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有时候从库正在消化relay log的时候，一直延迟，可以查看正在进行的操作，找到耗时操作：
root@xxx((none)) > show slave statusG *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.10.10.10 Master_User: mysqlsync Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.011496 Read_Master_Log_Pos: 249691543 Relay_Log_File: relay-bin.000022 Relay_Log_Pos: 784939541 Relay_Master_Log_File: mysql-bin.011406 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: 784939352 Relay_Log_Space: 96941716899 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: 200846 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: 177078818 Master_UUID: 09ecc3bf-5c9a-11e8-bfe1-246e988841c0 Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Reading event from the relay log 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 Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version: 1 row in set (0.01 sec) Tue Dec 22 15:37:28 2020 user@xxx((none)) > show relaylog events in 'relay-bin.000022' from 784939541 limit 10 G; *************************** 1. row *************************** Log_name: relay-bin.000022 Pos: 784939541 Event_type: Query Server_id: 177078818 End_log_pos: 784939422 Info: BEGIN *************************** 2. row *************************** Log_name: relay-bin.000022 Pos: 784939611 Event_type: Rows_query Server_id: 177078818 End_log_pos: 784939501 Info: # delete from history where clock < 1608162601 limit 600000 *************************** 3. row *************************** Log_name: relay-bin.000022 Pos: 784939690 Event_type: Table_map Server_id: 177078818 End_log_pos: 784939553 Info: table_id: 2889 (zabbix.history) *************************** 4. row *************************** Log_name: relay-bin.000022 Pos: 784939742 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784947759 Info: table_id: 2889 *************************** 5. row *************************** Log_name: relay-bin.000022 Pos: 784947948 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784955965 Info: table_id: 2889 *************************** 6. row *************************** Log_name: relay-bin.000022 Pos: 784956154 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784964171 Info: table_id: 2889 *************************** 7. row *************************** Log_name: relay-bin.000022 Pos: 784964360 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784972377 Info: table_id: 2889 *************************** 8. row *************************** Log_name: relay-bin.000022 Pos: 784972566 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784980583 Info: table_id: 2889 *************************** 9. row *************************** Log_name: relay-bin.000022 Pos: 784980772 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784988789 Info: table_id: 2889 *************************** 10. row *************************** Log_name: relay-bin.000022 Pos: 784988978 Event_type: Delete_rows Server_id: 177078818 End_log_pos: 784996995 Info: table_id: 2889 10 rows in set (0.00 sec) ERROR: No query specified Tue Dec 22 15:37:42 2020
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