Re: Parallel Hash take II

On Mon, Sep 18, 2017 at 1:06 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> If we don't adopt some approach along these lines, then I think we've
> got to articulate some alternative deadlock-avoidance rule and make
> sure every parallel query facility follows it. I welcome ideas on
> that front, but I don't think the rule mentioned above is a bad one,
> and I'd obviously like to minimize the amount of rework that we need
> to do. Assuming we do settle on the above rule, it clearly needs to
> be documented someplace -- not sure of the place. I think that it
> doesn't belong in README.parallel because it's an executor-specific
> rule, not necessarily a general rule to which other users of
> parallelism must adhere; they can choose their own strategies.

+1

Graefe's "Query Evaluation Techniques for Large Databases" has several
pages on deadlock avoidance strategies. It was written almost 25 years
ago, but still has some good insights IMV (you'll recall that Graefe
is the author of the Volcano paper; this reference paper seems like
his follow-up). Apparently, deadlock avoidance strategy becomes
important for parallel sort with partitioning. You may be able to get
some ideas from there. And even if you don't, his handling of the
topic is very deliberate and high level, which suggests that ours
should be, too.

--
Peter Geoghegan