Hi,
Yet another thing I noticed while working on [1] is this in
grouping_planner:
/*
* If the input rel is marked consider_parallel and there's nothing
that's
* not parallel-safe in the LIMIT clause, then the final_rel can be
marked
* consider_parallel as well. Note that if the query has rowMarks or is
* not a SELECT, consider_parallel will be false for every relation
in the
* query.
*/
if (current_rel->consider_parallel &&
is_parallel_safe(root, parse->limitOffset) &&
is_parallel_safe(root, parse->limitCount))
final_rel->consider_parallel = true;
If there is a need to add a LIMIT node, we don't consider generating
partial paths for the final relation below (see commit
0927d2f46ddd4cf7d6bf2cc84b3be923e0aedc52), so it seems unnecessary
anymore to assess the parallel-safety of the LIMIT and OFFSET clauses.
To save cycles, why not remove those tests from that function like the
attached?
Best regards,
Etsuro Fujita
[1] https://commitfest.postgresql.org/22/1950/
*** a/src/backend/optimizer/plan/planner.c
--- b/src/backend/optimizer/plan/planner.c
***************
*** 2141,2155 **** grouping_planner(PlannerInfo *root, bool inheritance_update,
final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);
/*
! * If the input rel is marked consider_parallel and there's nothing that's
! * not parallel-safe in the LIMIT clause, then the final_rel can be marked
! * consider_parallel as well. Note that if the query has rowMarks or is
! * not a SELECT, consider_parallel will be false for every relation in the
! * query.
*/
! if (current_rel->consider_parallel &&
! is_parallel_safe(root, parse->limitOffset) &&
! is_parallel_safe(root, parse->limitCount))
final_rel->consider_parallel = true;
/*
--- 2141,2152 ----
final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);
/*
! * If the input rel is marked consider_parallel and there's no need to add
! * a LIMIT node, then the final_rel can be marked consider_parallel as
! * well. Note that if the query has rowMarks or is not a SELECT,
! * consider_parallel will be false for every relation in the query.
*/
! if (current_rel->consider_parallel && !limit_needed(parse))
final_rel->consider_parallel = true;
/*
***************
*** 2263,2272 **** grouping_planner(PlannerInfo *root, bool inheritance_update,
* Generate partial paths for final_rel, too, if outer query levels might
* be able to make use of them.
*/
! if (final_rel->consider_parallel && root->query_level > 1 &&
! !limit_needed(parse))
{
! Assert(!parse->rowMarks && parse->commandType == CMD_SELECT);
foreach(lc, current_rel->partial_pathlist)
{
Path *partial_path = (Path *) lfirst(lc);
--- 2260,2269 ----
* Generate partial paths for final_rel, too, if outer query levels might
* be able to make use of them.
*/
! if (final_rel->consider_parallel && root->query_level > 1)
{
! Assert(!parse->rowMarks && !limit_needed(parse) &&
! parse->commandType == CMD_SELECT);
foreach(lc, current_rel->partial_pathlist)
{
Path *partial_path = (Path *) lfirst(lc);
