I have built a tool that takes backups using mariabackup, and passes the --slave-info option on command line regardless if the server is a slave or not.

I have just found out that if slave_parallel_workers is not zero, mariabackup gets confused and errors out with:

The --slave-info option requires GTID enabled for a multi-threaded slave.

Now, this is not a slave, let alone a multi threaded one – that parameter was a leftover.
So it should not error out.

Looking at the code I see:

 if (slave_parallel_workers_var != NULL &&

      atoi(slave_parallel_workers_var) > 0)

  {

    have_multi_threaded_slave= true;

  }

This is clearly incorrect; a proper way to detect if the server is a slave (and a multithreaded one) should be used.

I verified that{{ set global slave_parallel_workers=0 }}fixes the issue.