Re: lcr v5 - introduction of InvalidCommandId

Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2013-09-05 14:21:33 -0400, Tom Lane wrote:
>> Ideally I'd have made InvalidCommandId = 0 and FirstCommandId = 1,
>> but I suppose we can't have that without an on-disk compatibility break.

> The patch actually does change it exactly that way.

Oh. I hadn't looked at the patch, but I had (mis)read what Robert said
to think that you were proposing introducing InvalidCommandId = 0xFFFFFFFF
while leaving FirstCommandId alone. That would make more sense to me as
(1) it doesn't change the interpretation of anything that's (likely to be)
on disk; (2) it allows the check for overflow in CommandCounterIncrement
to not involve recovering from an *actual* overflow. With the horsing
around we've been seeing from the gcc boys lately, I don't have a warm
feeling about whether they won't break that test someday on the grounds
that "overflow is undefined behavior".

regards, tom lane