可能是复制线程system lock引起的大量unauthenticated user

我描述下整个过程：
刚开始告警是主从延时，上从库看了下
mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.0.18
                  Master_User: qc_repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000039
          Read_Master_Log_Pos: 460090672
               Relay_Log_File: mysql-relay-bin.000002
                Relay_Log_Pos: 444770992
        Relay_Master_Log_File: mysql-bin.000039
             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: 444770902
              Relay_Log_Space: 460090966
              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: 671
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: 71008354
                  Master_UUID: 3e547b24-135d-11e7-9676-525411d50ff7
             Master_Info_File: /data/mysql/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: System lock
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 3e547b24-135d-11e7-9676-525411d50ff7:36407029-37060714
            Executed_Gtid_Set: 3e547b24-135d-11e7-9676-525411d50ff7:1-37031363,
d4c68f4e-f18a-11e5-9127-0cc47ab72b72:1-30282323,
d5628a48-f18a-11e5-aea6-0cc47ab727cf:1-5194
                Auto_Position: 1
1 row in set (0.00 sec)processlists没什么异常
mysql> show processlist;
+-------+-------------+---------------------+------+---------+-------+----------------------------------+------------------+
| Id    | User        | Host                | db   | Command | Time  | State                            | Info             |
+-------+-------------+---------------------+------+---------+-------+----------------------------------+------------------+
|   147 | system user |                     | NULL | Connect | 54015 | Waiting for master to send event | NULL             |
|   148 | system user |                     | NULL | Connect |   708 | System lock                      | NULL             |
| 65675 | kanban      | 192.168.0.31:47232  | zkyq | Sleep   |    32 |                                  | NULL             |
| 71602 | kanban      | 192.168.0.31:47312  | vms  | Sleep   |    20 |                                  | NULL             |
| 72255 | kanban      | 192.168.0.31:47322  | vms  | Sleep   |   753 |                                  | NULL             |
| 72256 | kanban      | 192.168.0.31:47323  | vms  | Sleep   |   753 |                                  | NULL             |
| 76261 | root        | 192.168.55.16:37618 | NULL | Query   |     0 | init                             | show processlist |
+-------+-------------+---------------------+------+---------+-------+----------------------------------+------------------+
但是INNODB_TRX 表里有一行，当时差的时候已经快14：50分了
mysql> SELECT * FROM information_schema.INNODB_TRX\G;
*************************** 1. row ***************************
                    trx_id: 147178299
                 trx_state: RUNNING
               trx_started: 2017-08-09 14:38:21
     trx_requested_lock_id: NULL
          trx_wait_started: NULL
                trx_weight: 1
       trx_mysql_thread_id: 148
                 trx_query: NULL
       trx_operation_state: inserting
         trx_tables_in_use: 1
         trx_tables_locked: 1
          trx_lock_structs: 1
     trx_lock_memory_bytes: 360
           trx_rows_locked: 0
         trx_rows_modified: 0
   trx_concurrency_tickets: 0
       trx_isolation_level: REPEATABLE READ
         trx_unique_checks: 1
    trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
 trx_adaptive_hash_latched: 0
 trx_adaptive_hash_timeout: 10000
          trx_is_read_only: 0
trx_autocommit_non_locking: 0
1 row in set (0.01 sec)
后来就是突然出现大量的未验证连接
show processlistsmysql> show processlist;
+-------+----------------------+---------------------+--------------------+---------+-------+----------------------------------+---------------------------+
| Id    | User                 | Host                | db                 | Command | Time  | State                            | Info                      |
+-------+----------------------+---------------------+--------------------+---------+-------+----------------------------------+---------------------------+
|   147 | system user          |                     | NULL               | Connect | 54268 | Waiting for master to send event | NULL                      |
|   148 | system user          |                     | NULL               | Connect |   961 | System lock                      | NULL                      |
| 65675 | kanban               | 192.168.0.31:47232  | zkyq               | Sleep   |   285 |                                  | NULL                      |
| 71602 | kanban               | 192.168.0.31:47312  | vms                | Sleep   |    10 |                                  | NULL                      |
| 76537 | root                 | 192.168.55.16:37636 | NULL               | Query   |    33 | init                             | show engine innodb status |
| 76628 | qc_master            | localhost           | NULL               | Query   |    33 | executing                        | SHOW GLOBAL STATUS        |
| 76629 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76630 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76631 | qc_master            | localhost           | NULL               | Killed  |    31 | cleaning up                      | NULL                      |
| 76632 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76633 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76634 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76635 | qc_repl              | localhost           | NULL               | Killed  |    26 | cleaning up                      | NULL                      |
| 76636 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76637 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76638 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76639 | unauthenticated user | connecting host     | NULL               | Killed  |  NULL | login                            | NULL                      |
| 76640 | qc_master            | localhost           | NULL               | Query   |    24 | executing                        | SHOW GLOBAL STATUS        
。。略
53 rows in set (0.00 sec)
然后一直涨啊涨，涨到我怀疑人生
开始出现这个连接的时候，数据库就访问不了了，执行sql就一直hang住。
错误日志没有信息重启大法解决，但原因不明求解求解