Speed up planner's scanning for parallel-query hazards.

We need to scan the whole parse tree for parallel-unsafe functions.
If there are none, we'll later need to determine whether particular
subtrees contain any parallel-restricted functions.  The previous coding
retained no knowledge from the first scan, even though this is very
wasteful in the common case where the query contains only parallel-safe
functions.  We can bypass all of the later scans by remembering that fact.
This provides a small but measurable speed improvement when the case
applies, and shouldn't cost anything when it doesn't.

Patch by me, reviewed by Robert Haas

Discussion: <3740.1471538387@sss.pgh.pa.us>

src/backend/nodes/outfuncs.c

@@ -2029,6 +2029,7 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_BOOL_FIELD(dependsOnRole);
 	WRITE_BOOL_FIELD(parallelModeOK);
 	WRITE_BOOL_FIELD(parallelModeNeeded);
+	WRITE_CHAR_FIELD(maxParallelHazard);
 }
 
 static void

src/backend/optimizer/path/allpaths.c

@@ -78,7 +78,6 @@ static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel,
 static void create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel);
 static void set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 						  RangeTblEntry *rte);
-static bool function_rte_parallel_ok(RangeTblEntry *rte);
 static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
 static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel,
@@ -542,8 +541,7 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 
 				if (proparallel != PROPARALLEL_SAFE)
 					return;
-				if (has_parallel_hazard((Node *) rte->tablesample->args,
-										false))
+				if (!is_parallel_safe(root, (Node *) rte->tablesample->args))
 					return;
 			}
 
@@ -596,7 +594,7 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 
 		case RTE_FUNCTION:
 			/* Check for parallel-restricted functions. */
-			if (!function_rte_parallel_ok(rte))
+			if (!is_parallel_safe(root, (Node *) rte->functions))
 				return;
 			break;
 
@@ -629,40 +627,20 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 	 * outer join clauses work correctly.  It would likely break equivalence
 	 * classes, too.
 	 */
-	if (has_parallel_hazard((Node *) rel->baserestrictinfo, false))
+	if (!is_parallel_safe(root, (Node *) rel->baserestrictinfo))
 		return;
 
 	/*
 	 * Likewise, if the relation's outputs are not parallel-safe, give up.
 	 * (Usually, they're just Vars, but sometimes they're not.)
 	 */
-	if (has_parallel_hazard((Node *) rel->reltarget->exprs, false))
+	if (!is_parallel_safe(root, (Node *) rel->reltarget->exprs))
 		return;
 
 	/* We have a winner. */
 	rel->consider_parallel = true;
 }
 
-/*
- * Check whether a function RTE is scanning something parallel-restricted.
- */
-static bool
-function_rte_parallel_ok(RangeTblEntry *rte)
-{
-	ListCell   *lc;
-
-	foreach(lc, rte->functions)
-	{
-		RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);
-
-		Assert(IsA(rtfunc, RangeTblFunction));
-		if (has_parallel_hazard(rtfunc->funcexpr, false))
-			return false;
-	}
-
-	return true;
-}
-
 /*
  * set_plain_rel_pathlist
  *	  Build access paths for a plain relation (no subquery, no inheritance)

src/backend/optimizer/plan/planmain.c

@@ -71,14 +71,13 @@ query_planner(PlannerInfo *root, List *tlist,
 
 		/*
 		 * If query allows parallelism in general, check whether the quals are
-		 * parallel-restricted.  There's currently no real benefit to setting
-		 * this flag correctly because we can't yet reference subplans from
-		 * parallel workers.  But that might change someday, so set this
-		 * correctly anyway.
+		 * parallel-restricted.  (We need not check final_rel->reltarget
+		 * because it's empty at this point.  Anything parallel-restricted in
+		 * the query tlist will be dealt with later.)
 		 */
 		if (root->glob->parallelModeOK)
 			final_rel->consider_parallel =
-				!has_parallel_hazard(parse->jointree->quals, false);
+				is_parallel_safe(root, parse->jointree->quals);
 
 		/* The only path for it is a trivial Result path */
 		add_path(final_rel, (Path *)

src/backend/optimizer/plan/planner.c

@@ -23,6 +23,7 @@
 #include "access/sysattr.h"
 #include "access/xact.h"
 #include "catalog/pg_constraint_fn.h"
+#include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "executor/executor.h"
 #include "executor/nodeAgg.h"
@@ -241,12 +242,26 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	 * time and execution time, so don't generate a parallel plan if we're in
 	 * serializable mode.
 	 */
-	glob->parallelModeOK = (cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
-		IsUnderPostmaster && dynamic_shared_memory_type != DSM_IMPL_NONE &&
-		parse->commandType == CMD_SELECT && !parse->hasModifyingCTE &&
-		parse->utilityStmt == NULL && max_parallel_workers_per_gather > 0 &&
-		!IsParallelWorker() && !IsolationIsSerializable() &&
-		!has_parallel_hazard((Node *) parse, true);
+	if ((cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
+		IsUnderPostmaster &&
+		dynamic_shared_memory_type != DSM_IMPL_NONE &&
+		parse->commandType == CMD_SELECT &&
+		parse->utilityStmt == NULL &&
+		!parse->hasModifyingCTE &&
+		max_parallel_workers_per_gather > 0 &&
+		!IsParallelWorker() &&
+		!IsolationIsSerializable())
+	{
+		/* all the cheap tests pass, so scan the query tree */
+		glob->maxParallelHazard = max_parallel_hazard(parse);
+		glob->parallelModeOK = (glob->maxParallelHazard != PROPARALLEL_UNSAFE);
+	}
+	else
+	{
+		/* skip the query tree scan, just assume it's unsafe */
+		glob->maxParallelHazard = PROPARALLEL_UNSAFE;
+		glob->parallelModeOK = false;
+	}
 
 	/*
 	 * glob->parallelModeNeeded should tell us whether it's necessary to
@@ -1802,7 +1817,7 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 		 * computed by partial paths.
 		 */
 		if (current_rel->partial_pathlist &&
-			!has_parallel_hazard((Node *) scanjoin_target->exprs, false))
+			is_parallel_safe(root, (Node *) scanjoin_target->exprs))
 		{
 			/* Apply the scan/join target to each partial path */
 			foreach(lc, current_rel->partial_pathlist)
@@ -1948,8 +1963,8 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 	 * query.
 	 */
 	if (current_rel->consider_parallel &&
-		!has_parallel_hazard(parse->limitOffset, false) &&
-		!has_parallel_hazard(parse->limitCount, false))
+		is_parallel_safe(root, parse->limitOffset) &&
+		is_parallel_safe(root, parse->limitCount))
 		final_rel->consider_parallel = true;
 
 	/*
@@ -3326,8 +3341,8 @@ create_grouping_paths(PlannerInfo *root,
 	 * 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))
+		is_parallel_safe(root, (Node *) target->exprs) &&
+		is_parallel_safe(root, (Node *) parse->havingQual))
 		grouped_rel->consider_parallel = true;
 
 	/*
@@ -3881,8 +3896,8 @@ create_window_paths(PlannerInfo *root,
 	 * 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))
+		is_parallel_safe(root, (Node *) output_target->exprs) &&
+		is_parallel_safe(root, (Node *) activeWindows))
 		window_rel->consider_parallel = true;
 
 	/*
@@ -4272,7 +4287,7 @@ create_ordered_paths(PlannerInfo *root,
 	 * target list is parallel-safe.
 	 */
 	if (input_rel->consider_parallel &&
-		!has_parallel_hazard((Node *) target->exprs, false))
+		is_parallel_safe(root, (Node *) target->exprs))
 		ordered_rel->consider_parallel = true;
 
 	/*

src/backend/optimizer/util/clauses.c

@@ -91,8 +91,9 @@ typedef struct
 
 typedef struct
 {
-	bool		allow_restricted;
-} has_parallel_hazard_arg;
+	char		max_hazard;		/* worst proparallel hazard found so far */
+	char		max_interesting;	/* worst proparallel hazard of interest */
+} max_parallel_hazard_context;
 
 static bool contain_agg_clause_walker(Node *node, void *context);
 static bool get_agg_clause_costs_walker(Node *node,
@@ -103,8 +104,8 @@ static bool contain_subplans_walker(Node *node, void *context);
 static bool contain_mutable_functions_walker(Node *node, void *context);
 static bool contain_volatile_functions_walker(Node *node, void *context);
 static bool contain_volatile_functions_not_nextval_walker(Node *node, void *context);
-static bool has_parallel_hazard_walker(Node *node,
-						   has_parallel_hazard_arg *context);
+static bool max_parallel_hazard_walker(Node *node,
+						   max_parallel_hazard_context *context);
 static bool contain_nonstrict_functions_walker(Node *node, void *context);
 static bool contain_context_dependent_node(Node *clause);
 static bool contain_context_dependent_node_walker(Node *node, int *flags);
@@ -1100,46 +1101,98 @@ contain_volatile_functions_not_nextval_walker(Node *node, void *context)
 								  context);
 }
 
+
 /*****************************************************************************
  *		Check queries for parallel unsafe and/or restricted constructs
  *****************************************************************************/
 
 /*
- * Check whether a node tree contains parallel hazards.  This is used both on
- * the entire query tree, to see whether the query can be parallelized at all
- * (with allow_restricted = true), and also to evaluate whether a particular
- * expression is safe to run within a parallel worker (with allow_restricted =
- * false).  We could separate these concerns into two different functions, but
- * there's enough overlap that it doesn't seem worthwhile.
+ * max_parallel_hazard
+ *		Find the worst parallel-hazard level in the given query
+ *
+ * Returns the worst function hazard property (the earliest in this list:
+ * PROPARALLEL_UNSAFE, PROPARALLEL_RESTRICTED, PROPARALLEL_SAFE) that can
+ * be found in the given parsetree.  We use this to find out whether the query
+ * can be parallelized at all.  The caller will also save the result in
+ * PlannerGlobal so as to short-circuit checks of portions of the querytree
+ * later, in the common case where everything is SAFE.
+ */
+char
+max_parallel_hazard(Query *parse)
+{
+	max_parallel_hazard_context context;
+
+	context.max_hazard = PROPARALLEL_SAFE;
+	context.max_interesting = PROPARALLEL_UNSAFE;
+	(void) max_parallel_hazard_walker((Node *) parse, &context);
+	return context.max_hazard;
+}
+
+/*
+ * is_parallel_safe
+ *		Detect whether the given expr contains only parallel-safe functions
+ *
+ * root->glob->maxParallelHazard must previously have been set to the
+ * result of max_parallel_hazard() on the whole query.
  */
 bool
-has_parallel_hazard(Node *node, bool allow_restricted)
+is_parallel_safe(PlannerInfo *root, Node *node)
 {
-	has_parallel_hazard_arg context;
+	max_parallel_hazard_context context;
 
-	context.allow_restricted = allow_restricted;
-	return has_parallel_hazard_walker(node, &context);
+	/* If max_parallel_hazard found nothing unsafe, we don't need to look */
+	if (root->glob->maxParallelHazard == PROPARALLEL_SAFE)
+		return true;
+	/* Else use max_parallel_hazard's search logic, but stop on RESTRICTED */
+	context.max_hazard = PROPARALLEL_SAFE;
+	context.max_interesting = PROPARALLEL_RESTRICTED;
+	return !max_parallel_hazard_walker(node, &context);
+}
+
+/* core logic for all parallel-hazard checks */
+static bool
+max_parallel_hazard_test(char proparallel, max_parallel_hazard_context *context)
+{
+	switch (proparallel)
+	{
+		case PROPARALLEL_SAFE:
+			/* nothing to see here, move along */
+			break;
+		case PROPARALLEL_RESTRICTED:
+			/* increase max_hazard to RESTRICTED */
+			Assert(context->max_hazard != PROPARALLEL_UNSAFE);
+			context->max_hazard = proparallel;
+			/* done if we are not expecting any unsafe functions */
+			if (context->max_interesting == proparallel)
+				return true;
+			break;
+		case PROPARALLEL_UNSAFE:
+			context->max_hazard = proparallel;
+			/* we're always done at the first unsafe construct */
+			return true;
+		default:
+			elog(ERROR, "unrecognized proparallel value \"%c\"", proparallel);
+			break;
+	}
+	return false;
+}
+
+/* check_functions_in_node callback */
+static bool
+max_parallel_hazard_checker(Oid func_id, void *context)
+{
+	return max_parallel_hazard_test(func_parallel(func_id),
+									(max_parallel_hazard_context *) context);
 }
 
 static bool
-has_parallel_hazard_checker(Oid func_id, void *context)
-{
-	char		proparallel = func_parallel(func_id);
-
-	if (((has_parallel_hazard_arg *) context)->allow_restricted)
-		return (proparallel == PROPARALLEL_UNSAFE);
-	else
-		return (proparallel != PROPARALLEL_SAFE);
-}
-
-static bool
-has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
+max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 {
 	if (node == NULL)
 		return false;
 
 	/* Check for hazardous functions in node itself */
-	if (check_functions_in_node(node, has_parallel_hazard_checker,
+	if (check_functions_in_node(node, max_parallel_hazard_checker,
 								context))
 		return true;
 
@@ -1156,7 +1209,7 @@ has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
 	 */
 	if (IsA(node, CoerceToDomain))
 	{
-		if (!context->allow_restricted)
+		if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
 			return true;
 	}
 
@@ -1167,7 +1220,7 @@ has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
 	{
 		RestrictInfo *rinfo = (RestrictInfo *) node;
 
-		return has_parallel_hazard_walker((Node *) rinfo->clause, context);
+		return max_parallel_hazard_walker((Node *) rinfo->clause, context);
 	}
 
 	/*
@@ -1176,13 +1229,13 @@ has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
 	 * not worry about examining their contents; if they are unsafe, we would
 	 * have found that out while examining the whole tree before reduction of
 	 * sublinks to subplans.  (Really we should not see SubLink during a
-	 * not-allow_restricted scan, but if we do, return true.)
+	 * max_interesting == restricted scan, but if we do, return true.)
 	 */
 	else if (IsA(node, SubLink) ||
 			 IsA(node, SubPlan) ||
 			 IsA(node, AlternativeSubPlan))
 	{
-		if (!context->allow_restricted)
+		if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
 			return true;
 	}
 
@@ -1192,7 +1245,7 @@ has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
 	 */
 	else if (IsA(node, Param))
 	{
-		if (!context->allow_restricted)
+		if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
 			return true;
 	}
 
@@ -1207,20 +1260,24 @@ has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
 
 		/* SELECT FOR UPDATE/SHARE must be treated as unsafe */
 		if (query->rowMarks != NULL)
+		{
+			context->max_hazard = PROPARALLEL_UNSAFE;
 			return true;
+		}
 
 		/* Recurse into subselects */
 		return query_tree_walker(query,
-								 has_parallel_hazard_walker,
+								 max_parallel_hazard_walker,
 								 context, 0);
 	}
 
 	/* Recurse to check arguments */
 	return expression_tree_walker(node,
-								  has_parallel_hazard_walker,
+								  max_parallel_hazard_walker,
 								  context);
 }
 
+
 /*****************************************************************************
  *		Check clauses for nonstrict functions
  *****************************************************************************/

src/backend/optimizer/util/pathnode.c

@@ -2178,7 +2178,7 @@ create_projection_path(PlannerInfo *root,
 	pathnode->path.parallel_aware = false;
 	pathnode->path.parallel_safe = rel->consider_parallel &&
 		subpath->parallel_safe &&
-		!has_parallel_hazard((Node *) target->exprs, false);
+		is_parallel_safe(root, (Node *) target->exprs);
 	pathnode->path.parallel_workers = subpath->parallel_workers;
 	/* Projection does not change the sort order */
 	pathnode->path.pathkeys = subpath->pathkeys;
@@ -2285,7 +2285,7 @@ apply_projection_to_path(PlannerInfo *root,
 	 * target expressions, then we can't.
 	 */
 	if (IsA(path, GatherPath) &&
-		!has_parallel_hazard((Node *) target->exprs, false))
+		is_parallel_safe(root, (Node *) target->exprs))
 	{
 		GatherPath *gpath = (GatherPath *) path;
 
@@ -2306,7 +2306,7 @@ apply_projection_to_path(PlannerInfo *root,
 								   target);
 	}
 	else if (path->parallel_safe &&
-			 has_parallel_hazard((Node *) target->exprs, false))
+			 !is_parallel_safe(root, (Node *) target->exprs))
 	{
 		/*
 		 * We're inserting a parallel-restricted target list into a path

src/backend/optimizer/util/relnode.c

@@ -513,8 +513,8 @@ build_join_rel(PlannerInfo *root,
 	 * here.
 	 */
 	if (inner_rel->consider_parallel && outer_rel->consider_parallel &&
-		!has_parallel_hazard((Node *) restrictlist, false) &&
-		!has_parallel_hazard((Node *) joinrel->reltarget->exprs, false))
+		is_parallel_safe(root, (Node *) restrictlist) &&
+		is_parallel_safe(root, (Node *) joinrel->reltarget->exprs))
 		joinrel->consider_parallel = true;
 
 	/*

src/include/nodes/relation.h

@@ -126,6 +126,8 @@ typedef struct PlannerGlobal
 	bool		parallelModeOK; /* parallel mode potentially OK? */
 
 	bool		parallelModeNeeded;		/* parallel mode actually required? */
+
+	char		maxParallelHazard;		/* worst PROPARALLEL hazard level */
 } PlannerGlobal;
 
 /* macro for fetching the Plan associated with a SubPlan node */

src/include/optimizer/clauses.h

@@ -61,7 +61,8 @@ extern bool contain_subplans(Node *clause);
 extern bool contain_mutable_functions(Node *clause);
 extern bool contain_volatile_functions(Node *clause);
 extern bool contain_volatile_functions_not_nextval(Node *clause);
-extern bool has_parallel_hazard(Node *node, bool allow_restricted);
+extern char max_parallel_hazard(Query *parse);
+extern bool is_parallel_safe(PlannerInfo *root, Node *node);
 extern bool contain_nonstrict_functions(Node *clause);
 extern bool contain_leaked_vars(Node *clause);