Make sequential scans parallel-aware.

In addition, this path fills in a number of missing bits and pieces in
the parallel infrastructure.  Paths and plans now have a parallel_aware
flag indicating whether whatever parallel-aware logic they have should
be engaged.  It is believed that we will need this flag for a number of
path/plan types, not just sequential scans, which is why the flag is
generic rather than part of the SeqScan structures specifically.
Also, execParallel.c now gives parallel nodes a chance to initialize
their PlanState nodes from the DSM during parallel worker startup.

Amit Kapila, with a fair amount of adjustment by me.  Review of previous
patch versions by Haribabu Kommi and others.

1 files changed, 24 insertions, 20 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index e70a337328e..411b36c418e 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -101,7 +101,7 @@ static List *fix_indexorderby_references(PlannerInfo *root, IndexPath *index_pat
 static Node *fix_indexqual_operand(Node *node, IndexOptInfo *index, int indexcol);
 static List *get_switched_clauses(List *clauses, Relids outerrelids);
 static List *order_qual_clauses(PlannerInfo *root, List *clauses);
-static void copy_path_costsize(Plan *dest, Path *src);
+static void copy_generic_path_info(Plan *dest, Path *src);
 static void copy_plan_costsize(Plan *dest, Plan *src);
 static SeqScan *make_seqscan(List *qptlist, List *qpqual, Index scanrelid);
 static SampleScan *make_samplescan(List *qptlist, List *qpqual, Index scanrelid,
@@ -779,7 +779,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
 	 * prepare_sort_from_pathkeys on it before we do so on the individual
 	 * child plans, to make cross-checking the sort info easier.
 	 */
-	copy_path_costsize(plan, (Path *) best_path);
+	copy_generic_path_info(plan, (Path *) best_path);
 	plan->targetlist = tlist;
 	plan->qual = NIL;
 	plan->lefttree = NULL;
@@ -901,7 +901,7 @@ create_material_plan(PlannerInfo *root, MaterialPath *best_path)
 
 	plan = make_material(subplan);
 
-	copy_path_costsize(&plan->plan, (Path *) best_path);
+	copy_generic_path_info(&plan->plan, (Path *) best_path);
 
 	return plan;
 }
@@ -1129,7 +1129,7 @@ create_gather_plan(PlannerInfo *root, GatherPath *best_path)
 							  best_path->single_copy,
 							  subplan);
 
-	copy_path_costsize(&gather_plan->plan, &best_path->path);
+	copy_generic_path_info(&gather_plan->plan, &best_path->path);
 
 	/* use parallel mode for parallel plans. */
 	root->glob->parallelModeNeeded = true;
@@ -1178,7 +1178,7 @@ create_seqscan_plan(PlannerInfo *root, Path *best_path,
 							 scan_clauses,
 							 scan_relid);
 
-	copy_path_costsize(&scan_plan->plan, best_path);
+	copy_generic_path_info(&scan_plan->plan, best_path);
 
 	return scan_plan;
 }
@@ -1224,7 +1224,7 @@ create_samplescan_plan(PlannerInfo *root, Path *best_path,
 								scan_relid,
 								tsc);
 
-	copy_path_costsize(&scan_plan->scan.plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -1422,7 +1422,7 @@ create_indexscan_plan(PlannerInfo *root,
 											indexorderbyops,
 											best_path->indexscandir);
 
-	copy_path_costsize(&scan_plan->plan, &best_path->path);
+	copy_generic_path_info(&scan_plan->plan, &best_path->path);
 
 	return scan_plan;
 }
@@ -1538,7 +1538,7 @@ create_bitmap_scan_plan(PlannerInfo *root,
 									 bitmapqualorig,
 									 baserelid);
 
-	copy_path_costsize(&scan_plan->scan.plan, &best_path->path);
+	copy_generic_path_info(&scan_plan->scan.plan, &best_path->path);
 
 	return scan_plan;
 }
@@ -1795,7 +1795,7 @@ create_tidscan_plan(PlannerInfo *root, TidPath *best_path,
 							 scan_relid,
 							 tidquals);
 
-	copy_path_costsize(&scan_plan->scan.plan, &best_path->path);
+	copy_generic_path_info(&scan_plan->scan.plan, &best_path->path);
 
 	return scan_plan;
 }
@@ -1836,7 +1836,7 @@ create_subqueryscan_plan(PlannerInfo *root, Path *best_path,
 								  scan_relid,
 								  best_path->parent->subplan);
 
-	copy_path_costsize(&scan_plan->scan.plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -1879,7 +1879,7 @@ create_functionscan_plan(PlannerInfo *root, Path *best_path,
 	scan_plan = make_functionscan(tlist, scan_clauses, scan_relid,
 								  functions, rte->funcordinality);
 
-	copy_path_costsize(&scan_plan->scan.plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -1923,7 +1923,7 @@ create_valuesscan_plan(PlannerInfo *root, Path *best_path,
 	scan_plan = make_valuesscan(tlist, scan_clauses, scan_relid,
 								values_lists);
 
-	copy_path_costsize(&scan_plan->scan.plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -2016,7 +2016,7 @@ create_ctescan_plan(PlannerInfo *root, Path *best_path,
 	scan_plan = make_ctescan(tlist, scan_clauses, scan_relid,
 							 plan_id, cte_param_id);
 
-	copy_path_costsize(&scan_plan->scan.plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -2076,7 +2076,7 @@ create_worktablescan_plan(PlannerInfo *root, Path *best_path,
 	scan_plan = make_worktablescan(tlist, scan_clauses, scan_relid,
 								   cteroot->wt_param_id);
 
-	copy_path_costsize(&scan_plan->scan.plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -2132,7 +2132,7 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 												tlist, scan_clauses);
 
 	/* Copy cost data from Path to Plan; no need to make FDW do this */
-	copy_path_costsize(&scan_plan->scan.plan, &best_path->path);
+	copy_generic_path_info(&scan_plan->scan.plan, &best_path->path);
 
 	/* Copy foreign server OID; likewise, no need to make FDW do this */
 	scan_plan->fs_server = rel->serverid;
@@ -2238,7 +2238,7 @@ create_customscan_plan(PlannerInfo *root, CustomPath *best_path,
 	 * Copy cost data from Path to Plan; no need to make custom-plan providers
 	 * do this
 	 */
-	copy_path_costsize(&cplan->scan.plan, &best_path->path);
+	copy_generic_path_info(&cplan->scan.plan, &best_path->path);
 
 	/* Likewise, copy the relids that are represented by this custom scan */
 	cplan->custom_relids = best_path->path.parent->relids;
@@ -2355,7 +2355,7 @@ create_nestloop_plan(PlannerInfo *root,
 							  inner_plan,
 							  best_path->jointype);
 
-	copy_path_costsize(&join_plan->join.plan, &best_path->path);
+	copy_generic_path_info(&join_plan->join.plan, &best_path->path);
 
 	return join_plan;
 }
@@ -2650,7 +2650,7 @@ create_mergejoin_plan(PlannerInfo *root,
 							   best_path->jpath.jointype);
 
 	/* Costs of sort and material steps are included in path cost already */
-	copy_path_costsize(&join_plan->join.plan, &best_path->jpath.path);
+	copy_generic_path_info(&join_plan->join.plan, &best_path->jpath.path);
 
 	return join_plan;
 }
@@ -2775,7 +2775,7 @@ create_hashjoin_plan(PlannerInfo *root,
 							  (Plan *) hash_plan,
 							  best_path->jpath.jointype);
 
-	copy_path_costsize(&join_plan->join.plan, &best_path->jpath.path);
+	copy_generic_path_info(&join_plan->join.plan, &best_path->jpath.path);
 
 	return join_plan;
 }
@@ -3411,9 +3411,11 @@ order_qual_clauses(PlannerInfo *root, List *clauses)
 /*
  * Copy cost and size info from a Path node to the Plan node created from it.
  * The executor usually won't use this info, but it's needed by EXPLAIN.
+ *
+ * Also copy the parallel-aware flag, which the executor will use.
  */
 static void
-copy_path_costsize(Plan *dest, Path *src)
+copy_generic_path_info(Plan *dest, Path *src)
 {
 	if (src)
 	{
@@ -3421,6 +3423,7 @@ copy_path_costsize(Plan *dest, Path *src)
 		dest->total_cost = src->total_cost;
 		dest->plan_rows = src->rows;
 		dest->plan_width = src->parent->width;
+		dest->parallel_aware = src->parallel_aware;
 	}
 	else
 	{
@@ -3428,6 +3431,7 @@ copy_path_costsize(Plan *dest, Path *src)
 		dest->total_cost = 0;
 		dest->plan_rows = 0;
 		dest->plan_width = 0;
+		dest->parallel_aware = false;
 	}
 }