/*-------------------------------------------------------------------------
 *
 * allpaths.c
 *	  Routines to find possible search paths for processing a query
 *
 * Portions Copyright (c) 1996-2025, 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"
#include "nodes/supportnodes.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/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/plancat.h"
#include "optimizer/planner.h"
#include "optimizer/tlist.h"
#include "parser/parse_clause.h"
#include "parser/parsetree.h"
#include "partitioning/partbounds.h"
#include "port/pg_bitutils.h"
#include "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"


/* Bitmask flags for pushdown_safety_info.unsafeFlags */
#define UNSAFE_HAS_VOLATILE_FUNC		(1 << 0)
#define UNSAFE_HAS_SET_FUNC				(1 << 1)
#define UNSAFE_NOTIN_DISTINCTON_CLAUSE	(1 << 2)
#define UNSAFE_NOTIN_PARTITIONBY_CLAUSE	(1 << 3)
#define UNSAFE_TYPE_MISMATCH			(1 << 4)

/* results of subquery_is_pushdown_safe */
typedef struct pushdown_safety_info
{
	unsigned char *unsafeFlags; /* bitmask of reasons why this target list
								 * column is unsafe for qual pushdown, or 0 if
								 * no reason. */
	bool		unsafeVolatile; /* don't push down volatile quals */
	bool		unsafeLeaky;	/* don't push down leaky quals */
} pushdown_safety_info;

/* Return type for qual_is_pushdown_safe */
typedef enum pushdown_safe_type
{
	PUSHDOWN_UNSAFE,			/* unsafe to push qual into subquery */
	PUSHDOWN_SAFE,				/* safe to push qual into subquery */
	PUSHDOWN_WINDOWCLAUSE_RUNCOND,	/* unsafe, but may work as WindowClause
									 * run condition */
} pushdown_safe_type;

/* 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 pushdown_safe_type 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,
										   Bitmapset *extra_used_attrs);


/*
 * 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;

	/* 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];

		/* there may be empty slots corresponding to non-baserel RTEs */
		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 + outer-join rels.
	 */
	Assert(bms_equal(rel->relids, root->all_query_rels));

	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, we postpone gathering until
	 * the final scan/join targetlist is available (see grouping_planner).
	 */
	if (rel->reloptkind == RELOPT_BASEREL &&
		!bms_equal(rel->relids, root->all_query_rels))
		generate_useful_gather_paths(root, rel, false);

	/* Now find the cheapest of the paths for this rel */
	set_cheapest(rel);

#ifdef OPTIMIZER_DEBUG
	pprint(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;
		case RTE_GROUP:
			/* Shouldn't happen; we're only considering baserels here. */
			Assert(false);
			return;
	}

	/*
	 * 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 TID scans.
	 *
	 * If create_tidscan_paths returns true, then a TID scan path is forced.
	 * This happens when rel->baserestrictinfo contains CurrentOfExpr, because
	 * the executor can't handle any other type of path for such queries.
	 * Hence, we return without adding any other paths.
	 */
	if (create_tidscan_paths(root, rel))
		return;

	/* 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);
}

/*
 * 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_query_rels (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_query_rels) != 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_tuples;
	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 &&
		bms_is_empty(rel->attr_needed[InvalidAttrNumber - rel->min_attr]))
		rel->consider_partitionwise_join = true;

	/*
	 * Initialize to compute size estimates for whole append relation.
	 *
	 * We handle tuples estimates by setting "tuples" to the total number of
	 * tuples accumulated from each live child, rather than using "rows".
	 * Although an appendrel itself doesn't directly enforce any quals, its
	 * child relations may.  Therefore, setting "tuples" equal to "rows" for
	 * an appendrel isn't always appropriate, and can lead to inaccurate cost
	 * estimates.  For example, when estimating the number of distinct values
	 * from an appendrel, we would be unable to adjust the estimate based on
	 * the restriction selectivity (see estimate_num_groups).
	 *
	 * 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_tuples = 0;
	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;
		List	   *childrinfos;
		ListCell   *parentvars;
		ListCell   *childvars;
		ListCell   *lc;

		/* 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.
		 *
		 * We skip join quals that came from above outer joins that can null
		 * this rel, since they would be of no value while generating paths
		 * for the child.  This saves some effort while processing the child
		 * rel, and it also avoids an implementation restriction in
		 * adjust_appendrel_attrs (it can't apply nullingrels to a non-Var).
		 */
		childrinfos = NIL;
		foreach(lc, rel->joininfo)
		{
			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);

			if (!bms_overlap(rinfo->clause_relids, rel->nulling_relids))
				childrinfos = lappend(childrinfos,
									  adjust_appendrel_attrs(root,
															 (Node *) rinfo,
															 1, &appinfo));
		}
		childrel->joininfo = childrinfos;

		/*
		 * Now for the child's targetlist.
		 *
		 * 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->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_tuples += childrel->tuples;
		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->tuples = parent_tuples;
		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);

		/*
		 * 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	   *startup_subpaths = NIL;
	bool		startup_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;

		/*
		 * When the planner is considering cheap startup plans, we'll also
		 * collect all the cheapest_startup_paths (if set) and build an
		 * AppendPath containing those as subpaths.
		 */
		if (rel->consider_startup && childrel->cheapest_startup_path != NULL)
		{
			Path	   *cheapest_path;

			/*
			 * With an indication of how many tuples the query should provide,
			 * the optimizer tries to choose the path optimal for that
			 * specific number of tuples.
			 */
			if (root->tuple_fraction > 0.0)
				cheapest_path =
					get_cheapest_fractional_path(childrel,
												 root->tuple_fraction);
			else
				cheapest_path = childrel->cheapest_startup_path;

			/* cheapest_startup_path must not be a parameterized path. */
			Assert(cheapest_path->param_info == NULL);
			accumulate_append_subpath(cheapest_path,
									  &startup_subpaths,
									  NULL);
		}
		else
			startup_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));

	/* build an AppendPath for the cheap startup paths, if valid */
	if (startup_subpaths_valid)
		add_path(rel, (Path *) create_append_path(root, rel, startup_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,
								   pg_leftmost_one_pos32(list_length(live_childrels)) + 1);
			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,
							   pg_leftmost_one_pos32(list_length(live_childrels)) + 1);
		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 the cheapest-startup and cheapest-total cases, and also the
 * cheapest-fractional case when not all tuples need to be retrieved.  For each
 * interesting ordering, we collect all the cheapest startup subpaths, all the
 * cheapest total paths, and, if applicable, all the cheapest fractional 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->live_parts))
	{
		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;
		List	   *fractional_subpaths = NIL;
		bool		startup_neq_total = false;
		bool		match_partition_order;
		bool		match_partition_order_desc;
		int			end_index;
		int			first_index;
		int			direction;

		/*
		 * 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)));

		/*
		 * When the required pathkeys match the reverse of the partition
		 * order, we must build the list of paths in reverse starting with the
		 * last matching partition first.  We can get away without making any
		 * special cases for this in the loop below by just looping backward
		 * over the child relations in this case.
		 */
		if (match_partition_order_desc)
		{
			/* loop backward */
			first_index = list_length(live_childrels) - 1;
			end_index = -1;
			direction = -1;

			/*
			 * Set this to true to save us having to check for
			 * match_partition_order_desc in the loop below.
			 */
			match_partition_order = true;
		}
		else
		{
			/* for all other case, loop forward */
			first_index = 0;
			end_index = list_length(live_childrels);
			direction = 1;
		}

		/* Select the child paths for this ordering... */
		for (int i = first_index; i != end_index; i += direction)
		{
			RelOptInfo *childrel = list_nth_node(RelOptInfo, live_childrels, i);
			Path	   *cheapest_startup,
					   *cheapest_total,
					   *cheapest_fractional = NULL;

			/* 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);
			}

			/*
			 * When building a fractional path, determine a cheapest
			 * fractional path for each child relation too. Looking at startup
			 * and total costs is not enough, because the cheapest fractional
			 * path may be dominated by two separate paths (one for startup,
			 * one for total).
			 *
			 * When needed (building fractional path), determine the cheapest
			 * fractional path too.
			 */
			if (root->tuple_fraction > 0)
			{
				double		path_fraction = root->tuple_fraction;

				/*
				 * We should not have a dummy child relation here.  However,
				 * we cannot use childrel->rows to compute the tuple fraction,
				 * as childrel can be an upper relation with an unset row
				 * estimate.  Instead, we use the row estimate from the
				 * cheapest_total path, which should already have been forced
				 * to a sane value.
				 */
				Assert(cheapest_total->rows > 0);

				/* Convert absolute limit to a path fraction */
				if (path_fraction >= 1.0)
					path_fraction /= cheapest_total->rows;

				cheapest_fractional =
					get_cheapest_fractional_path_for_pathkeys(childrel->pathlist,
															  pathkeys,
															  NULL,
															  path_fraction);

				/*
				 * If we found no path with matching pathkeys, use the
				 * cheapest total path instead.
				 *
				 * XXX We might consider partially sorted paths too (with an
				 * incremental sort on top). But we'd have to build all the
				 * incremental paths, do the costing etc.
				 */
				if (!cheapest_fractional)
					cheapest_fractional = cheapest_total;
			}

			/*
			 * 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);

				if (cheapest_fractional)
				{
					cheapest_fractional = get_singleton_append_subpath(cheapest_fractional);
					fractional_subpaths = lappend(fractional_subpaths, cheapest_fractional);
				}
			}
			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);

				if (cheapest_fractional)
					accumulate_append_subpath(cheapest_fractional,
											  &fractional_subpaths, NULL);
			}
		}

		/* ... and build the Append or MergeAppend paths */
		if (match_partition_order)
		{
			/* 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));

			if (fractional_subpaths)
				add_path(rel, (Path *) create_append_path(root,
														  rel,
														  fractional_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));

			if (fractional_subpaths)
				add_path(rel, (Path *) create_merge_append_path(root,
																rel,
																fractional_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_copy_head(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 in current usage
	 * because set_rel_pathlist will do it later, but it's cheap so we keep it
	 * for safety and consistency with mark_dummy_rel.
	 */
	set_cheapest(rel);
}

/*
 * find_window_run_conditions
 *		Determine if 'wfunc' is really a WindowFunc and call its prosupport
 *		function to determine the function's monotonic properties.  We then
 *		see if 'opexpr' can be used to short-circuit execution.
 *
 * For example row_number() over (order by ...) always produces a value one
 * higher than the previous.  If someone has a window function in a subquery
 * and has a WHERE clause in the outer query to filter rows <= 10, then we may
 * as well stop processing the windowagg once the row number reaches 11.  Here
 * we check if 'opexpr' might help us to stop doing needless extra processing
 * in WindowAgg nodes.
 *
 * '*keep_original' is set to true if the caller should also use 'opexpr' for
 * its original purpose.  This is set to false if the caller can assume that
 * the run condition will handle all of the required filtering.
 *
 * Returns true if 'opexpr' was found to be useful and was added to the
 * WindowFunc's runCondition.  We also set *keep_original accordingly and add
 * 'attno' to *run_cond_attrs offset by FirstLowInvalidHeapAttributeNumber.
 * If the 'opexpr' cannot be used then we set *keep_original to true and
 * return false.
 */
static bool
find_window_run_conditions(Query *subquery, RangeTblEntry *rte, Index rti,
						   AttrNumber attno, WindowFunc *wfunc, OpExpr *opexpr,
						   bool wfunc_left, bool *keep_original,
						   Bitmapset **run_cond_attrs)
{
	Oid			prosupport;
	Expr	   *otherexpr;
	SupportRequestWFuncMonotonic req;
	SupportRequestWFuncMonotonic *res;
	WindowClause *wclause;
	List	   *opinfos;
	OpExpr	   *runopexpr;
	Oid			runoperator;
	ListCell   *lc;

	*keep_original = true;

	while (IsA(wfunc, RelabelType))
		wfunc = (WindowFunc *) ((RelabelType *) wfunc)->arg;

	/* we can only work with window functions */
	if (!IsA(wfunc, WindowFunc))
		return false;

	/* can't use it if there are subplans in the WindowFunc */
	if (contain_subplans((Node *) wfunc))
		return false;

	prosupport = get_func_support(wfunc->winfnoid);

	/* Check if there's a support function for 'wfunc' */
	if (!OidIsValid(prosupport))
		return false;

	/* get the Expr from the other side of the OpExpr */
	if (wfunc_left)
		otherexpr = lsecond(opexpr->args);
	else
		otherexpr = linitial(opexpr->args);

	/*
	 * The value being compared must not change during the evaluation of the
	 * window partition.
	 */
	if (!is_pseudo_constant_clause((Node *) otherexpr))
		return false;

	/* find the window clause belonging to the window function */
	wclause = (WindowClause *) list_nth(subquery->windowClause,
										wfunc->winref - 1);

	req.type = T_SupportRequestWFuncMonotonic;
	req.window_func = wfunc;
	req.window_clause = wclause;

	/* call the support function */
	res = (SupportRequestWFuncMonotonic *)
		DatumGetPointer(OidFunctionCall1(prosupport,
										 PointerGetDatum(&req)));

	/*
	 * Nothing to do if the function is neither monotonically increasing nor
	 * monotonically decreasing.
	 */
	if (res == NULL || res->monotonic == MONOTONICFUNC_NONE)
		return false;

	runopexpr = NULL;
	runoperator = InvalidOid;
	opinfos = get_op_index_interpretation(opexpr->opno);

	foreach(lc, opinfos)
	{
		OpIndexInterpretation *opinfo = (OpIndexInterpretation *) lfirst(lc);
		CompareType cmptype = opinfo->cmptype;

		/* handle < / <= */
		if (cmptype == COMPARE_LT || cmptype == COMPARE_LE)
		{
			/*
			 * < / <= is supported for monotonically increasing functions in
			 * the form <wfunc> op <pseudoconst> and <pseudoconst> op <wfunc>
			 * for monotonically decreasing functions.
			 */
			if ((wfunc_left && (res->monotonic & MONOTONICFUNC_INCREASING)) ||
				(!wfunc_left && (res->monotonic & MONOTONICFUNC_DECREASING)))
			{
				*keep_original = false;
				runopexpr = opexpr;
				runoperator = opexpr->opno;
			}
			break;
		}
		/* handle > / >= */
		else if (cmptype == COMPARE_GT || cmptype == COMPARE_GE)
		{
			/*
			 * > / >= is supported for monotonically decreasing functions in
			 * the form <wfunc> op <pseudoconst> and <pseudoconst> op <wfunc>
			 * for monotonically increasing functions.
			 */
			if ((wfunc_left && (res->monotonic & MONOTONICFUNC_DECREASING)) ||
				(!wfunc_left && (res->monotonic & MONOTONICFUNC_INCREASING)))
			{
				*keep_original = false;
				runopexpr = opexpr;
				runoperator = opexpr->opno;
			}
			break;
		}
		/* handle = */
		else if (cmptype == COMPARE_EQ)
		{
			CompareType newcmptype;

			/*
			 * When both monotonically increasing and decreasing then the
			 * return value of the window function will be the same each time.
			 * We can simply use 'opexpr' as the run condition without
			 * modifying it.
			 */
			if ((res->monotonic & MONOTONICFUNC_BOTH) == MONOTONICFUNC_BOTH)
			{
				*keep_original = false;
				runopexpr = opexpr;
				runoperator = opexpr->opno;
				break;
			}

			/*
			 * When monotonically increasing we make a qual with <wfunc> <=
			 * <value> or <value> >= <wfunc> in order to filter out values
			 * which are above the value in the equality condition.  For
			 * monotonically decreasing functions we want to filter values
			 * below the value in the equality condition.
			 */
			if (res->monotonic & MONOTONICFUNC_INCREASING)
				newcmptype = wfunc_left ? COMPARE_LE : COMPARE_GE;
			else
				newcmptype = wfunc_left ? COMPARE_GE : COMPARE_LE;

			/* We must keep the original equality qual */
			*keep_original = true;
			runopexpr = opexpr;

			/* determine the operator to use for the WindowFuncRunCondition */
			runoperator = get_opfamily_member_for_cmptype(opinfo->opfamily_id,
														  opinfo->oplefttype,
														  opinfo->oprighttype,
														  newcmptype);
			break;
		}
	}

	if (runopexpr != NULL)
	{
		WindowFuncRunCondition *wfuncrc;

		wfuncrc = makeNode(WindowFuncRunCondition);
		wfuncrc->opno = runoperator;
		wfuncrc->inputcollid = runopexpr->inputcollid;
		wfuncrc->wfunc_left = wfunc_left;
		wfuncrc->arg = copyObject(otherexpr);

		wfunc->runCondition = lappend(wfunc->runCondition, wfuncrc);

		/* record that this attno was used in a run condition */
		*run_cond_attrs = bms_add_member(*run_cond_attrs,
										 attno - FirstLowInvalidHeapAttributeNumber);
		return true;
	}

	/* unsupported OpExpr */
	return false;
}

/*
 * check_and_push_window_quals
 *		Check if 'clause' is a qual that can be pushed into a WindowFunc
 *		as a 'runCondition' qual.  These, when present, allow some unnecessary
 *		work to be skipped during execution.
 *
 * 'run_cond_attrs' will be populated with all targetlist resnos of subquery
 * targets (offset by FirstLowInvalidHeapAttributeNumber) that we pushed
 * window quals for.
 *
 * Returns true if the caller still must keep the original qual or false if
 * the caller can safely ignore the original qual because the WindowAgg node
 * will use the runCondition to stop returning tuples.
 */
static bool
check_and_push_window_quals(Query *subquery, RangeTblEntry *rte, Index rti,
							Node *clause, Bitmapset **run_cond_attrs)
{
	OpExpr	   *opexpr = (OpExpr *) clause;
	bool		keep_original = true;
	Var		   *var1;
	Var		   *var2;

	/* We're only able to use OpExprs with 2 operands */
	if (!IsA(opexpr, OpExpr))
		return true;

	if (list_length(opexpr->args) != 2)
		return true;

	/*
	 * Currently, we restrict this optimization to strict OpExprs.  The reason
	 * for this is that during execution, once the runcondition becomes false,
	 * we stop evaluating WindowFuncs.  To avoid leaving around stale window
	 * function result values, we set them to NULL.  Having only strict
	 * OpExprs here ensures that we properly filter out the tuples with NULLs
	 * in the top-level WindowAgg.
	 */
	set_opfuncid(opexpr);
	if (!func_strict(opexpr->opfuncid))
		return true;

	/*
	 * Check for plain Vars that reference window functions in the subquery.
	 * If we find any, we'll ask find_window_run_conditions() if 'opexpr' can
	 * be used as part of the run condition.
	 */

	/* Check the left side of the OpExpr */
	var1 = linitial(opexpr->args);
	if (IsA(var1, Var) && var1->varattno > 0)
	{
		TargetEntry *tle = list_nth(subquery->targetList, var1->varattno - 1);
		WindowFunc *wfunc = (WindowFunc *) tle->expr;

		if (find_window_run_conditions(subquery, rte, rti, tle->resno, wfunc,
									   opexpr, true, &keep_original,
									   run_cond_attrs))
			return keep_original;
	}

	/* and check the right side */
	var2 = lsecond(opexpr->args);
	if (IsA(var2, Var) && var2->varattno > 0)
	{
		TargetEntry *tle = list_nth(subquery->targetList, var2->varattno - 1);
		WindowFunc *wfunc = (WindowFunc *) tle->expr;

		if (find_window_run_conditions(subquery, rte, rti, tle->resno, wfunc,
									   opexpr, false, &keep_original,
									   run_cond_attrs))
			return keep_original;
	}

	return true;
}

/*
 * 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;
	bool		trivial_pathtarget;
	Relids		required_outer;
	pushdown_safety_info safetyInfo;
	double		tuple_fraction;
	RelOptInfo *sub_final_rel;
	Bitmapset  *run_cond_attrs = NULL;
	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 the reasons why columns are unsafe to reference.
	 * These reasons are stored in the bits inside unsafeFlags[i] when we
	 * discover reasons that column i of the subquery is unsafe to be used in
	 * a pushed-down qual.
	 */
	memset(&safetyInfo, 0, sizeof(safetyInfo));
	safetyInfo.unsafeFlags = (unsigned char *)
		palloc0((list_length(subquery->targetList) + 1) * sizeof(unsigned char));

	/*
	 * 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);
			Node	   *clause = (Node *) rinfo->clause;

			if (rinfo->pseudoconstant)
			{
				upperrestrictlist = lappend(upperrestrictlist, rinfo);
				continue;
			}

			switch (qual_is_pushdown_safe(subquery, rti, rinfo, &safetyInfo))
			{
				case PUSHDOWN_SAFE:
					/* Push it down */
					subquery_push_qual(subquery, rte, rti, clause);
					break;

				case PUSHDOWN_WINDOWCLAUSE_RUNCOND:

					/*
					 * Since we can't push the qual down into the subquery,
					 * check if it happens to reference a window function.  If
					 * so then it might be useful to use for the WindowAgg's
					 * runCondition.
					 */
					if (!subquery->hasWindowFuncs ||
						check_and_push_window_quals(subquery, rte, rti, clause,
													&run_cond_attrs))
					{
						/*
						 * subquery has no window funcs or the clause is not a
						 * suitable window run condition qual or it is, but
						 * the original must also be kept in the upper query.
						 */
						upperrestrictlist = lappend(upperrestrictlist, rinfo);
					}
					break;

				case PUSHDOWN_UNSAFE:
					upperrestrictlist = lappend(upperrestrictlist, rinfo);
					break;
			}
		}
		rel->baserestrictinfo = upperrestrictlist;
		/* We don't bother recomputing baserestrict_min_security */
	}

	pfree(safetyInfo.unsafeFlags);

	/*
	 * The upper query might not use all the subquery's output columns; if
	 * not, we can simplify.  Pass the attributes that were pushed down into
	 * WindowAgg run conditions to ensure we don't accidentally think those
	 * are unused.
	 */
	remove_unused_subquery_outputs(subquery, rel, run_cond_attrs);

	/*
	 * 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 ||
		root->hasHavingQual ||
		parse->distinctClause ||
		parse->sortClause ||
		bms_membership(root->all_baserels) == BMS_MULTIPLE)
		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, NULL);

	/* 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);

	/*
	 * Also detect whether the reltarget is trivial, so that we can pass that
	 * info to cost_subqueryscan (rather than re-deriving it multiple times).
	 * It's trivial if it fetches all the subplan output columns in order.
	 */
	if (list_length(rel->reltarget->exprs) != list_length(subquery->targetList))
		trivial_pathtarget = false;
	else
	{
		trivial_pathtarget = true;
		foreach(lc, rel->reltarget->exprs)
		{
			Node	   *node = (Node *) lfirst(lc);
			Var		   *var;

			if (!IsA(node, Var))
			{
				trivial_pathtarget = false;
				break;
			}
			var = (Var *) node;
			if (var->varno != rti ||
				var->varattno != foreach_current_index(lc) + 1)
			{
				trivial_pathtarget = false;
				break;
			}
		}
	}

	/*
	 * 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,
										  trivial_pathtarget,
										  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,
													  trivial_pathtarget,
													  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,
												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)
{
	Path	   *ctepath;
	Plan	   *cteplan;
	PlannerInfo *cteroot;
	Index		levelsup;
	List	   *pathkeys;
	int			ndx;
	ListCell   *lc;
	int			plan_id;
	Relids		required_outer;

	/*
	 * Find the referenced CTE, and locate the path and 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);

	Assert(list_length(root->glob->subpaths) == list_length(root->glob->subplans));
	ctepath = (Path *) list_nth(root->glob->subpaths, plan_id - 1);
	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);

	/* Convert the ctepath's pathkeys to outer query's representation */
	pathkeys = convert_subquery_pathkeys(root,
										 rel,
										 ctepath->pathkeys,
										 cteplan->targetlist);

	/*
	 * 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, pathkeys, 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));
}

/*
 * 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));
}

/*
 * 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 or partially-distinct 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 = compute_gather_rows(cheapest_partial_path);
	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 = compute_gather_rows(subpath);
		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_copy_head(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 (full or incremental) on top of it,
			 * so we can continue here.
			 */
			if (is_sorted)
				continue;

			/*
			 * Try at least sorting the cheapest path and also try
			 * incrementally sorting any path which is partially sorted
			 * already (no need to deal with paths which have presorted keys
			 * when incremental sort is disabled unless it's the cheapest
			 * input path).
			 */
			if (subpath != cheapest_partial_path &&
				(presorted_keys == 0 || !enable_incremental_sort))
				continue;

			/*
			 * Consider regular sort for any path that's not presorted or if
			 * incremental sort is disabled.  We've no need to consider both
			 * sort and incremental sort on the same path.  We assume that
			 * incremental sort is always faster when there are presorted
			 * keys.
			 *
			 * 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 (presorted_keys == 0 || !enable_incremental_sort)
			{
				subpath = (Path *) create_sort_path(root,
													rel,
													subpath,
													useful_pathkeys,
													-1.0);
			}
			else
				subpath = (Path *) create_incremental_sort_path(root,
																rel,
																subpath,
																useful_pathkeys,
																presorted_keys,
																-1);
			rows = compute_gather_rows(subpath);
			path = create_gather_merge_path(root, rel,
											subpath,
											rel->reltarget,
											subpath->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's and
			 * its call to apply_scanjoin_target_to_paths).
			 */
			if (!bms_equal(rel->relids, root->all_query_rels))
				generate_useful_gather_paths(root, rel, false);

			/* Find and save the cheapest paths for this rel */
			set_cheapest(rel);

#ifdef OPTIMIZER_DEBUG
			pprint(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 the reason for that inside
 * safetyInfo->unsafeFlags[k], but we don't reject the subquery overall since
 * column k might not be referenced by some/all quals.  The unsafeFlags[]
 * 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 reasons why they're unsafe in unsafeFlags[].
	 * (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 flags in unsafeFlags[k] when we
 * see 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.).  Subquery columns marked as
 * unsafe for this reason can still have WindowClause run conditions pushed
 * down.
 */
static void
check_output_expressions(Query *subquery, pushdown_safety_info *safetyInfo)
{
	List	   *flattened_targetList = subquery->targetList;
	ListCell   *lc;

	/*
	 * We must be careful with grouping Vars and join alias Vars in the
	 * subquery's outputs, as they hide the underlying expressions.
	 *
	 * We need to expand grouping Vars to their underlying expressions (the
	 * grouping clauses) because the grouping expressions themselves might be
	 * volatile or set-returning.  However, we do not need to expand join
	 * alias Vars, as their underlying structure does not introduce volatile
	 * or set-returning functions at the current level.
	 *
	 * In neither case do we need to recursively examine the Vars contained in
	 * these underlying expressions.  Even if they reference outputs from
	 * lower-level subqueries (at any depth), those references are guaranteed
	 * not to expand to volatile or set-returning functions, because
	 * subqueries containing such functions in their targetlists are never
	 * pulled up.
	 */
	if (subquery->hasGroupRTE)
	{
		flattened_targetList = (List *)
			flatten_group_exprs(NULL, subquery, (Node *) subquery->targetList);
	}

	foreach(lc, flattened_targetList)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(lc);

		if (tle->resjunk)
			continue;			/* ignore resjunk columns */

		/* Functions returning sets are unsafe (point 1) */
		if (subquery->hasTargetSRFs &&
			(safetyInfo->unsafeFlags[tle->resno] &
			 UNSAFE_HAS_SET_FUNC) == 0 &&
			expression_returns_set((Node *) tle->expr))
		{
			safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_HAS_SET_FUNC;
			continue;
		}

		/* Volatile functions are unsafe (point 2) */
		if ((safetyInfo->unsafeFlags[tle->resno] &
			 UNSAFE_HAS_VOLATILE_FUNC) == 0 &&
			contain_volatile_functions((Node *) tle->expr))
		{
			safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_HAS_VOLATILE_FUNC;
			continue;
		}

		/* If subquery uses DISTINCT ON, check point 3 */
		if (subquery->hasDistinctOn &&
			(safetyInfo->unsafeFlags[tle->resno] &
			 UNSAFE_NOTIN_DISTINCTON_CLAUSE) == 0 &&
			!targetIsInSortList(tle, InvalidOid, subquery->distinctClause))
		{
			/* non-DISTINCT column, so mark it unsafe */
			safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_NOTIN_DISTINCTON_CLAUSE;
			continue;
		}

		/* If subquery uses window functions, check point 4 */
		if (subquery->hasWindowFuncs &&
			(safetyInfo->unsafeFlags[tle->resno] &
			 UNSAFE_NOTIN_DISTINCTON_CLAUSE) == 0 &&
			!targetIsInAllPartitionLists(tle, subquery))
		{
			/* not present in all PARTITION BY clauses, so mark it unsafe */
			safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_NOTIN_PARTITIONBY_CLAUSE;
			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.  We set the UNSAFE_TYPE_MISMATCH bit in
 * unsafeFlags[k] 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 is the pushdown_safety_info to set unsafeFlags[] for.
 */
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->unsafeFlags[tle->resno] |= UNSAFE_TYPE_MISMATCH;
		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 pushdown_safe_type
qual_is_pushdown_safe(Query *subquery, Index rti, RestrictInfo *rinfo,
					  pushdown_safety_info *safetyInfo)
{
	pushdown_safe_type safe = PUSHDOWN_SAFE;
	Node	   *qual = (Node *) rinfo->clause;
	List	   *vars;
	ListCell   *vl;

	/* Refuse subselects (point 1) */
	if (contain_subplans(qual))
		return PUSHDOWN_UNSAFE;

	/* Refuse volatile quals if we found they'd be unsafe (point 2) */
	if (safetyInfo->unsafeVolatile &&
		contain_volatile_functions((Node *) rinfo))
		return PUSHDOWN_UNSAFE;

	/* Refuse leaky quals if told to (point 3) */
	if (safetyInfo->unsafeLeaky &&
		contain_leaked_vars(qual))
		return PUSHDOWN_UNSAFE;

	/*
	 * 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.
	 *
	 * By omitting the relevant flags, this also gives us a cheap sanity check
	 * that no aggregates or window functions appear in the qual.  Those would
	 * be unsafe to push down, but at least for the moment we could never see
	 * any in a qual anyhow.
	 */
	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 = PUSHDOWN_UNSAFE;
			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 = PUSHDOWN_UNSAFE;
			break;
		}

		/* Subqueries have no system columns */
		Assert(var->varattno >= 0);

		/* Check point 4 */
		if (var->varattno == 0)
		{
			safe = PUSHDOWN_UNSAFE;
			break;
		}

		/* Check point 5 */
		if (safetyInfo->unsafeFlags[var->varattno] != 0)
		{
			if (safetyInfo->unsafeFlags[var->varattno] &
				(UNSAFE_HAS_VOLATILE_FUNC | UNSAFE_HAS_SET_FUNC |
				 UNSAFE_NOTIN_DISTINCTON_CLAUSE | UNSAFE_TYPE_MISMATCH))
			{
				safe = PUSHDOWN_UNSAFE;
				break;
			}
			else
			{
				/* UNSAFE_NOTIN_PARTITIONBY_CLAUSE is ok for run conditions */
				safe = PUSHDOWN_WINDOWCLAUSE_RUNCOND;
				/* don't break, we might find another Var that's unsafe */
			}
		}
	}

	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,
										 subquery->resultRelation,
										 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.
 *
 * extra_used_attrs can be passed as non-NULL to mark any columns (offset by
 * FirstLowInvalidHeapAttributeNumber) that we should not remove.  This
 * parameter is modified by the function, so callers must make a copy if they
 * need to use the passed in Bitmapset after calling this function.
 *
 * 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 *extra_used_attrs)
{
	Bitmapset  *attrs_used;
	ListCell   *lc;

	/*
	 * Just point directly to extra_used_attrs. No need to bms_copy as none of
	 * the current callers use the Bitmapset after calling this function.
	 */
	attrs_used = extra_used_attrs;

	/*
	 * 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;

		/* Make partitionwise join paths for this partitioned child-join. */
		generate_partitionwise_join_paths(root, child_rel);

		/* If we failed to make any path for this child, we must give up. */
		if (child_rel->pathlist == NIL)
		{
			/*
			 * Mark the parent joinrel as unpartitioned so that later
			 * functions treat it correctly.
			 */
			rel->nparts = 0;
			return;
		}

		/* Else, identify the cheapest path for it. */
		set_cheapest(child_rel);

		/* Dummy children need not be scanned, so ignore those. */
		if (IS_DUMMY_REL(child_rel))
			continue;

#ifdef OPTIMIZER_DEBUG
		pprint(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);
}
