Re: ALTER TABLE lock strength reduction patch is unsafe

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Jan 28, 2014 at 12:36 PM, Alvaro Herrera
> <alvherre(at)2ndquadrant(dot)com> wrote:
>> Honestly, I would prefer that we push a patch that has been thoroughly
>> reviewed and in which we have more confidence, so that we can push
>> without a GUC. This means mark in CF as needs-review, then some other
>> developer reviews it and marks it as ready-for-committer.

> I also believe that would be the correct procedure. Personally, I
> think it would be great if Noah can review this, as he's very good at
> finding the kind of problems that are likely to crop up here, and has
> examined previous versions. I also have some interest in looking at
> it myself. But I doubt that either of us (or any other senior hacker)
> can do that by Thursday. I think all such people are hip-deep in
> other patches at the moment; I certainly am.

Yeah. I actually have little doubt that the patch is sane on its own
terms of discussion, that is that Simon has chosen locking levels that
are mutually consistent in an abstract sense. What sank the previous
iteration was that he'd failed to consider an implementation detail,
namely possible inconsistencies in SnapshotNow-based catalog fetches.
I'm afraid that there may be more such problems lurking under the
surface. Noah's pretty good at finding such things, but really two
or three of us need to sit down and think about it for awhile before
I'd have much confidence in such a fundamental change. And I sure don't
have time for this patch right now myself.

regards, tom lane