Re: parallelize queries containing subplans

On Thu, Jan 19, 2017 at 3:05 PM, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> During debugging I found that subplan created for below part of the
> query is parallel_unsafe, Is it a problem or there is some explanation
> of why it's not parallel_safe,

Okay, so basically we don't have any mechanism to perform parallel
scan on CTE. And, IMHO subplan built for CTE (using SS_process_ctes)
must come along with CTE scan. So I think we can avoid setting below
code because we will never be able to test its side effect, another
argument can be that if we don't consider the final effect, and just
see this subplan then by logic it should be marked parallel-safe or
unsafe as per it's path and it will not have any side effect, as it
will finally become parallel-unsafe. So it's your call to keep it
either way.

@@ -1213,6 +1216,7 @@ SS_process_ctes(PlannerInfo *root)
&splan->firstColCollation);
splan->useHashTable = false;
splan->unknownEqFalse = false;
+ splan->parallel_safe = best_path->parallel_safe;

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