gtid_slave_pos duplicate key errors after restore

When restoring a master backup where, for whatever reason, gtid_slave_pos contains entries (master<->master setup, intermediate slave, former slave promoted to master), and using classic master_log_file/pos to set up replication, a newly set up slave will run for a while, counting up its on "sub_id" from one, until reaching the masters "sub_id" values still present in the restored gtid_slave_pos. At that point replication will stop with a duplicate key error.

How to reproduce:

• set up a master, insert a "fake" entry into gtid_slave_pos:

  INSERT INTO mysql.gtid_slave_pos VALUES(0,5,1,23);

• take a master backup

  mysqldump --all-databases --single-transaction --master-data > dump.sql

• set up slave, set up replication basics:

  CHANGE MASTER TO MASTER_HOST='...'

                , MASTER_USER='...'

                , MASTER_PASSWORD='...';

• restore dump on slave

• start slave, check slave status to see that things are running, check mysql.gtid_slave_pos contents. Note the first line inserted by the slave, and the 2nd one originating from the master still being there:

+-----------+--------+-----------+--------+

| domain_id | sub_id | server_id | seq_no |

+-----------+--------+-----------+--------+

|         0 |      1 |        2 |      5 |

|         0 |      5 |         1 |     23 |

+-----------+--------+-----------+--------+

• perform some DDL or DML statements on the master

• check slave status:

                   Last_Error: Error during XID COMMIT: failed to update GTID state in mysql.gtid_slave_pos: 1062: Duplicate entry '0-5' for key 'PRIMARY'

The gtid_slave_pos table is truncated when setting the gtid_slave_pos variable with SET GLOBAL, but is left as is on

CHANGE MASTER TO MASTER_LOG_FILE='...', MASTER_LOG_POS=...;

Proposed fixes:

TRUNCATE the table on explicit CHANGE MASTER TO MASTER_LOG_FILE, and move the CHANGE MASTER TO command from beginning to end of mysqldump output