Re: Which query is best?

On Tue, Dec 15, 2009 at 7:22 AM, Syed Jaffar Hussain
<sjaffarhussain@xxxxxxxxx> wrote:
> Hi everyone,
>
> The following simple join query on one of our business critical RAC
> databases with two instances was frequently leading into a dead lock
> situation ultimately a causing database hang scenario:
>
> SELECT u.u_user_id, u..u_mcr_cust_id
> FROM table1 U,table2 A
> WHERE
> A.UCS_CHNL_ID = :b1 AND A.UCS_LOGIN_NAME = :b2 AND A.UCS_USER_ID =
> U.U_USER_ID FOR UPDATE
>

As I understand this query condition is based on user login name -
When exactly this dead lock happen ? when this same user is trying to
login twice from two different machines ? Maybe there are some old,
unused and not committed sessions ?

regards,
Marcin Przepiorowski
--
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