I am trying to set a foreign key constraint on a 5.7 InnoDB table with 30M+ rows.
It now already runs for over 1h on a quad core 64GB server. The processlist outputs the state
copy to tmp table for the issued alter table command.
InnoDB_buffer_pool_size is set to 32G and has room. The system does not swap.
Why does the system create a tmp table and can this somehow be increased in performance?