Steps followed to re-create the scenario where [slave] node_03 lagging once we executing stop slave ; start slave; during load on Master. [slave] node_03 MariaDB [(none)]> stop slave; Query OK, 0 rows affected (0.010 sec) [master] node_01 2022-05-12 21:07:39 16 [Note] Stop semi-sync binlog_dump to slave (server_id: 3) [slave] node_03 2022-05-12 21:07:39 12 [Note] Error reading relay log event: slave SQL thread was killed 2022-05-12 21:07:39 12 [Note] Slave SQL thread exiting, replication stopped in log 'node_01.000005' at position 17192380; GTID position '1-1-600332' 2022-05-12 21:07:39 12 [Note] master was 192.168.47.23:3306 2022-05-12 21:07:39 11 [Note] Slave I/O thread exiting, read up to log 'node_01.000005', position 17192380; GTID position 1-1-600332 2022-05-12 21:07:39 11 [Note] master was 192.168.47.23:3306 [slave] node_03 MariaDB [(none)]> start slave; Query OK, 0 rows affected (0.005 sec) [master] node_01 2022-05-12 21:07:53 244 [Note] Start binlog_dump to slave_server(3), pos(node_01.000005, 17192380), using_gtid(1), gtid('1-1-600332') [slave] node_03 2022-05-12 21:07:53 263 [Note] Slave I/O thread: Start semi-sync replication to master 'repuser@192.168.47.23:3306' in log 'node_01.000005' at position 17192380 2022-05-12 21:07:53 264 [Note] Slave SQL thread initialized, starting replication in log 'node_01.000005' at position 17192380, relay log './node_03-relay-bin.000001' position: 4; GTID position '1-1-600332' 2022-05-12 21:07:53 263 [Note] Slave I/O thread: connected to master 'repuser@192.168.47.23:3306',replication starts at GTID position '1-1-600332' 2022-05-12 21:08:53 263 [Note] Slave I/O thread: Failed reading log event, reconnecting to retry, log 'node_01.000005' at position 17192380; GTID position '1-1-600332' MariaDB [(none)]> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 192.168.47.23 Master_User: repuser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: node_01.000005 Read_Master_Log_Pos: 17192380 Relay_Log_File: node_03-relay-bin.000001 Relay_Log_Pos: 4 Relay_Master_Log_File: node_01.000005 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: 17192380 Relay_Log_Space: 256 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_SSL_Crl: Master_SSL_Crlpath: Using_Gtid: Slave_Pos Gtid_IO_Pos: 1-1-600332 Replicate_Do_Domain_Ids: Replicate_Ignore_Domain_Ids: Parallel_Mode: conservative 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 Slave_DDL_Groups: 0 Slave_Non_Transactional_Groups: 0 Slave_Transactional_Groups: 20986 1 row in set (0.000 sec) At this moment If I check from Maxscale Every 2.0s: maxctrl list servers Thu May 12 21:10:11 2022 ┌─────────┬───────────────┬──────┬─────────────┬─────────────────┬────────────┐ │ Server │ Address │ Port │ Connections │ State │ GTID │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_01 │ 192.168.47.23 │ 3306 │ 75 │ Master, Running │ 1-1-617117 │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_02 │ 192.168.47.24 │ 3306 │ 75 │ Slave, Running │ 1-1-617117 │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_03 │ 192.168.47.25 │ 3306 │ 0 │ Slave, Running │ 1-1-600332 │ └─────────┴───────────────┴──────┴─────────────┴─────────────────┴────────────┘ After few minutes again Every 2.0s: maxctrl list servers Thu May 12 21:11:46 2022 ┌─────────┬───────────────┬──────┬─────────────┬─────────────────┬────────────┐ │ Server │ Address │ Port │ Connections │ State │ GTID │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_01 │ 192.168.47.23 │ 3306 │ 75 │ Master, Running │ 1-1-627756 │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_02 │ 192.168.47.24 │ 3306 │ 75 │ Slave, Running │ 1-1-627756 │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_03 │ 192.168.47.25 │ 3306 │ 0 │ Slave, Running │ 1-1-600332 │ └─────────┴───────────────┴──────┴─────────────┴─────────────────┴────────────┘ [slave] node_03 IO Thread state was Connecting and Seconds_Behind_Master: NULL MariaDB [(none)]> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting to reconnect after a failed master event read Master_Host: 192.168.47.23 Master_User: repuser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: node_01.000005 Read_Master_Log_Pos: 17192380 Relay_Log_File: node_03-relay-bin.000001 Relay_Log_Pos: 4 Relay_Master_Log_File: node_01.000005 Slave_IO_Running: Connecting 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: 17192380 Relay_Log_Space: 256 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: 1 Master_SSL_Crl: Master_SSL_Crlpath: Using_Gtid: Slave_Pos Gtid_IO_Pos: 1-1-600332 Replicate_Do_Domain_Ids: Replicate_Ignore_Domain_Ids: Parallel_Mode: conservative 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 Slave_DDL_Groups: 0 Slave_Non_Transactional_Groups: 0 Slave_Transactional_Groups: 20986 1 row in set (0.000 sec) [slave]node_03 2022-05-12 21:10:53 263 [Note] Slave I/O thread: Failed reading log event, reconnecting to retry, log 'node_01.000005' at position 17192380; GTID position '1-1-600332' [master] node_01 2022-05-12 21:10:53 246 [Note] Start binlog_dump to slave_server(3), pos(node_01.000005, 17192380), using_gtid(1), gtid('1-1-600332') While another [slave] node_02 is working fine without any error and its sync with [master] node_01 Every 2.0s: maxctrl list servers Thu May 12 21:14:06 2022 ┌─────────┬───────────────┬──────┬─────────────┬─────────────────┬────────────┐ │ Server │ Address │ Port │ Connections │ State │ GTID │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_01 │ 192.168.47.23 │ 3306 │ 75 │ Master, Running │ 1-1-643416 │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_02 │ 192.168.47.24 │ 3306 │ 75 │ Slave, Running │ 1-1-643416 │ ├─────────┼───────────────┼──────┼─────────────┼─────────────────┼────────────┤ │ node_03 │ 192.168.47.25 │ 3306 │ 0 │ Slave, Running │ 1-1-600332 │ └─────────┴───────────────┴──────┴─────────────┴─────────────────┴────────────┘ [slave]node_02 MariaDB [(none)]> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 192.168.47.23 Master_User: repuser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: node_01.000005 Read_Master_Log_Pos: 54291856 Relay_Log_File: node_02-relay-bin.000002 Relay_Log_Pos: 54292153 Relay_Master_Log_File: node_01.000005 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: 54291856 Relay_Log_Space: 54292464 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_SSL_Crl: Master_SSL_Crlpath: Using_Gtid: Slave_Pos Gtid_IO_Pos: 1-1-645619 Replicate_Do_Domain_Ids: Replicate_Ignore_Domain_Ids: Parallel_Mode: conservative 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 Slave_DDL_Groups: 0 Slave_Non_Transactional_Groups: 0 Slave_Transactional_Groups: 66273 1 row in set (0.000 sec) ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Once we stop the overall load , [slave] node_03 will resume replication after sometime stating few seconds of lag SBM>0 [master] node_01 2022-05-12 21:16:13 246 [Note] Start semi-sync binlog_dump to slave (server_id: 3), pos(/var/lib/mysql/node_01.000005, 4) 2022-05-12 21:16:13 246 [Note] Stop semi-sync binlog_dump to slave (server_id: 3) 2022-05-12 21:16:13 246 [Warning] Aborted connection 246 to db: 'unconnected' user: 'repuser' host: '192.168.47.25' (A slave with the same server_uuid/server_id as this slave has co) 2022-05-12 21:16:13 245 [Note] Start semi-sync binlog_dump to slave (server_id: 3), pos(/var/lib/mysql/node_01.000005, 4) 2022-05-12 21:16:13 245 [Note] Stop semi-sync binlog_dump to slave (server_id: 3) 2022-05-12 21:16:13 245 [Warning] Aborted connection 245 to db: 'unconnected' user: 'repuser' host: '192.168.47.25' (A slave with the same server_uuid/server_id as this slave has co) 2022-05-12 21:16:13 247 [Note] Start semi-sync binlog_dump to slave (server_id: 3), pos(/var/lib/mysql/node_01.000005, 4) [slave] node_03 2022-05-12 21:16:53 263 [Note] Slave I/O thread: Failed reading log event, reconnecting to retry, log 'node_01.000005' at position 17192380; GTID position '1-1-600332' [slave] node_03 MariaDB [(none)]> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 192.168.47.23 Master_User: repuser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: node_01.000005 Read_Master_Log_Pos: 28653666 Relay_Log_File: node_03-relay-bin.000002 Relay_Log_Pos: 12165 Relay_Master_Log_File: node_01.000005 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: 17203849 Relay_Log_Space: 11462293 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: 555 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_SSL_Crl: Master_SSL_Crlpath: Using_Gtid: Slave_Pos Gtid_IO_Pos: 1-1-614322 Replicate_Do_Domain_Ids: Replicate_Ignore_Domain_Ids: Parallel_Mode: conservative SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Closing tables Slave_DDL_Groups: 0 Slave_Non_Transactional_Groups: 0 Slave_Transactional_Groups: 21001 1 row in set (0.000 sec) After few seconds node_03 will catchup with [master] node_01 and another [slave] node_02