On Mon, Apr 25, 2016 at 1:45 PM, Robert Haas <robertmh...@gmail.com> wrote:
>> I think the "degree" terminology is fundamentally tainted by the question
>> of whether or not it counts the leader, and that we will have bugs (or
>> indeed may have them today) caused by getting that wrong.
> This theory does not seem very plausible to me.  I don't really see
> how that could happen, although perhaps I'm blinded by being too close
> to the feature.  Also, you haven't presented entirely convincing
> evidence that other people are all united in the way they view this
> and that that way is different than PostgreSQL; and I've submitted
> some contrary evidence.

SQL Server definitely disables parallel query when max degree of
parallelism = 1. The default, 0, is "auto". I think that a DoP of 1 in
Oracle also disables parallelism.

> Even if Oracle for example does do it
> differently than what I've done here, slavishly following Oracle has
> never been a prerequisite for regarding a PostgreSQL feature as
> well-designed.  I think it is far more likely that going and
> offsetting the value of parallel_degree by 1 everywhere, as Peter has
> proposed, is going to introduce subtle bugs.

That was one approach that I mentioned as a theoretically sound way of
maintaining the "degree" terminology. This was several months back.
I'm not arguing for that.

I'm also not arguing for slavishly following Oracle or SQL Server.
Rather, my position is that as long as we're going to use their
terminology, we should also offer something roughly compatible with
their behavior. I think that not using their terminology is also a
reasonable solution.

I'm not sure about anyone else, but my complaint is entirely about the
baggage that the term "degree of parallelism" happens to have, and how
effectively that has been managed.

Peter Geoghegan

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