The alter_online grammars are for hunting server crashes when
concurrent DDL meets concurrent DML in transactions.

Please note that MySQL/InnoDB decide depending on the situation
if some ALTER TABLE operation will use the old ALTER TABLE
algorithm (COPY) or the new ALTER TABLE algorithm (INPLACE).

Recommended RQG setup:
   duration = 1200,
   queries  = 30000,
   threads  ~ 12
   lock-wait-timeout        = 2,
   innodb-lock-wait-timeout = 1,
   default-storage-engine   = 'InnoDB',