diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index c949dc1866..669acd7315 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -24,6 +24,7 @@
 #include "statistics/statistics.h"
 #include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
+#include "utils/memutils.h"
 #include "utils/selfuncs.h"
 
 /*
@@ -693,6 +694,7 @@ clause_selectivity_ext(PlannerInfo *root,
 	Selectivity s1 = 0.5;		/* default for any unhandled clause type */
 	RestrictInfo *rinfo = NULL;
 	bool		cacheable = false;
+	MemoryContext saved_cxt;
 
 	if (clause == NULL)			/* can this still happen? */
 		return s1;
@@ -756,6 +758,21 @@ clause_selectivity_ext(PlannerInfo *root,
 			clause = (Node *) rinfo->clause;
 	}
 
+	/*
+	 * Run all the remaining work in the short-lived planner_tmp_cxt, which
+	 * we'll reset at the bottom.  This allows selectivity-related code to not
+	 * be too concerned about leaking memory.
+	 */
+	saved_cxt = MemoryContextSwitchTo(root->planner_tmp_cxt);
+
+	/*
+	 * This function can be called recursively, in which case we'd better not
+	 * reset planner_tmp_cxt until we exit the topmost level.  Use of
+	 * planner_tmp_cxt_depth also makes it safe for other places to use and
+	 * reset planner_tmp_cxt in the same fashion.
+	 */
+	root->planner_tmp_cxt_depth++;
+
 	if (IsA(clause, Var))
 	{
 		Var		   *var = (Var *) clause;
@@ -967,6 +984,12 @@ clause_selectivity_ext(PlannerInfo *root,
 			rinfo->outer_selec = s1;
 	}
 
+	/* Exit and clean up the planner_tmp_cxt */
+	MemoryContextSwitchTo(saved_cxt);
+	Assert(root->planner_tmp_cxt_depth > 0);
+	if (--root->planner_tmp_cxt_depth == 0)
+		MemoryContextReset(root->planner_tmp_cxt);
+
 #ifdef SELECTIVITY_DEBUG
 	elog(DEBUG4, "clause_selectivity: s1 %f", s1);
 #endif							/* SELECTIVITY_DEBUG */
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index be4e182869..44b9555dbf 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -643,6 +643,17 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	root->plan_params = NIL;
 	root->outer_params = NULL;
 	root->planner_cxt = CurrentMemoryContext;
+	/* a subquery can share the main query's planner_tmp_cxt */
+	if (parent_root)
+	{
+		root->planner_tmp_cxt = parent_root->planner_tmp_cxt;
+		Assert(parent_root->planner_tmp_cxt_depth == 0);
+	}
+	else
+		root->planner_tmp_cxt = AllocSetContextCreate(root->planner_cxt,
+													  "Planner temp context",
+													  ALLOCSET_DEFAULT_SIZES);
+	root->planner_tmp_cxt_depth = 0;
 	root->init_plans = NIL;
 	root->cte_plan_ids = NIL;
 	root->multiexpr_params = NIL;
@@ -6514,6 +6525,10 @@ plan_cluster_use_sort(Oid tableOid, Oid indexOid)
 	root->glob = glob;
 	root->query_level = 1;
 	root->planner_cxt = CurrentMemoryContext;
+	root->planner_tmp_cxt = AllocSetContextCreate(root->planner_cxt,
+												  "Planner temp context",
+												  ALLOCSET_DEFAULT_SIZES);
+	root->planner_tmp_cxt_depth = 0;
 	root->wt_param_id = -1;
 	root->join_domains = list_make1(makeNode(JoinDomain));
 
@@ -6552,7 +6567,10 @@ plan_cluster_use_sort(Oid tableOid, Oid indexOid)
 	 * trust the index contents but use seqscan-and-sort.
 	 */
 	if (lc == NULL)				/* not in the list? */
+	{
+		MemoryContextDelete(root->planner_tmp_cxt);
 		return true;			/* use sort */
+	}
 
 	/*
 	 * Rather than doing all the pushups that would be needed to use
@@ -6584,6 +6602,9 @@ plan_cluster_use_sort(Oid tableOid, Oid indexOid)
 									  ForwardScanDirection, false,
 									  NULL, 1.0, false);
 
+	/* We assume this won't free *indexScanPath */
+	MemoryContextDelete(root->planner_tmp_cxt);
+
 	return (seqScanAndSortPath.total_cost < indexScanPath->path.total_cost);
 }
 
@@ -6636,6 +6657,10 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
 	root->glob = glob;
 	root->query_level = 1;
 	root->planner_cxt = CurrentMemoryContext;
+	root->planner_tmp_cxt = AllocSetContextCreate(root->planner_cxt,
+												  "Planner temp context",
+												  ALLOCSET_DEFAULT_SIZES);
+	root->planner_tmp_cxt_depth = 0;
 	root->wt_param_id = -1;
 	root->join_domains = list_make1(makeNode(JoinDomain));
 
@@ -6725,6 +6750,8 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
 		parallel_workers--;
 
 done:
+	MemoryContextDelete(root->planner_tmp_cxt);
+
 	index_close(index, NoLock);
 	table_close(heap, NoLock);
 
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index aa83dd3636..0ea8361190 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -987,7 +987,10 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	subroot->parent_root = root->parent_root;
 	subroot->plan_params = NIL;
 	subroot->outer_params = NULL;
-	subroot->planner_cxt = CurrentMemoryContext;
+	subroot->planner_cxt = root->planner_cxt;
+	subroot->planner_tmp_cxt = root->planner_tmp_cxt;
+	Assert(root->planner_tmp_cxt_depth == 0);
+	subroot->planner_tmp_cxt_depth = 0;
 	subroot->init_plans = NIL;
 	subroot->cte_plan_ids = NIL;
 	subroot->multiexpr_params = NIL;
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 534692bee1..d278a9773a 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -471,6 +471,11 @@ struct PlannerInfo
 	/* context holding PlannerInfo */
 	MemoryContext planner_cxt pg_node_attr(read_write_ignore);
 
+	/* short-lived context for purposes such as calling selectivity functions */
+	MemoryContext planner_tmp_cxt pg_node_attr(read_write_ignore);
+	/* nesting depth of uses of planner_tmp_cxt; reset it only at level 0 */
+	int			planner_tmp_cxt_depth;
+
 	/* # of pages in all non-dummy tables of query */
 	Cardinality total_table_pages;