Some replication errors are ignored if slave_parallel_threads > 0

The problem is observed on binary logs attached to MDEV-6549.

• put the attached set of binary logs into the master datadir;
• start master server with log-bin=mysql-bin, other options can stay default;
• start slave with default options;
• start replication with MASTER_USE_GTID = current_pos (maybe GTID is not necessary in the scenario, I didn't try without it);
• after a while, replication fails here:

*************************** 1. row ***************************

               Slave_IO_State: Waiting for master to send event

                  Master_Host: 127.0.0.1

                  Master_User: root

                  Master_Port: 9306

                Connect_Retry: 1

              Master_Log_File: mysql-bin.002277

          Read_Master_Log_Pos: 326

               Relay_Log_File: wheezy-64-relay-bin.002025

                Relay_Log_Pos: 613

        Relay_Master_Log_File: mysql-bin.001011

             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: 1062

                   Last_Error: Error 'Duplicate entry '15' for key 'PRIMARY'' on query. Default database: 'test1'. Query: 'INSERT   INTO test1 .   /* table10_int  table0_int  t2_temp_myisam_25855 */ table10_innodb_int  ( `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` ) SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM test1 .   /* t2_temp_innodb_25855  table0_int_autoinc  table1_myisam_int_autoinc */ table10_innodb_int  AS A WHERE col_tinyint BETWEEN -82 AND -82 + 2 /**/ AND ( `col_varchar_257_binary` IS NULL OR `col_varchar_257_binary` <> ROW_COUNT() )  UNION SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM ( SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`c

                 Skip_Counter: 0

          Exec_Master_Log_Pos: 326

              Relay_Log_Space: 8561745

              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: 1062

               Last_SQL_Error: Error 'Duplicate entry '15' for key 'PRIMARY'' on query. Default database: 'test1'. Query: 'INSERT   INTO test1 .   /* table10_int  table0_int  t2_temp_myisam_25855 */ table10_innodb_int  ( `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` ) SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM test1 .   /* t2_temp_innodb_25855  table0_int_autoinc  table1_myisam_int_autoinc */ table10_innodb_int  AS A WHERE col_tinyint BETWEEN -82 AND -82 + 2 /**/ AND ( `col_varchar_257_binary` IS NULL OR `col_varchar_257_binary` <> ROW_COUNT() )  UNION SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM ( SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`c

  Replicate_Ignore_Server_Ids: 

             Master_Server_Id: 1

               Master_SSL_Crl: 

           Master_SSL_Crlpath: 

                   Using_Gtid: Current_Pos

                  Gtid_IO_Pos: 0-1-11874

The failure might be caused by an old replication bug or an erroneous test, it is not the point here.
Trying to run start slave again does not help, it still aborts at the same position (naturally).
Then,

• run set global slave_parallel_threads=1;
• run start slave
• it fails again, but note that the position has advanced:

  MariaDB [test]> show slave status \G

  *************************** 1. row ***************************

  Slave_IO_State: Waiting for master to send event

  Master_Host: 127.0.0.1

  Master_User: root

  Master_Port: 9306

  Connect_Retry: 1

  Master_Log_File: mysql-bin.002277

  Read_Master_Log_Pos: 326

  Relay_Log_File: wheezy-64-relay-bin.002027

  Relay_Log_Pos: 613

  Relay_Master_Log_File: mysql-bin.001012

  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: 1062

  Last_Error: Error 'Duplicate entry '15' for key 'PRIMARY'' on query. Default database: 'test1'. Query: 'INSERT INTO test1 . /* table10_int table0_int t2_temp_myisam_25855 */ table10_innodb_int ( `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` ) SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM test1 . /* t2_temp_innodb_25855 table0_int_autoinc table1_myisam_int_autoinc */ table10_innodb_int AS A WHERE col_tinyint BETWEEN -82 AND -82 + 2 /**/ AND ( `col_varchar_257_binary` IS NULL OR `col_varchar_257_binary` <> ROW_COUNT() ) UNION SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM ( SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`c

  Skip_Counter: 0

  Exec_Master_Log_Pos: 326

  Relay_Log_Space: 8562815

  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: 1062

  Last_SQL_Error: Error 'Duplicate entry '15' for key 'PRIMARY'' on query. Default database: 'test1'. Query: 'INSERT INTO test1 . /* table10_int table0_int t2_temp_myisam_25855 */ table10_innodb_int ( `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` ) SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM test1 . /* t2_temp_innodb_25855 table0_int_autoinc table1_myisam_int_autoinc */ table10_innodb_int AS A WHERE col_tinyint BETWEEN -82 AND -82 + 2 /**/ AND ( `col_varchar_257_binary` IS NULL OR `col_varchar_257_binary` <> ROW_COUNT() ) UNION SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`col_tinyint`,`col_tinyint_unsigned`,`col_varchar_257_binary`,`col_varchar_257_latin1`,`col_varchar_257_utf8`,`pk` FROM ( SELECT `col_bigint`,`col_bigint_unsigned`,`col_timestamp`,`c

  Replicate_Ignore_Server_Ids:

  Master_Server_Id: 1

  Master_SSL_Crl:

  Master_SSL_Crlpath:

  Using_Gtid: Current_Pos

  Gtid_IO_Pos: 0-1-11874

  1 row in set (0.00 sec)

• run start slave yet another time. Now, the replication goes on:

  MariaDB [test]> show slave status \G

  *************************** 1. row ***************************

  Slave_IO_State: Waiting for master to send event

  Master_Host: 127.0.0.1

  Master_User: root

  Master_Port: 9306

  Connect_Retry: 1

  Master_Log_File: mysql-bin.002277

  Read_Master_Log_Pos: 326

  Relay_Log_File: wheezy-64-relay-bin.003535

  Relay_Log_Pos: 2332

  Relay_Master_Log_File: mysql-bin.001728

  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: 2045

  Relay_Log_Space: 3094464

  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: 397789

  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: 0-1-11874

I don't think it's supposed to happen.

The binary logs were produced using 10.0 tree on Power 8 machine, and weren't anyhow tampered with.

The test is executed on a usual Debian machine, with this server:

revision-id: sergii@pisem.net-20140805163520-tz0w14h8uju0ti9n

revno: 4330

branch-nick: 10.0