RE: A strange locking issue with parent-child relation

From: Amihay Gonen <>
Date: Wed, 18 Mar 2009 17:50:27 +0200
Message-ID: <>

This is application we have migrated from a db called velcois (birdstep) and we try to keep the same logic in the old db for now.

I told oracle to lock the son table , not parent table (a) .

From: Mercadante, Thomas F (LABOR) [] Sent: Wednesday, March 18, 2009 5:30 PM
To: Amihay Gonen; Subject: RE: A strange locking issue with parent-child relation


Why are you locking the table in exclusive mode? You told Oracle to lock the table and then you are surprised when it did it?

It looks like this is working as it should.


From: [] On Behalf Of Amihay Gonen Sent: Wednesday, March 18, 2009 10:55 AM To:
Cc: Yossi Itzkovich; Subject: A strange locking issue with parent-child relation

Hi ,
When I to insert !! to a parent table and other session is lock table in exclusive mode . The session hangs.

Although , according to oracle note 33453.1 , it seems no lock is required when doing insert in parent key .


  AN INSERT/DELETE/UPDATE ON THE PARENT TABLE CAUSES THE CHILD TABLE TO GET    LOCKED. A share lock (LMODE=4) of the entire child table is required    until the transaction containing the insert/delete/update statement    for the parent table is committed, thus preventing any modifications to the    child table. It even can be a SSX (LMODE=5) lock when deleting from the    parent table with a delete cascade constraint.

NOTE: In 7.1.6 and higher, INSERT into the parent table do not lock the child table. In Oracle 9.0.1 or higher, those looks became temporal: they are only needed during the execution time of the UPDATE/DELETE statements. Those locks are downgraded to 'mode 3 Row-X (SX)' locks when the execution is finished. In 9.2.0, the downgraded 'mode 3 Row-X (SX)' locks are no longer required except when deleting from a parent table with a 'delete cascade' constraint.

Here is test case

Drop table son;
Drop table a;
create table a (a number primary key);
create table son(a number);
create index son on son(a);
ALTER TABLE son ADD ( CONSTRAINT son FOREIGN KEY (a) REFERENCES a (a)); lock table son in exclusive mode;

  • from other session try to insert in to A
  • session is locked until commit;
Received on Wed Mar 18 2009 - 10:50:27 CDT

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