Re: ORA-600 Deadlock Issues
- From: Karthik <karthik@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 27 Jun 2005 13:41:41 +0530
The issue turned out to be a very interesting one.
try this.
open two db sessions.
(session 1)
create table p( x number primary key);
create table c( x number references p);
insert into p values(1);
insert into c values(1);
insert into p values (2);
insert into c values(2);
insert into p values(3);
insert into c values(3);
commit;
(session 1)
update p set x = 2 where x = 2;
(session 2)
update p set x = 1 where x = 1;
(session 1) -- this will hang
update c set x = 2 where x = 2;
(session 2)
update c set x = 1 where x = 1;
you will find session 1 comes out with deadlock detected error.
now
create index c_idx on c(x);
try the same test case and the hang will be gone.
look up chapter 7 of tom kytes' book - Indexes on Foreign Keys. (page
142 in my book).
"The number one cause of deadlocks in the Oracle database, in my
experience, is unindexed foreign keys" - says the Guru himself.
Thanks, Karthik
On 25-Jun-05, at 9:42 PM, Mladen Gogala wrote:
On 06/25/2005 03:04:25 AM, Egor Starostin wrote:
Are you sure that your first session doesn't receive ORA-60?
Probably, you just don't look in first session output.
I reproduced you case and ORA-60 was generated (which is expected).
Note that hanganalyze in your case shows lock, not a deadlock.
Deadlocks are printed in 'Cycles' section of hanganalyze trace file.
Sessions from 'Open Cahins' section are just locks.
That is correct, my first session did receive ora-0060 but I wasn't
able to
type fast enough. Yes, when I come to think of it, oracle will break
the
chain as soon as it discovers it. Hanganalyze will not have time enough
to catch it.
--
Mladen Gogala
Oracle DBA
--
//www.freelists.org/webpage/oracle-l
--
//www.freelists.org/webpage/oracle-l
Other related posts:
