Yes, an index on a foreign key with extra columns concatenated can be used by Oracle to avoid taking a shared lock on the child table when updating or deleting rows of the parent. However, this was not the case prior to 7.3.

(Note that it is a shared lock on the child table, rather than an exclusive lock on the parent table, that would be taken in the absence of such an index).

From what I understand, I thought we needed an index on the foreign key so that an exclusive table lock would not appear on the parent table. I have an index on the foreign key but I would like to drop this index and create one with the foreign key as the first field of a concatenated index. Would this index be OK for the above problem even if the foreign key is part of a concatenated index(considering it is in the first position)?