Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4216 insertions, 0 deletions

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
new file mode 100644
index 0000000..f3e7018
--- /dev/null
+++ b/src/backend/optimizer/path/allpaths.c
@@ -0,0 +1,4216 @@
+/*-------------------------------------------------------------------------
+ *
+ * allpaths.c
+ *	  Routines to find possible search paths for processing a query
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/optimizer/path/allpaths.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <limits.h>
+#include <math.h>
+
+#include "access/sysattr.h"
+#include "access/tsmapi.h"
+#include "catalog/pg_class.h"
+#include "catalog/pg_operator.h"
+#include "catalog/pg_proc.h"
+#include "foreign/fdwapi.h"
+#include "miscadmin.h"
+#include "nodes/makefuncs.h"
+#include "nodes/nodeFuncs.h"
+#ifdef OPTIMIZER_DEBUG
+#include "nodes/print.h"
+#endif
+#include "optimizer/appendinfo.h"
+#include "optimizer/clauses.h"
+#include "optimizer/cost.h"
+#include "optimizer/geqo.h"
+#include "optimizer/inherit.h"
+#include "optimizer/optimizer.h"
+#include "optimizer/pathnode.h"
+#include "optimizer/paths.h"
+#include "optimizer/plancat.h"
+#include "optimizer/planner.h"
+#include "optimizer/restrictinfo.h"
+#include "optimizer/tlist.h"
+#include "parser/parse_clause.h"
+#include "parser/parsetree.h"
+#include "partitioning/partbounds.h"
+#include "partitioning/partprune.h"
+#include "rewrite/rewriteManip.h"
+#include "utils/lsyscache.h"
+
+
+/* results of subquery_is_pushdown_safe */
+typedef struct pushdown_safety_info
+{
+	bool	   *unsafeColumns;	/* which output columns are unsafe to use */
+	bool		unsafeVolatile; /* don't push down volatile quals */
+	bool		unsafeLeaky;	/* don't push down leaky quals */
+} pushdown_safety_info;
+
+/* These parameters are set by GUC */
+bool		enable_geqo = false;	/* just in case GUC doesn't set it */
+int			geqo_threshold;
+int			min_parallel_table_scan_size;
+int			min_parallel_index_scan_size;
+
+/* Hook for plugins to get control in set_rel_pathlist() */
+set_rel_pathlist_hook_type set_rel_pathlist_hook = NULL;
+
+/* Hook for plugins to replace standard_join_search() */
+join_search_hook_type join_search_hook = NULL;
+
+
+static void set_base_rel_consider_startup(PlannerInfo *root);
+static void set_base_rel_sizes(PlannerInfo *root);
+static void set_base_rel_pathlists(PlannerInfo *root);
+static void set_rel_size(PlannerInfo *root, RelOptInfo *rel,
+						 Index rti, RangeTblEntry *rte);
+static void set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+							 Index rti, RangeTblEntry *rte);
+static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel,
+							   RangeTblEntry *rte);
+static void create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel);
+static void set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
+									  RangeTblEntry *rte);
+static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								   RangeTblEntry *rte);
+static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel,
+									 RangeTblEntry *rte);
+static void set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+										 RangeTblEntry *rte);
+static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel,
+							 RangeTblEntry *rte);
+static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								 RangeTblEntry *rte);
+static void set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
+								Index rti, RangeTblEntry *rte);
+static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+									Index rti, RangeTblEntry *rte);
+static void generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel,
+										 List *live_childrels,
+										 List *all_child_pathkeys);
+static Path *get_cheapest_parameterized_child_path(PlannerInfo *root,
+												   RelOptInfo *rel,
+												   Relids required_outer);
+static void accumulate_append_subpath(Path *path,
+									  List **subpaths,
+									  List **special_subpaths);
+static Path *get_singleton_append_subpath(Path *path);
+static void set_dummy_rel_pathlist(RelOptInfo *rel);
+static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								  Index rti, RangeTblEntry *rte);
+static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								  RangeTblEntry *rte);
+static void set_values_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								RangeTblEntry *rte);
+static void set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								   RangeTblEntry *rte);
+static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
+							 RangeTblEntry *rte);
+static void set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel,
+										 RangeTblEntry *rte);
+static void set_result_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								RangeTblEntry *rte);
+static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
+								   RangeTblEntry *rte);
+static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
+static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery,
+									  pushdown_safety_info *safetyInfo);
+static bool recurse_pushdown_safe(Node *setOp, Query *topquery,
+								  pushdown_safety_info *safetyInfo);
+static void check_output_expressions(Query *subquery,
+									 pushdown_safety_info *safetyInfo);
+static void compare_tlist_datatypes(List *tlist, List *colTypes,
+									pushdown_safety_info *safetyInfo);
+static bool targetIsInAllPartitionLists(TargetEntry *tle, Query *query);
+static bool qual_is_pushdown_safe(Query *subquery, Index rti,
+								  RestrictInfo *rinfo,
+								  pushdown_safety_info *safetyInfo);
+static void subquery_push_qual(Query *subquery,
+							   RangeTblEntry *rte, Index rti, Node *qual);
+static void recurse_push_qual(Node *setOp, Query *topquery,
+							  RangeTblEntry *rte, Index rti, Node *qual);
+static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);
+
+
+/*
+ * make_one_rel
+ *	  Finds all possible access paths for executing a query, returning a
+ *	  single rel that represents the join of all base rels in the query.
+ */
+RelOptInfo *
+make_one_rel(PlannerInfo *root, List *joinlist)
+{
+	RelOptInfo *rel;
+	Index		rti;
+	double		total_pages;
+
+	/*
+	 * Construct the all_baserels Relids set.
+	 */
+	root->all_baserels = NULL;
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *brel = root->simple_rel_array[rti];
+
+		/* there may be empty slots corresponding to non-baserel RTEs */
+		if (brel == NULL)
+			continue;
+
+		Assert(brel->relid == rti); /* sanity check on array */
+
+		/* ignore RTEs that are "other rels" */
+		if (brel->reloptkind != RELOPT_BASEREL)
+			continue;
+
+		root->all_baserels = bms_add_member(root->all_baserels, brel->relid);
+	}
+
+	/* Mark base rels as to whether we care about fast-start plans */
+	set_base_rel_consider_startup(root);
+
+	/*
+	 * Compute size estimates and consider_parallel flags for each base rel.
+	 */
+	set_base_rel_sizes(root);
+
+	/*
+	 * We should now have size estimates for every actual table involved in
+	 * the query, and we also know which if any have been deleted from the
+	 * query by join removal, pruned by partition pruning, or eliminated by
+	 * constraint exclusion.  So we can now compute total_table_pages.
+	 *
+	 * Note that appendrels are not double-counted here, even though we don't
+	 * bother to distinguish RelOptInfos for appendrel parents, because the
+	 * parents will have pages = 0.
+	 *
+	 * XXX if a table is self-joined, we will count it once per appearance,
+	 * which perhaps is the wrong thing ... but that's not completely clear,
+	 * and detecting self-joins here is difficult, so ignore it for now.
+	 */
+	total_pages = 0;
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *brel = root->simple_rel_array[rti];
+
+		if (brel == NULL)
+			continue;
+
+		Assert(brel->relid == rti); /* sanity check on array */
+
+		if (IS_DUMMY_REL(brel))
+			continue;
+
+		if (IS_SIMPLE_REL(brel))
+			total_pages += (double) brel->pages;
+	}
+	root->total_table_pages = total_pages;
+
+	/*
+	 * Generate access paths for each base rel.
+	 */
+	set_base_rel_pathlists(root);
+
+	/*
+	 * Generate access paths for the entire join tree.
+	 */
+	rel = make_rel_from_joinlist(root, joinlist);
+
+	/*
+	 * The result should join all and only the query's base rels.
+	 */
+	Assert(bms_equal(rel->relids, root->all_baserels));
+
+	return rel;
+}
+
+/*
+ * set_base_rel_consider_startup
+ *	  Set the consider_[param_]startup flags for each base-relation entry.
+ *
+ * For the moment, we only deal with consider_param_startup here; because the
+ * logic for consider_startup is pretty trivial and is the same for every base
+ * relation, we just let build_simple_rel() initialize that flag correctly to
+ * start with.  If that logic ever gets more complicated it would probably
+ * be better to move it here.
+ */
+static void
+set_base_rel_consider_startup(PlannerInfo *root)
+{
+	/*
+	 * Since parameterized paths can only be used on the inside of a nestloop
+	 * join plan, there is usually little value in considering fast-start
+	 * plans for them.  However, for relations that are on the RHS of a SEMI
+	 * or ANTI join, a fast-start plan can be useful because we're only going
+	 * to care about fetching one tuple anyway.
+	 *
+	 * To minimize growth of planning time, we currently restrict this to
+	 * cases where the RHS is a single base relation, not a join; there is no
+	 * provision for consider_param_startup to get set at all on joinrels.
+	 * Also we don't worry about appendrels.  costsize.c's costing rules for
+	 * nestloop semi/antijoins don't consider such cases either.
+	 */
+	ListCell   *lc;
+
+	foreach(lc, root->join_info_list)
+	{
+		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
+		int			varno;
+
+		if ((sjinfo->jointype == JOIN_SEMI || sjinfo->jointype == JOIN_ANTI) &&
+			bms_get_singleton_member(sjinfo->syn_righthand, &varno))
+		{
+			RelOptInfo *rel = find_base_rel(root, varno);
+
+			rel->consider_param_startup = true;
+		}
+	}
+}
+
+/*
+ * set_base_rel_sizes
+ *	  Set the size estimates (rows and widths) for each base-relation entry.
+ *	  Also determine whether to consider parallel paths for base relations.
+ *
+ * We do this in a separate pass over the base rels so that rowcount
+ * estimates are available for parameterized path generation, and also so
+ * that each rel's consider_parallel flag is set correctly before we begin to
+ * generate paths.
+ */
+static void
+set_base_rel_sizes(PlannerInfo *root)
+{
+	Index		rti;
+
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *rel = root->simple_rel_array[rti];
+		RangeTblEntry *rte;
+
+		/* there may be empty slots corresponding to non-baserel RTEs */
+		if (rel == NULL)
+			continue;
+
+		Assert(rel->relid == rti);	/* sanity check on array */
+
+		/* ignore RTEs that are "other rels" */
+		if (rel->reloptkind != RELOPT_BASEREL)
+			continue;
+
+		rte = root->simple_rte_array[rti];
+
+		/*
+		 * If parallelism is allowable for this query in general, see whether
+		 * it's allowable for this rel in particular.  We have to do this
+		 * before set_rel_size(), because (a) if this rel is an inheritance
+		 * parent, set_append_rel_size() will use and perhaps change the rel's
+		 * consider_parallel flag, and (b) for some RTE types, set_rel_size()
+		 * goes ahead and makes paths immediately.
+		 */
+		if (root->glob->parallelModeOK)
+			set_rel_consider_parallel(root, rel, rte);
+
+		set_rel_size(root, rel, rti, rte);
+	}
+}
+
+/*
+ * set_base_rel_pathlists
+ *	  Finds all paths available for scanning each base-relation entry.
+ *	  Sequential scan and any available indices are considered.
+ *	  Each useful path is attached to its relation's 'pathlist' field.
+ */
+static void
+set_base_rel_pathlists(PlannerInfo *root)
+{
+	Index		rti;
+
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *rel = root->simple_rel_array[rti];
+
+		/* there may be empty slots corresponding to non-baserel RTEs */
+		if (rel == NULL)
+			continue;
+
+		Assert(rel->relid == rti);	/* sanity check on array */
+
+		/* ignore RTEs that are "other rels" */
+		if (rel->reloptkind != RELOPT_BASEREL)
+			continue;
+
+		set_rel_pathlist(root, rel, rti, root->simple_rte_array[rti]);
+	}
+}
+
+/*
+ * set_rel_size
+ *	  Set size estimates for a base relation
+ */
+static void
+set_rel_size(PlannerInfo *root, RelOptInfo *rel,
+			 Index rti, RangeTblEntry *rte)
+{
+	if (rel->reloptkind == RELOPT_BASEREL &&
+		relation_excluded_by_constraints(root, rel, rte))
+	{
+		/*
+		 * We proved we don't need to scan the rel via constraint exclusion,
+		 * so set up a single dummy path for it.  Here we only check this for
+		 * regular baserels; if it's an otherrel, CE was already checked in
+		 * set_append_rel_size().
+		 *
+		 * In this case, we go ahead and set up the relation's path right away
+		 * instead of leaving it for set_rel_pathlist to do.  This is because
+		 * we don't have a convention for marking a rel as dummy except by
+		 * assigning a dummy path to it.
+		 */
+		set_dummy_rel_pathlist(rel);
+	}
+	else if (rte->inh)
+	{
+		/* It's an "append relation", process accordingly */
+		set_append_rel_size(root, rel, rti, rte);
+	}
+	else
+	{
+		switch (rel->rtekind)
+		{
+			case RTE_RELATION:
+				if (rte->relkind == RELKIND_FOREIGN_TABLE)
+				{
+					/* Foreign table */
+					set_foreign_size(root, rel, rte);
+				}
+				else if (rte->relkind == RELKIND_PARTITIONED_TABLE)
+				{
+					/*
+					 * We could get here if asked to scan a partitioned table
+					 * with ONLY.  In that case we shouldn't scan any of the
+					 * partitions, so mark it as a dummy rel.
+					 */
+					set_dummy_rel_pathlist(rel);
+				}
+				else if (rte->tablesample != NULL)
+				{
+					/* Sampled relation */
+					set_tablesample_rel_size(root, rel, rte);
+				}
+				else
+				{
+					/* Plain relation */
+					set_plain_rel_size(root, rel, rte);
+				}
+				break;
+			case RTE_SUBQUERY:
+
+				/*
+				 * Subqueries don't support making a choice between
+				 * parameterized and unparameterized paths, so just go ahead
+				 * and build their paths immediately.
+				 */
+				set_subquery_pathlist(root, rel, rti, rte);
+				break;
+			case RTE_FUNCTION:
+				set_function_size_estimates(root, rel);
+				break;
+			case RTE_TABLEFUNC:
+				set_tablefunc_size_estimates(root, rel);
+				break;
+			case RTE_VALUES:
+				set_values_size_estimates(root, rel);
+				break;
+			case RTE_CTE:
+
+				/*
+				 * CTEs don't support making a choice between parameterized
+				 * and unparameterized paths, so just go ahead and build their
+				 * paths immediately.
+				 */
+				if (rte->self_reference)
+					set_worktable_pathlist(root, rel, rte);
+				else
+					set_cte_pathlist(root, rel, rte);
+				break;
+			case RTE_NAMEDTUPLESTORE:
+				/* Might as well just build the path immediately */
+				set_namedtuplestore_pathlist(root, rel, rte);
+				break;
+			case RTE_RESULT:
+				/* Might as well just build the path immediately */
+				set_result_pathlist(root, rel, rte);
+				break;
+			default:
+				elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
+				break;
+		}
+	}
+
+	/*
+	 * We insist that all non-dummy rels have a nonzero rowcount estimate.
+	 */
+	Assert(rel->rows > 0 || IS_DUMMY_REL(rel));
+}
+
+/*
+ * set_rel_pathlist
+ *	  Build access paths for a base relation
+ */
+static void
+set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+				 Index rti, RangeTblEntry *rte)
+{
+	if (IS_DUMMY_REL(rel))
+	{
+		/* We already proved the relation empty, so nothing more to do */
+	}
+	else if (rte->inh)
+	{
+		/* It's an "append relation", process accordingly */
+		set_append_rel_pathlist(root, rel, rti, rte);
+	}
+	else
+	{
+		switch (rel->rtekind)
+		{
+			case RTE_RELATION:
+				if (rte->relkind == RELKIND_FOREIGN_TABLE)
+				{
+					/* Foreign table */
+					set_foreign_pathlist(root, rel, rte);
+				}
+				else if (rte->tablesample != NULL)
+				{
+					/* Sampled relation */
+					set_tablesample_rel_pathlist(root, rel, rte);
+				}
+				else
+				{
+					/* Plain relation */
+					set_plain_rel_pathlist(root, rel, rte);
+				}
+				break;
+			case RTE_SUBQUERY:
+				/* Subquery --- fully handled during set_rel_size */
+				break;
+			case RTE_FUNCTION:
+				/* RangeFunction */
+				set_function_pathlist(root, rel, rte);
+				break;
+			case RTE_TABLEFUNC:
+				/* Table Function */
+				set_tablefunc_pathlist(root, rel, rte);
+				break;
+			case RTE_VALUES:
+				/* Values list */
+				set_values_pathlist(root, rel, rte);
+				break;
+			case RTE_CTE:
+				/* CTE reference --- fully handled during set_rel_size */
+				break;
+			case RTE_NAMEDTUPLESTORE:
+				/* tuplestore reference --- fully handled during set_rel_size */
+				break;
+			case RTE_RESULT:
+				/* simple Result --- fully handled during set_rel_size */
+				break;
+			default:
+				elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
+				break;
+		}
+	}
+
+	/*
+	 * Allow a plugin to editorialize on the set of Paths for this base
+	 * relation.  It could add new paths (such as CustomPaths) by calling
+	 * add_path(), or add_partial_path() if parallel aware.  It could also
+	 * delete or modify paths added by the core code.
+	 */
+	if (set_rel_pathlist_hook)
+		(*set_rel_pathlist_hook) (root, rel, rti, rte);
+
+	/*
+	 * If this is a baserel, we should normally consider gathering any partial
+	 * paths we may have created for it.  We have to do this after calling the
+	 * set_rel_pathlist_hook, else it cannot add partial paths to be included
+	 * here.
+	 *
+	 * However, if this is an inheritance child, skip it.  Otherwise, we could
+	 * end up with a very large number of gather nodes, each trying to grab
+	 * its own pool of workers.  Instead, we'll consider gathering partial
+	 * paths for the parent appendrel.
+	 *
+	 * Also, if this is the topmost scan/join rel (that is, the only baserel),
+	 * we postpone gathering until the final scan/join targetlist is available
+	 * (see grouping_planner).
+	 */
+	if (rel->reloptkind == RELOPT_BASEREL &&
+		bms_membership(root->all_baserels) != BMS_SINGLETON)
+		generate_useful_gather_paths(root, rel, false);
+
+	/* Now find the cheapest of the paths for this rel */
+	set_cheapest(rel);
+
+#ifdef OPTIMIZER_DEBUG
+	debug_print_rel(root, rel);
+#endif
+}
+
+/*
+ * set_plain_rel_size
+ *	  Set size estimates for a plain relation (no subquery, no inheritance)
+ */
+static void
+set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	/*
+	 * Test any partial indexes of rel for applicability.  We must do this
+	 * first since partial unique indexes can affect size estimates.
+	 */
+	check_index_predicates(root, rel);
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_baserel_size_estimates(root, rel);
+}
+
+/*
+ * If this relation could possibly be scanned from within a worker, then set
+ * its consider_parallel flag.
+ */
+static void
+set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
+						  RangeTblEntry *rte)
+{
+	/*
+	 * The flag has previously been initialized to false, so we can just
+	 * return if it becomes clear that we can't safely set it.
+	 */
+	Assert(!rel->consider_parallel);
+
+	/* Don't call this if parallelism is disallowed for the entire query. */
+	Assert(root->glob->parallelModeOK);
+
+	/* This should only be called for baserels and appendrel children. */
+	Assert(IS_SIMPLE_REL(rel));
+
+	/* Assorted checks based on rtekind. */
+	switch (rte->rtekind)
+	{
+		case RTE_RELATION:
+
+			/*
+			 * Currently, parallel workers can't access the leader's temporary
+			 * tables.  We could possibly relax this if we wrote all of its
+			 * local buffers at the start of the query and made no changes
+			 * thereafter (maybe we could allow hint bit changes), and if we
+			 * taught the workers to read them.  Writing a large number of
+			 * temporary buffers could be expensive, though, and we don't have
+			 * the rest of the necessary infrastructure right now anyway.  So
+			 * for now, bail out if we see a temporary table.
+			 */
+			if (get_rel_persistence(rte->relid) == RELPERSISTENCE_TEMP)
+				return;
+
+			/*
+			 * Table sampling can be pushed down to workers if the sample
+			 * function and its arguments are safe.
+			 */
+			if (rte->tablesample != NULL)
+			{
+				char		proparallel = func_parallel(rte->tablesample->tsmhandler);
+
+				if (proparallel != PROPARALLEL_SAFE)
+					return;
+				if (!is_parallel_safe(root, (Node *) rte->tablesample->args))
+					return;
+			}
+
+			/*
+			 * Ask FDWs whether they can support performing a ForeignScan
+			 * within a worker.  Most often, the answer will be no.  For
+			 * example, if the nature of the FDW is such that it opens a TCP
+			 * connection with a remote server, each parallel worker would end
+			 * up with a separate connection, and these connections might not
+			 * be appropriately coordinated between workers and the leader.
+			 */
+			if (rte->relkind == RELKIND_FOREIGN_TABLE)
+			{
+				Assert(rel->fdwroutine);
+				if (!rel->fdwroutine->IsForeignScanParallelSafe)
+					return;
+				if (!rel->fdwroutine->IsForeignScanParallelSafe(root, rel, rte))
+					return;
+			}
+
+			/*
+			 * There are additional considerations for appendrels, which we'll
+			 * deal with in set_append_rel_size and set_append_rel_pathlist.
+			 * For now, just set consider_parallel based on the rel's own
+			 * quals and targetlist.
+			 */
+			break;
+
+		case RTE_SUBQUERY:
+
+			/*
+			 * There's no intrinsic problem with scanning a subquery-in-FROM
+			 * (as distinct from a SubPlan or InitPlan) in a parallel worker.
+			 * If the subquery doesn't happen to have any parallel-safe paths,
+			 * then flagging it as consider_parallel won't change anything,
+			 * but that's true for plain tables, too.  We must set
+			 * consider_parallel based on the rel's own quals and targetlist,
+			 * so that if a subquery path is parallel-safe but the quals and
+			 * projection we're sticking onto it are not, we correctly mark
+			 * the SubqueryScanPath as not parallel-safe.  (Note that
+			 * set_subquery_pathlist() might push some of these quals down
+			 * into the subquery itself, but that doesn't change anything.)
+			 *
+			 * We can't push sub-select containing LIMIT/OFFSET to workers as
+			 * there is no guarantee that the row order will be fully
+			 * deterministic, and applying LIMIT/OFFSET will lead to
+			 * inconsistent results at the top-level.  (In some cases, where
+			 * the result is ordered, we could relax this restriction.  But it
+			 * doesn't currently seem worth expending extra effort to do so.)
+			 */
+			{
+				Query	   *subquery = castNode(Query, rte->subquery);
+
+				if (limit_needed(subquery))
+					return;
+			}
+			break;
+
+		case RTE_JOIN:
+			/* Shouldn't happen; we're only considering baserels here. */
+			Assert(false);
+			return;
+
+		case RTE_FUNCTION:
+			/* Check for parallel-restricted functions. */
+			if (!is_parallel_safe(root, (Node *) rte->functions))
+				return;
+			break;
+
+		case RTE_TABLEFUNC:
+			/* not parallel safe */
+			return;
+
+		case RTE_VALUES:
+			/* Check for parallel-restricted functions. */
+			if (!is_parallel_safe(root, (Node *) rte->values_lists))
+				return;
+			break;
+
+		case RTE_CTE:
+
+			/*
+			 * CTE tuplestores aren't shared among parallel workers, so we
+			 * force all CTE scans to happen in the leader.  Also, populating
+			 * the CTE would require executing a subplan that's not available
+			 * in the worker, might be parallel-restricted, and must get
+			 * executed only once.
+			 */
+			return;
+
+		case RTE_NAMEDTUPLESTORE:
+
+			/*
+			 * tuplestore cannot be shared, at least without more
+			 * infrastructure to support that.
+			 */
+			return;
+
+		case RTE_RESULT:
+			/* RESULT RTEs, in themselves, are no problem. */
+			break;
+	}
+
+	/*
+	 * If there's anything in baserestrictinfo that's parallel-restricted, we
+	 * give up on parallelizing access to this relation.  We could consider
+	 * instead postponing application of the restricted quals until we're
+	 * above all the parallelism in the plan tree, but it's not clear that
+	 * that would be a win in very many cases, and it might be tricky to make
+	 * outer join clauses work correctly.  It would likely break equivalence
+	 * classes, too.
+	 */
+	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 (!is_parallel_safe(root, (Node *) rel->reltarget->exprs))
+		return;
+
+	/* We have a winner. */
+	rel->consider_parallel = true;
+}
+
+/*
+ * set_plain_rel_pathlist
+ *	  Build access paths for a plain relation (no subquery, no inheritance)
+ */
+static void
+set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Relids		required_outer;
+
+	/*
+	 * We don't support pushing join clauses into the quals of a seqscan, but
+	 * it could still have required parameterization due to LATERAL refs in
+	 * its tlist.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Consider sequential scan */
+	add_path(rel, create_seqscan_path(root, rel, required_outer, 0));
+
+	/* If appropriate, consider parallel sequential scan */
+	if (rel->consider_parallel && required_outer == NULL)
+		create_plain_partial_paths(root, rel);
+
+	/* Consider index scans */
+	create_index_paths(root, rel);
+
+	/* Consider TID scans */
+	create_tidscan_paths(root, rel);
+}
+
+/*
+ * create_plain_partial_paths
+ *	  Build partial access paths for parallel scan of a plain relation
+ */
+static void
+create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
+{
+	int			parallel_workers;
+
+	parallel_workers = compute_parallel_worker(rel, rel->pages, -1,
+											   max_parallel_workers_per_gather);
+
+	/* If any limit was set to zero, the user doesn't want a parallel scan. */
+	if (parallel_workers <= 0)
+		return;
+
+	/* Add an unordered partial path based on a parallel sequential scan. */
+	add_partial_path(rel, create_seqscan_path(root, rel, NULL, parallel_workers));
+}
+
+/*
+ * set_tablesample_rel_size
+ *	  Set size estimates for a sampled relation
+ */
+static void
+set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	TableSampleClause *tsc = rte->tablesample;
+	TsmRoutine *tsm;
+	BlockNumber pages;
+	double		tuples;
+
+	/*
+	 * Test any partial indexes of rel for applicability.  We must do this
+	 * first since partial unique indexes can affect size estimates.
+	 */
+	check_index_predicates(root, rel);
+
+	/*
+	 * Call the sampling method's estimation function to estimate the number
+	 * of pages it will read and the number of tuples it will return.  (Note:
+	 * we assume the function returns sane values.)
+	 */
+	tsm = GetTsmRoutine(tsc->tsmhandler);
+	tsm->SampleScanGetSampleSize(root, rel, tsc->args,
+								 &pages, &tuples);
+
+	/*
+	 * For the moment, because we will only consider a SampleScan path for the
+	 * rel, it's okay to just overwrite the pages and tuples estimates for the
+	 * whole relation.  If we ever consider multiple path types for sampled
+	 * rels, we'll need more complication.
+	 */
+	rel->pages = pages;
+	rel->tuples = tuples;
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_baserel_size_estimates(root, rel);
+}
+
+/*
+ * set_tablesample_rel_pathlist
+ *	  Build access paths for a sampled relation
+ */
+static void
+set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Relids		required_outer;
+	Path	   *path;
+
+	/*
+	 * We don't support pushing join clauses into the quals of a samplescan,
+	 * but it could still have required parameterization due to LATERAL refs
+	 * in its tlist or TABLESAMPLE arguments.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Consider sampled scan */
+	path = create_samplescan_path(root, rel, required_outer);
+
+	/*
+	 * If the sampling method does not support repeatable scans, we must avoid
+	 * plans that would scan the rel multiple times.  Ideally, we'd simply
+	 * avoid putting the rel on the inside of a nestloop join; but adding such
+	 * a consideration to the planner seems like a great deal of complication
+	 * to support an uncommon usage of second-rate sampling methods.  Instead,
+	 * if there is a risk that the query might perform an unsafe join, just
+	 * wrap the SampleScan in a Materialize node.  We can check for joins by
+	 * counting the membership of all_baserels (note that this correctly
+	 * counts inheritance trees as single rels).  If we're inside a subquery,
+	 * we can't easily check whether a join might occur in the outer query, so
+	 * just assume one is possible.
+	 *
+	 * GetTsmRoutine is relatively expensive compared to the other tests here,
+	 * so check repeatable_across_scans last, even though that's a bit odd.
+	 */
+	if ((root->query_level > 1 ||
+		 bms_membership(root->all_baserels) != BMS_SINGLETON) &&
+		!(GetTsmRoutine(rte->tablesample->tsmhandler)->repeatable_across_scans))
+	{
+		path = (Path *) create_material_path(rel, path);
+	}
+
+	add_path(rel, path);
+
+	/* For the moment, at least, there are no other paths to consider */
+}
+
+/*
+ * set_foreign_size
+ *		Set size estimates for a foreign table RTE
+ */
+static void
+set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	/* Mark rel with estimated output rows, width, etc */
+	set_foreign_size_estimates(root, rel);
+
+	/* Let FDW adjust the size estimates, if it can */
+	rel->fdwroutine->GetForeignRelSize(root, rel, rte->relid);
+
+	/* ... but do not let it set the rows estimate to zero */
+	rel->rows = clamp_row_est(rel->rows);
+
+	/*
+	 * Also, make sure rel->tuples is not insane relative to rel->rows.
+	 * Notably, this ensures sanity if pg_class.reltuples contains -1 and the
+	 * FDW doesn't do anything to replace that.
+	 */
+	rel->tuples = Max(rel->tuples, rel->rows);
+}
+
+/*
+ * set_foreign_pathlist
+ *		Build access paths for a foreign table RTE
+ */
+static void
+set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	/* Call the FDW's GetForeignPaths function to generate path(s) */
+	rel->fdwroutine->GetForeignPaths(root, rel, rte->relid);
+}
+
+/*
+ * set_append_rel_size
+ *	  Set size estimates for a simple "append relation"
+ *
+ * The passed-in rel and RTE represent the entire append relation.  The
+ * relation's contents are computed by appending together the output of the
+ * individual member relations.  Note that in the non-partitioned inheritance
+ * case, the first member relation is actually the same table as is mentioned
+ * in the parent RTE ... but it has a different RTE and RelOptInfo.  This is
+ * a good thing because their outputs are not the same size.
+ */
+static void
+set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
+					Index rti, RangeTblEntry *rte)
+{
+	int			parentRTindex = rti;
+	bool		has_live_children;
+	double		parent_rows;
+	double		parent_size;
+	double	   *parent_attrsizes;
+	int			nattrs;
+	ListCell   *l;
+
+	/* Guard against stack overflow due to overly deep inheritance tree. */
+	check_stack_depth();
+
+	Assert(IS_SIMPLE_REL(rel));
+
+	/*
+	 * If this is a partitioned baserel, set the consider_partitionwise_join
+	 * flag; currently, we only consider partitionwise joins with the baserel
+	 * if its targetlist doesn't contain a whole-row Var.
+	 */
+	if (enable_partitionwise_join &&
+		rel->reloptkind == RELOPT_BASEREL &&
+		rte->relkind == RELKIND_PARTITIONED_TABLE &&
+		rel->attr_needed[InvalidAttrNumber - rel->min_attr] == NULL)
+		rel->consider_partitionwise_join = true;
+
+	/*
+	 * Initialize to compute size estimates for whole append relation.
+	 *
+	 * We handle width estimates by weighting the widths of different child
+	 * rels proportionally to their number of rows.  This is sensible because
+	 * the use of width estimates is mainly to compute the total relation
+	 * "footprint" if we have to sort or hash it.  To do this, we sum the
+	 * total equivalent size (in "double" arithmetic) and then divide by the
+	 * total rowcount estimate.  This is done separately for the total rel
+	 * width and each attribute.
+	 *
+	 * Note: if you consider changing this logic, beware that child rels could
+	 * have zero rows and/or width, if they were excluded by constraints.
+	 */
+	has_live_children = false;
+	parent_rows = 0;
+	parent_size = 0;
+	nattrs = rel->max_attr - rel->min_attr + 1;
+	parent_attrsizes = (double *) palloc0(nattrs * sizeof(double));
+
+	foreach(l, root->append_rel_list)
+	{
+		AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
+		int			childRTindex;
+		RangeTblEntry *childRTE;
+		RelOptInfo *childrel;
+		ListCell   *parentvars;
+		ListCell   *childvars;
+
+		/* append_rel_list contains all append rels; ignore others */
+		if (appinfo->parent_relid != parentRTindex)
+			continue;
+
+		childRTindex = appinfo->child_relid;
+		childRTE = root->simple_rte_array[childRTindex];
+
+		/*
+		 * The child rel's RelOptInfo was already created during
+		 * add_other_rels_to_query.
+		 */
+		childrel = find_base_rel(root, childRTindex);
+		Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL);
+
+		/* We may have already proven the child to be dummy. */
+		if (IS_DUMMY_REL(childrel))
+			continue;
+
+		/*
+		 * We have to copy the parent's targetlist and quals to the child,
+		 * with appropriate substitution of variables.  However, the
+		 * baserestrictinfo quals were already copied/substituted when the
+		 * child RelOptInfo was built.  So we don't need any additional setup
+		 * before applying constraint exclusion.
+		 */
+		if (relation_excluded_by_constraints(root, childrel, childRTE))
+		{
+			/*
+			 * This child need not be scanned, so we can omit it from the
+			 * appendrel.
+			 */
+			set_dummy_rel_pathlist(childrel);
+			continue;
+		}
+
+		/*
+		 * Constraint exclusion failed, so copy the parent's join quals and
+		 * targetlist to the child, with appropriate variable substitutions.
+		 *
+		 * NB: the resulting childrel->reltarget->exprs may contain arbitrary
+		 * expressions, which otherwise would not occur in a rel's targetlist.
+		 * Code that might be looking at an appendrel child must cope with
+		 * such.  (Normally, a rel's targetlist would only include Vars and
+		 * PlaceHolderVars.)  XXX we do not bother to update the cost or width
+		 * fields of childrel->reltarget; not clear if that would be useful.
+		 */
+		childrel->joininfo = (List *)
+			adjust_appendrel_attrs(root,
+								   (Node *) rel->joininfo,
+								   1, &appinfo);
+		childrel->reltarget->exprs = (List *)
+			adjust_appendrel_attrs(root,
+								   (Node *) rel->reltarget->exprs,
+								   1, &appinfo);
+
+		/*
+		 * We have to make child entries in the EquivalenceClass data
+		 * structures as well.  This is needed either if the parent
+		 * participates in some eclass joins (because we will want to consider
+		 * inner-indexscan joins on the individual children) or if the parent
+		 * has useful pathkeys (because we should try to build MergeAppend
+		 * paths that produce those sort orderings).
+		 */
+		if (rel->has_eclass_joins || has_useful_pathkeys(root, rel))
+			add_child_rel_equivalences(root, appinfo, rel, childrel);
+		childrel->has_eclass_joins = rel->has_eclass_joins;
+
+		/*
+		 * Note: we could compute appropriate attr_needed data for the child's
+		 * variables, by transforming the parent's attr_needed through the
+		 * translated_vars mapping.  However, currently there's no need
+		 * because attr_needed is only examined for base relations not
+		 * otherrels.  So we just leave the child's attr_needed empty.
+		 */
+
+		/*
+		 * If we consider partitionwise joins with the parent rel, do the same
+		 * for partitioned child rels.
+		 *
+		 * Note: here we abuse the consider_partitionwise_join flag by setting
+		 * it for child rels that are not themselves partitioned.  We do so to
+		 * tell try_partitionwise_join() that the child rel is sufficiently
+		 * valid to be used as a per-partition input, even if it later gets
+		 * proven to be dummy.  (It's not usable until we've set up the
+		 * reltarget and EC entries, which we just did.)
+		 */
+		if (rel->consider_partitionwise_join)
+			childrel->consider_partitionwise_join = true;
+
+		/*
+		 * If parallelism is allowable for this query in general, see whether
+		 * it's allowable for this childrel in particular.  But if we've
+		 * already decided the appendrel is not parallel-safe as a whole,
+		 * there's no point in considering parallelism for this child.  For
+		 * consistency, do this before calling set_rel_size() for the child.
+		 */
+		if (root->glob->parallelModeOK && rel->consider_parallel)
+			set_rel_consider_parallel(root, childrel, childRTE);
+
+		/*
+		 * Compute the child's size.
+		 */
+		set_rel_size(root, childrel, childRTindex, childRTE);
+
+		/*
+		 * It is possible that constraint exclusion detected a contradiction
+		 * within a child subquery, even though we didn't prove one above. If
+		 * so, we can skip this child.
+		 */
+		if (IS_DUMMY_REL(childrel))
+			continue;
+
+		/* We have at least one live child. */
+		has_live_children = true;
+
+		/*
+		 * If any live child is not parallel-safe, treat the whole appendrel
+		 * as not parallel-safe.  In future we might be able to generate plans
+		 * in which some children are farmed out to workers while others are
+		 * not; but we don't have that today, so it's a waste to consider
+		 * partial paths anywhere in the appendrel unless it's all safe.
+		 * (Child rels visited before this one will be unmarked in
+		 * set_append_rel_pathlist().)
+		 */
+		if (!childrel->consider_parallel)
+			rel->consider_parallel = false;
+
+		/*
+		 * Accumulate size information from each live child.
+		 */
+		Assert(childrel->rows > 0);
+
+		parent_rows += childrel->rows;
+		parent_size += childrel->reltarget->width * childrel->rows;
+
+		/*
+		 * Accumulate per-column estimates too.  We need not do anything for
+		 * PlaceHolderVars in the parent list.  If child expression isn't a
+		 * Var, or we didn't record a width estimate for it, we have to fall
+		 * back on a datatype-based estimate.
+		 *
+		 * By construction, child's targetlist is 1-to-1 with parent's.
+		 */
+		forboth(parentvars, rel->reltarget->exprs,
+				childvars, childrel->reltarget->exprs)
+		{
+			Var		   *parentvar = (Var *) lfirst(parentvars);
+			Node	   *childvar = (Node *) lfirst(childvars);
+
+			if (IsA(parentvar, Var) && parentvar->varno == parentRTindex)
+			{
+				int			pndx = parentvar->varattno - rel->min_attr;
+				int32		child_width = 0;
+
+				if (IsA(childvar, Var) &&
+					((Var *) childvar)->varno == childrel->relid)
+				{
+					int			cndx = ((Var *) childvar)->varattno - childrel->min_attr;
+
+					child_width = childrel->attr_widths[cndx];
+				}
+				if (child_width <= 0)
+					child_width = get_typavgwidth(exprType(childvar),
+												  exprTypmod(childvar));
+				Assert(child_width > 0);
+				parent_attrsizes[pndx] += child_width * childrel->rows;
+			}
+		}
+	}
+
+	if (has_live_children)
+	{
+		/*
+		 * Save the finished size estimates.
+		 */
+		int			i;
+
+		Assert(parent_rows > 0);
+		rel->rows = parent_rows;
+		rel->reltarget->width = rint(parent_size / parent_rows);
+		for (i = 0; i < nattrs; i++)
+			rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows);
+
+		/*
+		 * Set "raw tuples" count equal to "rows" for the appendrel; needed
+		 * because some places assume rel->tuples is valid for any baserel.
+		 */
+		rel->tuples = parent_rows;
+
+		/*
+		 * Note that we leave rel->pages as zero; this is important to avoid
+		 * double-counting the appendrel tree in total_table_pages.
+		 */
+	}
+	else
+	{
+		/*
+		 * All children were excluded by constraints, so mark the whole
+		 * appendrel dummy.  We must do this in this phase so that the rel's
+		 * dummy-ness is visible when we generate paths for other rels.
+		 */
+		set_dummy_rel_pathlist(rel);
+	}
+
+	pfree(parent_attrsizes);
+}
+
+/*
+ * set_append_rel_pathlist
+ *	  Build access paths for an "append relation"
+ */
+static void
+set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+						Index rti, RangeTblEntry *rte)
+{
+	int			parentRTindex = rti;
+	List	   *live_childrels = NIL;
+	ListCell   *l;
+
+	/*
+	 * Generate access paths for each member relation, and remember the
+	 * non-dummy children.
+	 */
+	foreach(l, root->append_rel_list)
+	{
+		AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
+		int			childRTindex;
+		RangeTblEntry *childRTE;
+		RelOptInfo *childrel;
+
+		/* append_rel_list contains all append rels; ignore others */
+		if (appinfo->parent_relid != parentRTindex)
+			continue;
+
+		/* Re-locate the child RTE and RelOptInfo */
+		childRTindex = appinfo->child_relid;
+		childRTE = root->simple_rte_array[childRTindex];
+		childrel = root->simple_rel_array[childRTindex];
+
+		/*
+		 * If set_append_rel_size() decided the parent appendrel was
+		 * parallel-unsafe at some point after visiting this child rel, we
+		 * need to propagate the unsafety marking down to the child, so that
+		 * we don't generate useless partial paths for it.
+		 */
+		if (!rel->consider_parallel)
+			childrel->consider_parallel = false;
+
+		/*
+		 * Compute the child's access paths.
+		 */
+		set_rel_pathlist(root, childrel, childRTindex, childRTE);
+
+		/*
+		 * If child is dummy, ignore it.
+		 */
+		if (IS_DUMMY_REL(childrel))
+			continue;
+
+		/*
+		 * Child is live, so add it to the live_childrels list for use below.
+		 */
+		live_childrels = lappend(live_childrels, childrel);
+	}
+
+	/* Add paths to the append relation. */
+	add_paths_to_append_rel(root, rel, live_childrels);
+}
+
+
+/*
+ * add_paths_to_append_rel
+ *		Generate paths for the given append relation given the set of non-dummy
+ *		child rels.
+ *
+ * The function collects all parameterizations and orderings supported by the
+ * non-dummy children. For every such parameterization or ordering, it creates
+ * an append path collecting one path from each non-dummy child with given
+ * parameterization or ordering. Similarly it collects partial paths from
+ * non-dummy children to create partial append paths.
+ */
+void
+add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
+						List *live_childrels)
+{
+	List	   *subpaths = NIL;
+	bool		subpaths_valid = true;
+	List	   *partial_subpaths = NIL;
+	List	   *pa_partial_subpaths = NIL;
+	List	   *pa_nonpartial_subpaths = NIL;
+	bool		partial_subpaths_valid = true;
+	bool		pa_subpaths_valid;
+	List	   *all_child_pathkeys = NIL;
+	List	   *all_child_outers = NIL;
+	ListCell   *l;
+	double		partial_rows = -1;
+
+	/* If appropriate, consider parallel append */
+	pa_subpaths_valid = enable_parallel_append && rel->consider_parallel;
+
+	/*
+	 * For every non-dummy child, remember the cheapest path.  Also, identify
+	 * all pathkeys (orderings) and parameterizations (required_outer sets)
+	 * available for the non-dummy member relations.
+	 */
+	foreach(l, live_childrels)
+	{
+		RelOptInfo *childrel = lfirst(l);
+		ListCell   *lcp;
+		Path	   *cheapest_partial_path = NULL;
+
+		/*
+		 * If child has an unparameterized cheapest-total path, add that to
+		 * the unparameterized Append path we are constructing for the parent.
+		 * If not, there's no workable unparameterized path.
+		 *
+		 * With partitionwise aggregates, the child rel's pathlist may be
+		 * empty, so don't assume that a path exists here.
+		 */
+		if (childrel->pathlist != NIL &&
+			childrel->cheapest_total_path->param_info == NULL)
+			accumulate_append_subpath(childrel->cheapest_total_path,
+									  &subpaths, NULL);
+		else
+			subpaths_valid = false;
+
+		/* Same idea, but for a partial plan. */
+		if (childrel->partial_pathlist != NIL)
+		{
+			cheapest_partial_path = linitial(childrel->partial_pathlist);
+			accumulate_append_subpath(cheapest_partial_path,
+									  &partial_subpaths, NULL);
+		}
+		else
+			partial_subpaths_valid = false;
+
+		/*
+		 * Same idea, but for a parallel append mixing partial and non-partial
+		 * paths.
+		 */
+		if (pa_subpaths_valid)
+		{
+			Path	   *nppath = NULL;
+
+			nppath =
+				get_cheapest_parallel_safe_total_inner(childrel->pathlist);
+
+			if (cheapest_partial_path == NULL && nppath == NULL)
+			{
+				/* Neither a partial nor a parallel-safe path?  Forget it. */
+				pa_subpaths_valid = false;
+			}
+			else if (nppath == NULL ||
+					 (cheapest_partial_path != NULL &&
+					  cheapest_partial_path->total_cost < nppath->total_cost))
+			{
+				/* Partial path is cheaper or the only option. */
+				Assert(cheapest_partial_path != NULL);
+				accumulate_append_subpath(cheapest_partial_path,
+										  &pa_partial_subpaths,
+										  &pa_nonpartial_subpaths);
+			}
+			else
+			{
+				/*
+				 * Either we've got only a non-partial path, or we think that
+				 * a single backend can execute the best non-partial path
+				 * faster than all the parallel backends working together can
+				 * execute the best partial path.
+				 *
+				 * It might make sense to be more aggressive here.  Even if
+				 * the best non-partial path is more expensive than the best
+				 * partial path, it could still be better to choose the
+				 * non-partial path if there are several such paths that can
+				 * be given to different workers.  For now, we don't try to
+				 * figure that out.
+				 */
+				accumulate_append_subpath(nppath,
+										  &pa_nonpartial_subpaths,
+										  NULL);
+			}
+		}
+
+		/*
+		 * Collect lists of all the available path orderings and
+		 * parameterizations for all the children.  We use these as a
+		 * heuristic to indicate which sort orderings and parameterizations we
+		 * should build Append and MergeAppend paths for.
+		 */
+		foreach(lcp, childrel->pathlist)
+		{
+			Path	   *childpath = (Path *) lfirst(lcp);
+			List	   *childkeys = childpath->pathkeys;
+			Relids		childouter = PATH_REQ_OUTER(childpath);
+
+			/* Unsorted paths don't contribute to pathkey list */
+			if (childkeys != NIL)
+			{
+				ListCell   *lpk;
+				bool		found = false;
+
+				/* Have we already seen this ordering? */
+				foreach(lpk, all_child_pathkeys)
+				{
+					List	   *existing_pathkeys = (List *) lfirst(lpk);
+
+					if (compare_pathkeys(existing_pathkeys,
+										 childkeys) == PATHKEYS_EQUAL)
+					{
+						found = true;
+						break;
+					}
+				}
+				if (!found)
+				{
+					/* No, so add it to all_child_pathkeys */
+					all_child_pathkeys = lappend(all_child_pathkeys,
+												 childkeys);
+				}
+			}
+
+			/* Unparameterized paths don't contribute to param-set list */
+			if (childouter)
+			{
+				ListCell   *lco;
+				bool		found = false;
+
+				/* Have we already seen this param set? */
+				foreach(lco, all_child_outers)
+				{
+					Relids		existing_outers = (Relids) lfirst(lco);
+
+					if (bms_equal(existing_outers, childouter))
+					{
+						found = true;
+						break;
+					}
+				}
+				if (!found)
+				{
+					/* No, so add it to all_child_outers */
+					all_child_outers = lappend(all_child_outers,
+											   childouter);
+				}
+			}
+		}
+	}
+
+	/*
+	 * If we found unparameterized paths for all children, build an unordered,
+	 * unparameterized Append path for the rel.  (Note: this is correct even
+	 * if we have zero or one live subpath due to constraint exclusion.)
+	 */
+	if (subpaths_valid)
+		add_path(rel, (Path *) create_append_path(root, rel, subpaths, NIL,
+												  NIL, NULL, 0, false,
+												  -1));
+
+	/*
+	 * Consider an append of unordered, unparameterized partial paths.  Make
+	 * it parallel-aware if possible.
+	 */
+	if (partial_subpaths_valid && partial_subpaths != NIL)
+	{
+		AppendPath *appendpath;
+		ListCell   *lc;
+		int			parallel_workers = 0;
+
+		/* Find the highest number of workers requested for any subpath. */
+		foreach(lc, partial_subpaths)
+		{
+			Path	   *path = lfirst(lc);
+
+			parallel_workers = Max(parallel_workers, path->parallel_workers);
+		}
+		Assert(parallel_workers > 0);
+
+		/*
+		 * If the use of parallel append is permitted, always request at least
+		 * log2(# of children) workers.  We assume it can be useful to have
+		 * extra workers in this case because they will be spread out across
+		 * the children.  The precise formula is just a guess, but we don't
+		 * want to end up with a radically different answer for a table with N
+		 * partitions vs. an unpartitioned table with the same data, so the
+		 * use of some kind of log-scaling here seems to make some sense.
+		 */
+		if (enable_parallel_append)
+		{
+			parallel_workers = Max(parallel_workers,
+								   fls(list_length(live_childrels)));
+			parallel_workers = Min(parallel_workers,
+								   max_parallel_workers_per_gather);
+		}
+		Assert(parallel_workers > 0);
+
+		/* Generate a partial append path. */
+		appendpath = create_append_path(root, rel, NIL, partial_subpaths,
+										NIL, NULL, parallel_workers,
+										enable_parallel_append,
+										-1);
+
+		/*
+		 * Make sure any subsequent partial paths use the same row count
+		 * estimate.
+		 */
+		partial_rows = appendpath->path.rows;
+
+		/* Add the path. */
+		add_partial_path(rel, (Path *) appendpath);
+	}
+
+	/*
+	 * Consider a parallel-aware append using a mix of partial and non-partial
+	 * paths.  (This only makes sense if there's at least one child which has
+	 * a non-partial path that is substantially cheaper than any partial path;
+	 * otherwise, we should use the append path added in the previous step.)
+	 */
+	if (pa_subpaths_valid && pa_nonpartial_subpaths != NIL)
+	{
+		AppendPath *appendpath;
+		ListCell   *lc;
+		int			parallel_workers = 0;
+
+		/*
+		 * Find the highest number of workers requested for any partial
+		 * subpath.
+		 */
+		foreach(lc, pa_partial_subpaths)
+		{
+			Path	   *path = lfirst(lc);
+
+			parallel_workers = Max(parallel_workers, path->parallel_workers);
+		}
+
+		/*
+		 * Same formula here as above.  It's even more important in this
+		 * instance because the non-partial paths won't contribute anything to
+		 * the planned number of parallel workers.
+		 */
+		parallel_workers = Max(parallel_workers,
+							   fls(list_length(live_childrels)));
+		parallel_workers = Min(parallel_workers,
+							   max_parallel_workers_per_gather);
+		Assert(parallel_workers > 0);
+
+		appendpath = create_append_path(root, rel, pa_nonpartial_subpaths,
+										pa_partial_subpaths,
+										NIL, NULL, parallel_workers, true,
+										partial_rows);
+		add_partial_path(rel, (Path *) appendpath);
+	}
+
+	/*
+	 * Also build unparameterized ordered append paths based on the collected
+	 * list of child pathkeys.
+	 */
+	if (subpaths_valid)
+		generate_orderedappend_paths(root, rel, live_childrels,
+									 all_child_pathkeys);
+
+	/*
+	 * Build Append paths for each parameterization seen among the child rels.
+	 * (This may look pretty expensive, but in most cases of practical
+	 * interest, the child rels will expose mostly the same parameterizations,
+	 * so that not that many cases actually get considered here.)
+	 *
+	 * The Append node itself cannot enforce quals, so all qual checking must
+	 * be done in the child paths.  This means that to have a parameterized
+	 * Append path, we must have the exact same parameterization for each
+	 * child path; otherwise some children might be failing to check the
+	 * moved-down quals.  To make them match up, we can try to increase the
+	 * parameterization of lesser-parameterized paths.
+	 */
+	foreach(l, all_child_outers)
+	{
+		Relids		required_outer = (Relids) lfirst(l);
+		ListCell   *lcr;
+
+		/* Select the child paths for an Append with this parameterization */
+		subpaths = NIL;
+		subpaths_valid = true;
+		foreach(lcr, live_childrels)
+		{
+			RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
+			Path	   *subpath;
+
+			if (childrel->pathlist == NIL)
+			{
+				/* failed to make a suitable path for this child */
+				subpaths_valid = false;
+				break;
+			}
+
+			subpath = get_cheapest_parameterized_child_path(root,
+															childrel,
+															required_outer);
+			if (subpath == NULL)
+			{
+				/* failed to make a suitable path for this child */
+				subpaths_valid = false;
+				break;
+			}
+			accumulate_append_subpath(subpath, &subpaths, NULL);
+		}
+
+		if (subpaths_valid)
+			add_path(rel, (Path *)
+					 create_append_path(root, rel, subpaths, NIL,
+										NIL, required_outer, 0, false,
+										-1));
+	}
+
+	/*
+	 * When there is only a single child relation, the Append path can inherit
+	 * any ordering available for the child rel's path, so that it's useful to
+	 * consider ordered partial paths.  Above we only considered the cheapest
+	 * partial path for each child, but let's also make paths using any
+	 * partial paths that have pathkeys.
+	 */
+	if (list_length(live_childrels) == 1)
+	{
+		RelOptInfo *childrel = (RelOptInfo *) linitial(live_childrels);
+
+		/* skip the cheapest partial path, since we already used that above */
+		for_each_from(l, childrel->partial_pathlist, 1)
+		{
+			Path	   *path = (Path *) lfirst(l);
+			AppendPath *appendpath;
+
+			/* skip paths with no pathkeys. */
+			if (path->pathkeys == NIL)
+				continue;
+
+			appendpath = create_append_path(root, rel, NIL, list_make1(path),
+											NIL, NULL,
+											path->parallel_workers, true,
+											partial_rows);
+			add_partial_path(rel, (Path *) appendpath);
+		}
+	}
+}
+
+/*
+ * generate_orderedappend_paths
+ *		Generate ordered append paths for an append relation
+ *
+ * Usually we generate MergeAppend paths here, but there are some special
+ * cases where we can generate simple Append paths, because the subpaths
+ * can provide tuples in the required order already.
+ *
+ * We generate a path for each ordering (pathkey list) appearing in
+ * all_child_pathkeys.
+ *
+ * We consider both cheapest-startup and cheapest-total cases, ie, for each
+ * interesting ordering, collect all the cheapest startup subpaths and all the
+ * cheapest total paths, and build a suitable path for each case.
+ *
+ * We don't currently generate any parameterized ordered paths here.  While
+ * it would not take much more code here to do so, it's very unclear that it
+ * is worth the planning cycles to investigate such paths: there's little
+ * use for an ordered path on the inside of a nestloop.  In fact, it's likely
+ * that the current coding of add_path would reject such paths out of hand,
+ * because add_path gives no credit for sort ordering of parameterized paths,
+ * and a parameterized MergeAppend is going to be more expensive than the
+ * corresponding parameterized Append path.  If we ever try harder to support
+ * parameterized mergejoin plans, it might be worth adding support for
+ * parameterized paths here to feed such joins.  (See notes in
+ * optimizer/README for why that might not ever happen, though.)
+ */
+static void
+generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel,
+							 List *live_childrels,
+							 List *all_child_pathkeys)
+{
+	ListCell   *lcp;
+	List	   *partition_pathkeys = NIL;
+	List	   *partition_pathkeys_desc = NIL;
+	bool		partition_pathkeys_partial = true;
+	bool		partition_pathkeys_desc_partial = true;
+
+	/*
+	 * Some partitioned table setups may allow us to use an Append node
+	 * instead of a MergeAppend.  This is possible in cases such as RANGE
+	 * partitioned tables where it's guaranteed that an earlier partition must
+	 * contain rows which come earlier in the sort order.  To detect whether
+	 * this is relevant, build pathkey descriptions of the partition ordering,
+	 * for both forward and reverse scans.
+	 */
+	if (rel->part_scheme != NULL && IS_SIMPLE_REL(rel) &&
+		partitions_are_ordered(rel->boundinfo, rel->nparts))
+	{
+		partition_pathkeys = build_partition_pathkeys(root, rel,
+													  ForwardScanDirection,
+													  &partition_pathkeys_partial);
+
+		partition_pathkeys_desc = build_partition_pathkeys(root, rel,
+														   BackwardScanDirection,
+														   &partition_pathkeys_desc_partial);
+
+		/*
+		 * You might think we should truncate_useless_pathkeys here, but
+		 * allowing partition keys which are a subset of the query's pathkeys
+		 * can often be useful.  For example, consider a table partitioned by
+		 * RANGE (a, b), and a query with ORDER BY a, b, c.  If we have child
+		 * paths that can produce the a, b, c ordering (perhaps via indexes on
+		 * (a, b, c)) then it works to consider the appendrel output as
+		 * ordered by a, b, c.
+		 */
+	}
+
+	/* Now consider each interesting sort ordering */
+	foreach(lcp, all_child_pathkeys)
+	{
+		List	   *pathkeys = (List *) lfirst(lcp);
+		List	   *startup_subpaths = NIL;
+		List	   *total_subpaths = NIL;
+		bool		startup_neq_total = false;
+		ListCell   *lcr;
+		bool		match_partition_order;
+		bool		match_partition_order_desc;
+
+		/*
+		 * Determine if this sort ordering matches any partition pathkeys we
+		 * have, for both ascending and descending partition order.  If the
+		 * partition pathkeys happen to be contained in pathkeys then it still
+		 * works, as described above, providing that the partition pathkeys
+		 * are complete and not just a prefix of the partition keys.  (In such
+		 * cases we'll be relying on the child paths to have sorted the
+		 * lower-order columns of the required pathkeys.)
+		 */
+		match_partition_order =
+			pathkeys_contained_in(pathkeys, partition_pathkeys) ||
+			(!partition_pathkeys_partial &&
+			 pathkeys_contained_in(partition_pathkeys, pathkeys));
+
+		match_partition_order_desc = !match_partition_order &&
+			(pathkeys_contained_in(pathkeys, partition_pathkeys_desc) ||
+			 (!partition_pathkeys_desc_partial &&
+			  pathkeys_contained_in(partition_pathkeys_desc, pathkeys)));
+
+		/* Select the child paths for this ordering... */
+		foreach(lcr, live_childrels)
+		{
+			RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
+			Path	   *cheapest_startup,
+					   *cheapest_total;
+
+			/* Locate the right paths, if they are available. */
+			cheapest_startup =
+				get_cheapest_path_for_pathkeys(childrel->pathlist,
+											   pathkeys,
+											   NULL,
+											   STARTUP_COST,
+											   false);
+			cheapest_total =
+				get_cheapest_path_for_pathkeys(childrel->pathlist,
+											   pathkeys,
+											   NULL,
+											   TOTAL_COST,
+											   false);
+
+			/*
+			 * If we can't find any paths with the right order just use the
+			 * cheapest-total path; we'll have to sort it later.
+			 */
+			if (cheapest_startup == NULL || cheapest_total == NULL)
+			{
+				cheapest_startup = cheapest_total =
+					childrel->cheapest_total_path;
+				/* Assert we do have an unparameterized path for this child */
+				Assert(cheapest_total->param_info == NULL);
+			}
+
+			/*
+			 * Notice whether we actually have different paths for the
+			 * "cheapest" and "total" cases; frequently there will be no point
+			 * in two create_merge_append_path() calls.
+			 */
+			if (cheapest_startup != cheapest_total)
+				startup_neq_total = true;
+
+			/*
+			 * Collect the appropriate child paths.  The required logic varies
+			 * for the Append and MergeAppend cases.
+			 */
+			if (match_partition_order)
+			{
+				/*
+				 * We're going to make a plain Append path.  We don't need
+				 * most of what accumulate_append_subpath would do, but we do
+				 * want to cut out child Appends or MergeAppends if they have
+				 * just a single subpath (and hence aren't doing anything
+				 * useful).
+				 */
+				cheapest_startup = get_singleton_append_subpath(cheapest_startup);
+				cheapest_total = get_singleton_append_subpath(cheapest_total);
+
+				startup_subpaths = lappend(startup_subpaths, cheapest_startup);
+				total_subpaths = lappend(total_subpaths, cheapest_total);
+			}
+			else if (match_partition_order_desc)
+			{
+				/*
+				 * As above, but we need to reverse the order of the children,
+				 * because nodeAppend.c doesn't know anything about reverse
+				 * ordering and will scan the children in the order presented.
+				 */
+				cheapest_startup = get_singleton_append_subpath(cheapest_startup);
+				cheapest_total = get_singleton_append_subpath(cheapest_total);
+
+				startup_subpaths = lcons(cheapest_startup, startup_subpaths);
+				total_subpaths = lcons(cheapest_total, total_subpaths);
+			}
+			else
+			{
+				/*
+				 * Otherwise, rely on accumulate_append_subpath to collect the
+				 * child paths for the MergeAppend.
+				 */
+				accumulate_append_subpath(cheapest_startup,
+										  &startup_subpaths, NULL);
+				accumulate_append_subpath(cheapest_total,
+										  &total_subpaths, NULL);
+			}
+		}
+
+		/* ... and build the Append or MergeAppend paths */
+		if (match_partition_order || match_partition_order_desc)
+		{
+			/* We only need Append */
+			add_path(rel, (Path *) create_append_path(root,
+													  rel,
+													  startup_subpaths,
+													  NIL,
+													  pathkeys,
+													  NULL,
+													  0,
+													  false,
+													  -1));
+			if (startup_neq_total)
+				add_path(rel, (Path *) create_append_path(root,
+														  rel,
+														  total_subpaths,
+														  NIL,
+														  pathkeys,
+														  NULL,
+														  0,
+														  false,
+														  -1));
+		}
+		else
+		{
+			/* We need MergeAppend */
+			add_path(rel, (Path *) create_merge_append_path(root,
+															rel,
+															startup_subpaths,
+															pathkeys,
+															NULL));
+			if (startup_neq_total)
+				add_path(rel, (Path *) create_merge_append_path(root,
+																rel,
+																total_subpaths,
+																pathkeys,
+																NULL));
+		}
+	}
+}
+
+/*
+ * get_cheapest_parameterized_child_path
+ *		Get cheapest path for this relation that has exactly the requested
+ *		parameterization.
+ *
+ * Returns NULL if unable to create such a path.
+ */
+static Path *
+get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
+									  Relids required_outer)
+{
+	Path	   *cheapest;
+	ListCell   *lc;
+
+	/*
+	 * Look up the cheapest existing path with no more than the needed
+	 * parameterization.  If it has exactly the needed parameterization, we're
+	 * done.
+	 */
+	cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
+											  NIL,
+											  required_outer,
+											  TOTAL_COST,
+											  false);
+	Assert(cheapest != NULL);
+	if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
+		return cheapest;
+
+	/*
+	 * Otherwise, we can "reparameterize" an existing path to match the given
+	 * parameterization, which effectively means pushing down additional
+	 * joinquals to be checked within the path's scan.  However, some existing
+	 * paths might check the available joinquals already while others don't;
+	 * therefore, it's not clear which existing path will be cheapest after
+	 * reparameterization.  We have to go through them all and find out.
+	 */
+	cheapest = NULL;
+	foreach(lc, rel->pathlist)
+	{
+		Path	   *path = (Path *) lfirst(lc);
+
+		/* Can't use it if it needs more than requested parameterization */
+		if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
+			continue;
+
+		/*
+		 * Reparameterization can only increase the path's cost, so if it's
+		 * already more expensive than the current cheapest, forget it.
+		 */
+		if (cheapest != NULL &&
+			compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
+			continue;
+
+		/* Reparameterize if needed, then recheck cost */
+		if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
+		{
+			path = reparameterize_path(root, path, required_outer, 1.0);
+			if (path == NULL)
+				continue;		/* failed to reparameterize this one */
+			Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));
+
+			if (cheapest != NULL &&
+				compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
+				continue;
+		}
+
+		/* We have a new best path */
+		cheapest = path;
+	}
+
+	/* Return the best path, or NULL if we found no suitable candidate */
+	return cheapest;
+}
+
+/*
+ * accumulate_append_subpath
+ *		Add a subpath to the list being built for an Append or MergeAppend.
+ *
+ * It's possible that the child is itself an Append or MergeAppend path, in
+ * which case we can "cut out the middleman" and just add its child paths to
+ * our own list.  (We don't try to do this earlier because we need to apply
+ * both levels of transformation to the quals.)
+ *
+ * Note that if we omit a child MergeAppend in this way, we are effectively
+ * omitting a sort step, which seems fine: if the parent is to be an Append,
+ * its result would be unsorted anyway, while if the parent is to be a
+ * MergeAppend, there's no point in a separate sort on a child.
+ *
+ * Normally, either path is a partial path and subpaths is a list of partial
+ * paths, or else path is a non-partial plan and subpaths is a list of those.
+ * However, if path is a parallel-aware Append, then we add its partial path
+ * children to subpaths and the rest to special_subpaths.  If the latter is
+ * NULL, we don't flatten the path at all (unless it contains only partial
+ * paths).
+ */
+static void
+accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
+{
+	if (IsA(path, AppendPath))
+	{
+		AppendPath *apath = (AppendPath *) path;
+
+		if (!apath->path.parallel_aware || apath->first_partial_path == 0)
+		{
+			*subpaths = list_concat(*subpaths, apath->subpaths);
+			return;
+		}
+		else if (special_subpaths != NULL)
+		{
+			List	   *new_special_subpaths;
+
+			/* Split Parallel Append into partial and non-partial subpaths */
+			*subpaths = list_concat(*subpaths,
+									list_copy_tail(apath->subpaths,
+												   apath->first_partial_path));
+			new_special_subpaths =
+				list_truncate(list_copy(apath->subpaths),
+							  apath->first_partial_path);
+			*special_subpaths = list_concat(*special_subpaths,
+											new_special_subpaths);
+			return;
+		}
+	}
+	else if (IsA(path, MergeAppendPath))
+	{
+		MergeAppendPath *mpath = (MergeAppendPath *) path;
+
+		*subpaths = list_concat(*subpaths, mpath->subpaths);
+		return;
+	}
+
+	*subpaths = lappend(*subpaths, path);
+}
+
+/*
+ * get_singleton_append_subpath
+ *		Returns the single subpath of an Append/MergeAppend, or just
+ *		return 'path' if it's not a single sub-path Append/MergeAppend.
+ *
+ * Note: 'path' must not be a parallel-aware path.
+ */
+static Path *
+get_singleton_append_subpath(Path *path)
+{
+	Assert(!path->parallel_aware);
+
+	if (IsA(path, AppendPath))
+	{
+		AppendPath *apath = (AppendPath *) path;
+
+		if (list_length(apath->subpaths) == 1)
+			return (Path *) linitial(apath->subpaths);
+	}
+	else if (IsA(path, MergeAppendPath))
+	{
+		MergeAppendPath *mpath = (MergeAppendPath *) path;
+
+		if (list_length(mpath->subpaths) == 1)
+			return (Path *) linitial(mpath->subpaths);
+	}
+
+	return path;
+}
+
+/*
+ * set_dummy_rel_pathlist
+ *	  Build a dummy path for a relation that's been excluded by constraints
+ *
+ * Rather than inventing a special "dummy" path type, we represent this as an
+ * AppendPath with no members (see also IS_DUMMY_APPEND/IS_DUMMY_REL macros).
+ *
+ * (See also mark_dummy_rel, which does basically the same thing, but is
+ * typically used to change a rel into dummy state after we already made
+ * paths for it.)
+ */
+static void
+set_dummy_rel_pathlist(RelOptInfo *rel)
+{
+	/* Set dummy size estimates --- we leave attr_widths[] as zeroes */
+	rel->rows = 0;
+	rel->reltarget->width = 0;
+
+	/* Discard any pre-existing paths; no further need for them */
+	rel->pathlist = NIL;
+	rel->partial_pathlist = NIL;
+
+	/* Set up the dummy path */
+	add_path(rel, (Path *) create_append_path(NULL, rel, NIL, NIL,
+											  NIL, rel->lateral_relids,
+											  0, false, -1));
+
+	/*
+	 * We set the cheapest-path fields immediately, just in case they were
+	 * pointing at some discarded path.  This is redundant when we're called
+	 * from set_rel_size(), but not when called from elsewhere, and doing it
+	 * twice is harmless anyway.
+	 */
+	set_cheapest(rel);
+}
+
+/* quick-and-dirty test to see if any joining is needed */
+static bool
+has_multiple_baserels(PlannerInfo *root)
+{
+	int			num_base_rels = 0;
+	Index		rti;
+
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *brel = root->simple_rel_array[rti];
+
+		if (brel == NULL)
+			continue;
+
+		/* ignore RTEs that are "other rels" */
+		if (brel->reloptkind == RELOPT_BASEREL)
+			if (++num_base_rels > 1)
+				return true;
+	}
+	return false;
+}
+
+/*
+ * set_subquery_pathlist
+ *		Generate SubqueryScan access paths for a subquery RTE
+ *
+ * We don't currently support generating parameterized paths for subqueries
+ * by pushing join clauses down into them; it seems too expensive to re-plan
+ * the subquery multiple times to consider different alternatives.
+ * (XXX that could stand to be reconsidered, now that we use Paths.)
+ * So the paths made here will be parameterized if the subquery contains
+ * LATERAL references, otherwise not.  As long as that's true, there's no need
+ * for a separate set_subquery_size phase: just make the paths right away.
+ */
+static void
+set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
+					  Index rti, RangeTblEntry *rte)
+{
+	Query	   *parse = root->parse;
+	Query	   *subquery = rte->subquery;
+	Relids		required_outer;
+	pushdown_safety_info safetyInfo;
+	double		tuple_fraction;
+	RelOptInfo *sub_final_rel;
+	ListCell   *lc;
+
+	/*
+	 * Must copy the Query so that planning doesn't mess up the RTE contents
+	 * (really really need to fix the planner to not scribble on its input,
+	 * someday ... but see remove_unused_subquery_outputs to start with).
+	 */
+	subquery = copyObject(subquery);
+
+	/*
+	 * If it's a LATERAL subquery, it might contain some Vars of the current
+	 * query level, requiring it to be treated as parameterized, even though
+	 * we don't support pushing down join quals into subqueries.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/*
+	 * Zero out result area for subquery_is_pushdown_safe, so that it can set
+	 * flags as needed while recursing.  In particular, we need a workspace
+	 * for keeping track of unsafe-to-reference columns.  unsafeColumns[i]
+	 * will be set true if we find that output column i of the subquery is
+	 * unsafe to use in a pushed-down qual.
+	 */
+	memset(&safetyInfo, 0, sizeof(safetyInfo));
+	safetyInfo.unsafeColumns = (bool *)
+		palloc0((list_length(subquery->targetList) + 1) * sizeof(bool));
+
+	/*
+	 * If the subquery has the "security_barrier" flag, it means the subquery
+	 * originated from a view that must enforce row-level security.  Then we
+	 * must not push down quals that contain leaky functions.  (Ideally this
+	 * would be checked inside subquery_is_pushdown_safe, but since we don't
+	 * currently pass the RTE to that function, we must do it here.)
+	 */
+	safetyInfo.unsafeLeaky = rte->security_barrier;
+
+	/*
+	 * If there are any restriction clauses that have been attached to the
+	 * subquery relation, consider pushing them down to become WHERE or HAVING
+	 * quals of the subquery itself.  This transformation is useful because it
+	 * may allow us to generate a better plan for the subquery than evaluating
+	 * all the subquery output rows and then filtering them.
+	 *
+	 * There are several cases where we cannot push down clauses. Restrictions
+	 * involving the subquery are checked by subquery_is_pushdown_safe().
+	 * Restrictions on individual clauses are checked by
+	 * qual_is_pushdown_safe().  Also, we don't want to push down
+	 * pseudoconstant clauses; better to have the gating node above the
+	 * subquery.
+	 *
+	 * Non-pushed-down clauses will get evaluated as qpquals of the
+	 * SubqueryScan node.
+	 *
+	 * XXX Are there any cases where we want to make a policy decision not to
+	 * push down a pushable qual, because it'd result in a worse plan?
+	 */
+	if (rel->baserestrictinfo != NIL &&
+		subquery_is_pushdown_safe(subquery, subquery, &safetyInfo))
+	{
+		/* OK to consider pushing down individual quals */
+		List	   *upperrestrictlist = NIL;
+		ListCell   *l;
+
+		foreach(l, rel->baserestrictinfo)
+		{
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
+
+			if (!rinfo->pseudoconstant &&
+				qual_is_pushdown_safe(subquery, rti, rinfo, &safetyInfo))
+			{
+				Node	   *clause = (Node *) rinfo->clause;
+
+				/* Push it down */
+				subquery_push_qual(subquery, rte, rti, clause);
+			}
+			else
+			{
+				/* Keep it in the upper query */
+				upperrestrictlist = lappend(upperrestrictlist, rinfo);
+			}
+		}
+		rel->baserestrictinfo = upperrestrictlist;
+		/* We don't bother recomputing baserestrict_min_security */
+	}
+
+	pfree(safetyInfo.unsafeColumns);
+
+	/*
+	 * The upper query might not use all the subquery's output columns; if
+	 * not, we can simplify.
+	 */
+	remove_unused_subquery_outputs(subquery, rel);
+
+	/*
+	 * We can safely pass the outer tuple_fraction down to the subquery if the
+	 * outer level has no joining, aggregation, or sorting to do. Otherwise
+	 * we'd better tell the subquery to plan for full retrieval. (XXX This
+	 * could probably be made more intelligent ...)
+	 */
+	if (parse->hasAggs ||
+		parse->groupClause ||
+		parse->groupingSets ||
+		parse->havingQual ||
+		parse->distinctClause ||
+		parse->sortClause ||
+		has_multiple_baserels(root))
+		tuple_fraction = 0.0;	/* default case */
+	else
+		tuple_fraction = root->tuple_fraction;
+
+	/* plan_params should not be in use in current query level */
+	Assert(root->plan_params == NIL);
+
+	/* Generate a subroot and Paths for the subquery */
+	rel->subroot = subquery_planner(root->glob, subquery,
+									root,
+									false, tuple_fraction);
+
+	/* Isolate the params needed by this specific subplan */
+	rel->subplan_params = root->plan_params;
+	root->plan_params = NIL;
+
+	/*
+	 * It's possible that constraint exclusion proved the subquery empty. If
+	 * so, it's desirable to produce an unadorned dummy path so that we will
+	 * recognize appropriate optimizations at this query level.
+	 */
+	sub_final_rel = fetch_upper_rel(rel->subroot, UPPERREL_FINAL, NULL);
+
+	if (IS_DUMMY_REL(sub_final_rel))
+	{
+		set_dummy_rel_pathlist(rel);
+		return;
+	}
+
+	/*
+	 * Mark rel with estimated output rows, width, etc.  Note that we have to
+	 * do this before generating outer-query paths, else cost_subqueryscan is
+	 * not happy.
+	 */
+	set_subquery_size_estimates(root, rel);
+
+	/*
+	 * For each Path that subquery_planner produced, make a SubqueryScanPath
+	 * in the outer query.
+	 */
+	foreach(lc, sub_final_rel->pathlist)
+	{
+		Path	   *subpath = (Path *) lfirst(lc);
+		List	   *pathkeys;
+
+		/* Convert subpath's pathkeys to outer representation */
+		pathkeys = convert_subquery_pathkeys(root,
+											 rel,
+											 subpath->pathkeys,
+											 make_tlist_from_pathtarget(subpath->pathtarget));
+
+		/* Generate outer path using this subpath */
+		add_path(rel, (Path *)
+				 create_subqueryscan_path(root, rel, subpath,
+										  pathkeys, required_outer));
+	}
+
+	/* If outer rel allows parallelism, do same for partial paths. */
+	if (rel->consider_parallel && bms_is_empty(required_outer))
+	{
+		/* If consider_parallel is false, there should be no partial paths. */
+		Assert(sub_final_rel->consider_parallel ||
+			   sub_final_rel->partial_pathlist == NIL);
+
+		/* Same for partial paths. */
+		foreach(lc, sub_final_rel->partial_pathlist)
+		{
+			Path	   *subpath = (Path *) lfirst(lc);
+			List	   *pathkeys;
+
+			/* Convert subpath's pathkeys to outer representation */
+			pathkeys = convert_subquery_pathkeys(root,
+												 rel,
+												 subpath->pathkeys,
+												 make_tlist_from_pathtarget(subpath->pathtarget));
+
+			/* Generate outer path using this subpath */
+			add_partial_path(rel, (Path *)
+							 create_subqueryscan_path(root, rel, subpath,
+													  pathkeys,
+													  required_outer));
+		}
+	}
+}
+
+/*
+ * set_function_pathlist
+ *		Build the (single) access path for a function RTE
+ */
+static void
+set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Relids		required_outer;
+	List	   *pathkeys = NIL;
+
+	/*
+	 * We don't support pushing join clauses into the quals of a function
+	 * scan, but it could still have required parameterization due to LATERAL
+	 * refs in the function expression.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/*
+	 * The result is considered unordered unless ORDINALITY was used, in which
+	 * case it is ordered by the ordinal column (the last one).  See if we
+	 * care, by checking for uses of that Var in equivalence classes.
+	 */
+	if (rte->funcordinality)
+	{
+		AttrNumber	ordattno = rel->max_attr;
+		Var		   *var = NULL;
+		ListCell   *lc;
+
+		/*
+		 * Is there a Var for it in rel's targetlist?  If not, the query did
+		 * not reference the ordinality column, or at least not in any way
+		 * that would be interesting for sorting.
+		 */
+		foreach(lc, rel->reltarget->exprs)
+		{
+			Var		   *node = (Var *) lfirst(lc);
+
+			/* checking varno/varlevelsup is just paranoia */
+			if (IsA(node, Var) &&
+				node->varattno == ordattno &&
+				node->varno == rel->relid &&
+				node->varlevelsup == 0)
+			{
+				var = node;
+				break;
+			}
+		}
+
+		/*
+		 * Try to build pathkeys for this Var with int8 sorting.  We tell
+		 * build_expression_pathkey not to build any new equivalence class; if
+		 * the Var isn't already mentioned in some EC, it means that nothing
+		 * cares about the ordering.
+		 */
+		if (var)
+			pathkeys = build_expression_pathkey(root,
+												(Expr *) var,
+												NULL,	/* below outer joins */
+												Int8LessOperator,
+												rel->relids,
+												false);
+	}
+
+	/* Generate appropriate path */
+	add_path(rel, create_functionscan_path(root, rel,
+										   pathkeys, required_outer));
+}
+
+/*
+ * set_values_pathlist
+ *		Build the (single) access path for a VALUES RTE
+ */
+static void
+set_values_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Relids		required_outer;
+
+	/*
+	 * We don't support pushing join clauses into the quals of a values scan,
+	 * but it could still have required parameterization due to LATERAL refs
+	 * in the values expressions.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_valuesscan_path(root, rel, required_outer));
+}
+
+/*
+ * set_tablefunc_pathlist
+ *		Build the (single) access path for a table func RTE
+ */
+static void
+set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Relids		required_outer;
+
+	/*
+	 * We don't support pushing join clauses into the quals of a tablefunc
+	 * scan, but it could still have required parameterization due to LATERAL
+	 * refs in the function expression.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_tablefuncscan_path(root, rel,
+											required_outer));
+}
+
+/*
+ * set_cte_pathlist
+ *		Build the (single) access path for a non-self-reference CTE RTE
+ *
+ * There's no need for a separate set_cte_size phase, since we don't
+ * support join-qual-parameterized paths for CTEs.
+ */
+static void
+set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Plan	   *cteplan;
+	PlannerInfo *cteroot;
+	Index		levelsup;
+	int			ndx;
+	ListCell   *lc;
+	int			plan_id;
+	Relids		required_outer;
+
+	/*
+	 * Find the referenced CTE, and locate the plan previously made for it.
+	 */
+	levelsup = rte->ctelevelsup;
+	cteroot = root;
+	while (levelsup-- > 0)
+	{
+		cteroot = cteroot->parent_root;
+		if (!cteroot)			/* shouldn't happen */
+			elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
+	}
+
+	/*
+	 * Note: cte_plan_ids can be shorter than cteList, if we are still working
+	 * on planning the CTEs (ie, this is a side-reference from another CTE).
+	 * So we mustn't use forboth here.
+	 */
+	ndx = 0;
+	foreach(lc, cteroot->parse->cteList)
+	{
+		CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
+
+		if (strcmp(cte->ctename, rte->ctename) == 0)
+			break;
+		ndx++;
+	}
+	if (lc == NULL)				/* shouldn't happen */
+		elog(ERROR, "could not find CTE \"%s\"", rte->ctename);
+	if (ndx >= list_length(cteroot->cte_plan_ids))
+		elog(ERROR, "could not find plan for CTE \"%s\"", rte->ctename);
+	plan_id = list_nth_int(cteroot->cte_plan_ids, ndx);
+	if (plan_id <= 0)
+		elog(ERROR, "no plan was made for CTE \"%s\"", rte->ctename);
+	cteplan = (Plan *) list_nth(root->glob->subplans, plan_id - 1);
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_cte_size_estimates(root, rel, cteplan->plan_rows);
+
+	/*
+	 * We don't support pushing join clauses into the quals of a CTE scan, but
+	 * it could still have required parameterization due to LATERAL refs in
+	 * its tlist.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_ctescan_path(root, rel, required_outer));
+}
+
+/*
+ * set_namedtuplestore_pathlist
+ *		Build the (single) access path for a named tuplestore RTE
+ *
+ * There's no need for a separate set_namedtuplestore_size phase, since we
+ * don't support join-qual-parameterized paths for tuplestores.
+ */
+static void
+set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel,
+							 RangeTblEntry *rte)
+{
+	Relids		required_outer;
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_namedtuplestore_size_estimates(root, rel);
+
+	/*
+	 * We don't support pushing join clauses into the quals of a tuplestore
+	 * scan, but it could still have required parameterization due to LATERAL
+	 * refs in its tlist.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_namedtuplestorescan_path(root, rel, required_outer));
+
+	/* Select cheapest path (pretty easy in this case...) */
+	set_cheapest(rel);
+}
+
+/*
+ * set_result_pathlist
+ *		Build the (single) access path for an RTE_RESULT RTE
+ *
+ * There's no need for a separate set_result_size phase, since we
+ * don't support join-qual-parameterized paths for these RTEs.
+ */
+static void
+set_result_pathlist(PlannerInfo *root, RelOptInfo *rel,
+					RangeTblEntry *rte)
+{
+	Relids		required_outer;
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_result_size_estimates(root, rel);
+
+	/*
+	 * We don't support pushing join clauses into the quals of a Result scan,
+	 * but it could still have required parameterization due to LATERAL refs
+	 * in its tlist.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_resultscan_path(root, rel, required_outer));
+
+	/* Select cheapest path (pretty easy in this case...) */
+	set_cheapest(rel);
+}
+
+/*
+ * set_worktable_pathlist
+ *		Build the (single) access path for a self-reference CTE RTE
+ *
+ * There's no need for a separate set_worktable_size phase, since we don't
+ * support join-qual-parameterized paths for CTEs.
+ */
+static void
+set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Path	   *ctepath;
+	PlannerInfo *cteroot;
+	Index		levelsup;
+	Relids		required_outer;
+
+	/*
+	 * We need to find the non-recursive term's path, which is in the plan
+	 * level that's processing the recursive UNION, which is one level *below*
+	 * where the CTE comes from.
+	 */
+	levelsup = rte->ctelevelsup;
+	if (levelsup == 0)			/* shouldn't happen */
+		elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
+	levelsup--;
+	cteroot = root;
+	while (levelsup-- > 0)
+	{
+		cteroot = cteroot->parent_root;
+		if (!cteroot)			/* shouldn't happen */
+			elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
+	}
+	ctepath = cteroot->non_recursive_path;
+	if (!ctepath)				/* shouldn't happen */
+		elog(ERROR, "could not find path for CTE \"%s\"", rte->ctename);
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_cte_size_estimates(root, rel, ctepath->rows);
+
+	/*
+	 * We don't support pushing join clauses into the quals of a worktable
+	 * scan, but it could still have required parameterization due to LATERAL
+	 * refs in its tlist.  (I'm not sure this is actually possible given the
+	 * restrictions on recursive references, but it's easy enough to support.)
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_worktablescan_path(root, rel, required_outer));
+}
+
+/*
+ * generate_gather_paths
+ *		Generate parallel access paths for a relation by pushing a Gather or
+ *		Gather Merge on top of a partial path.
+ *
+ * This must not be called until after we're done creating all partial paths
+ * for the specified relation.  (Otherwise, add_partial_path might delete a
+ * path that some GatherPath or GatherMergePath has a reference to.)
+ *
+ * If we're generating paths for a scan or join relation, override_rows will
+ * be false, and we'll just use the relation's size estimate.  When we're
+ * being called for a partially-grouped path, though, we need to override
+ * the rowcount estimate.  (It's not clear that the particular value we're
+ * using here is actually best, but the underlying rel has no estimate so
+ * we must do something.)
+ */
+void
+generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
+{
+	Path	   *cheapest_partial_path;
+	Path	   *simple_gather_path;
+	ListCell   *lc;
+	double		rows;
+	double	   *rowsp = NULL;
+
+	/* If there are no partial paths, there's nothing to do here. */
+	if (rel->partial_pathlist == NIL)
+		return;
+
+	/* Should we override the rel's rowcount estimate? */
+	if (override_rows)
+		rowsp = &rows;
+
+	/*
+	 * The output of Gather is always unsorted, so there's only one partial
+	 * path of interest: the cheapest one.  That will be the one at the front
+	 * of partial_pathlist because of the way add_partial_path works.
+	 */
+	cheapest_partial_path = linitial(rel->partial_pathlist);
+	rows =
+		cheapest_partial_path->rows * cheapest_partial_path->parallel_workers;
+	simple_gather_path = (Path *)
+		create_gather_path(root, rel, cheapest_partial_path, rel->reltarget,
+						   NULL, rowsp);
+	add_path(rel, simple_gather_path);
+
+	/*
+	 * For each useful ordering, we can consider an order-preserving Gather
+	 * Merge.
+	 */
+	foreach(lc, rel->partial_pathlist)
+	{
+		Path	   *subpath = (Path *) lfirst(lc);
+		GatherMergePath *path;
+
+		if (subpath->pathkeys == NIL)
+			continue;
+
+		rows = subpath->rows * subpath->parallel_workers;
+		path = create_gather_merge_path(root, rel, subpath, rel->reltarget,
+										subpath->pathkeys, NULL, rowsp);
+		add_path(rel, &path->path);
+	}
+}
+
+/*
+ * get_useful_pathkeys_for_relation
+ *		Determine which orderings of a relation might be useful.
+ *
+ * Getting data in sorted order can be useful either because the requested
+ * order matches the final output ordering for the overall query we're
+ * planning, or because it enables an efficient merge join.  Here, we try
+ * to figure out which pathkeys to consider.
+ *
+ * This allows us to do incremental sort on top of an index scan under a gather
+ * merge node, i.e. parallelized.
+ *
+ * If the require_parallel_safe is true, we also require the expressions to
+ * be parallel safe (which allows pushing the sort below Gather Merge).
+ *
+ * XXX At the moment this can only ever return a list with a single element,
+ * because it looks at query_pathkeys only. So we might return the pathkeys
+ * directly, but it seems plausible we'll want to consider other orderings
+ * in the future. For example, we might want to consider pathkeys useful for
+ * merge joins.
+ */
+static List *
+get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel,
+								 bool require_parallel_safe)
+{
+	List	   *useful_pathkeys_list = NIL;
+
+	/*
+	 * Considering query_pathkeys is always worth it, because it might allow
+	 * us to avoid a total sort when we have a partially presorted path
+	 * available or to push the total sort into the parallel portion of the
+	 * query.
+	 */
+	if (root->query_pathkeys)
+	{
+		ListCell   *lc;
+		int			npathkeys = 0;	/* useful pathkeys */
+
+		foreach(lc, root->query_pathkeys)
+		{
+			PathKey    *pathkey = (PathKey *) lfirst(lc);
+			EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
+
+			/*
+			 * We can only build a sort for pathkeys that contain a
+			 * safe-to-compute-early EC member computable from the current
+			 * relation's reltarget, so ignore the remainder of the list as
+			 * soon as we find a pathkey without such a member.
+			 *
+			 * It's still worthwhile to return any prefix of the pathkeys list
+			 * that meets this requirement, as we may be able to do an
+			 * incremental sort.
+			 *
+			 * If requested, ensure the sort expression is parallel-safe too.
+			 */
+			if (!relation_can_be_sorted_early(root, rel, pathkey_ec,
+											  require_parallel_safe))
+				break;
+
+			npathkeys++;
+		}
+
+		/*
+		 * The whole query_pathkeys list matches, so append it directly, to
+		 * allow comparing pathkeys easily by comparing list pointer. If we
+		 * have to truncate the pathkeys, we gotta do a copy though.
+		 */
+		if (npathkeys == list_length(root->query_pathkeys))
+			useful_pathkeys_list = lappend(useful_pathkeys_list,
+										   root->query_pathkeys);
+		else if (npathkeys > 0)
+			useful_pathkeys_list = lappend(useful_pathkeys_list,
+										   list_truncate(list_copy(root->query_pathkeys),
+														 npathkeys));
+	}
+
+	return useful_pathkeys_list;
+}
+
+/*
+ * generate_useful_gather_paths
+ *		Generate parallel access paths for a relation by pushing a Gather or
+ *		Gather Merge on top of a partial path.
+ *
+ * Unlike plain generate_gather_paths, this looks both at pathkeys of input
+ * paths (aiming to preserve the ordering), but also considers ordering that
+ * might be useful for nodes above the gather merge node, and tries to add
+ * a sort (regular or incremental) to provide that.
+ */
+void
+generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
+{
+	ListCell   *lc;
+	double		rows;
+	double	   *rowsp = NULL;
+	List	   *useful_pathkeys_list = NIL;
+	Path	   *cheapest_partial_path = NULL;
+
+	/* If there are no partial paths, there's nothing to do here. */
+	if (rel->partial_pathlist == NIL)
+		return;
+
+	/* Should we override the rel's rowcount estimate? */
+	if (override_rows)
+		rowsp = &rows;
+
+	/* generate the regular gather (merge) paths */
+	generate_gather_paths(root, rel, override_rows);
+
+	/* consider incremental sort for interesting orderings */
+	useful_pathkeys_list = get_useful_pathkeys_for_relation(root, rel, true);
+
+	/* used for explicit (full) sort paths */
+	cheapest_partial_path = linitial(rel->partial_pathlist);
+
+	/*
+	 * Consider sorted paths for each interesting ordering. We generate both
+	 * incremental and full sort.
+	 */
+	foreach(lc, useful_pathkeys_list)
+	{
+		List	   *useful_pathkeys = lfirst(lc);
+		ListCell   *lc2;
+		bool		is_sorted;
+		int			presorted_keys;
+
+		foreach(lc2, rel->partial_pathlist)
+		{
+			Path	   *subpath = (Path *) lfirst(lc2);
+			GatherMergePath *path;
+
+			is_sorted = pathkeys_count_contained_in(useful_pathkeys,
+													subpath->pathkeys,
+													&presorted_keys);
+
+			/*
+			 * We don't need to consider the case where a subpath is already
+			 * fully sorted because generate_gather_paths already creates a
+			 * gather merge path for every subpath that has pathkeys present.
+			 *
+			 * But since the subpath is already sorted, we know we don't need
+			 * to consider adding a sort (other either kind) on top of it, so
+			 * we can continue here.
+			 */
+			if (is_sorted)
+				continue;
+
+			/*
+			 * Consider regular sort for the cheapest partial path (for each
+			 * useful pathkeys). We know the path is not sorted, because we'd
+			 * not get here otherwise.
+			 *
+			 * This is not redundant with the gather paths created in
+			 * generate_gather_paths, because that doesn't generate ordered
+			 * output. Here we add an explicit sort to match the useful
+			 * ordering.
+			 */
+			if (cheapest_partial_path == subpath)
+			{
+				Path	   *tmp;
+
+				tmp = (Path *) create_sort_path(root,
+												rel,
+												subpath,
+												useful_pathkeys,
+												-1.0);
+
+				rows = tmp->rows * tmp->parallel_workers;
+
+				path = create_gather_merge_path(root, rel,
+												tmp,
+												rel->reltarget,
+												tmp->pathkeys,
+												NULL,
+												rowsp);
+
+				add_path(rel, &path->path);
+
+				/* Fall through */
+			}
+
+			/*
+			 * Consider incremental sort, but only when the subpath is already
+			 * partially sorted on a pathkey prefix.
+			 */
+			if (enable_incremental_sort && presorted_keys > 0)
+			{
+				Path	   *tmp;
+
+				/*
+				 * We should have already excluded pathkeys of length 1
+				 * because then presorted_keys > 0 would imply is_sorted was
+				 * true.
+				 */
+				Assert(list_length(useful_pathkeys) != 1);
+
+				tmp = (Path *) create_incremental_sort_path(root,
+															rel,
+															subpath,
+															useful_pathkeys,
+															presorted_keys,
+															-1);
+
+				path = create_gather_merge_path(root, rel,
+												tmp,
+												rel->reltarget,
+												tmp->pathkeys,
+												NULL,
+												rowsp);
+
+				add_path(rel, &path->path);
+			}
+		}
+	}
+}
+
+/*
+ * make_rel_from_joinlist
+ *	  Build access paths using a "joinlist" to guide the join path search.
+ *
+ * See comments for deconstruct_jointree() for definition of the joinlist
+ * data structure.
+ */
+static RelOptInfo *
+make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
+{
+	int			levels_needed;
+	List	   *initial_rels;
+	ListCell   *jl;
+
+	/*
+	 * Count the number of child joinlist nodes.  This is the depth of the
+	 * dynamic-programming algorithm we must employ to consider all ways of
+	 * joining the child nodes.
+	 */
+	levels_needed = list_length(joinlist);
+
+	if (levels_needed <= 0)
+		return NULL;			/* nothing to do? */
+
+	/*
+	 * Construct a list of rels corresponding to the child joinlist nodes.
+	 * This may contain both base rels and rels constructed according to
+	 * sub-joinlists.
+	 */
+	initial_rels = NIL;
+	foreach(jl, joinlist)
+	{
+		Node	   *jlnode = (Node *) lfirst(jl);
+		RelOptInfo *thisrel;
+
+		if (IsA(jlnode, RangeTblRef))
+		{
+			int			varno = ((RangeTblRef *) jlnode)->rtindex;
+
+			thisrel = find_base_rel(root, varno);
+		}
+		else if (IsA(jlnode, List))
+		{
+			/* Recurse to handle subproblem */
+			thisrel = make_rel_from_joinlist(root, (List *) jlnode);
+		}
+		else
+		{
+			elog(ERROR, "unrecognized joinlist node type: %d",
+				 (int) nodeTag(jlnode));
+			thisrel = NULL;		/* keep compiler quiet */
+		}
+
+		initial_rels = lappend(initial_rels, thisrel);
+	}
+
+	if (levels_needed == 1)
+	{
+		/*
+		 * Single joinlist node, so we're done.
+		 */
+		return (RelOptInfo *) linitial(initial_rels);
+	}
+	else
+	{
+		/*
+		 * Consider the different orders in which we could join the rels,
+		 * using a plugin, GEQO, or the regular join search code.
+		 *
+		 * We put the initial_rels list into a PlannerInfo field because
+		 * has_legal_joinclause() needs to look at it (ugly :-().
+		 */
+		root->initial_rels = initial_rels;
+
+		if (join_search_hook)
+			return (*join_search_hook) (root, levels_needed, initial_rels);
+		else if (enable_geqo && levels_needed >= geqo_threshold)
+			return geqo(root, levels_needed, initial_rels);
+		else
+			return standard_join_search(root, levels_needed, initial_rels);
+	}
+}
+
+/*
+ * standard_join_search
+ *	  Find possible joinpaths for a query by successively finding ways
+ *	  to join component relations into join relations.
+ *
+ * 'levels_needed' is the number of iterations needed, ie, the number of
+ *		independent jointree items in the query.  This is > 1.
+ *
+ * 'initial_rels' is a list of RelOptInfo nodes for each independent
+ *		jointree item.  These are the components to be joined together.
+ *		Note that levels_needed == list_length(initial_rels).
+ *
+ * Returns the final level of join relations, i.e., the relation that is
+ * the result of joining all the original relations together.
+ * At least one implementation path must be provided for this relation and
+ * all required sub-relations.
+ *
+ * To support loadable plugins that modify planner behavior by changing the
+ * join searching algorithm, we provide a hook variable that lets a plugin
+ * replace or supplement this function.  Any such hook must return the same
+ * final join relation as the standard code would, but it might have a
+ * different set of implementation paths attached, and only the sub-joinrels
+ * needed for these paths need have been instantiated.
+ *
+ * Note to plugin authors: the functions invoked during standard_join_search()
+ * modify root->join_rel_list and root->join_rel_hash.  If you want to do more
+ * than one join-order search, you'll probably need to save and restore the
+ * original states of those data structures.  See geqo_eval() for an example.
+ */
+RelOptInfo *
+standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
+{
+	int			lev;
+	RelOptInfo *rel;
+
+	/*
+	 * This function cannot be invoked recursively within any one planning
+	 * problem, so join_rel_level[] can't be in use already.
+	 */
+	Assert(root->join_rel_level == NULL);
+
+	/*
+	 * We employ a simple "dynamic programming" algorithm: we first find all
+	 * ways to build joins of two jointree items, then all ways to build joins
+	 * of three items (from two-item joins and single items), then four-item
+	 * joins, and so on until we have considered all ways to join all the
+	 * items into one rel.
+	 *
+	 * root->join_rel_level[j] is a list of all the j-item rels.  Initially we
+	 * set root->join_rel_level[1] to represent all the single-jointree-item
+	 * relations.
+	 */
+	root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
+
+	root->join_rel_level[1] = initial_rels;
+
+	for (lev = 2; lev <= levels_needed; lev++)
+	{
+		ListCell   *lc;
+
+		/*
+		 * Determine all possible pairs of relations to be joined at this
+		 * level, and build paths for making each one from every available
+		 * pair of lower-level relations.
+		 */
+		join_search_one_level(root, lev);
+
+		/*
+		 * Run generate_partitionwise_join_paths() and
+		 * generate_useful_gather_paths() for each just-processed joinrel.  We
+		 * could not do this earlier because both regular and partial paths
+		 * can get added to a particular joinrel at multiple times within
+		 * join_search_one_level.
+		 *
+		 * After that, we're done creating paths for the joinrel, so run
+		 * set_cheapest().
+		 */
+		foreach(lc, root->join_rel_level[lev])
+		{
+			rel = (RelOptInfo *) lfirst(lc);
+
+			/* Create paths for partitionwise joins. */
+			generate_partitionwise_join_paths(root, rel);
+
+			/*
+			 * Except for the topmost scan/join rel, consider gathering
+			 * partial paths.  We'll do the same for the topmost scan/join rel
+			 * once we know the final targetlist (see grouping_planner).
+			 */
+			if (lev < levels_needed)
+				generate_useful_gather_paths(root, rel, false);
+
+			/* Find and save the cheapest paths for this rel */
+			set_cheapest(rel);
+
+#ifdef OPTIMIZER_DEBUG
+			debug_print_rel(root, rel);
+#endif
+		}
+	}
+
+	/*
+	 * We should have a single rel at the final level.
+	 */
+	if (root->join_rel_level[levels_needed] == NIL)
+		elog(ERROR, "failed to build any %d-way joins", levels_needed);
+	Assert(list_length(root->join_rel_level[levels_needed]) == 1);
+
+	rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
+
+	root->join_rel_level = NULL;
+
+	return rel;
+}
+
+/*****************************************************************************
+ *			PUSHING QUALS DOWN INTO SUBQUERIES
+ *****************************************************************************/
+
+/*
+ * subquery_is_pushdown_safe - is a subquery safe for pushing down quals?
+ *
+ * subquery is the particular component query being checked.  topquery
+ * is the top component of a set-operations tree (the same Query if no
+ * set-op is involved).
+ *
+ * Conditions checked here:
+ *
+ * 1. If the subquery has a LIMIT clause, we must not push down any quals,
+ * since that could change the set of rows returned.
+ *
+ * 2. If the subquery contains EXCEPT or EXCEPT ALL set ops we cannot push
+ * quals into it, because that could change the results.
+ *
+ * 3. If the subquery uses DISTINCT, we cannot push volatile quals into it.
+ * This is because upper-level quals should semantically be evaluated only
+ * once per distinct row, not once per original row, and if the qual is
+ * volatile then extra evaluations could change the results.  (This issue
+ * does not apply to other forms of aggregation such as GROUP BY, because
+ * when those are present we push into HAVING not WHERE, so that the quals
+ * are still applied after aggregation.)
+ *
+ * 4. If the subquery contains window functions, we cannot push volatile quals
+ * into it.  The issue here is a bit different from DISTINCT: a volatile qual
+ * might succeed for some rows of a window partition and fail for others,
+ * thereby changing the partition contents and thus the window functions'
+ * results for rows that remain.
+ *
+ * 5. If the subquery contains any set-returning functions in its targetlist,
+ * we cannot push volatile quals into it.  That would push them below the SRFs
+ * and thereby change the number of times they are evaluated.  Also, a
+ * volatile qual could succeed for some SRF output rows and fail for others,
+ * a behavior that cannot occur if it's evaluated before SRF expansion.
+ *
+ * 6. If the subquery has nonempty grouping sets, we cannot push down any
+ * quals.  The concern here is that a qual referencing a "constant" grouping
+ * column could get constant-folded, which would be improper because the value
+ * is potentially nullable by grouping-set expansion.  This restriction could
+ * be removed if we had a parsetree representation that shows that such
+ * grouping columns are not really constant.  (There are other ideas that
+ * could be used to relax this restriction, but that's the approach most
+ * likely to get taken in the future.  Note that there's not much to be gained
+ * so long as subquery_planner can't move HAVING clauses to WHERE within such
+ * a subquery.)
+ *
+ * In addition, we make several checks on the subquery's output columns to see
+ * if it is safe to reference them in pushed-down quals.  If output column k
+ * is found to be unsafe to reference, we set safetyInfo->unsafeColumns[k]
+ * to true, but we don't reject the subquery overall since column k might not
+ * be referenced by some/all quals.  The unsafeColumns[] array will be
+ * consulted later by qual_is_pushdown_safe().  It's better to do it this way
+ * than to make the checks directly in qual_is_pushdown_safe(), because when
+ * the subquery involves set operations we have to check the output
+ * expressions in each arm of the set op.
+ *
+ * Note: pushing quals into a DISTINCT subquery is theoretically dubious:
+ * we're effectively assuming that the quals cannot distinguish values that
+ * the DISTINCT's equality operator sees as equal, yet there are many
+ * counterexamples to that assumption.  However use of such a qual with a
+ * DISTINCT subquery would be unsafe anyway, since there's no guarantee which
+ * "equal" value will be chosen as the output value by the DISTINCT operation.
+ * So we don't worry too much about that.  Another objection is that if the
+ * qual is expensive to evaluate, running it for each original row might cost
+ * more than we save by eliminating rows before the DISTINCT step.  But it
+ * would be very hard to estimate that at this stage, and in practice pushdown
+ * seldom seems to make things worse, so we ignore that problem too.
+ *
+ * Note: likewise, pushing quals into a subquery with window functions is a
+ * bit dubious: the quals might remove some rows of a window partition while
+ * leaving others, causing changes in the window functions' results for the
+ * surviving rows.  We insist that such a qual reference only partitioning
+ * columns, but again that only protects us if the qual does not distinguish
+ * values that the partitioning equality operator sees as equal.  The risks
+ * here are perhaps larger than for DISTINCT, since no de-duplication of rows
+ * occurs and thus there is no theoretical problem with such a qual.  But
+ * we'll do this anyway because the potential performance benefits are very
+ * large, and we've seen no field complaints about the longstanding comparable
+ * behavior with DISTINCT.
+ */
+static bool
+subquery_is_pushdown_safe(Query *subquery, Query *topquery,
+						  pushdown_safety_info *safetyInfo)
+{
+	SetOperationStmt *topop;
+
+	/* Check point 1 */
+	if (subquery->limitOffset != NULL || subquery->limitCount != NULL)
+		return false;
+
+	/* Check point 6 */
+	if (subquery->groupClause && subquery->groupingSets)
+		return false;
+
+	/* Check points 3, 4, and 5 */
+	if (subquery->distinctClause ||
+		subquery->hasWindowFuncs ||
+		subquery->hasTargetSRFs)
+		safetyInfo->unsafeVolatile = true;
+
+	/*
+	 * If we're at a leaf query, check for unsafe expressions in its target
+	 * list, and mark any unsafe ones in unsafeColumns[].  (Non-leaf nodes in
+	 * setop trees have only simple Vars in their tlists, so no need to check
+	 * them.)
+	 */
+	if (subquery->setOperations == NULL)
+		check_output_expressions(subquery, safetyInfo);
+
+	/* Are we at top level, or looking at a setop component? */
+	if (subquery == topquery)
+	{
+		/* Top level, so check any component queries */
+		if (subquery->setOperations != NULL)
+			if (!recurse_pushdown_safe(subquery->setOperations, topquery,
+									   safetyInfo))
+				return false;
+	}
+	else
+	{
+		/* Setop component must not have more components (too weird) */
+		if (subquery->setOperations != NULL)
+			return false;
+		/* Check whether setop component output types match top level */
+		topop = castNode(SetOperationStmt, topquery->setOperations);
+		Assert(topop);
+		compare_tlist_datatypes(subquery->targetList,
+								topop->colTypes,
+								safetyInfo);
+	}
+	return true;
+}
+
+/*
+ * Helper routine to recurse through setOperations tree
+ */
+static bool
+recurse_pushdown_safe(Node *setOp, Query *topquery,
+					  pushdown_safety_info *safetyInfo)
+{
+	if (IsA(setOp, RangeTblRef))
+	{
+		RangeTblRef *rtr = (RangeTblRef *) setOp;
+		RangeTblEntry *rte = rt_fetch(rtr->rtindex, topquery->rtable);
+		Query	   *subquery = rte->subquery;
+
+		Assert(subquery != NULL);
+		return subquery_is_pushdown_safe(subquery, topquery, safetyInfo);
+	}
+	else if (IsA(setOp, SetOperationStmt))
+	{
+		SetOperationStmt *op = (SetOperationStmt *) setOp;
+
+		/* EXCEPT is no good (point 2 for subquery_is_pushdown_safe) */
+		if (op->op == SETOP_EXCEPT)
+			return false;
+		/* Else recurse */
+		if (!recurse_pushdown_safe(op->larg, topquery, safetyInfo))
+			return false;
+		if (!recurse_pushdown_safe(op->rarg, topquery, safetyInfo))
+			return false;
+	}
+	else
+	{
+		elog(ERROR, "unrecognized node type: %d",
+			 (int) nodeTag(setOp));
+	}
+	return true;
+}
+
+/*
+ * check_output_expressions - check subquery's output expressions for safety
+ *
+ * There are several cases in which it's unsafe to push down an upper-level
+ * qual if it references a particular output column of a subquery.  We check
+ * each output column of the subquery and set unsafeColumns[k] to true if
+ * that column is unsafe for a pushed-down qual to reference.  The conditions
+ * checked here are:
+ *
+ * 1. We must not push down any quals that refer to subselect outputs that
+ * return sets, else we'd introduce functions-returning-sets into the
+ * subquery's WHERE/HAVING quals.
+ *
+ * 2. We must not push down any quals that refer to subselect outputs that
+ * contain volatile functions, for fear of introducing strange results due
+ * to multiple evaluation of a volatile function.
+ *
+ * 3. If the subquery uses DISTINCT ON, we must not push down any quals that
+ * refer to non-DISTINCT output columns, because that could change the set
+ * of rows returned.  (This condition is vacuous for DISTINCT, because then
+ * there are no non-DISTINCT output columns, so we needn't check.  Note that
+ * subquery_is_pushdown_safe already reported that we can't use volatile
+ * quals if there's DISTINCT or DISTINCT ON.)
+ *
+ * 4. If the subquery has any window functions, we must not push down quals
+ * that reference any output columns that are not listed in all the subquery's
+ * window PARTITION BY clauses.  We can push down quals that use only
+ * partitioning columns because they should succeed or fail identically for
+ * every row of any one window partition, and totally excluding some
+ * partitions will not change a window function's results for remaining
+ * partitions.  (Again, this also requires nonvolatile quals, but
+ * subquery_is_pushdown_safe handles that.)
+ */
+static void
+check_output_expressions(Query *subquery, pushdown_safety_info *safetyInfo)
+{
+	ListCell   *lc;
+
+	foreach(lc, subquery->targetList)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(lc);
+
+		if (tle->resjunk)
+			continue;			/* ignore resjunk columns */
+
+		/* We need not check further if output col is already known unsafe */
+		if (safetyInfo->unsafeColumns[tle->resno])
+			continue;
+
+		/* Functions returning sets are unsafe (point 1) */
+		if (subquery->hasTargetSRFs &&
+			expression_returns_set((Node *) tle->expr))
+		{
+			safetyInfo->unsafeColumns[tle->resno] = true;
+			continue;
+		}
+
+		/* Volatile functions are unsafe (point 2) */
+		if (contain_volatile_functions((Node *) tle->expr))
+		{
+			safetyInfo->unsafeColumns[tle->resno] = true;
+			continue;
+		}
+
+		/* If subquery uses DISTINCT ON, check point 3 */
+		if (subquery->hasDistinctOn &&
+			!targetIsInSortList(tle, InvalidOid, subquery->distinctClause))
+		{
+			/* non-DISTINCT column, so mark it unsafe */
+			safetyInfo->unsafeColumns[tle->resno] = true;
+			continue;
+		}
+
+		/* If subquery uses window functions, check point 4 */
+		if (subquery->hasWindowFuncs &&
+			!targetIsInAllPartitionLists(tle, subquery))
+		{
+			/* not present in all PARTITION BY clauses, so mark it unsafe */
+			safetyInfo->unsafeColumns[tle->resno] = true;
+			continue;
+		}
+	}
+}
+
+/*
+ * For subqueries using UNION/UNION ALL/INTERSECT/INTERSECT ALL, we can
+ * push quals into each component query, but the quals can only reference
+ * subquery columns that suffer no type coercions in the set operation.
+ * Otherwise there are possible semantic gotchas.  So, we check the
+ * component queries to see if any of them have output types different from
+ * the top-level setop outputs.  unsafeColumns[k] is set true if column k
+ * has different type in any component.
+ *
+ * We don't have to care about typmods here: the only allowed difference
+ * between set-op input and output typmods is input is a specific typmod
+ * and output is -1, and that does not require a coercion.
+ *
+ * tlist is a subquery tlist.
+ * colTypes is an OID list of the top-level setop's output column types.
+ * safetyInfo->unsafeColumns[] is the result array.
+ */
+static void
+compare_tlist_datatypes(List *tlist, List *colTypes,
+						pushdown_safety_info *safetyInfo)
+{
+	ListCell   *l;
+	ListCell   *colType = list_head(colTypes);
+
+	foreach(l, tlist)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(l);
+
+		if (tle->resjunk)
+			continue;			/* ignore resjunk columns */
+		if (colType == NULL)
+			elog(ERROR, "wrong number of tlist entries");
+		if (exprType((Node *) tle->expr) != lfirst_oid(colType))
+			safetyInfo->unsafeColumns[tle->resno] = true;
+		colType = lnext(colTypes, colType);
+	}
+	if (colType != NULL)
+		elog(ERROR, "wrong number of tlist entries");
+}
+
+/*
+ * targetIsInAllPartitionLists
+ *		True if the TargetEntry is listed in the PARTITION BY clause
+ *		of every window defined in the query.
+ *
+ * It would be safe to ignore windows not actually used by any window
+ * function, but it's not easy to get that info at this stage; and it's
+ * unlikely to be useful to spend any extra cycles getting it, since
+ * unreferenced window definitions are probably infrequent in practice.
+ */
+static bool
+targetIsInAllPartitionLists(TargetEntry *tle, Query *query)
+{
+	ListCell   *lc;
+
+	foreach(lc, query->windowClause)
+	{
+		WindowClause *wc = (WindowClause *) lfirst(lc);
+
+		if (!targetIsInSortList(tle, InvalidOid, wc->partitionClause))
+			return false;
+	}
+	return true;
+}
+
+/*
+ * qual_is_pushdown_safe - is a particular rinfo safe to push down?
+ *
+ * rinfo is a restriction clause applying to the given subquery (whose RTE
+ * has index rti in the parent query).
+ *
+ * Conditions checked here:
+ *
+ * 1. rinfo's clause must not contain any SubPlans (mainly because it's
+ * unclear that it will work correctly: SubLinks will already have been
+ * transformed into SubPlans in the qual, but not in the subquery).  Note that
+ * SubLinks that transform to initplans are safe, and will be accepted here
+ * because what we'll see in the qual is just a Param referencing the initplan
+ * output.
+ *
+ * 2. If unsafeVolatile is set, rinfo's clause must not contain any volatile
+ * functions.
+ *
+ * 3. If unsafeLeaky is set, rinfo's clause must not contain any leaky
+ * functions that are passed Var nodes, and therefore might reveal values from
+ * the subquery as side effects.
+ *
+ * 4. rinfo's clause must not refer to the whole-row output of the subquery
+ * (since there is no easy way to name that within the subquery itself).
+ *
+ * 5. rinfo's clause must not refer to any subquery output columns that were
+ * found to be unsafe to reference by subquery_is_pushdown_safe().
+ */
+static bool
+qual_is_pushdown_safe(Query *subquery, Index rti, RestrictInfo *rinfo,
+					  pushdown_safety_info *safetyInfo)
+{
+	bool		safe = true;
+	Node	   *qual = (Node *) rinfo->clause;
+	List	   *vars;
+	ListCell   *vl;
+
+	/* Refuse subselects (point 1) */
+	if (contain_subplans(qual))
+		return false;
+
+	/* Refuse volatile quals if we found they'd be unsafe (point 2) */
+	if (safetyInfo->unsafeVolatile &&
+		contain_volatile_functions((Node *) rinfo))
+		return false;
+
+	/* Refuse leaky quals if told to (point 3) */
+	if (safetyInfo->unsafeLeaky &&
+		contain_leaked_vars(qual))
+		return false;
+
+	/*
+	 * It would be unsafe to push down window function calls, but at least for
+	 * the moment we could never see any in a qual anyhow.  (The same applies
+	 * to aggregates, which we check for in pull_var_clause below.)
+	 */
+	Assert(!contain_window_function(qual));
+
+	/*
+	 * Examine all Vars used in clause.  Since it's a restriction clause, all
+	 * such Vars must refer to subselect output columns ... unless this is
+	 * part of a LATERAL subquery, in which case there could be lateral
+	 * references.
+	 */
+	vars = pull_var_clause(qual, PVC_INCLUDE_PLACEHOLDERS);
+	foreach(vl, vars)
+	{
+		Var		   *var = (Var *) lfirst(vl);
+
+		/*
+		 * XXX Punt if we find any PlaceHolderVars in the restriction clause.
+		 * It's not clear whether a PHV could safely be pushed down, and even
+		 * less clear whether such a situation could arise in any cases of
+		 * practical interest anyway.  So for the moment, just refuse to push
+		 * down.
+		 */
+		if (!IsA(var, Var))
+		{
+			safe = false;
+			break;
+		}
+
+		/*
+		 * Punt if we find any lateral references.  It would be safe to push
+		 * these down, but we'd have to convert them into outer references,
+		 * which subquery_push_qual lacks the infrastructure to do.  The case
+		 * arises so seldom that it doesn't seem worth working hard on.
+		 */
+		if (var->varno != rti)
+		{
+			safe = false;
+			break;
+		}
+
+		/* Subqueries have no system columns */
+		Assert(var->varattno >= 0);
+
+		/* Check point 4 */
+		if (var->varattno == 0)
+		{
+			safe = false;
+			break;
+		}
+
+		/* Check point 5 */
+		if (safetyInfo->unsafeColumns[var->varattno])
+		{
+			safe = false;
+			break;
+		}
+	}
+
+	list_free(vars);
+
+	return safe;
+}
+
+/*
+ * subquery_push_qual - push down a qual that we have determined is safe
+ */
+static void
+subquery_push_qual(Query *subquery, RangeTblEntry *rte, Index rti, Node *qual)
+{
+	if (subquery->setOperations != NULL)
+	{
+		/* Recurse to push it separately to each component query */
+		recurse_push_qual(subquery->setOperations, subquery,
+						  rte, rti, qual);
+	}
+	else
+	{
+		/*
+		 * We need to replace Vars in the qual (which must refer to outputs of
+		 * the subquery) with copies of the subquery's targetlist expressions.
+		 * Note that at this point, any uplevel Vars in the qual should have
+		 * been replaced with Params, so they need no work.
+		 *
+		 * This step also ensures that when we are pushing into a setop tree,
+		 * each component query gets its own copy of the qual.
+		 */
+		qual = ReplaceVarsFromTargetList(qual, rti, 0, rte,
+										 subquery->targetList,
+										 REPLACEVARS_REPORT_ERROR, 0,
+										 &subquery->hasSubLinks);
+
+		/*
+		 * Now attach the qual to the proper place: normally WHERE, but if the
+		 * subquery uses grouping or aggregation, put it in HAVING (since the
+		 * qual really refers to the group-result rows).
+		 */
+		if (subquery->hasAggs || subquery->groupClause || subquery->groupingSets || subquery->havingQual)
+			subquery->havingQual = make_and_qual(subquery->havingQual, qual);
+		else
+			subquery->jointree->quals =
+				make_and_qual(subquery->jointree->quals, qual);
+
+		/*
+		 * We need not change the subquery's hasAggs or hasSubLinks flags,
+		 * since we can't be pushing down any aggregates that weren't there
+		 * before, and we don't push down subselects at all.
+		 */
+	}
+}
+
+/*
+ * Helper routine to recurse through setOperations tree
+ */
+static void
+recurse_push_qual(Node *setOp, Query *topquery,
+				  RangeTblEntry *rte, Index rti, Node *qual)
+{
+	if (IsA(setOp, RangeTblRef))
+	{
+		RangeTblRef *rtr = (RangeTblRef *) setOp;
+		RangeTblEntry *subrte = rt_fetch(rtr->rtindex, topquery->rtable);
+		Query	   *subquery = subrte->subquery;
+
+		Assert(subquery != NULL);
+		subquery_push_qual(subquery, rte, rti, qual);
+	}
+	else if (IsA(setOp, SetOperationStmt))
+	{
+		SetOperationStmt *op = (SetOperationStmt *) setOp;
+
+		recurse_push_qual(op->larg, topquery, rte, rti, qual);
+		recurse_push_qual(op->rarg, topquery, rte, rti, qual);
+	}
+	else
+	{
+		elog(ERROR, "unrecognized node type: %d",
+			 (int) nodeTag(setOp));
+	}
+}
+
+/*****************************************************************************
+ *			SIMPLIFYING SUBQUERY TARGETLISTS
+ *****************************************************************************/
+
+/*
+ * remove_unused_subquery_outputs
+ *		Remove subquery targetlist items we don't need
+ *
+ * It's possible, even likely, that the upper query does not read all the
+ * output columns of the subquery.  We can remove any such outputs that are
+ * not needed by the subquery itself (e.g., as sort/group columns) and do not
+ * affect semantics otherwise (e.g., volatile functions can't be removed).
+ * This is useful not only because we might be able to remove expensive-to-
+ * compute expressions, but because deletion of output columns might allow
+ * optimizations such as join removal to occur within the subquery.
+ *
+ * To avoid affecting column numbering in the targetlist, we don't physically
+ * remove unused tlist entries, but rather replace their expressions with NULL
+ * constants.  This is implemented by modifying subquery->targetList.
+ */
+static void
+remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
+{
+	Bitmapset  *attrs_used = NULL;
+	ListCell   *lc;
+
+	/*
+	 * Do nothing if subquery has UNION/INTERSECT/EXCEPT: in principle we
+	 * could update all the child SELECTs' tlists, but it seems not worth the
+	 * trouble presently.
+	 */
+	if (subquery->setOperations)
+		return;
+
+	/*
+	 * If subquery has regular DISTINCT (not DISTINCT ON), we're wasting our
+	 * time: all its output columns must be used in the distinctClause.
+	 */
+	if (subquery->distinctClause && !subquery->hasDistinctOn)
+		return;
+
+	/*
+	 * Collect a bitmap of all the output column numbers used by the upper
+	 * query.
+	 *
+	 * Add all the attributes needed for joins or final output.  Note: we must
+	 * look at rel's targetlist, not the attr_needed data, because attr_needed
+	 * isn't computed for inheritance child rels, cf set_append_rel_size().
+	 * (XXX might be worth changing that sometime.)
+	 */
+	pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used);
+
+	/* Add all the attributes used by un-pushed-down restriction clauses. */
+	foreach(lc, rel->baserestrictinfo)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+		pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used);
+	}
+
+	/*
+	 * If there's a whole-row reference to the subquery, we can't remove
+	 * anything.
+	 */
+	if (bms_is_member(0 - FirstLowInvalidHeapAttributeNumber, attrs_used))
+		return;
+
+	/*
+	 * Run through the tlist and zap entries we don't need.  It's okay to
+	 * modify the tlist items in-place because set_subquery_pathlist made a
+	 * copy of the subquery.
+	 */
+	foreach(lc, subquery->targetList)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(lc);
+		Node	   *texpr = (Node *) tle->expr;
+
+		/*
+		 * If it has a sortgroupref number, it's used in some sort/group
+		 * clause so we'd better not remove it.  Also, don't remove any
+		 * resjunk columns, since their reason for being has nothing to do
+		 * with anybody reading the subquery's output.  (It's likely that
+		 * resjunk columns in a sub-SELECT would always have ressortgroupref
+		 * set, but even if they don't, it seems imprudent to remove them.)
+		 */
+		if (tle->ressortgroupref || tle->resjunk)
+			continue;
+
+		/*
+		 * If it's used by the upper query, we can't remove it.
+		 */
+		if (bms_is_member(tle->resno - FirstLowInvalidHeapAttributeNumber,
+						  attrs_used))
+			continue;
+
+		/*
+		 * If it contains a set-returning function, we can't remove it since
+		 * that could change the number of rows returned by the subquery.
+		 */
+		if (subquery->hasTargetSRFs &&
+			expression_returns_set(texpr))
+			continue;
+
+		/*
+		 * If it contains volatile functions, we daren't remove it for fear
+		 * that the user is expecting their side-effects to happen.
+		 */
+		if (contain_volatile_functions(texpr))
+			continue;
+
+		/*
+		 * OK, we don't need it.  Replace the expression with a NULL constant.
+		 * Preserve the exposed type of the expression, in case something
+		 * looks at the rowtype of the subquery's result.
+		 */
+		tle->expr = (Expr *) makeNullConst(exprType(texpr),
+										   exprTypmod(texpr),
+										   exprCollation(texpr));
+	}
+}
+
+/*
+ * create_partial_bitmap_paths
+ *	  Build partial bitmap heap path for the relation
+ */
+void
+create_partial_bitmap_paths(PlannerInfo *root, RelOptInfo *rel,
+							Path *bitmapqual)
+{
+	int			parallel_workers;
+	double		pages_fetched;
+
+	/* Compute heap pages for bitmap heap scan */
+	pages_fetched = compute_bitmap_pages(root, rel, bitmapqual, 1.0,
+										 NULL, NULL);
+
+	parallel_workers = compute_parallel_worker(rel, pages_fetched, -1,
+											   max_parallel_workers_per_gather);
+
+	if (parallel_workers <= 0)
+		return;
+
+	add_partial_path(rel, (Path *) create_bitmap_heap_path(root, rel,
+														   bitmapqual, rel->lateral_relids, 1.0, parallel_workers));
+}
+
+/*
+ * Compute the number of parallel workers that should be used to scan a
+ * relation.  We compute the parallel workers based on the size of the heap to
+ * be scanned and the size of the index to be scanned, then choose a minimum
+ * of those.
+ *
+ * "heap_pages" is the number of pages from the table that we expect to scan, or
+ * -1 if we don't expect to scan any.
+ *
+ * "index_pages" is the number of pages from the index that we expect to scan, or
+ * -1 if we don't expect to scan any.
+ *
+ * "max_workers" is caller's limit on the number of workers.  This typically
+ * comes from a GUC.
+ */
+int
+compute_parallel_worker(RelOptInfo *rel, double heap_pages, double index_pages,
+						int max_workers)
+{
+	int			parallel_workers = 0;
+
+	/*
+	 * If the user has set the parallel_workers reloption, use that; otherwise
+	 * select a default number of workers.
+	 */
+	if (rel->rel_parallel_workers != -1)
+		parallel_workers = rel->rel_parallel_workers;
+	else
+	{
+		/*
+		 * If the number of pages being scanned is insufficient to justify a
+		 * parallel scan, just return zero ... unless it's an inheritance
+		 * child. In that case, we want to generate a parallel path here
+		 * anyway.  It might not be worthwhile just for this relation, but
+		 * when combined with all of its inheritance siblings it may well pay
+		 * off.
+		 */
+		if (rel->reloptkind == RELOPT_BASEREL &&
+			((heap_pages >= 0 && heap_pages < min_parallel_table_scan_size) ||
+			 (index_pages >= 0 && index_pages < min_parallel_index_scan_size)))
+			return 0;
+
+		if (heap_pages >= 0)
+		{
+			int			heap_parallel_threshold;
+			int			heap_parallel_workers = 1;
+
+			/*
+			 * Select the number of workers based on the log of the size of
+			 * the relation.  This probably needs to be a good deal more
+			 * sophisticated, but we need something here for now.  Note that
+			 * the upper limit of the min_parallel_table_scan_size GUC is
+			 * chosen to prevent overflow here.
+			 */
+			heap_parallel_threshold = Max(min_parallel_table_scan_size, 1);
+			while (heap_pages >= (BlockNumber) (heap_parallel_threshold * 3))
+			{
+				heap_parallel_workers++;
+				heap_parallel_threshold *= 3;
+				if (heap_parallel_threshold > INT_MAX / 3)
+					break;		/* avoid overflow */
+			}
+
+			parallel_workers = heap_parallel_workers;
+		}
+
+		if (index_pages >= 0)
+		{
+			int			index_parallel_workers = 1;
+			int			index_parallel_threshold;
+
+			/* same calculation as for heap_pages above */
+			index_parallel_threshold = Max(min_parallel_index_scan_size, 1);
+			while (index_pages >= (BlockNumber) (index_parallel_threshold * 3))
+			{
+				index_parallel_workers++;
+				index_parallel_threshold *= 3;
+				if (index_parallel_threshold > INT_MAX / 3)
+					break;		/* avoid overflow */
+			}
+
+			if (parallel_workers > 0)
+				parallel_workers = Min(parallel_workers, index_parallel_workers);
+			else
+				parallel_workers = index_parallel_workers;
+		}
+	}
+
+	/* In no case use more than caller supplied maximum number of workers */
+	parallel_workers = Min(parallel_workers, max_workers);
+
+	return parallel_workers;
+}
+
+/*
+ * generate_partitionwise_join_paths
+ * 		Create paths representing partitionwise join for given partitioned
+ * 		join relation.
+ *
+ * This must not be called until after we are done adding paths for all
+ * child-joins. Otherwise, add_path might delete a path to which some path
+ * generated here has a reference.
+ */
+void
+generate_partitionwise_join_paths(PlannerInfo *root, RelOptInfo *rel)
+{
+	List	   *live_children = NIL;
+	int			cnt_parts;
+	int			num_parts;
+	RelOptInfo **part_rels;
+
+	/* Handle only join relations here. */
+	if (!IS_JOIN_REL(rel))
+		return;
+
+	/* We've nothing to do if the relation is not partitioned. */
+	if (!IS_PARTITIONED_REL(rel))
+		return;
+
+	/* The relation should have consider_partitionwise_join set. */
+	Assert(rel->consider_partitionwise_join);
+
+	/* Guard against stack overflow due to overly deep partition hierarchy. */
+	check_stack_depth();
+
+	num_parts = rel->nparts;
+	part_rels = rel->part_rels;
+
+	/* Collect non-dummy child-joins. */
+	for (cnt_parts = 0; cnt_parts < num_parts; cnt_parts++)
+	{
+		RelOptInfo *child_rel = part_rels[cnt_parts];
+
+		/* If it's been pruned entirely, it's certainly dummy. */
+		if (child_rel == NULL)
+			continue;
+
+		/* Add partitionwise join paths for partitioned child-joins. */
+		generate_partitionwise_join_paths(root, child_rel);
+
+		set_cheapest(child_rel);
+
+		/* Dummy children will not be scanned, so ignore those. */
+		if (IS_DUMMY_REL(child_rel))
+			continue;
+
+#ifdef OPTIMIZER_DEBUG
+		debug_print_rel(root, child_rel);
+#endif
+
+		live_children = lappend(live_children, child_rel);
+	}
+
+	/* If all child-joins are dummy, parent join is also dummy. */
+	if (!live_children)
+	{
+		mark_dummy_rel(rel);
+		return;
+	}
+
+	/* Build additional paths for this rel from child-join paths. */
+	add_paths_to_append_rel(root, rel, live_children);
+	list_free(live_children);
+}
+
+
+/*****************************************************************************
+ *			DEBUG SUPPORT
+ *****************************************************************************/
+
+#ifdef OPTIMIZER_DEBUG
+
+static void
+print_relids(PlannerInfo *root, Relids relids)
+{
+	int			x;
+	bool		first = true;
+
+	x = -1;
+	while ((x = bms_next_member(relids, x)) >= 0)
+	{
+		if (!first)
+			printf(" ");
+		if (x < root->simple_rel_array_size &&
+			root->simple_rte_array[x])
+			printf("%s", root->simple_rte_array[x]->eref->aliasname);
+		else
+			printf("%d", x);
+		first = false;
+	}
+}
+
+static void
+print_restrictclauses(PlannerInfo *root, List *clauses)
+{
+	ListCell   *l;
+
+	foreach(l, clauses)
+	{
+		RestrictInfo *c = lfirst(l);
+
+		print_expr((Node *) c->clause, root->parse->rtable);
+		if (lnext(clauses, l))
+			printf(", ");
+	}
+}
+
+static void
+print_path(PlannerInfo *root, Path *path, int indent)
+{
+	const char *ptype;
+	bool		join = false;
+	Path	   *subpath = NULL;
+	int			i;
+
+	switch (nodeTag(path))
+	{
+		case T_Path:
+			switch (path->pathtype)
+			{
+				case T_SeqScan:
+					ptype = "SeqScan";
+					break;
+				case T_SampleScan:
+					ptype = "SampleScan";
+					break;
+				case T_FunctionScan:
+					ptype = "FunctionScan";
+					break;
+				case T_TableFuncScan:
+					ptype = "TableFuncScan";
+					break;
+				case T_ValuesScan:
+					ptype = "ValuesScan";
+					break;
+				case T_CteScan:
+					ptype = "CteScan";
+					break;
+				case T_NamedTuplestoreScan:
+					ptype = "NamedTuplestoreScan";
+					break;
+				case T_Result:
+					ptype = "Result";
+					break;
+				case T_WorkTableScan:
+					ptype = "WorkTableScan";
+					break;
+				default:
+					ptype = "???Path";
+					break;
+			}
+			break;
+		case T_IndexPath:
+			ptype = "IdxScan";
+			break;
+		case T_BitmapHeapPath:
+			ptype = "BitmapHeapScan";
+			break;
+		case T_BitmapAndPath:
+			ptype = "BitmapAndPath";
+			break;
+		case T_BitmapOrPath:
+			ptype = "BitmapOrPath";
+			break;
+		case T_TidPath:
+			ptype = "TidScan";
+			break;
+		case T_SubqueryScanPath:
+			ptype = "SubqueryScan";
+			break;
+		case T_ForeignPath:
+			ptype = "ForeignScan";
+			break;
+		case T_CustomPath:
+			ptype = "CustomScan";
+			break;
+		case T_NestPath:
+			ptype = "NestLoop";
+			join = true;
+			break;
+		case T_MergePath:
+			ptype = "MergeJoin";
+			join = true;
+			break;
+		case T_HashPath:
+			ptype = "HashJoin";
+			join = true;
+			break;
+		case T_AppendPath:
+			ptype = "Append";
+			break;
+		case T_MergeAppendPath:
+			ptype = "MergeAppend";
+			break;
+		case T_GroupResultPath:
+			ptype = "GroupResult";
+			break;
+		case T_MaterialPath:
+			ptype = "Material";
+			subpath = ((MaterialPath *) path)->subpath;
+			break;
+		case T_MemoizePath:
+			ptype = "Memoize";
+			subpath = ((MemoizePath *) path)->subpath;
+			break;
+		case T_UniquePath:
+			ptype = "Unique";
+			subpath = ((UniquePath *) path)->subpath;
+			break;
+		case T_GatherPath:
+			ptype = "Gather";
+			subpath = ((GatherPath *) path)->subpath;
+			break;
+		case T_GatherMergePath:
+			ptype = "GatherMerge";
+			subpath = ((GatherMergePath *) path)->subpath;
+			break;
+		case T_ProjectionPath:
+			ptype = "Projection";
+			subpath = ((ProjectionPath *) path)->subpath;
+			break;
+		case T_ProjectSetPath:
+			ptype = "ProjectSet";
+			subpath = ((ProjectSetPath *) path)->subpath;
+			break;
+		case T_SortPath:
+			ptype = "Sort";
+			subpath = ((SortPath *) path)->subpath;
+			break;
+		case T_IncrementalSortPath:
+			ptype = "IncrementalSort";
+			subpath = ((SortPath *) path)->subpath;
+			break;
+		case T_GroupPath:
+			ptype = "Group";
+			subpath = ((GroupPath *) path)->subpath;
+			break;
+		case T_UpperUniquePath:
+			ptype = "UpperUnique";
+			subpath = ((UpperUniquePath *) path)->subpath;
+			break;
+		case T_AggPath:
+			ptype = "Agg";
+			subpath = ((AggPath *) path)->subpath;
+			break;
+		case T_GroupingSetsPath:
+			ptype = "GroupingSets";
+			subpath = ((GroupingSetsPath *) path)->subpath;
+			break;
+		case T_MinMaxAggPath:
+			ptype = "MinMaxAgg";
+			break;
+		case T_WindowAggPath:
+			ptype = "WindowAgg";
+			subpath = ((WindowAggPath *) path)->subpath;
+			break;
+		case T_SetOpPath:
+			ptype = "SetOp";
+			subpath = ((SetOpPath *) path)->subpath;
+			break;
+		case T_RecursiveUnionPath:
+			ptype = "RecursiveUnion";
+			break;
+		case T_LockRowsPath:
+			ptype = "LockRows";
+			subpath = ((LockRowsPath *) path)->subpath;
+			break;
+		case T_ModifyTablePath:
+			ptype = "ModifyTable";
+			break;
+		case T_LimitPath:
+			ptype = "Limit";
+			subpath = ((LimitPath *) path)->subpath;
+			break;
+		default:
+			ptype = "???Path";
+			break;
+	}
+
+	for (i = 0; i < indent; i++)
+		printf("\t");
+	printf("%s", ptype);
+
+	if (path->parent)
+	{
+		printf("(");
+		print_relids(root, path->parent->relids);
+		printf(")");
+	}
+	if (path->param_info)
+	{
+		printf(" required_outer (");
+		print_relids(root, path->param_info->ppi_req_outer);
+		printf(")");
+	}
+	printf(" rows=%.0f cost=%.2f..%.2f\n",
+		   path->rows, path->startup_cost, path->total_cost);
+
+	if (path->pathkeys)
+	{
+		for (i = 0; i < indent; i++)
+			printf("\t");
+		printf("  pathkeys: ");
+		print_pathkeys(path->pathkeys, root->parse->rtable);
+	}
+
+	if (join)
+	{
+		JoinPath   *jp = (JoinPath *) path;
+
+		for (i = 0; i < indent; i++)
+			printf("\t");
+		printf("  clauses: ");
+		print_restrictclauses(root, jp->joinrestrictinfo);
+		printf("\n");
+
+		if (IsA(path, MergePath))
+		{
+			MergePath  *mp = (MergePath *) path;
+
+			for (i = 0; i < indent; i++)
+				printf("\t");
+			printf("  sortouter=%d sortinner=%d materializeinner=%d\n",
+				   ((mp->outersortkeys) ? 1 : 0),
+				   ((mp->innersortkeys) ? 1 : 0),
+				   ((mp->materialize_inner) ? 1 : 0));
+		}
+
+		print_path(root, jp->outerjoinpath, indent + 1);
+		print_path(root, jp->innerjoinpath, indent + 1);
+	}
+
+	if (subpath)
+		print_path(root, subpath, indent + 1);
+}
+
+void
+debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
+{
+	ListCell   *l;
+
+	printf("RELOPTINFO (");
+	print_relids(root, rel->relids);
+	printf("): rows=%.0f width=%d\n", rel->rows, rel->reltarget->width);
+
+	if (rel->baserestrictinfo)
+	{
+		printf("\tbaserestrictinfo: ");
+		print_restrictclauses(root, rel->baserestrictinfo);
+		printf("\n");
+	}
+
+	if (rel->joininfo)
+	{
+		printf("\tjoininfo: ");
+		print_restrictclauses(root, rel->joininfo);
+		printf("\n");
+	}
+
+	printf("\tpath list:\n");
+	foreach(l, rel->pathlist)
+		print_path(root, lfirst(l), 1);
+	if (rel->cheapest_parameterized_paths)
+	{
+		printf("\n\tcheapest parameterized paths:\n");
+		foreach(l, rel->cheapest_parameterized_paths)
+			print_path(root, lfirst(l), 1);
+	}
+	if (rel->cheapest_startup_path)
+	{
+		printf("\n\tcheapest startup path:\n");
+		print_path(root, rel->cheapest_startup_path, 1);
+	}
+	if (rel->cheapest_total_path)
+	{
+		printf("\n\tcheapest total path:\n");
+		print_path(root, rel->cheapest_total_path, 1);
+	}
+	printf("\n");
+	fflush(stdout);
+}
+
+#endif							/* OPTIMIZER_DEBUG */