Set consider_parallel correctly for upper planner rels.

Commit 3fc6e2d introduced new "upper"
RelOptInfo structures but didn't set consider_parallel for them
correctly, a point I completely missed when reviewing it.  Later,
commit e06a389 made the situation
worse by doing it incorrectly for the grouping relation.  Try to
straighten all of that out.  Along the way, get rid of the annoying
wholePlanParallelSafe flag, which was only necessarily because of
the fact that upper planning stages didn't use paths at the time
that code was written.

The most important immediate impact of these changes is that
force_parallel_mode will provide useful test coverage in quite a few
more scenarios than it did previously, but it's also necessary
preparation for fixing some problems related to subqueries.

Patch by me, reviewed by Tom Lane.

Author: robertmhaas

src/backend/nodes/outfuncs.c

@@ -2018,7 +2018,6 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_BOOL_FIELD(hasRowSecurity);
 	WRITE_BOOL_FIELD(parallelModeOK);
 	WRITE_BOOL_FIELD(parallelModeNeeded);
-	WRITE_BOOL_FIELD(wholePlanParallelSafe);
 	WRITE_BOOL_FIELD(hasForeignJoin);
 }
 

src/backend/optimizer/plan/createplan.c

@@ -320,10 +320,6 @@ create_plan(PlannerInfo *root, Path *best_path)
 	 */
 	SS_attach_initplans(root, plan);
 
-	/* Update parallel safety information if needed. */
-	if (!best_path->parallel_safe)
-		root->glob->wholePlanParallelSafe = false;
-
 	/* Check we successfully assigned all NestLoopParams to plan nodes */
 	if (root->curOuterParams != NIL)
 		elog(ERROR, "failed to assign all NestLoopParams to plan nodes");

src/backend/optimizer/plan/planner.c

@@ -108,10 +108,6 @@ static double get_number_of_groups(PlannerInfo *root,
 					 double path_rows,
 					 List *rollup_lists,
 					 List *rollup_groupclauses);
-static void set_grouped_rel_consider_parallel(PlannerInfo *root,
-								  RelOptInfo *grouped_rel,
-								  PathTarget *target,
-								  const AggClauseCosts *agg_costs);
 static Size estimate_hashagg_tablesize(Path *path,
 						   const AggClauseCosts *agg_costs,
 						   double dNumGroups);
@@ -255,29 +251,14 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	/*
 	 * glob->parallelModeNeeded should tell us whether it's necessary to
 	 * impose the parallel mode restrictions, but we don't actually want to
-	 * impose them unless we choose a parallel plan, so that people who
-	 * mislabel their functions but don't use parallelism anyway aren't
-	 * harmed. But when force_parallel_mode is set, we enable the restrictions
-	 * whenever possible for testing purposes.
-	 *
-	 * glob->wholePlanParallelSafe should tell us whether it's OK to stick a
-	 * Gather node on top of the entire plan.  However, it only needs to be
-	 * accurate when force_parallel_mode is 'on' or 'regress', so we don't
-	 * bother doing the work otherwise.  The value we set here is just a
-	 * preliminary guess; it may get changed from true to false later, but not
-	 * vice versa.
+	 * impose them unless we choose a parallel plan, so it is normally set
+	 * only if a parallel plan is chosen (see create_gather_plan).  That way,
+	 * people who mislabel their functions but don't use parallelism anyway
+	 * aren't harmed.  But when force_parallel_mode is set, we enable the
+	 * restrictions whenever possible for testing purposes.
 	 */
-	if (force_parallel_mode == FORCE_PARALLEL_OFF || !glob->parallelModeOK)
-	{
-		glob->parallelModeNeeded = false;
-		glob->wholePlanParallelSafe = false;	/* either false or don't care */
-	}
-	else
-	{
-		glob->parallelModeNeeded = true;
-		glob->wholePlanParallelSafe =
-			!has_parallel_hazard((Node *) parse, false);
-	}
+	glob->parallelModeNeeded = glob->parallelModeOK &&
+		(force_parallel_mode != FORCE_PARALLEL_OFF);
 
 	/* Determine what fraction of the plan is likely to be scanned */
 	if (cursorOptions & CURSOR_OPT_FAST_PLAN)
@@ -327,20 +308,11 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 			top_plan = materialize_finished_plan(top_plan);
 	}
 
-	/*
-	 * At present, we don't copy subplans to workers.  The presence of a
-	 * subplan in one part of the plan doesn't preclude the use of parallelism
-	 * in some other part of the plan, but it does preclude the possibility of
-	 * regarding the entire plan parallel-safe.
-	 */
-	if (glob->subplans != NULL)
-		glob->wholePlanParallelSafe = false;
-
 	/*
 	 * Optionally add a Gather node for testing purposes, provided this is
 	 * actually a safe thing to do.
 	 */
-	if (glob->wholePlanParallelSafe &&
+	if (best_path->parallel_safe &&
 		force_parallel_mode != FORCE_PARALLEL_OFF)
 	{
 		Gather	   *gather = makeNode(Gather);
@@ -1925,6 +1897,21 @@ 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 &&
+		!has_parallel_hazard(parse->limitOffset, false) &&
+		!has_parallel_hazard(parse->limitCount, false))
+		final_rel->consider_parallel = true;
+
+	/*
+	 * Generate paths for the final rel.
+	 */
 	foreach(lc, current_rel->pathlist)
 	{
 		Path	   *path = (Path *) lfirst(lc);
@@ -3203,56 +3190,6 @@ get_number_of_groups(PlannerInfo *root,
 	return dNumGroups;
 }
 
-/*
- * set_grouped_rel_consider_parallel
- *	  Determine if it's safe to generate partial paths for grouping.
- */
-static void
-set_grouped_rel_consider_parallel(PlannerInfo *root, RelOptInfo *grouped_rel,
-								  PathTarget *target,
-								  const AggClauseCosts *agg_costs)
-{
-	Query	   *parse = root->parse;
-
-	Assert(grouped_rel->reloptkind == RELOPT_UPPER_REL);
-
-	/*
-	 * If there are no aggregates or GROUP BY clause, then no parallel
-	 * aggregation is possible.  At present, it doesn't matter whether
-	 * consider_parallel gets set in this case, because none of the upper rels
-	 * on top of this one try to set the flag or examine it, so we just bail
-	 * out as quickly as possible.  We might need to be more clever here in
-	 * the future.
-	 */
-	if (!parse->hasAggs && parse->groupClause == NIL)
-		return;
-
-	/*
-	 * Similarly, bail out quickly if GROUPING SETS are present; we can't
-	 * support those at present.
-	 */
-	if (parse->groupingSets)
-		return;
-
-	/*
-	 * If parallel-restricted functions are present in the target list or the
-	 * HAVING clause, we cannot safely go parallel.
-	 */
-	if (has_parallel_hazard((Node *) target->exprs, false) ||
-		has_parallel_hazard((Node *) parse->havingQual, false))
-		return;
-
-	/*
-	 * If we have any non-partial-capable aggregates, or if any of them can't
-	 * be serialized, we can't go parallel.
-	 */
-	if (agg_costs->hasNonPartial || agg_costs->hasNonSerial)
-		return;
-
-	/* OK, consider parallelization */
-	grouped_rel->consider_parallel = true;
-}
-
 /*
  * estimate_hashagg_tablesize
  *	  estimate the number of bytes that a hash aggregate hashtable will
@@ -3314,12 +3251,23 @@ create_grouping_paths(PlannerInfo *root,
 	double		dNumPartialGroups = 0;
 	bool		can_hash;
 	bool		can_sort;
+	bool		try_parallel_aggregation;
 
 	ListCell   *lc;
 
 	/* For now, do all work in the (GROUP_AGG, NULL) upperrel */
 	grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG, NULL);
 
+	/*
+	 * If the input relation is not parallel-safe, then the grouped relation
+	 * can't be parallel-safe, either.  Otherwise, it's parallel-safe if the
+	 * target list and HAVING quals are parallel-safe.
+	 */
+	if (input_rel->consider_parallel &&
+		!has_parallel_hazard((Node *) target->exprs, false) &&
+		!has_parallel_hazard((Node *) parse->havingQual, false))
+		grouped_rel->consider_parallel = true;
+
 	/*
 	 * Check for degenerate grouping.
 	 */
@@ -3407,15 +3355,6 @@ create_grouping_paths(PlannerInfo *root,
 									  rollup_lists,
 									  rollup_groupclauses);
 
-	/*
-	 * Partial paths in the input rel could allow us to perform aggregation in
-	 * parallel. set_grouped_rel_consider_parallel() will determine if it's
-	 * going to be safe to do so.
-	 */
-	if (input_rel->partial_pathlist != NIL)
-		set_grouped_rel_consider_parallel(root, grouped_rel,
-										  target, &agg_costs);
-
 	/*
 	 * Determine whether it's possible to perform sort-based implementations
 	 * of grouping.  (Note that if groupClause is empty,
@@ -3447,6 +3386,46 @@ create_grouping_paths(PlannerInfo *root,
 				agg_costs.numOrderedAggs == 0 &&
 				grouping_is_hashable(parse->groupClause));
 
+	/*
+	 * If grouped_rel->consider_parallel is true, then paths that we generate
+	 * for this grouping relation could be run inside of a worker, but that
+	 * doesn't mean we can actually use the PartialAggregate/FinalizeAggregate
+	 * execution strategy.  Figure that out.
+	 */
+	if (!grouped_rel->consider_parallel)
+	{
+		/* Not even parallel-safe. */
+		try_parallel_aggregation = false;
+	}
+	else if (input_rel->partial_pathlist == NIL)
+	{
+		/* Nothing to use as input for partial aggregate. */
+		try_parallel_aggregation = false;
+	}
+	else if (!parse->hasAggs && parse->groupClause == NIL)
+	{
+		/*
+		 * We don't know how to do parallel aggregation unless we have either
+		 * some aggregates or a grouping clause.
+		 */
+		try_parallel_aggregation = false;
+	}
+	else if (parse->groupingSets)
+	{
+		/* We don't know how to do grouping sets in parallel. */
+		try_parallel_aggregation = false;
+	}
+	else if (agg_costs.hasNonPartial || agg_costs.hasNonSerial)
+	{
+		/* Insufficient support for partial mode. */
+		try_parallel_aggregation = false;
+	}
+	else
+	{
+		/* Everything looks good. */
+		try_parallel_aggregation = true;
+	}
+
 	/*
 	 * Before generating paths for grouped_rel, we first generate any possible
 	 * partial paths; that way, later code can easily consider both parallel
@@ -3455,7 +3434,7 @@ create_grouping_paths(PlannerInfo *root,
 	 * Gather node on top is insufficient to create a final path, as would be
 	 * the case for a scan/join rel.
 	 */
-	if (grouped_rel->consider_parallel)
+	if (try_parallel_aggregation)
 	{
 		Path	   *cheapest_partial_path = linitial(input_rel->partial_pathlist);
 
@@ -3498,7 +3477,7 @@ create_grouping_paths(PlannerInfo *root,
 
 		if (can_sort)
 		{
-			/* Checked in set_grouped_rel_consider_parallel() */
+			/* This was checked before setting try_parallel_aggregation */
 			Assert(parse->hasAggs || parse->groupClause);
 
 			/*
@@ -3831,6 +3810,16 @@ create_window_paths(PlannerInfo *root,
 	/* For now, do all work in the (WINDOW, NULL) upperrel */
 	window_rel = fetch_upper_rel(root, UPPERREL_WINDOW, NULL);
 
+	/*
+	 * If the input relation is not parallel-safe, then the window relation
+	 * can't be parallel-safe, either.  Otherwise, we need to examine the
+	 * target list and active windows for non-parallel-safe constructs.
+	 */
+	if (input_rel->consider_parallel &&
+		!has_parallel_hazard((Node *) output_target->exprs, false) &&
+		!has_parallel_hazard((Node *) activeWindows, false))
+		window_rel->consider_parallel = true;
+
 	/*
 	 * Consider computing window functions starting from the existing
 	 * cheapest-total path (which will likely require a sort) as well as any
@@ -3986,6 +3975,15 @@ create_distinct_paths(PlannerInfo *root,
 	/* For now, do all work in the (DISTINCT, NULL) upperrel */
 	distinct_rel = fetch_upper_rel(root, UPPERREL_DISTINCT, NULL);
 
+	/*
+	 * We don't compute anything at this level, so distinct_rel will be
+	 * parallel-safe if the input rel is parallel-safe.  In particular, if
+	 * there is a DISTINCT ON (...) clause, any path for the input_rel will
+	 * output those expressions, and will not be parallel-safe unless those
+	 * expressions are parallel-safe.
+	 */
+	distinct_rel->consider_parallel = input_rel->consider_parallel;
+
 	/* Estimate number of distinct rows there will be */
 	if (parse->groupClause || parse->groupingSets || parse->hasAggs ||
 		root->hasHavingQual)
@@ -4169,6 +4167,15 @@ create_ordered_paths(PlannerInfo *root,
 	/* For now, do all work in the (ORDERED, NULL) upperrel */
 	ordered_rel = fetch_upper_rel(root, UPPERREL_ORDERED, NULL);
 
+	/*
+	 * If the input relation is not parallel-safe, then the ordered relation
+	 * can't be parallel-safe, either.  Otherwise, it's parallel-safe if the
+	 * target list is parallel-safe.
+	 */
+	if (input_rel->consider_parallel &&
+		!has_parallel_hazard((Node *) target->exprs, false))
+		ordered_rel->consider_parallel = true;
+
 	foreach(lc, input_rel->pathlist)
 	{
 		Path	   *path = (Path *) lfirst(lc);

src/backend/optimizer/util/pathnode.c

@@ -2177,7 +2177,8 @@ create_projection_path(PlannerInfo *root,
 	pathnode->path.param_info = NULL;
 	pathnode->path.parallel_aware = false;
 	pathnode->path.parallel_safe = rel->consider_parallel &&
-		subpath->parallel_safe;
+		subpath->parallel_safe &&
+		!has_parallel_hazard((Node *) target->exprs, false);
 	pathnode->path.parallel_workers = subpath->parallel_workers;
 	/* Projection does not change the sort order */
 	pathnode->path.pathkeys = subpath->pathkeys;
@@ -2304,6 +2305,16 @@ apply_projection_to_path(PlannerInfo *root,
 								   gpath->subpath,
 								   target);
 	}
+	else if (path->parallel_safe &&
+			 has_parallel_hazard((Node *) target->exprs, false))
+	{
+		/*
+		 * We're inserting a parallel-restricted target list into a path
+		 * currently marked parallel-safe, so we have to mark it as no longer
+		 * safe.
+		 */
+		path->parallel_safe = false;
+	}
 
 	return path;
 }

src/include/nodes/relation.h

@@ -127,8 +127,6 @@ typedef struct PlannerGlobal
 
 	bool		parallelModeNeeded;		/* parallel mode actually required? */
 
-	bool		wholePlanParallelSafe;	/* is the entire plan parallel safe? */
-
 	bool		hasForeignJoin; /* does have a pushed down foreign join */
 } PlannerGlobal;
 
@@ -655,7 +653,7 @@ typedef struct ForeignKeyOptInfo
 	struct EquivalenceClass *eclass[INDEX_MAX_KEYS];
 	/* List of non-EC RestrictInfos matching each column's condition */
 	List	   *rinfos[INDEX_MAX_KEYS];
-} ForeignKeyOptInfo;
+}	ForeignKeyOptInfo;
 
 
 /*

src/test/regress/expected/aggregates.out

@@ -575,6 +575,12 @@ select max(unique1) from tenk1 where unique1 > 42;
  9999
 (1 row)
 
+-- the planner may choose a generic aggregate here if parallel query is
+-- enabled, since that plan will be parallel safe and the "optimized"
+-- plan, which has almost identical cost, will not be.  we want to test
+-- the optimized plan, so temporarily disable parallel query.
+begin;
+set local max_parallel_workers_per_gather = 0;
 explain (costs off)
   select max(unique1) from tenk1 where unique1 > 42000;
                                 QUERY PLAN                                 
@@ -592,6 +598,7 @@ select max(unique1) from tenk1 where unique1 > 42000;
 
 (1 row)
 
+rollback;
 -- multi-column index (uses tenk1_thous_tenthous)
 explain (costs off)
   select max(tenthous) from tenk1 where thousand = 33;