Deadlock when deleting a not linked data record in a parent table

Question

Hello, who knows about this problem with Oracle 10g:
Our installation of Oracle 10.2g behaves different from Oracle 9.2 concerning locking of data records:
To prevent that different users edit a complex data record at the same time and store it, the user has to put
the data record into the "edit mode" and we lock it with "Select CharFieldZ from TableX where ID = 1 for UPDATE NOWAIT".
In this data record references (= foreign keys) to other tables are used; with foreign key constraints we
prevent those data records of these tables from being deleted, which are used in data records of tableX: on
deleting such a record Oracle gives an error message ORA-02292, which the application translates for the
user: "You cannot delete this record, because it is used somewhere else".
Now when locking data record A under Oracle 10.2g, which contains a foreign Key upon data record 1 of tableF,
and trying to delete data record 2 of tableF, a deadlock appears, even when this data record is not used
anywhere else.
Further conditions:
- Data record 2 was created before locking of data record A.
- In the same session tableF was opened for reading before.
Is there a parameter, which leads Oracle 10.2g to return to the former behavoir ?
or: how is it possible to prevent a deadlock anyhow else ?
Thanks in advance
Lothar Weidl-Walther
Germany
Edited by: schatzag on 04.02.2009 14:22
for easier demonstration the SQL-scripts:
Installation:
DELETE TableF;
DELETE TableX;
CREATE TABLE TableF
( ID INTEGER NOT NULL,
NAME VARCHAR2(30 BYTE) NOT NULL);
CREATE UNIQUE INDEX PK_TableF ON TableF(ID);
ALTER TABLE TableF ADD CONSTRAINT PK_TableF PRIMARY KEY(ID);
INSERT INTO TableF VALUES (1, 'Record1');
INSERT INTO TableF VALUES (2, 'Record2');
commit;
CREATE TABLE TableX
( ID INTEGER NOT NULL,
NAME VARCHAR2(30 BYTE) NOT NULL,
CharFieldZ VARCHAR2(100 BYTE),
TableF_ID INTEGER);
ALTER TABLE TableX ADD (
CONSTRAINT FK_TableX_TableF
FOREIGN KEY (TableF_ID)
REFERENCES TableF (ID));
INSERT INTO TableX VALUES (1, 'ComplexRecord1', 'User1', 1);
commit;
Session1:
SELECT CharFieldZ FROM TableX WHERE ID = 1 FOR UPDATE NOWAIT;
SELECT * FROM TableF;
Session2:
DELETE FROM TableF WHERE ID = 2;
Edited by: schatzag on 04.02.2009 14:26

Answer 1

I'm not aware that the locking mechanism did change between Oracle 9i and 10g. Can you provide a simple and reproducable example?
You current description is very "uncomplete", e.g. this statement would lock the full table, but I think that is not what your application does.
Select CharFieldZ from TableX for UPDATE NOWAITAs Peter already mentioned you should check if there are any other differences between the databases. Let me mention just a few points that I can think of at the moment:
* indexes
* FK constraints with DELETE CASCADE
* higher oracle block size (can lead to more ITL locks)
Edited by: Sven W. on Feb 4, 2009 2:18 PM