Re: [PATCHES] NO WAIT ... - Mailing list pgsql-hackers

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


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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@candle.pha.pa.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
> > 
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--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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