Inserting null into child table locks parent table

Hello out there,

last week, we upgraded our Oracle installation from 9.0.1.4 for 9.2.0.5 on W2kSP4.
Now I discovered some different locking behaviour of the new version. When I do the following:

create table test1 (col1 number(2) primary key, col2 varchar2(10));

create table test2 (tcol1 number(2) primary key,

   col1 number(2) references test1(col1));

insert into table test2 values (1,null);

I'm having a TM-Lock (ROW SHARE) on test1 which did not occur with Oracle 9.0.1. Indexing col1 on test2 does not help. Normally I would not care but in my special case I'm calling a stored procedure in an autonomous transaction which makes a lock table test1 in exclusive mode so that I'm getting a deadlock.

Is there a way to prevent Oracle from locking the parent table when inserting null into the child? (Other than dropping the constraint :-)

Many thanks in advance,
Lothar

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