Re: Alter index rename concurrently to

On 2018-08-02 16:51:10 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > [ reasons why DDL under less than AEL sucks ]
>
> Unfortunately, none of these problems are made to go away with an
> AcceptInvalidationMessages at statement start. That just makes the
> window smaller. But DDL effects could still be seen - or not -
> partway through a statement, with just as much ensuing hilarity
> as in your example. Maybe more.

I think it's a lot easier to explain that every newly issued statement
sees the effect of DDL, and already running statements may see it, than
something else. I don't agree that parse analysis is a good hook to
force that, as I've written.

> The real issue here, and the reason why I'm very unhappy with the mad rush
> in certain quarters to try to reduce locking levels for DDL, is exactly
> that it generally results in uncertainty about when the effects will be
> seen. I do not think your proposal does much more than put a fig leaf
> over that problem.

I think it's a significant issue operationally, which is why that
pressure exists. I don't know what makes it a "mad rush", given these
discussions have been going on for *years*?

Greetings,

Andres Freund