Re: Multi-xacts and our process problem

On Tue, May 12, 2015 at 12:29:56AM +0300, Heikki Linnakangas wrote:
> On 05/12/2015 12:00 AM, Bruce Momjian wrote:
> >Multi-xacts were made durable in Postgres 9.3 (released 2013-09-09) to
> >allow primary-key-column-only locks. 1.7 years later, we are still
> >dealing with bugs related to this feature. Obviously, something is
> >wrong.
> >
> >There were many 9.3 minor releases containing multi-xacts fixes, and
> >these fixes have extended into 9.4. After the first few bug-fix
> >releases, I questioned whether we needed to revert or rework the
> >feature, but got no positive response. Only in the past few weeks have
> >we got additional people involved.
>
> The "revert or rework" ship had already sailed at that point. I

True.

> don't think we had much choice than just soldier through the bugs
> after the release.

The problem is we "soldiered on" without adding any resources to the
problem or doing a systematic review once it became clear one was
necessary.

> >I think we now know that our inaction didn't serve us well. The
> >question is how can we identify chronic problems and get resources
> >involved sooner. I feel we have been "asleep at the wheel" to some
> >extent on this.
>
> Yeah. I think the problem was that no-one realized that this was a
> significant change to the on-disk format. It was deceptively
> backwards-compatible. When it comes to permanent on-disk structures,
> we should all be more vigilant in the review.

Yes, and the size/age of the patch helped mask problems too. Are these
the lessons we need to learn?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +