Re: [PATCHES] NO WAIT ...

TODO updated:

< * Add GUC variable to prevent waiting on locks
> * Add NO WAIT option to various SQL commands

---------------------------------------------------------------------------

Barry Lind wrote:
> I agree with Tom here. I have used the Oracle NOWAIT feature in the
> past and think it is a great feature IMHO. But when you need to use it,
> you want it to apply very specifically to a single statement. Using a
> sledge hammer when you need a tweezers isn't the right way to go.
>
> thanks,
> --Barry
>
> Tom Lane wrote:
> > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> >
> >>The question is whether we should have a GUC variable to control no
> >>waiting on locks or add NO WAIT to specific SQL commands.
> >
> >
> > That's only a minor part of the issue. The major problem I have with
> > the patch is that it affects *all* locks, including system-internal
> > lock attempts that the user is probably not even aware of much less
> > able to control. It's like giving someone a poorly-aligned shotgun
> > when what they need is a rifle --- they'll end up putting holes in
> > a lot of other things besides what they intended.
> >
> > I think that what we actually want is something that is narrowly
> > tailored to affect only row-level locks taken by SELECT FOR UPDATE,
> > and maybe one or two other places that (a) people can make specific
> > use-cases for, and (b) we can be certain are only invoked by user
> > commands and never indirectly from behind-the-scenes system operations.
> >
> > The reason for proposing syntax rather than a GUC variable is the same
> > one of control. If you set a GUC variable then it will be hard to
> > prevent it from breaking operations other than the one you thought you
> > intended. (Example: you think you are only causing your SELECT FOR
> > UPDATE to error out, but what about ones done behind the scenes for
> > foreign key checks?) GUC variables are good for stuff that tends to
> > apply application-wide, which is why I thought regex_flavor wasn't too
> > dangerous, but they're terrible for functions that you want to apply to
> > only certain specific operations. And I can't imagine an app where that
> > wouldn't be true for NO WAIT.
> >
> > regards, tom lane
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 5: Have you checked our extensive FAQ?
> >
> > http://www.postgresql.org/docs/faqs/FAQ.html
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 1: subscribe and unsubscribe commands go to majordomo(at)postgresql(dot)org
>

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073