay_Log_Pos: 169205552
Relay_Master_Log_File: binlog.000100
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: 169205385
Relay_Log_Space: 4455141196
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: 5351
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: 50
Master_UUID: 0b961fcc-41c2-11e7-84fd-286ed488c7da
Master_Info_File: mysql.slave_master_info
SQL_Delay: 3600
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Waiting for Slave Worker to release partition
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: 0b961fcc-41c2-11e7-84fd-286ed488c7da:111060115-163843692
Executed_Gtid_Set: 0b961fcc-41c2-11e7-84fd-286ed488c7da:1-156400100
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
打完收工。
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