Re: 9.4 broken on alpha

On Wed, Aug 26, 2015 at 12:49:46PM -0400, Tom Lane wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > A buildfarm machine would be mandatory, too.
>
> That, however, is not negotiable.

Right. I think the still-open question around PostgreSQL on Alpha is whether
9.1 through 9.4 are meaningfully supported there. Step one for anyone
interested in Alpha support is to activate a buildfarm member covering that
range of versions. Without that, the PostgreSQL community is just listening
for bug fix contributions.

On Wed, Aug 26, 2015 at 01:34:38PM -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > But I really strongly object to re-introducing alpha support. Having to
> > care about data dependency barriers is a huge pita, and it complicates
> > code for everyone. And we'd have to investigate a lot of code to
> > actually make it work reliably. For what benefit?
>
> I hear you, but that's only an issue for multi-CPU machines no? If we
> just say "we doubt this works on multi-CPU Alphas, if it breaks you get to
> keep both pieces", then we're basically at the same place we were before.
>
> To be clear: I don't want to do the work you're speaking of, either.
> But if we have people who were successfully using PG on Alphas before,
> the coherency issues must not have been a problem for them. Can't we
> just (continue to) ignore the issue?

The landscape changed with the 9.5 cycle's push to use more lock-free
algorithms. Dropping Alpha support simplified review for those algorithms.
True, we could ignore Alpha for review purposes and accept unstudied damage to
reliability on Alpha. To some extent, that characterizes any platform whose
test reports don't reach us. It's different when we know Alpha has special
needs and we make changes in the area of those needs without even attempting
to meet them. We made a decision to instead break compatibility explicitly,
and I don't think this thread has impugned that decision.

As it is, we've implicitly prepared to ship Alpha-supporting PostgreSQL 9.4
until 2019, by which time the newest Alpha hardware will be 15 years old.
Computer museums would be our only audience for continued support. I do have
a sentimental weakness for computer museums, but not at the price of drag on
important performance work.

nm