returns a duplicate key error and retry the operation a few
times because transactions with trx->mysql_thd == NULL are not
allowed to wait and could easily get lock wait timeout.

Overwriting existent rows in the stats tables during rename is important
because ALTER table that recreates the table will fail to rename the stats
properly. Internally InnoDB sees a new (temp) table being created and later
renamed to the real table, while the real table's stats are still in the
stats tables.