Обсуждение: SELECT ... FOR UPDATE

I am interested in using the SELECT ... FOR UPDATE feature but it doesn't
work quite the way I had hoped.  If there is a better/different way of doing
this please enlighten me.

If I issue:

BEGIN;
SELECT * FROM atable WHERE atable.key = 10 FOR UPDDATE;

in one session and then issue the same commands from a 2nd session, the 2nd
session simply waits until the 1st session issues COMMIT or ROLLBACK.  While
the 2nd session is waiting I am, apparently locked out.  What I would like
is for the 2nd session to determine if the lock can be obtained and if not,
offer the user a choice of waiting or escaping from the SELECT.  Is this
possible?

Using 7.0.3

On Wed, 28 Mar 2001, Marcos Minshew wrote:

> I am interested in using the SELECT ... FOR UPDATE feature but it doesn't
> work quite the way I had hoped.  If there is a better/different way of doing
> this please enlighten me.
> 
> If I issue:
> 
> BEGIN;
> SELECT * FROM atable WHERE atable.key = 10 FOR UPDDATE;
> 
> in one session and then issue the same commands from a 2nd session, the 2nd
> session simply waits until the 1st session issues COMMIT or ROLLBACK.  While
> the 2nd session is waiting I am, apparently locked out.  What I would like
> is for the 2nd session to determine if the lock can be obtained and if not,
> offer the user a choice of waiting or escaping from the SELECT.  Is this
> possible?
> 
> Using 7.0.3

(I actually almost wrote an email asking this same question)

Has the documentation been updated recently or something I can find it
elsewhere (ie, not pg manual)?  I think (maybe) I am not the only person
confused by documentation for LOCK and MVCC.  "lack of detail / examples"
would probably say it best...


Thanks,
-Cedar