Re: ORA-600 Deadlock Issues

From: Karthik <karthik_at_apple.com>
Date: Mon, 27 Jun 2005 13:41:41 +0530
Message-Id: <d0d1fde80c48c400ac7d0a88e78ff169@apple.com>

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
>
>
> --
> http://www.freelists.org/webpage/oracle-l
>

--
http://www.freelists.org/webpage/oracle-l

Received on Mon Jun 27 2005 - 04:12:46 CDT