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[Sachin Setiya <sachin.setiya@xxxxxxxxxxx>]

Hello Everyone!

I setup a classical master-slave server. Master is constantly running
query like this
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
insert into t1 values(1,1,1,1,1);
flush logs;
insert into t1 values(1,1,1,1,1);
{there are arround million querys}

Then I executed Show slave status (couple of times in a second), and
found Seconds_behind_master is changing arbitrarily
MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Queueing master event to the relay log
                  Master_Host: localhost
                  Master_User: root
                  Master_Port: 16000
                Connect_Retry: 60
              Master_Log_File: master-bin.014595
          Read_Master_Log_Pos: 4
               Relay_Log_File: slave-relay-bin.029186
                Relay_Log_Pos: 3557
        Relay_Master_Log_File: master-bin.014593
             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: 3257
              Relay_Log_Space: 184375
              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: 148
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: Current_Pos
                  Gtid_IO_Pos: 0-1-145942
      Replicate_Do_Domain_Ids:
  Replicate_Ignore_Domain_Ids:
                Parallel_Mode: conservative
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Reading event from the relay log
1 row in set (0.01 sec)

MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: localhost
                  Master_User: root
                  Master_Port: 16000
                Connect_Retry: 60
              Master_Log_File: master-bin.014632
          Read_Master_Log_Pos: 3257
               Relay_Log_File: slave-relay-bin.029264
                Relay_Log_Pos: 1548
        Relay_Master_Log_File: master-bin.014632
             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: 1248
              Relay_Log_Space: 179996
              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: Current_Pos
                  Gtid_IO_Pos: 0-1-146322
      Replicate_Do_Domain_Ids:
  Replicate_Ignore_Domain_Ids:
                Parallel_Mode: conservative
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: init
1 row in set (0.00 sec)

MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Queueing master event to the relay log
                  Master_Host: localhost
                  Master_User: root
                  Master_Port: 16000
                Connect_Retry: 60
              Master_Log_File: master-bin.014670
          Read_Master_Log_Pos: 299
               Relay_Log_File: slave-relay-bin.029336
                Relay_Log_Pos: 3557
        Relay_Master_Log_File: master-bin.014668
             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: 3257
              Relay_Log_Space: 184569
              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: 150
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: Current_Pos
                  Gtid_IO_Pos: 0-1-146692
      Replicate_Do_Domain_Ids:
  Replicate_Ignore_Domain_Ids:
                Parallel_Mode: conservative
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Reading event from the relay log

-- 
Regards
Sachin Setiya
Software Engineer at  MariaDB