主从环境中 ，如果主中的binlog已经被从读到中继日志，但是还没有被sql应用，这时从库上的从IO进程停掉了，sql进程仍然会把已经读到中继日志中的内容应用：
也就是说这两个是独立的。
例：
在从库上
mysql> stop slave SQL_THREAD;
Query OK, 0 rows affected (0.00 sec)
mysql> show slave status \G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.118.161
Master_User: song
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: 1.000021
Read_Master_Log_Pos: 337
Relay_Log_File: a.000020
Relay_Log_Pos: 392
Relay_Master_Log_File: 1.000021
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: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 337
Relay_Log_Space: 706
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: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 2
Master_UUID: dab340ff-d2cc-11e4-a6c8-000c292f3ddd
Master_Info_File: /var/lib/mysql/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:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0
1 row in set (0.00 sec)
在主上执行：
mysql> create table test(id int);
Query OK, 0 rows affected (0.04 sec)
mysql> insert into test values (1);
Query OK, 1 row affected (0.01 sec)
mysql> insert into test values (2);
Query OK, 1 row affected (0.01 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
在从上查看
mysql> show slave status \G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.118.161
Master_User: song
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: 1.000021
Read_Master_Log_Pos: 816 --这个值增加了
Relay_Log_File: a.000020
Relay_Log_Pos: 392
Relay_Master_Log_File: 1.000021
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: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 337 --这个值没变，因为sql进程是停着的
Relay_Log_Space: 1185
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: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 2
Master_UUID: dab340ff-d2cc-11e4-a6c8-000c292f3ddd
Master_Info_File: /var/lib/mysql/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:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0
1 row in set (0.00 sec)
mysql>
mysql> stop slave IO_THREAD;
Query OK, 0 rows affected (0.01 sec)
mysql> start slave SQL_THREAD;
Query OK, 0 rows affected (0.03 sec)
mysql> SHOW SLAVE STATUS \G
*************************** 1. row ***************************
Slave_IO_State:
Master_Host: 192.168.118.161
Master_User: song
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: 1.000021
Read_Master_Log_Pos: 816
Relay_Log_File: a.000020
Relay_Log_Pos: 871
Relay_Master_Log_File: 1.000021
Slave_IO_Running: No
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: 816 --应用了sql
Relay_Log_Space: 1185
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: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 2
Master_UUID: dab340ff-d2cc-11e4-a6c8-000c292f3ddd
Master_Info_File: /var/lib/mysql/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0
1 row in set (0.00 sec)
mysql> select count(*) from test; --数据已经被同步过来
+----------+
| count(*) |
+----------+
| 2 |
+----------+
1 row in set (0.30 sec)