- the problem was caused by EXPLAIN INSERT SELECT. For that statement,
the code would call select_insert::prepare2(), which would call
handler->ha_start_bulk_insert(). The corresponding handler->end_bulk_insert()
call is made from select_insert::send_eof or select_insert::abort_result_set
which are never called for EXPLAIN INSERT SELECT.
- Fixed by re-using approach of mysql-5.6: don't call ha_start_bulk_insert() if
we are in EXPLAIN.
