Re: WIP: Upper planner pathification

On 4 March 2016 at 09:29, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Mar 3, 2016 at 2:19 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> This leads me to the conclusion that all these new node types should
>> set parallel_aware to false and copy up the other two fields from the
>> child, except for LockRows and ModifyTable which should set them all
>> to false/0. Correct? If so, I'll go fix.
>
> Well, I'd probably bubble it up regardless. The fact that the overall
> plan writes data will cause everything in the plan to have
> parallel_safe = false and parallel_degree = 0, so you'll get the same
> outcome either way. However, that way, if writes eventually become
> safe, then this won't need adjusting. But it doesn't really matter
> much; feel free to do it as you say if you prefer.

This would help me too. I hit a problem with this when adding Group
Parallel Aggregate, as the sort path is conditionally added in
create_grouping_paths() which causes the parallel_degree for the
subpath which is later passed into create_agg_path() to become 0. in
create_agg_path() I was using the parallel_degree variable to
determine if I should construct a normal serial agg path, or a chain
of partial agg -> gather -> final agg paths. To get around the problem
I added a parallel_degree parameter to create_agg_path() of which that
parameter so far seems to only exist in create_seqscan_path(), which
naturally is a bit special as it's a "leaf node" in the path tree.
Propagating these would mean I could remove that parameter again.

--
David Rowley http://www.2ndQuadrant.com/
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