Insert hangs due to pk violation (plsql)

Question

Hello everybody,
i'm unable to cope with the following problem:
1) suppose to have a table with a single column and it's primary key
CREATE TABLE TABUSRLG
TUL_CODUSR VARCHAR2(30 BYTE)
ALTER TABLE TABUSRLG ADD (
PRIMARY KEY
(TUL_CODUSR) ENABLE);
2) from a session execute
insert into tabusrlg values 'A';
and DON'T rollabck or commit
3) from another session try the same insert
insert into tabusrlg values 'A';
this insert hangs (and i agree with this)
but ...
Is there a way to prevent the insert to hangs ? i'd like tpo skip the insert in this case without waiting for a timeout.
Usually when i want to update a record i execute a select for update nowait ;
if the instruction throws an exception the record is locked and i don't try the update
I'm looking for something similar but in this case i don't find a way to sort out it
Any suggestion ?
Many thanks in advance
Stefano

Answer 1

Stefano,
I am still not clear Why should Oracle hold a Lock and prevent from another session Inserting data?
I was not able to replicate the situation. Can anybody send steps to replicate the scenario?
SESSION 1:
CREATE TABLE test_table (col varchar2(10));
select username,
a.sid,
a.type,
lmode,
request
from v$lock a, v$session b
where a.sid = b.sid
  AND username = USER;
USERNAME     SID     TYPE     LMODE     REQUEST
PURVESH          23     AE          4          0
PURVESH          17     AE          4          0
PURVESH          143     JQ          4          0
PURVESH          143     AE          6          0
PURVESH          23     TO          3          0 
insert into test_table values ('A');
select username,
a.sid,
a.type,
lmode,
request
from v$lock a, v$session b
where a.sid = b.sid
  AND username = USER;
USERNAME     SID     TYPE     LMODE     REQUEST
PURVESH          23     AE          4          0
PURVESH          17     AE          4          0
PURVESH          143     JQ          6          0
PURVESH          143     AE          4          0
PURVESH          23     TO          3          0
PURVESH          23     TM          3          0
PURVESH          23     TX          6          0
-- As you see here a Table Row Level lock (TX) and a Table Lock (TM) is placed to prevent Table Structure modification.
SESSION 2:
insert into test_table values ('B');
select username,
a.sid,
a.type,
lmode,
request
from v$lock a, v$session b
where a.sid = b.sid
  AND username = USER;
USERNAME     SID     TYPE     LMODE     REQUEST
PURVESH          23     AE          4          0
PURVESH          17     AE          4          0
PURVESH          143     JQ          6          0
PURVESH          143     AE          4          0
PURVESH          23     TO          3          0
PURVESH          17     TM          3          0
PURVESH          23     TM          3          0
PURVESH          17     TX          6          0
PURVESH          23     TX          6          0
The above data proves that another session was not prevented from inserting a record into the same table. SID 17 has placed another TX and TM in Mode 3.I could not understand why are you thinking of alternatives without finding out where the actual problem lies?
I would recommend you to check out what locks are being held on your table and investigate the reason.
You can definitely let us know if you face any issue, just ensure to post appropriate data for our analysis.
Regards,
P.