Re: Allowing parallel-safe initplans

On Thu, Apr 13, 2023 at 12:43 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Pursuant to the discussion at [1], here's a patch that removes our
> old restriction that a plan node having initPlans can't be marked
> parallel-safe (dating to commit ab77a5a45). That was really a special
> case of the fact that we couldn't transmit subplans to parallel
> workers at all. We fixed that in commit 5e6d8d2bb and follow-ons,
> but this case never got addressed.

The patch looks good to me. Some comments from me:

* For the diff in standard_planner, I was wondering why not move the
initPlans up to the Gather node, just as we did before. So I tried that
way but did not notice the breakage of regression tests as stated in the
comments. Would you please confirm that?

* Not related to this patch. In SS_make_initplan_from_plan, the comment
says that the node's parParam and args lists remain empty. I wonder if
we need to explicitly set node->parParam and node->args to NIL before
that comment, or can we depend on makeNode to initialize them to NIL?

> There's only one existing test case that visibly changes plan with
> these changes. The new plan is clearly saner-looking than before,
> and testing with some data loaded into the table confirms that it
> is faster. I'm not sure if it's worth devising more test cases.

I also think it's better to have more test cases covering this change.

Thanks
Richard