Comment 5 for bug 897258

I believe the issue hovers around the innodb_lazy_drop_table option. I've turn this off and re ran the same command, the database is quite large and the optimization is still running without a crash.

As the error points out:

InnoDB: Error: Waited for 600 secs for hash index ref_count (1) to drop to 0.
index: "eval_datetime" table: "wc_acj/#sql2-1239-12d9"
111128 10:13:01 InnoDB: Assertion failure in thread 140040330925840 in file dict/dict0dict.c line 1821

here is the code from dict0dict.c line 1818 - 1822

  /* To avoid a hang here we commit suicide if the
  ref_count doesn't drop to zero in 600 seconds. */
  if (retries >= 60000) {
   ut_error;
  }

so - ut_error just generates an assertion, at this point i'm not sure what happens.