Re: [HACKERS] parallelize queries containing subplans

On Wed, Dec 28, 2016 at 11:47 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> Attached patch implements the above idea.  This will enable
> parallelism for queries containing un-correlated subplans, an example
> of which is as follows:

I have reviewed the patch (pq_pushdown_subplan_v1.patch), Mostly patch
looks clean to me.
I have also done some basic functional testing and it's working fine.

I have one comment.

+ else if (IsA(node, AlternativeSubPlan))
+ {
+ AlternativeSubPlan *asplan = (AlternativeSubPlan *) node;
+ ListCell   *lc;
+
+ Assert(context->root);
+
+ foreach(lc, asplan->subplans)
+ {
+ SubPlan    *splan = (SubPlan *) lfirst(lc);
+ Plan   *plan;
+
+ Assert(IsA(splan, SubPlan));
+
+ plan = planner_subplan_get_plan(context->root, splan);
+ if (!plan->parallel_safe)
+ return true;
+ } }

I see no reason why we need to process the subplan list of
AlternativeSubPlan here, Anyway expression_tree_walker will take care
of processing each subplan of AlternativeSubPlan. Now in the case
where all the subplans in AlternativeSubPlan are parallel_safe we will
process this list twice. But, more than that it will be cleaner to not
handle AlternativeSubPlan here unless there is some strong reason?

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com