text: /*-------------------------------------------------------------------------
   *
   * relation.h
   *	  Definitions for planner's internal data structures.
   *
   *
   * Portions Copyright (c) 2005-2010, Greenplum inc
   * Portions Copyright (c) 2012-Present Pivotal Software, Inc.
   * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/nodes/relation.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef RELATION_H
  #define RELATION_H
  
  #include "access/sdir.h"
  #include "lib/stringinfo.h"
  #include "nodes/params.h"
  #include "nodes/parsenodes.h"
  #include "nodes/plannodes.h"
  #include "nodes/primnodes.h"
  #include "storage/block.h"
  #include "nodes/plannerconfig.h"
  #include "cdb/cdbpathlocus.h"
  #include "foreign/foreign.h"
  
  
  /*
   * Relids
   *		Set of relation identifiers (indexes into the rangetable).
   */
  typedef Bitmapset *Relids;
  
  /*
   * Estimated costs
   */
  typedef double EstimatedBytes;  /* an estimated number of bytes */
  
  /*
   * When looking for a "cheapest path", this enum specifies whether we want
   * cheapest startup cost or cheapest total cost.
   */
  typedef enum CostSelector
  {
  	STARTUP_COST, TOTAL_COST
  } CostSelector;
  
  /*
   * The cost estimate produced by cost_qual_eval() includes both a one-time
   * (startup) cost, and a per-tuple cost.
   */
  typedef struct QualCost
  {
  	Cost		startup;		/* one-time cost */
  	Cost		per_tuple;		/* per-evaluation cost */
  } QualCost;
  
  /*
   * Costing aggregate function execution requires these statistics about
   * the aggregates to be executed by a given Agg node.  Note that the costs
   * include the execution costs of the aggregates' argument expressions as
   * well as the aggregate functions themselves.  Also, the fields must be
   * defined so that initializing the struct to zeroes with memset is correct.
   */
  typedef struct AggClauseCosts
  {
  	int			numAggs;		/* total number of aggregate functions */
  	int			numOrderedAggs; /* number w/ DISTINCT/ORDER BY/WITHIN GROUP */
  	int			numPureOrderedAggs; /* CDB: number that use ORDER BY/WITHIN GROUP, not counting DISTINCT */
  	bool		hasNonCombine;	/* CDB: any agg func w/o a combine func? */
  	bool		hasNonPartial;	/* does any agg not support partial mode? */
  	bool		hasNonSerial;	/* is any partial agg non-serializable? */
  	QualCost	transCost;		/* total per-input-row execution costs */
  	Cost		finalCost;		/* total per-aggregated-row costs */
  	Size		transitionSpace;	/* space for pass-by-ref transition data */
  
  	List	   *distinctAggrefs;	/* CDB: List of Aggrfefs with aggdistinct */
  } AggClauseCosts;
  
  /*
   * This enum identifies the different types of "upper" (post-scan/join)
   * relations that we might deal with during planning.
   */
  typedef enum UpperRelationKind
  {
  	UPPERREL_SETOP,				/* result of UNION/INTERSECT/EXCEPT, if any */
  	UPPERREL_GROUP_AGG,			/* result of grouping/aggregation, if any */
  	UPPERREL_WINDOW,			/* result of window functions, if any */
  	UPPERREL_DISTINCT,			/* result of "SELECT DISTINCT", if any */
  	UPPERREL_ORDERED,			/* result of ORDER BY, if any */
  	UPPERREL_FINAL				/* result of any remaining top-level actions */
  	/* NB: UPPERREL_FINAL must be last enum entry; it's used to size arrays */
  } UpperRelationKind;
  
  
  /*
   * Context for apply shareinput processing during planning.  We could fold
   * this into PlannerGlobal, but this encapsulates it nicely.
   */
  typedef struct ApplyShareInputContext
  {
  	List	   *curr_rtable;
  	int		   *share_refcounts;
  	int			share_refcounts_sz;		/* allocated sized of 'share_refcounts' */
  	List *motStack;
  	List *qdShares;
  
  	ShareInputScan **producers;
  	int		   *sliceMarks;			/* one for each producer */
  	int			producer_count;
  
  	PlanSlice  *slices;
  
  } ApplyShareInputContext;
  
  /*----------
   * PlannerGlobal
   *		Global information for planning/optimization
   *
   * PlannerGlobal holds state for an entire planner invocation; this state
   * is shared across all levels of sub-Queries that exist in the command being
   * planned.
   *----------
   */
  typedef struct PlannerGlobal
  {
  	NodeTag		type;
  
  	ParamListInfo boundParams;	/* Param values provided to planner() */
  
  	List	   *subplans;		/* Plans for SubPlan nodes */
  
  	List	   *subroots;		/* PlannerInfos for SubPlan nodes */
  
  	int		   *subplan_sliceIds;	/* slice IDs for SubPlan nodes. */
  
  	Bitmapset  *rewindPlanIDs;	/* indices of subplans that require REWIND */
  
  	List	   *finalrtable;	/* "flat" rangetable for executor */
  
  	List	   *finalrowmarks;	/* "flat" list of PlanRowMarks */
  
  	List	   *resultRelations;	/* "flat" list of integer RT indexes */
  
  	List	   *relationOids;	/* OIDs of relations the plan depends on */
  
  	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
  
  	int			nParamExec;		/* number of PARAM_EXEC Params used */
  
  	Index		lastPHId;		/* highest PlaceHolderVar ID assigned */
  
  	Index		lastRowMarkId;	/* highest PlanRowMark ID assigned */
  
  	int			lastPlanNodeId; /* highest plan node ID assigned */
  
  	bool		transientPlan;	/* redo plan when TransactionXmin changes? */
  	bool		oneoffPlan;		/* redo plan on every execution? */
  	bool		simplyUpdatable; /* can be used with CURRENT OF? */
  
  	ApplyShareInputContext share;	/* workspace for GPDB plan sharing */
  
  	bool		dependsOnRole;	/* is plan specific to current role? */
  
  	bool		parallelModeOK; /* parallel mode potentially OK? */
  
  	bool		parallelModeNeeded;		/* parallel mode actually required? */
  
  	/*
  	 * Slice table. Built by cdbllize_build_slice_table() near the end of
  	 * planning, and copied to the final PlannedStmt.
  	 */
  	int			numSlices;
  	struct PlanSlice *slices;
  
  } PlannerGlobal;
  
  /*----------
   * PlannerInfo
   *		Per-query information for planning/optimization
   *
   * This struct is conventionally called "root" in all the planner routines.
   * It holds links to all of the planner's working state, in addition to the
   * original Query.  Note that at present the planner extensively modifies
   * the passed-in Query data structure; someday that should stop.
   *----------
   */
  typedef struct PlannerInfo
  {
  	NodeTag		type;
  
  	Query	   *parse;			/* the Query being planned */
  
  	PlannerGlobal *glob;		/* global info for current planner run */
  
  	Index		query_level;	/* 1 at the outermost Query */
  
  	struct PlannerInfo *parent_root;	/* NULL at outermost Query */
  
  	/*
  	 * plan_params contains the expressions that this query level needs to
  	 * make available to a lower query level that is currently being planned.
  	 * outer_params contains the paramIds of PARAM_EXEC Params that outer
  	 * query levels will make available to this query level.
  	 */
  	List	   *plan_params;	/* list of PlannerParamItems, see below */
  	Bitmapset  *outer_params;
  
  	/*
  	 * simple_rel_array holds pointers to "base rels" and "other rels" (see
  	 * comments for RelOptInfo for more info).  It is indexed by rangetable
  	 * index (so entry 0 is always wasted).  Entries can be NULL when an RTE
  	 * does not correspond to a base relation, such as a join RTE or an
  	 * unreferenced view RTE; or if the RelOptInfo hasn't been made yet.
  	 */
  	struct RelOptInfo **simple_rel_array;		/* All 1-rel RelOptInfos */
  	int			simple_rel_array_size;	/* allocated size of array */
  
  	/*
  	 * simple_rte_array is the same length as simple_rel_array and holds
  	 * pointers to the associated rangetable entries.  This lets us avoid
  	 * rt_fetch(), which can be a bit slow once large inheritance sets have
  	 * been expanded.
  	 */
  	RangeTblEntry **simple_rte_array;	/* rangetable as an array */
  
  	/*
  	 * all_baserels is a Relids set of all base relids (but not "other"
  	 * relids) in the query; that is, the Relids identifier of the final join
  	 * we need to form.  This is computed in make_one_rel, just before we
  	 * start making Paths.
  	 */
  	Relids		all_baserels;
  
  	/*
  	 * nullable_baserels is a Relids set of base relids that are nullable by
  	 * some outer join in the jointree; these are rels that are potentially
  	 * nullable below the WHERE clause, SELECT targetlist, etc.  This is
  	 * computed in deconstruct_jointree.
  	 */
  	Relids		nullable_baserels;
  
  	/*
  	 * join_rel_list is a list of all join-relation RelOptInfos we have
  	 * considered in this planning run.  For small problems we just scan the
  	 * list to do lookups, but when there are many join relations we build a
  	 * hash table for faster lookups.  The hash table is present and valid
  	 * when join_rel_hash is not NULL.  Note that we still maintain the list
  	 * even when using the hash table for lookups; this simplifies life for
  	 * GEQO.
  	 */
  	List	   *join_rel_list;	/* list of join-relation RelOptInfos */
  	struct HTAB *join_rel_hash; /* optional hashtable for join relations */
  
  	/*
  	 * When doing a dynamic-programming-style join search, join_rel_level[k]
  	 * is a list of all join-relation RelOptInfos of level k, and
  	 * join_cur_level is the current level.  New join-relation RelOptInfos are
  	 * automatically added to the join_rel_level[join_cur_level] list.
  	 * join_rel_level is NULL if not in use.
  	 */
  	List	  **join_rel_level; /* lists of join-relation RelOptInfos */
  	int			join_cur_level; /* index of list being extended */
  
  	List	   *init_plans;		/* init SubPlans for query */
  
  	List	   *cte_plan_ids;	/* per-CTE-item list of subplan IDs */
  
  	List	   *multiexpr_params;		/* List of Lists of Params for
  										 * MULTIEXPR subquery outputs */
  
  	List	   *eq_classes;		/* list of active EquivalenceClasses */
  
  	List	   *non_eq_clauses;	/* list of non-equivalence clauses */
  
  	List	   *canon_pathkeys; /* list of "canonical" PathKeys */
  
  	PartitionNode *result_partitions;
  	List	   *result_aosegnos;
  
  	List       *list_cteplaninfo; /* list of CtePlannerInfo, one for each CTE */
  
  	/*
  	 * Outer join info
  	 */
  	List	   *left_join_clauses;		/* list of RestrictInfos for
  										 * mergejoinable outer join clauses
  										 * w/nonnullable var on left */
  
  	List	   *right_join_clauses;		/* list of RestrictInfos for
  										 * mergejoinable outer join clauses
  										 * w/nonnullable var on right */
  
  	List	   *full_join_clauses;		/* list of RestrictInfos for
  										 * mergejoinable full join clauses */
  
  	List	   *join_info_list; /* list of SpecialJoinInfos */
  
  	List	   *append_rel_list;	/* list of AppendRelInfos */
  
  	List	   *rowMarks;		/* list of PlanRowMarks */
  
  	List	   *placeholder_list;		/* list of PlaceHolderInfos */
  
  	List	   *fkey_list;		/* list of ForeignKeyOptInfos */
  
  	List	   *query_pathkeys; /* desired pathkeys for query_planner() */
  
  	List	   *group_pathkeys; /* groupClause pathkeys, if any */
  	List	   *window_pathkeys;	/* pathkeys of bottom window, if any */
  	List	   *distinct_pathkeys;		/* distinctClause pathkeys, if any */
  	List	   *sort_pathkeys;	/* sortClause pathkeys, if any */
  
  	List	   *initial_rels;	/* RelOptInfos we are now trying to join */
  
  	/* Use fetch_upper_rel() to get any particular upper rel */
  	List	   *upper_rels[UPPERREL_FINAL + 1]; /* upper-rel RelOptInfos */
  
  	/* Result tlists chosen by grouping_planner for upper-stage processing */
  	struct PathTarget *upper_targets[UPPERREL_FINAL + 1];
  
  	/*
  	 * grouping_planner passes back its final processed targetlist here, for
  	 * use in relabeling the topmost tlist of the finished Plan.
  	 */
  	List	   *processed_tlist;
  
  	/* Fields filled during create_plan() for use in setrefs.c */
  	AttrNumber *grouping_map;	/* for GroupingFunc fixup */
  	int			grouping_map_size;
  	List	   *minmax_aggs;	/* List of MinMaxAggInfos */
  
  	MemoryContext planner_cxt;	/* context holding PlannerInfo */
  
  	double		total_table_pages;		/* # of pages in all tables of query */
  
  	double		tuple_fraction; /* tuple_fraction passed to query_planner */
  	double		limit_tuples;	/* limit_tuples passed to query_planner */
  
  	bool		hasInheritedTarget;		/* true if parse->resultRelation is an
  										 * inheritance child rel */
  	bool		hasJoinRTEs;	/* true if any RTEs are RTE_JOIN kind */
  	bool		hasLateralRTEs; /* true if any RTEs are marked LATERAL */
  	bool		hasDeletedRTEs; /* true if any RTE was deleted from jointree */
  	bool		hasHavingQual;	/* true if havingQual was non-null */
  	bool		hasPseudoConstantQuals; /* true if any RestrictInfo has
  										 * pseudoconstant = true */
  	bool		hasRecursion;	/* true if planning a recursive WITH item */
  
  	/* These fields are used only when hasRecursion is true: */
  	int			wt_param_id;	/* PARAM_EXEC ID for the work table */
  	struct Path *non_recursive_path;	/* a path for non-recursive term */
  
  	/* These fields are workspace for createplan.c */
  	Relids		curOuterRels;	/* outer rels above current node */
  	List	   *curOuterParams; /* not-yet-assigned NestLoopParams */
  	int			numMotions;
  
  	PlanSlice  *curSlice;
  
  	PlannerConfig *config;		/* Planner configuration */
  
  	List	   *dynamicScans;	/* DynamicScanInfos */
  
  	/* optional private data for join_search_hook, e.g., GEQO */
  	void	   *join_search_private;
  
  	int			upd_del_replicated_table;
  	bool		is_split_update;	/* true if UPDATE that modifies
  									 * distribution key columns */
  	bool		is_correlated_subplan; /* true for correlated subqueries nested within subplans */
  } PlannerInfo;
  
  /*
   * CtePlanInfo
   *    Information for subplans that are associated with a CTE.
   */
  typedef struct CtePlanInfo
  {
  	/*
  	 * A subplan, prepared for sharing among many CTE references by
  	 * prepare_plan_for_sharing(), that implements the CTE. NULL if the
  	 * CTE is not shared among references.
  	 */
  	Plan *shared_plan;
  
  	/*
  	 * The subroot corresponding to the subplan.
  	 */
  	PlannerInfo *subroot;
  } CtePlanInfo;
  
  /*----------
   * DynamicScanInfo
   *		Information about scans on partitioned tables.
   *
   * Scans on partitioned tables are expanded into Append paths early
   * in the planning. For each such expansion, we create a DynamicScanInfo
   * struct.
   *----------
   */
  typedef struct
  {
  	/*
  	 * The scans are numbered, so that a Partition Selector can
  	 * refer to the scan.
  	 */
  	int			dynamicScanId;
  
  	/* Parent relation this is for */
  	int			rtindex;
  	Oid			parentOid;
  
  	/* RTindexes of the leaf relations */
  	Relids		children;
  
  	/* Partitioning key information */
  	List	   *partKeyAttnos;
  
  	/* Set to true, if a PartitionSelector has been created for this scan */
  	bool		hasSelector;
  } DynamicScanInfo;
  
  /*
   * In places where it's known that simple_rte_array[] must have been prepared
   * already, we just index into it to fetch RTEs.  In code that might be
   * executed before or after entering query_planner(), use this macro.
   */
  #define planner_rt_fetch(rti, root) \
  	((root)->simple_rte_array ? (root)->simple_rte_array[rti] : \
  	 rt_fetch(rti, (root)->parse->rtable))
  
  
  /*
   * Fetch the Plan associated with a SubPlan node during planning.
   */
  static inline struct Plan *planner_subplan_get_plan(struct PlannerInfo *root, SubPlan *subplan) 
  {
  	return (Plan *) list_nth(root->glob->subplans, subplan->plan_id - 1);
  }
  
  /**
   * Fetch the root (PlannerInfo) for a subplan
   */
  static inline struct PlannerInfo *planner_subplan_get_root(struct PlannerInfo *root, SubPlan *subplan)
  {
  	return (PlannerInfo *) list_nth(root->glob->subroots, subplan->plan_id - 1);
  }
  
  /*
   * Rewrite the Plan associated with a SubPlan node during planning.
   */
  static inline void planner_subplan_put_plan(struct PlannerInfo *root, SubPlan *subplan, Plan *plan) 
  {
  	ListCell *cell = list_nth_cell(root->glob->subplans, subplan->plan_id-1);
  	cell->data.ptr_value = plan;
  }
  
  /*----------
   * RelOptInfo
   *		Per-relation information for planning/optimization
   *
   * For planning purposes, a "base rel" is either a plain relation (a table)
   * or the output of a sub-SELECT or function that appears in the range table.
   * In either case it is uniquely identified by an RT index.  A "joinrel"
   * is the joining of two or more base rels.  A joinrel is identified by
   * the set of RT indexes for its component baserels.  We create RelOptInfo
   * nodes for each baserel and joinrel, and store them in the PlannerInfo's
   * simple_rel_array and join_rel_list respectively.
   *
   * Note that there is only one joinrel for any given set of component
   * baserels, no matter what order we assemble them in; so an unordered
   * set is the right datatype to identify it with.
   *
   * We also have "other rels", which are like base rels in that they refer to
   * single RT indexes; but they are not part of the join tree, and are given
   * a different RelOptKind to identify them.
   * Currently the only kind of otherrels are those made for member relations
   * of an "append relation", that is an inheritance set or UNION ALL subquery.
   * An append relation has a parent RTE that is a base rel, which represents
   * the entire append relation.  The member RTEs are otherrels.  The parent
   * is present in the query join tree but the members are not.  The member
   * RTEs and otherrels are used to plan the scans of the individual tables or
   * subqueries of the append set; then the parent baserel is given Append
   * and/or MergeAppend paths comprising the best paths for the individual
   * member rels.  (See comments for AppendRelInfo for more information.)
   *
   * At one time we also made otherrels to represent join RTEs, for use in
   * handling join alias Vars.  Currently this is not needed because all join
   * alias Vars are expanded to non-aliased form during preprocess_expression.
   *
   * There is also a RelOptKind for "upper" relations, which are RelOptInfos
   * that describe post-scan/join processing steps, such as aggregation.
   * Many of the fields in these RelOptInfos are meaningless, but their Path
   * fields always hold Paths showing ways to do that processing step.
   *
   * Lastly, there is a RelOptKind for "dead" relations, which are base rels
   * that we have proven we don't need to join after all.
   *
   * Parts of this data structure are specific to various scan and join
   * mechanisms.  It didn't seem worth creating new node types for them.
   *
   *		relids - Set of base-relation identifiers; it is a base relation
   *				if there is just one, a join relation if more than one
   *		rows - estimated number of tuples in the relation after restriction
   *			   clauses have been applied (ie, output rows of a plan for it)
   *		consider_startup - true if there is any value in keeping plain paths for
   *						   this rel on the basis of having cheap startup cost
   *		consider_param_startup - the same for parameterized paths
   *		reltarget - Default Path output tlist for this rel; normally contains
   *					Var and PlaceHolderVar nodes for the values we need to
   *					output from this relation.
   *					List is in no particular order, but all rels of an
   *					appendrel set must use corresponding orders.
   *					NOTE: in an appendrel child relation, may contain
   *					arbitrary expressions pulled up from a subquery!
   *		pathlist - List of Path nodes, one for each potentially useful
   *				   method of generating the relation
   *		ppilist - ParamPathInfo nodes for parameterized Paths, if any
   *		cheapest_startup_path - the pathlist member with lowest startup cost
   *			(regardless of ordering) among the unparameterized paths;
   *			or NULL if there is no unparameterized path
   *		cheapest_total_path - the pathlist member with lowest total cost
   *			(regardless of ordering) among the unparameterized paths;
   *			or if there is no unparameterized path, the path with lowest
   *			total cost among the paths with minimum parameterization
   *		cheapest_unique_path - for caching cheapest path to produce unique
   *			(no duplicates) output from relation; NULL if not yet requested
   *		cheapest_parameterized_paths - best paths for their parameterizations;
   *			always includes cheapest_total_path, even if that's unparameterized
   *		direct_lateral_relids - rels this rel has direct LATERAL references to
   *		lateral_relids - required outer rels for LATERAL, as a Relids set
   *			(includes both direct and indirect lateral references)
   *
   * If the relation is a base relation it will have these fields set:
   *
   *		relid - RTE index (this is redundant with the relids field, but
   *				is provided for convenience of access)
   *		rtekind - distinguishes plain relation, subquery, or function RTE
   *		min_attr, max_attr - range of valid AttrNumbers for rel
   *		attr_needed - array of bitmapsets indicating the highest joinrel
   *				in which each attribute is needed; if bit 0 is set then
   *				the attribute is needed as part of final targetlist
   *		attr_widths - cache space for per-attribute width estimates;
   *					  zero means not computed yet
   *		lateral_vars - lateral cross-references of rel, if any (list of
   *					   Vars and PlaceHolderVars)
   *		lateral_referencers - relids of rels that reference this one laterally
   *				(includes both direct and indirect lateral references)
   *		indexlist - list of IndexOptInfo nodes for relation's indexes
   *					(always NIL if it's not a table)
   *		pages - number of disk pages in relation (zero if not a table)
   *		tuples - number of tuples in relation (not considering restrictions)
   *		allvisfrac - fraction of disk pages that are marked all-visible
   *		subroot - PlannerInfo for subquery (NULL if it's not a subquery)
   *		subplan_params - list of PlannerParamItems to be passed to subquery
   *
   *		Note: for a subquery, tuples and subroot are not set immediately
   *		upon creation of the RelOptInfo object; they are filled in when
   *		set_subquery_pathlist processes the object.
   *
   *		For otherrels that are appendrel members, these fields are filled
   *		in just as for a baserel, except we don't bother with lateral_vars.
   *
   * If the relation is either a foreign table or a join of foreign tables that
   * all belong to the same foreign server and are assigned to the same user to
   * check access permissions as (cf checkAsUser), these fields will be set:
   *
   *		serverid - OID of foreign server, if foreign table (else InvalidOid)
   *		userid - OID of user to check access as (InvalidOid means current user)
   *		useridiscurrent - we've assumed that userid equals current user
   *		fdwroutine - function hooks for FDW, if foreign table (else NULL)
   *		fdw_private - private state for FDW, if foreign table (else NULL)
   *
   * The presence of the remaining fields depends on the restrictions
   * and joins that the relation participates in:
   *
   *		baserestrictinfo - List of RestrictInfo nodes, containing info about
   *					each non-join qualification clause in which this relation
   *					participates (only used for base rels)
   *		baserestrictcost - Estimated cost of evaluating the baserestrictinfo
   *					clauses at a single tuple (only used for base rels)
   *		joininfo  - List of RestrictInfo nodes, containing info about each
   *					join clause in which this relation participates (but
   *					note this excludes clauses that might be derivable from
   *					EquivalenceClasses)
   *		has_eclass_joins - flag that EquivalenceClass joins are possible
   *
   * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for
   * base rels, because for a join rel the set of clauses that are treated as
   * restrict clauses varies depending on which sub-relations we choose to join.
   * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be
   * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but
   * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2}
   * and should not be processed again at the level of {1 2 3}.)	Therefore,
   * the restrictinfo list in the join case appears in individual JoinPaths
   * (field joinrestrictinfo), not in the parent relation.  But it's OK for
   * the RelOptInfo to store the joininfo list, because that is the same
   * for a given rel no matter how we form it.
   *
   * We store baserestrictcost in the RelOptInfo (for base relations) because
   * we know we will need it at least once (to price the sequential scan)
   * and may need it multiple times to price index scans.
   *----------
   */
  typedef enum RelOptKind
  {
  	RELOPT_BASEREL,
  	RELOPT_JOINREL,
  	RELOPT_OTHER_MEMBER_REL,
  	RELOPT_UPPER_REL,
  	RELOPT_DEADREL
  } RelOptKind;
  
  typedef struct RelOptInfo
  {
  	NodeTag		type;
  
  	RelOptKind	reloptkind;
  
  	/* all relations included in this RelOptInfo */
  	Relids		relids;			/* set of base relids (rangetable indexes) */
  
  	/* size estimates generated by planner */
  	double		rows;			/* estimated number of result tuples */
  	bool		onerow;			/* true => rel is inherently 1 row or empty */
  
  	/* per-relation planner control flags */
  	bool		consider_startup;		/* keep cheap-startup-cost paths? */
  	bool		consider_param_startup; /* ditto, for parameterized paths? */
  	bool		consider_parallel;		/* consider parallel paths? */
  
  	/* default result targetlist for Paths scanning this relation */
  	struct PathTarget *reltarget;		/* list of Vars/Exprs, cost, width */
  
  	/* materialization information */
  	List	   *pathlist;		/* Path structures */
  	List	   *ppilist;		/* ParamPathInfos used in pathlist */
  	List	   *partial_pathlist;		/* partial Paths */
  	struct Path *cheapest_startup_path;
  	struct Path *cheapest_total_path;
  	struct Path *cheapest_unique_path;
  	List	   *cheapest_parameterized_paths;
  
  	/* parameterization information needed for both base rels and join rels */
  	/* (see also lateral_vars and lateral_referencers) */
  	Relids		direct_lateral_relids;	/* rels directly laterally referenced */
  	Relids		lateral_relids; /* minimum parameterization of rel */
  
  	/* information about a base rel (not set for join rels!) */
  	Index		relid;
  	Oid			reltablespace;	/* containing tablespace */
  	RTEKind		rtekind;		/* RELATION, SUBQUERY, or FUNCTION */
  	AttrNumber	min_attr;		/* smallest attrno of rel (often <0) */
  	AttrNumber	max_attr;		/* largest attrno of rel */
  	Relids	   *attr_needed;	/* array indexed [min_attr .. max_attr] */
  	int32	   *attr_widths;	/* array indexed [min_attr .. max_attr] */
  	List	   *lateral_vars;	/* LATERAL Vars and PHVs referenced by rel */
  	Relids		lateral_referencers;	/* rels that reference me laterally */
  	List	   *indexlist;		/* list of IndexOptInfo */
  	BlockNumber pages;			/* size estimates derived from pg_class */
  	double		tuples;
      struct GpPolicy   *cdbpolicy;      /* distribution of stored tuples */
  	char		relstorage;		/* from pg_class.relstorage */
  	double		allvisfrac;
  	PlannerInfo *subroot;		/* if subquery (in GPDB: or CTE) */
  	List	   *subplan_params; /* if subquery */
  	int			rel_parallel_workers;	/* wanted number of parallel workers */
  
  	/* Information about foreign tables and foreign joins */
  	Oid			serverid;		/* identifies server for the table or join */
  	Oid			userid;			/* identifies user to check access as */
  	bool		useridiscurrent;	/* join is only valid for current user */
  	/* use "struct FdwRoutine" to avoid including fdwapi.h here */
  	struct FdwRoutine *fdwroutine;
  	void	   *fdw_private;
  
  	/* used by external scan */
  	struct ExtTableEntry *extEntry;
  
  	/* used by various scans and joins: */
  	List	   *baserestrictinfo;		/* RestrictInfo structures (if base
  										 * rel) */
  	QualCost	baserestrictcost;		/* cost of evaluating the above */
  	List	   *joininfo;		/* RestrictInfo structures for join clauses
  								 * involving this rel */
  	bool		has_eclass_joins;		/* T means joininfo is incomplete */
  
  	/*
  	 * In a subquery, if this base relation contains quals that must
  	 * be evaluated at "outerquery" locus, and the base relation has a
  	 * different locus, they are kept here in 'upperrestrictinfo', instead of
  	 * 'baserestrictinfo'.
  	 */
  	List	   *upperrestrictinfo;		/* RestrictInfo structures (if base
  										 * rel) */
  
  	/* used by foreign scan */
  	ForeignTable		*ftEntry;
  } RelOptInfo;
  
  /*
   * IndexOptInfo
   *		Per-index information for planning/optimization
   *
   *		indexkeys[], indexcollations[], opfamily[], and opcintype[]
   *		each have ncolumns entries.
   *
   *		sortopfamily[], reverse_sort[], and nulls_first[] likewise have
   *		ncolumns entries, if the index is ordered; but if it is unordered,
   *		those pointers are NULL.
   *
   *		Zeroes in the indexkeys[] array indicate index columns that are
   *		expressions; there is one element in indexprs for each such column.
   *
   *		For an ordered index, reverse_sort[] and nulls_first[] describe the
   *		sort ordering of a forward indexscan; we can also consider a backward
   *		indexscan, which will generate the reverse ordering.
   *
   *		The indexprs and indpred expressions have been run through
   *		prepqual.c and eval_const_expressions() for ease of matching to
   *		WHERE clauses. indpred is in implicit-AND form.
   *
   *		indextlist is a TargetEntry list representing the index columns.
   *		It provides an equivalent base-relation Var for each simple column,
   *		and links to the matching indexprs element for each expression column.
   *
   *		While most of these fields are filled when the IndexOptInfo is created
   *		(by plancat.c), indrestrictinfo and predOK are set later, in
   *		check_index_predicates().
   */
  typedef struct IndexOptInfo
  {
  	NodeTag		type;
  
  	Oid			indexoid;		/* OID of the index relation */
  	Oid			reltablespace;	/* tablespace of index (not table) */
  	RelOptInfo *rel;			/* back-link to index's table */
  
  	/* index-size statistics (from pg_class and elsewhere) */
  	BlockNumber pages;			/* number of disk pages in index */
  	double		tuples;			/* number of index tuples in index */
  	int			tree_height;	/* index tree height, or -1 if unknown */
  
  	/* index descriptor information */
  	int			ncolumns;		/* number of columns in index */
  	int		   *indexkeys;		/* column numbers of index's keys, or 0 */
  	Oid		   *indexcollations;	/* OIDs of collations of index columns */
  	Oid		   *opfamily;		/* OIDs of operator families for columns */
  	Oid		   *opcintype;		/* OIDs of opclass declared input data types */
  	Oid		   *sortopfamily;	/* OIDs of btree opfamilies, if orderable */
  	bool	   *reverse_sort;	/* is sort order descending? */
  	bool	   *nulls_first;	/* do NULLs come first in the sort order? */
  	bool	   *canreturn;		/* which index cols can be returned in an
  								 * index-only scan? */
  	Oid			relam;			/* OID of the access method (in pg_am) */
  
  	List	   *indexprs;		/* expressions for non-simple index columns */
  	List	   *indpred;		/* predicate if a partial index, else NIL */
  
  	List	   *indextlist;		/* targetlist representing index columns */
  
  	List	   *indrestrictinfo;/* parent relation's baserestrictinfo list,
  								 * less any conditions implied by the index's
  								 * predicate (unless it's a target rel, see
  								 * comments in check_index_predicates()) */
  
  	bool		predOK;			/* true if index predicate matches query */
  	bool		unique;			/* true if a unique index */
  	bool		immediate;		/* is uniqueness enforced immediately? */
  	bool		hypothetical;	/* true if index doesn't really exist */
  
  	/* Remaining fields are copied from the index AM's API struct: */
  	bool		amcanorderbyop; /* does AM support order by operator result? */
  	bool		amoptionalkey;	/* can query omit key for the first column? */
  	bool		amsearcharray;	/* can AM handle ScalarArrayOpExpr quals? */
  	bool		amsearchnulls;	/* can AM search for NULL/NOT NULL entries? */
  	bool		amhasgettuple;	/* does AM have amgettuple interface? */
  	bool		amhasgetbitmap; /* does AM have amgetbitmap interface? */
      int         num_leading_eq; /* CDB: always 0, except amcostestimate proc may
                                   * set it briefly; it is transferred forthwith
                                   * to the IndexPath (q.v.), then reset. Kludge.
                                   */
  
  	/* Rather than include amapi.h here, we declare amcostestimate like this */
  	void		(*amcostestimate) ();	/* AM's cost estimator */
  } IndexOptInfo;
  
  /*
   * ForeignKeyOptInfo
   *		Per-foreign-key information for planning/optimization
   *
   * The per-FK-column arrays can be fixed-size because we allow at most
   * INDEX_MAX_KEYS columns in a foreign key constraint.  Each array has
   * nkeys valid entries.
   */
  typedef struct ForeignKeyOptInfo
  {
  	NodeTag		type;
  
  	/* Basic data about the foreign key (fetched from catalogs): */
  	Index		con_relid;		/* RT index of the referencing table */
  	Index		ref_relid;		/* RT index of the referenced table */
  	int			nkeys;			/* number of columns in the foreign key */
  	AttrNumber	conkey[INDEX_MAX_KEYS]; /* cols in referencing table */
  	AttrNumber	confkey[INDEX_MAX_KEYS];		/* cols in referenced table */
  	Oid			conpfeqop[INDEX_MAX_KEYS];		/* PK = FK operator OIDs */
  
  	/* Derived info about whether FK's equality conditions match the query: */
  	int			nmatched_ec;	/* # of FK cols matched by ECs */
  	int			nmatched_rcols; /* # of FK cols matched by non-EC rinfos */
  	int			nmatched_ri;	/* total # of non-EC rinfos matched to FK */
  	/* Pointer to eclass matching each column's condition, if there is one */
  	struct EquivalenceClass *eclass[INDEX_MAX_KEYS];
  	/* List of non-EC RestrictInfos matching each column's condition */
  	List	   *rinfos[INDEX_MAX_KEYS];
  } ForeignKeyOptInfo;
  
  
  /*
   * CdbRelColumnInfo
   *
   * Describes a synthetic column to be added to a baserel's targetlist.
   * The pseudocols field of the RTE points to a List of CdbRelColumnInfo.
   */
  typedef struct CdbRelColumnInfo
  {
  	NodeTag		type;                   /* T_CdbRelColumnInfo */
  
      AttrNumber  pseudoattno;            /* FirstLowInvalidHeapAttributeNumber
                                           *  minus the 0-based position of the
                                           *  CdbRelColumnInfo node in the
                                           *  rte->pseudocols list
                                           */
      AttrNumber  targetresno;            /* 1-based position of the pseudo
                                           *  column in the rel's targetlist
                                           */
      Expr       *defexpr;                /* expr to be evaluated in targetlist */
  	Relids	    where_needed;           /* set of relids whose quals use col */
  	int32	    attr_width;             /* expected #bytes for column value */
      char        colname[NAMEDATALEN+1]; /* name for EXPLAIN */
  } CdbRelColumnInfo;
  
  /*
   * EquivalenceClasses
   *
   * Whenever we can determine that a mergejoinable equality clause A = B is
   * not delayed by any outer join, we create an EquivalenceClass containing
   * the expressions A and B to record this knowledge.  If we later find another
   * equivalence B = C, we add C to the existing EquivalenceClass; this may
   * require merging two existing EquivalenceClasses.  At the end of the qual
   * distribution process, we have sets of values that are known all transitively
   * equal to each other, where "equal" is according to the rules of the btree
   * operator family(s) shown in ec_opfamilies, as well as the collation shown
   * by ec_collation.  (We restrict an EC to contain only equalities whose
   * operators belong to the same set of opfamilies.  This could probably be
   * relaxed, but for now it's not worth the trouble, since nearly all equality
   * operators belong to only one btree opclass anyway.  Similarly, we suppose
   * that all or none of the input datatypes are collatable, so that a single
   * collation value is sufficient.)
   *
   * We also use EquivalenceClasses as the base structure for PathKeys, letting
   * us represent knowledge about different sort orderings being equivalent.
   * Since every PathKey must reference an EquivalenceClass, we will end up
   * with single-member EquivalenceClasses whenever a sort key expression has
   * not been equivalenced to anything else.  It is also possible that such an
   * EquivalenceClass will contain a volatile expression ("ORDER BY random()"),
   * which is a case that can't arise otherwise since clauses containing
   * volatile functions are never considered mergejoinable.  We mark such
   * EquivalenceClasses specially to prevent them from being merged with
   * ordinary EquivalenceClasses.  Also, for volatile expressions we have
   * to be careful to match the EquivalenceClass to the correct targetlist
   * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
   * So we record the SortGroupRef of the originating sort clause.
   *
   * We allow equality clauses appearing below the nullable side of an outer join
   * to form EquivalenceClasses, but these have a slightly different meaning:
   * the included values might be all NULL rather than all the same non-null
   * values.  See src/backend/optimizer/README for more on that point.
   *
   * NB: if ec_merged isn't NULL, this class has been merged into another, and
   * should be ignored in favor of using the pointed-to class.
   */
  typedef struct EquivalenceClass
  {
  	NodeTag		type;
  
  	List	   *ec_opfamilies;	/* btree operator family OIDs */
  	Oid			ec_collation;	/* collation, if datatypes are collatable */
  	List	   *ec_members;		/* list of EquivalenceMembers */
  	List	   *ec_sources;		/* list of generating RestrictInfos */
  	List	   *ec_derives;		/* list of derived RestrictInfos */
  	Relids		ec_relids;		/* all relids appearing in ec_members, except
  								 * for child members (see below) */
  	bool		ec_has_const;	/* any pseudoconstants in ec_members? */
  	bool		ec_has_volatile;	/* the (sole) member is a volatile expr */
  	bool		ec_below_outer_join;	/* equivalence applies below an OJ */
  	bool		ec_broken;		/* failed to generate needed clauses? */
  	Index		ec_sortref;		/* originating sortclause label, or 0 */
  	struct EquivalenceClass *ec_merged; /* set if merged into another EC */
  } EquivalenceClass;
  
  /*
   * If an EC contains a const and isn't below-outer-join, any PathKey depending
   * on it must be redundant, since there's only one possible value of the key.
   */
  #define EC_MUST_BE_REDUNDANT(eclass)  \
  	((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)
  
  /*
   * EquivalenceMember - one member expression of an EquivalenceClass
   *
   * em_is_child signifies that this element was built by transposing a member
   * for an appendrel parent relation to represent the corresponding expression
   * for an appendrel child.  These members are used for determining the
   * pathkeys of scans on the child relation and for explicitly sorting the
   * child when necessary to build a MergeAppend path for the whole appendrel
   * tree.  An em_is_child member has no impact on the properties of the EC as a
   * whole; in particular the EC's ec_relids field does NOT include the child
   * relation.  An em_is_child member should never be marked em_is_const nor
   * cause ec_has_const or ec_has_volatile to be set, either.  Thus, em_is_child
   * members are not really full-fledged members of the EC, but just reflections
   * or doppelgangers of real members.  Most operations on EquivalenceClasses
   * should ignore em_is_child members, and those that don't should test
   * em_relids to make sure they only consider relevant members.
   *
   * em_datatype is usually the same as exprType(em_expr), but can be
   * different when dealing with a binary-compatible opfamily; in particular
   * anyarray_ops would never work without this.  Use em_datatype when
   * looking up a specific btree operator to work with this expression.
   */
  typedef struct EquivalenceMember
  {
  	NodeTag		type;
  
  	Expr	   *em_expr;		/* the expression represented */
  	Relids		em_relids;		/* all relids appearing in em_expr */
  	Relids		em_nullable_relids;		/* nullable by lower outer joins */
  	bool		em_is_const;	/* expression is pseudoconstant? */
  	bool		em_is_child;	/* derived version for a child relation? */
  	Oid			em_datatype;	/* the "nominal type" used by the opfamily */
  } EquivalenceMember;
  
  /*
   * PathKeys
   *
   * The sort ordering of a path is represented by a list of PathKey nodes.
   * An empty list implies no known ordering.  Otherwise the first item
   * represents the primary sort key, the second the first secondary sort key,
   * etc.  The value being sorted is represented by linking to an
   * EquivalenceClass containing that value and including pk_opfamily among its
   * ec_opfamilies.  The EquivalenceClass tells which collation to use, too.
   * This is a convenient method because it makes it trivial to detect
   * equivalent and closely-related orderings. (See optimizer/README for more
   * information.)
   *
   * Note: pk_strategy is either BTLessStrategyNumber (for ASC) or
   * BTGreaterStrategyNumber (for DESC).  We assume that all ordering-capable
   * index types will use btree-compatible strategy numbers.
   */
  typedef struct PathKey
  {
  	NodeTag		type;
  
  	EquivalenceClass *pk_eclass;	/* the value that is ordered */
  	Oid			pk_opfamily;	/* btree opfamily defining the ordering */
  	int			pk_strategy;	/* sort direction (ASC or DESC) */
  	bool		pk_nulls_first; /* do NULLs come before normal values? */
  } PathKey;
  
  /*
   * DistributionKeys
   *
   * Like PathKey, but is used to represent data distribution by hash across
   * segments (DISTRIBUTED BY), rather than sort ordering.
   */
  typedef struct DistributionKey
  {
  	NodeTag		type;
  
  	List	   *dk_eclasses;	/* the value that is distributed */
  
  	/* Hash operator family that determines the hash function to use */
  	Oid			dk_opfamily;
  } DistributionKey;
  
  /*
   * CdbEquivClassIsConstant
   *      is true if the equivalence class represents a pseudo-constant
   *
   * This is copied from MUST_BE_REDUNDANT in pathkeys.c
   */
  #define CdbEquivClassIsConstant(eclass)						\
  	((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)
  
  /*
   * PathTarget
   *
   * This struct contains what we need to know during planning about the
   * targetlist (output columns) that a Path will compute.  Each RelOptInfo
   * includes a default PathTarget, which its individual Paths may simply
   * reference.  However, in some cases a Path may compute outputs different
   * from other Paths, and in that case we make a custom PathTarget for it.
   * For example, an indexscan might return index expressions that would
   * otherwise need to be explicitly calculated.  (Note also that "upper"
   * relations generally don't have useful default PathTargets.)
   *
   * exprs contains bare expressions; they do not have TargetEntry nodes on top,
   * though those will appear in finished Plans.
   *
   * sortgrouprefs[] is an array of the same length as exprs, containing the
   * corresponding sort/group refnos, or zeroes for expressions not referenced
   * by sort/group clauses.  If sortgrouprefs is NULL (which it generally is in
   * RelOptInfo.reltarget targets; only upper-level Paths contain this info),
   * we have not identified sort/group columns in this tlist.  This allows us to
   * deal with sort/group refnos when needed with less expense than including
   * TargetEntry nodes in the exprs list.
   */
  typedef struct PathTarget
  {
  	NodeTag		type;
  	List	   *exprs;			/* list of expressions to be computed */
  	Index	   *sortgrouprefs;	/* corresponding sort/group refnos, or 0 */
  	QualCost	cost;			/* cost of evaluating the expressions */
  	int			width;			/* estimated avg width of result tuples */
  } PathTarget;
  
  /* Convenience macro to get a sort/group refno from a PathTarget */
  #define get_pathtarget_sortgroupref(target, colno) \
  	((target)->sortgrouprefs ? (target)->sortgrouprefs[colno] : (Index) 0)
  
  
  /*
   * ParamPathInfo
   *
   * All parameterized paths for a given relation with given required outer rels
   * link to a single ParamPathInfo, which stores common information such as
   * the estimated rowcount for this parameterization.  We do this partly to
   * avoid recalculations, but mostly to ensure that the estimated rowcount
   * is in fact the same for every such path.
   *
   * Note: ppi_clauses is only used in ParamPathInfos for base relation paths;
   * in join cases it's NIL because the set of relevant clauses varies depending
   * on how the join is formed.  The relevant clauses will appear in each
   * parameterized join path's joinrestrictinfo list, instead.
   */
  typedef struct ParamPathInfo
  {
  	NodeTag		type;
  
  	Relids		ppi_req_outer;	/* rels supplying parameters used by path */
  	double		ppi_rows;		/* estimated number of result tuples */
  	List	   *ppi_clauses;	/* join clauses available from outer rels */
  } ParamPathInfo;
  
  
  /*
   * Type "Path" is used as-is for sequential-scan paths, as well as some other
   * simple plan types that we don't need any extra information in the path for.
   * For other path types it is the first component of a larger struct.
   *
   * "pathtype" is the NodeTag of the Plan node we could build from this Path.
   * It is partially redundant with the Path's NodeTag, but allows us to use
   * the same Path type for multiple Plan types when there is no need to
   * distinguish the Plan type during path processing.
   *
   * "parent" identifies the relation this Path scans, and "pathtarget"
   * describes the precise set of output columns the Path would compute.
   * In simple cases all Paths for a given rel share the same targetlist,
   * which we represent by having path->pathtarget equal to parent->reltarget.
   *
   * "param_info", if not NULL, links to a ParamPathInfo that identifies outer
   * relation(s) that provide parameter values to each scan of this path.
   * That means this path can only be joined to those rels by means of nestloop
   * joins with this path on the inside.  Also note that a parameterized path
   * is responsible for testing all "movable" joinclauses involving this rel
   * and the specified outer rel(s).
   *
   * "rows" is the same as parent->rows in simple paths, but in parameterized
   * paths and UniquePaths it can be less than parent->rows, reflecting the
   * fact that we've filtered by extra join conditions or removed duplicates.
   *
   * "pathkeys" is a List of PathKey nodes (see above), describing the sort
   * ordering of the path's output rows.
   */
  typedef struct Path
  {
  	NodeTag		type;
  
  	NodeTag		pathtype;		/* tag identifying scan/join method */
  
  	RelOptInfo *parent;			/* the relation this path can build */
  	PathTarget *pathtarget;		/* list of Vars/Exprs, cost, width */
  
  	ParamPathInfo *param_info;	/* parameterization info, or NULL if none */
  
  	bool		parallel_aware; /* engage parallel-aware logic? */
  	bool		parallel_safe;	/* OK to use as part of parallel plan? */
  	int			parallel_workers;		/* desired # of workers; 0 = not
  										 * parallel */
  
  	/* estimated size/costs for path (see costsize.c for more info) */
  	double		rows;			/* estimated number of result tuples */
  	Cost		startup_cost;	/* cost expended before fetching any tuples */
  	Cost		total_cost;		/* total cost (assuming all tuples fetched) */
  
  	EstimatedBytes  memory;     /* executor RAM needed for Path + kids */
  
  	CdbPathLocus    locus;      /* distribution of the result tuples */
  
  	bool        motionHazard;   /* true => path contains a CdbMotion operator
  					without a slackening operator above it */
  
  	bool		rescannable;    /* CDB: true => path can accept ExecRescan call
                                   */
  	List	   *pathkeys;		/* sort ordering of path's output */
  	/* pathkeys is a List of PathKey nodes; see above */
  
  	/*
  	 * sameslice_relids indicates which (base) relations will be executed in
  	 * the same slice, if this path is chosen. It is used in partition planning,
  	 * to decide if it's safe to create a PartitionSelector node that affects
  	 * other nodes at a distance. That can only be done if the PartitionSelector
  	 * would be executed in the same slice.
  	 *
  	 * This is a conservative estimate, it's always safe to set it to NULL if
  	 * unsure, and the worst that will happen is that you lose out on potential
  	 * optimizations.
  	 */
  	Relids		sameslice_relids;
  } Path;
  
  /* 
   * AppendOnlyPath is used for append-only table scans. 
   */
  typedef struct AppendOnlyPath
  {
  	Path		path;
  
  	/* for now it's pretty plain.. */
  } AppendOnlyPath;
  
  /*
   * AOCSPath is used for append-only column store table scans.
   */
  typedef struct AOCSPath
  {
  	Path		path;
  
  	/* for now it's pretty plain.. */
  } AOCSPath;
  
  
  /*
   * ExternalPath is used for external table scans.
   */
  typedef struct ExternalPath
  {
  	Path		path;
  
  	/* for now it's pretty plain.. */
  } ExternalPath;
  
  /*
   * PartitionSelectorPath is used for injection of partition selectors
   */
  typedef struct PartitionSelectorPath
  {
  	Path		path;
  
      Path	   *subpath;
  
  	DynamicScanInfo *dsinfo;
  	List	   *partKeyExprs;
  	List	   *partKeyAttnos;
  } PartitionSelectorPath;
  
  /* Macro for extracting a path's parameterization relids; beware double eval */
  #define PATH_REQ_OUTER(path)  \
  	((path)->param_info ? (path)->param_info->ppi_req_outer : (Relids) NULL)
  
  /*
   * GPDB: CTEs are planned differently from upstream.
   */
  typedef struct CtePath
  {
  	Path		path;
  
  	Path	   *subpath; /* if NULL, this is a shared CTE reference;
  						  * get the plan from the CtePlanInfo */
  } CtePath;
  
  /*----------
   * IndexPath represents an index scan over a single index.
   *
   * This struct is used for both regular indexscans and index-only scans;
   * path.pathtype is T_IndexScan or T_IndexOnlyScan to show which is meant.
   *
   * 'indexinfo' is the index to be scanned.
   *
   * 'indexclauses' is a list of index qualification clauses, with implicit
   * AND semantics across the list.  Each clause is a RestrictInfo node from
   * the query's WHERE or JOIN conditions.  An empty list implies a full
   * index scan.
   *
   * 'indexquals' has the same structure as 'indexclauses', but it contains
   * the actual index qual conditions that can be used with the index.
   * In simple cases this is identical to 'indexclauses', but when special
   * indexable operators appear in 'indexclauses', they are replaced by the
   * derived indexscannable conditions in 'indexquals'.
   *
   * 'indexqualcols' is an integer list of index column numbers (zero-based)
   * of the same length as 'indexquals', showing which index column each qual
   * is meant to be used with.  'indexquals' is required to be ordered by
   * index column, so 'indexqualcols' must form a nondecreasing sequence.
   * (The order of multiple quals for the same index column is unspecified.)
   *
   * 'indexorderbys', if not NIL, is a list of ORDER BY expressions that have
   * been found to be usable as ordering operators for an amcanorderbyop index.
   * The list must match the path's pathkeys, ie, one expression per pathkey
   * in the same order.  These are not RestrictInfos, just bare expressions,
   * since they generally won't yield booleans.  Also, unlike the case for
   * quals, it's guaranteed that each expression has the index key on the left
   * side of the operator.
   *
   * 'indexorderbycols' is an integer list of index column numbers (zero-based)
   * of the same length as 'indexorderbys', showing which index column each
   * ORDER BY expression is meant to be used with.  (There is no restriction
   * on which index column each ORDER BY can be used with.)
   *
   * 'indexscandir' is one of:
   *		ForwardScanDirection: forward scan of an ordered index
   *		BackwardScanDirection: backward scan of an ordered index
   *		NoMovementScanDirection: scan of an unordered index, or don't care
   * (The executor doesn't care whether it gets ForwardScanDirection or
   * NoMovementScanDirection for an indexscan, but the planner wants to
   * distinguish ordered from unordered indexes for building pathkeys.)
   *
   * 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that
   * we need not recompute them when considering using the same index in a
   * bitmap index/heap scan (see BitmapHeapPath).  The costs of the IndexPath
   * itself represent the costs of an IndexScan or IndexOnlyScan plan type.
   *----------
   */
  typedef struct IndexPath
  {
  	Path		path;
  	IndexOptInfo *indexinfo;
  	List	   *indexclauses;
  	List	   *indexquals;
  	List	   *indexqualcols;
  	List	   *indexorderbys;
  	List	   *indexorderbycols;
  	ScanDirection indexscandir;
  	Cost		indextotalcost;
  	Selectivity indexselectivity;
      int         num_leading_eq; /* CDB: number of leading key columns matched by
                                   * equality predicates in indexquals.  If equal
                                   * to indexinfo->ncolumns, at most one distinct
                                   * value of the index key can satisfy the quals.
                                   * Further if the index is unique, we can assume
                                   * at most one visible row satisfies the quals.
                                   */
  } IndexPath;
  
  /*
   * BitmapHeapPath represents one or more indexscans that generate TID bitmaps
   * instead of directly accessing the heap, followed by AND/OR combinations
   * to produce a single bitmap, followed by a heap scan that uses the bitmap.
   * Note that the output is always considered unordered, since it will come
   * out in physical heap order no matter what the underlying indexes did.
   *
   * The individual indexscans are represented by IndexPath nodes, and any
   * logic on top of them is represented by a tree of BitmapAndPath and
   * BitmapOrPath nodes.  Notice that we can use the same IndexPath node both
   * to represent a regular (or index-only) index scan plan, and as the child
   * of a BitmapHeapPath that represents scanning the same index using a
   * BitmapIndexScan.  The startup_cost and total_cost figures of an IndexPath
   * always represent the costs to use it as a regular (or index-only)
   * IndexScan.  The costs of a BitmapIndexScan can be computed using the
   * IndexPath's indextotalcost and indexselectivity.
   */
  typedef struct BitmapHeapPath
  {
  	Path		path;
  	Path	   *bitmapqual;		/* IndexPath, BitmapAndPath, BitmapOrPath */
  } BitmapHeapPath;
  
  /*
   * BitmapAndPath represents a BitmapAnd plan node; it can only appear as
   * part of the substructure of a BitmapHeapPath.  The Path structure is
   * a bit more heavyweight than we really need for this, but for simplicity
   * we make it a derivative of Path anyway.
   */
  typedef struct BitmapAndPath
  {
  	Path		path;
  	List	   *bitmapquals;	/* IndexPaths and BitmapOrPaths */
  	Selectivity bitmapselectivity;
  } BitmapAndPath;
  
  /*
   * BitmapOrPath represents a BitmapOr plan node; it can only appear as
   * part of the substructure of a BitmapHeapPath.  The Path structure is
   * a bit more heavyweight than we really need for this, but for simplicity
   * we make it a derivative of Path anyway.
   */
  typedef struct BitmapOrPath
  {
  	Path		path;
  	List	   *bitmapquals;	/* IndexPaths and BitmapAndPaths */
  	Selectivity bitmapselectivity;
  } BitmapOrPath;
  
  /*
   * TidPath represents a scan by TID
   *
   * tidquals is an implicitly OR'ed list of qual expressions of the form
   * "CTID = pseudoconstant" or "CTID = ANY(pseudoconstant_array)".
   * Note they are bare expressions, not RestrictInfos.
   */
  typedef struct TidPath
  {
  	Path		path;
  	List	   *tidquals;		/* qual(s) involving CTID = something */
  } TidPath;
  
  /*
   * CdbMotionPath represents transmission of the child Path results
   * from a set of sending processes to a set of receiving processes.
   *
   * Normally, the distribution is determined by the 'locus' of the path.
   * However, if the distribution cannot be represented by a DistributionKeys,
   * an alternative representation is to mark the locus as Strewn, and list
   * the hash columns in 'policy'. In the normal case, 'policy' is not used.
   */
  typedef struct CdbMotionPath
  {
  	Path		path;
      Path	   *subpath;
  	bool		is_explicit_motion;
  
  	GpPolicy   *policy;
  } CdbMotionPath;
  
  /*
   * SubqueryScanPath represents a scan of an unflattened subquery-in-FROM
   *
   * Note that the subpath comes from a different planning domain; for example
   * RTE indexes within it mean something different from those known to the
   * SubqueryScanPath.  path.parent->subroot is the planning context needed to
   * interpret the subpath.
   */
  typedef struct SubqueryScanPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing subquery execution */
  
  	/* In gpdb, we need to rebuild a SubqueryScanPath if MotionPath push down*/
  	Relids      required_outer;
  } SubqueryScanPath;
  
  /*
   * TableFunctionScanPath represents a scan of an unflattened subquery-in-FROM
   *
   * Note that the subpath comes from a different planning domain, like in
   * SubqueryScanPath.
   */
  typedef struct TableFunctionScanPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing subquery execution */
  } TableFunctionScanPath;
  
  /*
   * ForeignPath represents a potential scan of a foreign table, foreign join
   * or foreign upper-relation.
   *
   * fdw_private stores FDW private data about the scan.  While fdw_private is
   * not actually touched by the core code during normal operations, it's
   * generally a good idea to use a representation that can be dumped by
   * nodeToString(), so that you can examine the structure during debugging
   * with tools like pprint().
   */
  typedef struct ForeignPath
  {
  	Path		path;
  	Path	   *fdw_outerpath;
  	List	   *fdw_private;
  } ForeignPath;
  
  /*
   * CustomPath represents a table scan done by some out-of-core extension.
   *
   * We provide a set of hooks here - which the provider must take care to set
   * up correctly - to allow extensions to supply their own methods of scanning
   * a relation.  For example, a provider might provide GPU acceleration, a
   * cache-based scan, or some other kind of logic we haven't dreamed up yet.
   *
   * CustomPaths can be injected into the planning process for a relation by
   * set_rel_pathlist_hook functions.
   *
   * Core code must avoid assuming that the CustomPath is only as large as
   * the structure declared here; providers are allowed to make it the first
   * element in a larger structure.  (Since the planner never copies Paths,
   * this doesn't add any complication.)  However, for consistency with the
   * FDW case, we provide a "custom_private" field in CustomPath; providers
   * may prefer to use that rather than define another struct type.
   */
  
  struct CustomPathMethods;
  
  typedef struct CustomPath
  {
  	Path		path;
  	uint32		flags;			/* mask of CUSTOMPATH_* flags, see above */
  	List	   *custom_paths;	/* list of child Path nodes, if any */
  	List	   *custom_private;
  	const struct CustomPathMethods *methods;
  } CustomPath;
  
  /*
   * AppendPath represents an Append plan, ie, successive execution of
   * several member plans.
   *
   * Note: it is possible for "subpaths" to contain only one, or even no,
   * elements.  These cases are optimized during create_append_plan.
   * In particular, an AppendPath with no subpaths is a "dummy" path that
   * is created to represent the case that a relation is provably empty.
   */
  typedef struct AppendPath
  {
  	Path		path;
  	List	   *subpaths;		/* list of component Paths */
  } AppendPath;
  
  #define IS_DUMMY_PATH(p) \
  	(IsA((p), AppendPath) && ((AppendPath *) (p))->subpaths == NIL)
  
  /* A relation that's been proven empty will have one path that is dummy */
  #define IS_DUMMY_REL(r) \
  	((r)->cheapest_total_path != NULL && \
  	 IS_DUMMY_PATH((r)->cheapest_total_path))
  
  /*
   * MergeAppendPath represents a MergeAppend plan, ie, the merging of sorted
   * results from several member plans to produce similarly-sorted output.
   */
  typedef struct MergeAppendPath
  {
  	Path		path;
  	List	   *subpaths;		/* list of component Paths */
  	double		limit_tuples;	/* hard limit on output tuples, or -1 */
  } MergeAppendPath;
  
  /*
   * ResultPath represents use of a Result plan node to compute a variable-free
   * targetlist with no underlying tables (a "SELECT expressions" query).
   * The query could have a WHERE clause, too, represented by "quals".
   *
   * Note that quals is a list of bare clauses, not RestrictInfos.
   */
  typedef struct ResultPath
  {
  	Path		path;
  	List	   *quals;
  } ResultPath;
  
  /*
   * MaterialPath represents use of a Material plan node, i.e., caching of
   * the output of its subpath.  This is used when the subpath is expensive
   * and needs to be scanned repeatedly, or when we need mark/restore ability
   * and the subpath doesn't have it.
   */
  typedef struct MaterialPath
  {
  	Path		path;
  	Path	   *subpath;
      bool        cdb_strict;     /* true  => consume and store all input tuples
                                   *            before yielding output tuples
                                   * false => memoize tuples as they stream thru
                                   */
  
  	/*
  	 * If 'cdb_shield_child_from_rescans' is set, the sub-plan is not
  	 * rescannable, and the Material never call rescan on it. (The Material
  	 * node will keep all tuples, even if REWIND/BACKWARD/MARK executor flags
  	 * are not set.)
  	 */
  	bool		cdb_shield_child_from_rescans;
  } MaterialPath;
  
  /*
   * UniquePath represents elimination of distinct rows from the output of
   * its subpath.
   *
   * This can represent significantly different plans: either hash-based or
   * sort-based implementation, or a no-op if the input path can be proven
   * distinct already.  The decision is sufficiently localized that it's not
   * worth having separate Path node types.  (Note: in the no-op case, we could
   * eliminate the UniquePath node entirely and just return the subpath; but
   * it's convenient to have a UniquePath in the path tree to signal upper-level
   * routines that the input is known distinct.)
   */
  typedef enum
  {
  	UNIQUE_PATH_NOOP,			/* input is known unique already */
  	UNIQUE_PATH_HASH,			/* use hashing */
  	UNIQUE_PATH_SORT			/* use sorting */
  } UniquePathMethod;
  
  typedef struct UniquePath
  {
  	Path		path;
  	Path	   *subpath;
  	UniquePathMethod umethod;
  	List	   *in_operators;	/* equality operators of the IN clause */
  	List	   *uniq_exprs;		/* expressions to be made unique */
      Relids      distinct_on_rowid_relids;
                                  /* CDB: set of relids whose row ids are to be
                                   * uniqueified.
                                   */
      bool        must_repartition;
                                  /* CDB: true => add Motion atop subpath  */
  } UniquePath;
  
  /*
   * GatherPath runs several copies of a plan in parallel and collects the
   * results.  The parallel leader may also execute the plan, unless the
   * single_copy flag is set.
   */
  typedef struct GatherPath
  {
  	Path		path;
  	Path	   *subpath;		/* path for each worker */
  	bool		single_copy;	/* path must not be executed >1x */
  } GatherPath;
  
  /*
   * All join-type paths share these fields.
   */
  
  typedef struct JoinPath
  {
  	Path		path;
  
  	JoinType	jointype;
  
  	Path	   *outerjoinpath;	/* path for the outer side of the join */
  	Path	   *innerjoinpath;	/* path for the inner side of the join */
  
  	List	   *joinrestrictinfo;		/* RestrictInfos to apply to join */
  
  	/*
  	 * See the notes for RelOptInfo and ParamPathInfo to understand why
  	 * joinrestrictinfo is needed in JoinPath, and can't be merged into the
  	 * parent RelOptInfo.
  	 */
  } JoinPath;
  
  /*
   * IsJoinPath
   *      Returns true if the node type is one that derives from JoinPath.
   */
  #define IsJoinPath(node)        \
      (IsA((node), NestPath) ||   \
       IsA((node), HashPath) ||   \
       IsA((node), MergePath))
  
  /*
   * A nested-loop path needs no special fields.
   */
  
  typedef JoinPath NestPath;
  
  /*
   * A mergejoin path has these fields.
   *
   * Unlike other path types, a MergePath node doesn't represent just a single
   * run-time plan node: it can represent up to four.  Aside from the MergeJoin
   * node itself, there can be a Sort node for the outer input, a Sort node
   * for the inner input, and/or a Material node for the inner input.  We could
   * represent these nodes by separate path nodes, but considering how many
   * different merge paths are investigated during a complex join problem,
   * it seems better to avoid unnecessary palloc overhead.
   *
   * path_mergeclauses lists the clauses (in the form of RestrictInfos)
   * that will be used in the merge.
   *
   * Note that the mergeclauses are a subset of the parent relation's
   * restriction-clause list.  Any join clauses that are not mergejoinable
   * appear only in the parent's restrict list, and must be checked by a
   * qpqual at execution time.
   *
   * outersortkeys (resp. innersortkeys) is NIL if the outer path
   * (resp. inner path) is already ordered appropriately for the
   * mergejoin.  If it is not NIL then it is a PathKeys list describing
   * the ordering that must be created by an explicit Sort node.
   *
   * materialize_inner is TRUE if a Material node should be placed atop the
   * inner input.  This may appear with or without an inner Sort step.
   */
  
  typedef struct MergePath
  {
  	JoinPath	jpath;
  	List	   *path_mergeclauses;		/* join clauses to be used for merge */
  	List	   *outersortkeys;	/* keys for explicit sort, if any */
  	List	   *innersortkeys;	/* keys for explicit sort, if any */
  	bool		materialize_inner;		/* add Materialize to inner? */
  } MergePath;
  
  /*
   * A hashjoin path has these fields.
   *
   * The remarks above for mergeclauses apply for hashclauses as well.
   *
   * Hashjoin does not care what order its inputs appear in, so we have
   * no need for sortkeys.
   */
  
  typedef struct HashPath
  {
  	JoinPath	jpath;
  	List	   *path_hashclauses;		/* join clauses used for hashing */
  	int			num_batches;	/* number of batches expected */
  } HashPath;
  
  /*
   * ProjectionPath represents a projection (that is, targetlist computation)
   *
   * Nominally, this path node represents using a Result plan node to do a
   * projection step.  However, if the input plan node supports projection,
   * we can just modify its output targetlist to do the required calculations
   * directly, and not need a Result.  In some places in the planner we can just
   * jam the desired PathTarget into the input path node (and adjust its cost
   * accordingly), so we don't need a ProjectionPath.  But in other places
   * it's necessary to not modify the input path node, so we need a separate
   * ProjectionPath node, which is marked dummy to indicate that we intend to
   * assign the work to the input plan node.  The estimated cost for the
   * ProjectionPath node will account for whether a Result will be used or not.
   */
  typedef struct ProjectionPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	bool		dummypp;		/* true if no separate Result is needed */
  
  	List	   *cdb_restrict_clauses;
  } ProjectionPath;
  
  /*
   * SortPath represents an explicit sort step
   *
   * The sort keys are, by definition, the same as path.pathkeys.
   *
   * Note: the Sort plan node cannot project, so path.pathtarget must be the
   * same as the input's pathtarget.
   */
  typedef struct SortPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  } SortPath;
  
  /*
   * GroupPath represents grouping (of presorted input)
   *
   * groupClause represents the columns to be grouped on; the input path
   * must be at least that well sorted.
   *
   * We can also apply a qual to the grouped rows (equivalent of HAVING)
   */
  typedef struct GroupPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	List	   *groupClause;	/* a list of SortGroupClause's */
  	List	   *qual;			/* quals (HAVING quals), if any */
  } GroupPath;
  
  /*
   * UpperUniquePath represents adjacent-duplicate removal (in presorted input)
   *
   * The columns to be compared are the first numkeys columns of the path's
   * pathkeys.  The input is presumed already sorted that way.
   */
  typedef struct UpperUniquePath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	int			numkeys;		/* number of pathkey columns to compare */
  } UpperUniquePath;
  
  /*
   * AggPath represents generic computation of aggregate functions
   *
   * This may involve plain grouping (but not grouping sets), using either
   * sorted or hashed grouping; for the AGG_SORTED case, the input must be
   * appropriately presorted.
   */
  typedef struct AggPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	AggStrategy aggstrategy;	/* basic strategy, see nodes.h */
  	AggSplit	aggsplit;		/* agg-splitting mode, see nodes.h */
  	double		numGroups;		/* estimated number of groups in input */
  	List	   *groupClause;	/* a list of SortGroupClause's */
  	List	   *qual;			/* quals (HAVING quals), if any */
  	bool		streaming;
  } AggPath;
  
  /*
   * GroupingSetsPath represents a GROUPING SETS aggregation
   *
   * Currently we only support this in sorted not hashed form, so the input
   * must always be appropriately presorted.
   */
  typedef struct GroupingSetsPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	AggSplit	aggsplit;		/* agg-splitting mode, see nodes.h */
  	List	   *rollup_groupclauses;	/* list of lists of SortGroupClause's */
  	List	   *rollup_lists;	/* parallel list of lists of grouping sets */
  	List	   *qual;			/* quals (HAVING quals), if any */
  } GroupingSetsPath;
  
  /*
   * MinMaxAggPath represents computation of MIN/MAX aggregates from indexes
   */
  typedef struct MinMaxAggPath
  {
  	Path		path;
  	List	   *mmaggregates;	/* list of MinMaxAggInfo */
  	List	   *quals;			/* HAVING quals, if any */
  } MinMaxAggPath;
  
  /*
   * WindowAggPath represents generic computation of window functions
   *
   * Note: winpathkeys is separate from path.pathkeys because the actual sort
   * order might be an extension of winpathkeys; but createplan.c needs to
   * know exactly how many pathkeys match the window clause.
   */
  typedef struct WindowAggPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	WindowClause *winclause;	/* WindowClause we'll be using */
  	List	   *winpathkeys;	/* PathKeys for PARTITION keys + ORDER keys */
  } WindowAggPath;
  
  /*
   * SetOpPath represents a set-operation, that is INTERSECT or EXCEPT
   */
  typedef struct SetOpPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	SetOpCmd	cmd;			/* what to do, see nodes.h */
  	SetOpStrategy strategy;		/* how to do it, see nodes.h */
  	List	   *distinctList;	/* SortGroupClauses identifying target cols */
  	AttrNumber	flagColIdx;		/* where is the flag column, if any */
  	int			firstFlag;		/* flag value for first input relation */
  	double		numGroups;		/* estimated number of groups in input */
  } SetOpPath;
  
  /*
   * RecursiveUnionPath represents a recursive UNION node
   */
  typedef struct RecursiveUnionPath
  {
  	Path		path;
  	Path	   *leftpath;		/* paths representing input sources */
  	Path	   *rightpath;
  	List	   *distinctList;	/* SortGroupClauses identifying target cols */
  	int			wtParam;		/* ID of Param representing work table */
  	double		numGroups;		/* estimated number of groups in input */
  } RecursiveUnionPath;
  
  /*
   * LockRowsPath represents acquiring row locks for SELECT FOR UPDATE/SHARE
   */
  typedef struct LockRowsPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	List	   *rowMarks;		/* a list of PlanRowMark's */
  	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
  } LockRowsPath;
  
  /*
   * SplitUpdatePath
   */
  typedef struct SplitUpdatePath
  {
  	Path		path;
  	Path	   *subpath;
  	Index		resultRelation;
  } SplitUpdatePath;
  
  /*
   * ModifyTablePath represents performing INSERT/UPDATE/DELETE modifications
   *
   * We represent most things that will be in the ModifyTable plan node
   * literally, except we have child Path(s) not Plan(s).  But analysis of the
   * OnConflictExpr is deferred to createplan.c, as is collection of FDW data.
   */
  typedef struct ModifyTablePath
  {
  	Path		path;
  	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
  	bool		canSetTag;		/* do we set the command tag/es_processed? */
  	Index		nominalRelation;	/* Parent RT index for use of EXPLAIN */
  	List	   *resultRelations;	/* integer list of RT indexes */
  	List	   *is_split_updates;
  	List	   *subpaths;		/* Path(s) producing source data */
  	List	   *subroots;		/* per-target-table PlannerInfos */
  	List	   *withCheckOptionLists;	/* per-target-table WCO lists */
  	List	   *returningLists; /* per-target-table RETURNING tlists */
  	List	   *rowMarks;		/* PlanRowMarks (non-locking only) */
  	OnConflictExpr *onconflict; /* ON CONFLICT clause, or NULL */
  	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
  } ModifyTablePath;
  
  /*
   * LimitPath represents applying LIMIT/OFFSET restrictions
   */
  typedef struct LimitPath
  {
  	Path		path;
  	Path	   *subpath;		/* path representing input source */
  	Node	   *limitOffset;	/* OFFSET parameter, or NULL if none */
  	Node	   *limitCount;		/* COUNT parameter, or NULL if none */
  } LimitPath;
  
  
  /*
   * Restriction clause info.
   *
   * We create one of these for each AND sub-clause of a restriction condition
   * (WHERE or JOIN/ON clause).  Since the restriction clauses are logically
   * ANDed, we can use any one of them or any subset of them to filter out
   * tuples, without having to evaluate the rest.  The RestrictInfo node itself
   * stores data used by the optimizer while choosing the best query plan.
   *
   * If a restriction clause references a single base relation, it will appear
   * in the baserestrictinfo list of the RelOptInfo for that base rel.
   *
   * If a restriction clause references more than one base rel, it will
   * appear in the joininfo list of every RelOptInfo that describes a strict
   * subset of the base rels mentioned in the clause.  The joininfo lists are
   * used to drive join tree building by selecting plausible join candidates.
   * The clause cannot actually be applied until we have built a join rel
   * containing all the base rels it references, however.
   *
   * When we construct a join rel that includes all the base rels referenced
   * in a multi-relation restriction clause, we place that clause into the
   * joinrestrictinfo lists of paths for the join rel, if neither left nor
   * right sub-path includes all base rels referenced in the clause.  The clause
   * will be applied at that join level, and will not propagate any further up
   * the join tree.  (Note: the "predicate migration" code was once intended to
   * push restriction clauses up and down the plan tree based on evaluation
   * costs, but it's dead code and is unlikely to be resurrected in the
   * foreseeable future.)
   *
   * Note that in the presence of more than two rels, a multi-rel restriction
   * might reach different heights in the join tree depending on the join
   * sequence we use.  So, these clauses cannot be associated directly with
   * the join RelOptInfo, but must be kept track of on a per-join-path basis.
   *
   * RestrictInfos that represent equivalence conditions (i.e., mergejoinable
   * equalities that are not outerjoin-delayed) are handled a bit differently.
   * Initially we attach them to the EquivalenceClasses that are derived from
   * them.  When we construct a scan or join path, we look through all the
   * EquivalenceClasses and generate derived RestrictInfos representing the
   * minimal set of conditions that need to be checked for this particular scan
   * or join to enforce that all members of each EquivalenceClass are in fact
   * equal in all rows emitted by the scan or join.
   *
   * When dealing with outer joins we have to be very careful about pushing qual
   * clauses up and down the tree.  An outer join's own JOIN/ON conditions must
   * be evaluated exactly at that join node, unless they are "degenerate"
   * conditions that reference only Vars from the nullable side of the join.
   * Quals appearing in WHERE or in a JOIN above the outer join cannot be pushed
   * down below the outer join, if they reference any nullable Vars.
   * RestrictInfo nodes contain a flag to indicate whether a qual has been
   * pushed down to a lower level than its original syntactic placement in the
   * join tree would suggest.  If an outer join prevents us from pushing a qual
   * down to its "natural" semantic level (the level associated with just the
   * base rels used in the qual) then we mark the qual with a "required_relids"
   * value including more than just the base rels it actually uses.  By
   * pretending that the qual references all the rels required to form the outer
   * join, we prevent it from being evaluated below the outer join's joinrel.
   * When we do form the outer join's joinrel, we still need to distinguish
   * those quals that are actually in that join's JOIN/ON condition from those
   * that appeared elsewhere in the tree and were pushed down to the join rel
   * because they used no other rels.  That's what the is_pushed_down flag is
   * for; it tells us that a qual is not an OUTER JOIN qual for the set of base
   * rels listed in required_relids.  A clause that originally came from WHERE
   * or an INNER JOIN condition will *always* have its is_pushed_down flag set.
   * It's possible for an OUTER JOIN clause to be marked is_pushed_down too,
   * if we decide that it can be pushed down into the nullable side of the join.
   * In that case it acts as a plain filter qual for wherever it gets evaluated.
   * (In short, is_pushed_down is only false for non-degenerate outer join
   * conditions.  Possibly we should rename it to reflect that meaning?  But
   * see also the comments for RINFO_IS_PUSHED_DOWN, below.)
   *
   * RestrictInfo nodes also contain an outerjoin_delayed flag, which is true
   * if the clause's applicability must be delayed due to any outer joins
   * appearing below it (ie, it has to be postponed to some join level higher
   * than the set of relations it actually references).
   *
   * There is also an outer_relids field, which is NULL except for outer join
   * clauses; for those, it is the set of relids on the outer side of the
   * clause's outer join.  (These are rels that the clause cannot be applied to
   * in parameterized scans, since pushing it into the join's outer side would
   * lead to wrong answers.)
   *
   * There is also a nullable_relids field, which is the set of rels the clause
   * references that can be forced null by some outer join below the clause.
   *
   * outerjoin_delayed = true is subtly different from nullable_relids != NULL:
   * a clause might reference some nullable rels and yet not be
   * outerjoin_delayed because it also references all the other rels of the
   * outer join(s). A clause that is not outerjoin_delayed can be enforced
   * anywhere it is computable.
   *
   * In general, the referenced clause might be arbitrarily complex.  The
   * kinds of clauses we can handle as indexscan quals, mergejoin clauses,
   * or hashjoin clauses are limited (e.g., no volatile functions).  The code
   * for each kind of path is responsible for identifying the restrict clauses
   * it can use and ignoring the rest.  Clauses not implemented by an indexscan,
   * mergejoin, or hashjoin will be placed in the plan qual or joinqual field
   * of the finished Plan node, where they will be enforced by general-purpose
   * qual-expression-evaluation code.  (But we are still entitled to count
   * their selectivity when estimating the result tuple count, if we
   * can guess what it is...)
   *
   * When the referenced clause is an OR clause, we generate a modified copy
   * in which additional RestrictInfo nodes are inserted below the top-level
   * OR/AND structure.  This is a convenience for OR indexscan processing:
   * indexquals taken from either the top level or an OR subclause will have
   * associated RestrictInfo nodes.
   *
   * The can_join flag is set true if the clause looks potentially useful as
   * a merge or hash join clause, that is if it is a binary opclause with
   * nonoverlapping sets of relids referenced in the left and right sides.
   * (Whether the operator is actually merge or hash joinable isn't checked,
   * however.)
   *
   * The pseudoconstant flag is set true if the clause contains no Vars of
   * the current query level and no volatile functions.  Such a clause can be
   * pulled out and used as a one-time qual in a gating Result node.  We keep
   * pseudoconstant clauses in the same lists as other RestrictInfos so that
   * the regular clause-pushing machinery can assign them to the correct join
   * level, but they need to be treated specially for cost and selectivity
   * estimates.  Note that a pseudoconstant clause can never be an indexqual
   * or merge or hash join clause, so it's of no interest to large parts of
   * the planner.
   *
   * When join clauses are generated from EquivalenceClasses, there may be
   * several equally valid ways to enforce join equivalence, of which we need
   * apply only one.  We mark clauses of this kind by setting parent_ec to
   * point to the generating EquivalenceClass.  Multiple clauses with the same
   * parent_ec in the same join are redundant.
   */
  
  typedef struct RestrictInfo
  {
  	NodeTag		type;
  
  	Expr	   *clause;			/* the represented clause of WHERE or JOIN */
  
  	bool		is_pushed_down; /* TRUE if clause was pushed down in level */
  
  	bool		outerjoin_delayed;		/* TRUE if delayed by lower outer join */
  
  	bool		can_join;		/* see comment above */
  
  	bool		pseudoconstant; /* see comment above */
  
  	/*
  	 * GPDB: does the clause refer to outer query levels? (Which implies that
  	 * it must be evaluted in the same slice as the parent query)
  	 */
  	bool		contain_outer_query_references;
  
  	/* The set of relids (varnos) actually referenced in the clause: */
  	Relids		clause_relids;
  
  	/* The set of relids required to evaluate the clause: */
  	Relids		required_relids;
  
  	/* If an outer-join clause, the outer-side relations, else NULL: */
  	Relids		outer_relids;
  
  	/* The relids used in the clause that are nullable by lower outer joins: */
  	Relids		nullable_relids;
  
  	/* These fields are set for any binary opclause: */
  	Relids		left_relids;	/* relids in left side of clause */
  	Relids		right_relids;	/* relids in right side of clause */
  
  	/* This field is NULL unless clause is an OR clause: */
  	Expr	   *orclause;		/* modified clause with RestrictInfos */
  
  	/* This field is NULL unless clause is potentially redundant: */
  	EquivalenceClass *parent_ec;	/* generating EquivalenceClass */
  
  	/* cache space for cost and selectivity */
  	QualCost	eval_cost;		/* eval cost of clause; -1 if not yet set */
  	Selectivity norm_selec;		/* selectivity for "normal" (JOIN_INNER)
  								 * semantics; -1 if not yet set; >1 means a
  								 * redundant clause */
  	Selectivity outer_selec;	/* selectivity for outer join semantics; -1 if
  								 * not yet set */
  
  	/* valid if clause is mergejoinable, else NIL */
  	List	   *mergeopfamilies;	/* opfamilies containing clause operator */
  
  	/* cache space for mergeclause processing; NULL if not yet set */
  	EquivalenceClass *left_ec;	/* EquivalenceClass containing lefthand */
  	EquivalenceClass *right_ec; /* EquivalenceClass containing righthand */
  	EquivalenceMember *left_em; /* EquivalenceMember for lefthand */
  	EquivalenceMember *right_em;	/* EquivalenceMember for righthand */
  	List	   *scansel_cache;	/* list of MergeScanSelCache structs */
  
  	/* transient workspace for use while considering a specific join path */
  	bool		outer_is_left;	/* T = outer var on left, F = on right */
  
  	/* valid if clause is hashjoinable, else InvalidOid: */
  	Oid			hashjoinoperator;		/* copy of clause operator */
  
  	/* cache space for hashclause processing; -1 if not yet set */
  	Selectivity left_bucketsize;	/* avg bucketsize of left side */
  	Selectivity right_bucketsize;		/* avg bucketsize of right side */
  } RestrictInfo;
  
  /*
   * This macro embodies the correct way to test whether a RestrictInfo is
   * "pushed down" to a given outer join, that is, should be treated as a filter
   * clause rather than a join clause at that outer join.  This is certainly so
   * if is_pushed_down is true; but examining that is not sufficient anymore,
   * because outer-join clauses will get pushed down to lower outer joins when
   * we generate a path for the lower outer join that is parameterized by the
   * LHS of the upper one.  We can detect such a clause by noting that its
   * required_relids exceed the scope of the join.
   */
  #define RINFO_IS_PUSHED_DOWN(rinfo, joinrelids) \
  	((rinfo)->is_pushed_down || \
  	 !bms_is_subset((rinfo)->required_relids, joinrelids))
  
  /*
   * Since mergejoinscansel() is a relatively expensive function, and would
   * otherwise be invoked many times while planning a large join tree,
   * we go out of our way to cache its results.  Each mergejoinable
   * RestrictInfo carries a list of the specific sort orderings that have
   * been considered for use with it, and the resulting selectivities.
   */
  typedef struct MergeScanSelCache
  {
  	/* Ordering details (cache lookup key) */
  	Oid			opfamily;		/* btree opfamily defining the ordering */
  	Oid			collation;		/* collation for the ordering */
  	int			strategy;		/* sort direction (ASC or DESC) */
  	bool		nulls_first;	/* do NULLs come before normal values? */
  	/* Results */
  	Selectivity leftstartsel;	/* first-join fraction for clause left side */
  	Selectivity leftendsel;		/* last-join fraction for clause left side */
  	Selectivity rightstartsel;	/* first-join fraction for clause right side */
  	Selectivity rightendsel;	/* last-join fraction for clause right side */
  } MergeScanSelCache;
  
  /*
   * Placeholder node for an expression to be evaluated below the top level
   * of a plan tree.  This is used during planning to represent the contained
   * expression.  At the end of the planning process it is replaced by either
   * the contained expression or a Var referring to a lower-level evaluation of
   * the contained expression.  Typically the evaluation occurs below an outer
   * join, and Var references above the outer join might thereby yield NULL
   * instead of the expression value.
   *
   * Although the planner treats this as an expression node type, it is not
   * recognized by the parser or executor, so we declare it here rather than
   * in primnodes.h.
   */
  
  typedef struct PlaceHolderVar
  {
  	Expr		xpr;
  	Expr	   *phexpr;			/* the represented expression */
  	Relids		phrels;			/* base relids syntactically within expr src */
  	Index		phid;			/* ID for PHV (unique within planner run) */
  	Index		phlevelsup;		/* > 0 if PHV belongs to outer query */
  } PlaceHolderVar;
  
  /*
   * "Special join" info.
   *
   * One-sided outer joins constrain the order of joining partially but not
   * completely.  We flatten such joins into the planner's top-level list of
   * relations to join, but record information about each outer join in a
   * SpecialJoinInfo struct.  These structs are kept in the PlannerInfo node's
   * join_info_list.
   *
   * Similarly, semijoins and antijoins created by flattening IN (subselect)
   * and EXISTS(subselect) clauses create partial constraints on join order.
   * These are likewise recorded in SpecialJoinInfo structs.
   *
   * We make SpecialJoinInfos for FULL JOINs even though there is no flexibility
   * of planning for them, because this simplifies make_join_rel()'s API.
   *
   * min_lefthand and min_righthand are the sets of base relids that must be
   * available on each side when performing the special join.  lhs_strict is
   * true if the special join's condition cannot succeed when the LHS variables
   * are all NULL (this means that an outer join can commute with upper-level
   * outer joins even if it appears in their RHS).  We don't bother to set
   * lhs_strict for FULL JOINs, however.
   *
   * It is not valid for either min_lefthand or min_righthand to be empty sets;
   * if they were, this would break the logic that enforces join order.
   *
   * syn_lefthand and syn_righthand are the sets of base relids that are
   * syntactically below this special join.  (These are needed to help compute
   * min_lefthand and min_righthand for higher joins.)
   *
   * delay_upper_joins is set TRUE if we detect a pushed-down clause that has
   * to be evaluated after this join is formed (because it references the RHS).
   * Any outer joins that have such a clause and this join in their RHS cannot
   * commute with this join, because that would leave noplace to check the
   * pushed-down clause.  (We don't track this for FULL JOINs, either.)
   *
   * For a semijoin, we also extract the join operators and their RHS arguments
   * and set semi_operators, semi_rhs_exprs, semi_can_btree, and semi_can_hash.
   * This is done in support of possibly unique-ifying the RHS, so we don't
   * bother unless at least one of semi_can_btree and semi_can_hash can be set
   * true.  (You might expect that this information would be computed during
   * join planning; but it's helpful to have it available during planning of
   * parameterized table scans, so we store it in the SpecialJoinInfo structs.)
   *
   * jointype is never JOIN_RIGHT; a RIGHT JOIN is handled by switching
   * the inputs to make it a LEFT JOIN.  So the allowed values of jointype
   * in a join_info_list member are only LEFT, FULL, SEMI, or ANTI.
   *
   * For purposes of join selectivity estimation, we create transient
   * SpecialJoinInfo structures for regular inner joins; so it is possible
   * to have jointype == JOIN_INNER in such a structure, even though this is
   * not allowed within join_info_list.  We also create transient
   * SpecialJoinInfos with jointype == JOIN_INNER for outer joins, since for
   * cost estimation purposes it is sometimes useful to know the join size under
   * plain innerjoin semantics.  Note that lhs_strict, delay_upper_joins, and
   * of course the semi_xxx fields are not set meaningfully within such structs.
   */
  
  typedef struct SpecialJoinInfo
  {
  	NodeTag		type;
  	Relids		min_lefthand;	/* base relids in minimum LHS for join */
  	Relids		min_righthand;	/* base relids in minimum RHS for join */
  	Relids		syn_lefthand;	/* base relids syntactically within LHS */
  	Relids		syn_righthand;	/* base relids syntactically within RHS */
  	JoinType	jointype;		/* always INNER, LEFT, FULL, SEMI, or ANTI */
  	bool		lhs_strict;		/* joinclause is strict for some LHS rel */
  	bool		delay_upper_joins;		/* can't commute with upper RHS */
  	/* Remaining fields are set only for JOIN_SEMI jointype: */
  	bool		semi_can_btree; /* true if semi_operators are all btree */
  	bool		semi_can_hash;	/* true if semi_operators are all hash */
  	List	   *semi_operators; /* OIDs of equality join operators */
  	List	   *semi_rhs_exprs; /* righthand-side expressions of these ops */
  } SpecialJoinInfo;
  
  /*
   * Append-relation info.
   *
   * When we expand an inheritable table or a UNION-ALL subselect into an
   * "append relation" (essentially, a list of child RTEs), we build an
   * AppendRelInfo for each child RTE.  The list of AppendRelInfos indicates
   * which child RTEs must be included when expanding the parent, and each
   * node carries information needed to translate Vars referencing the parent
   * into Vars referencing that child.
   *
   * These structs are kept in the PlannerInfo node's append_rel_list.
   * Note that we just throw all the structs into one list, and scan the
   * whole list when desiring to expand any one parent.  We could have used
   * a more complex data structure (eg, one list per parent), but this would
   * be harder to update during operations such as pulling up subqueries,
   * and not really any easier to scan.  Considering that typical queries
   * will not have many different append parents, it doesn't seem worthwhile
   * to complicate things.
   *
   * Note: after completion of the planner prep phase, any given RTE is an
   * append parent having entries in append_rel_list if and only if its
   * "inh" flag is set.  We clear "inh" for plain tables that turn out not
   * to have inheritance children, and (in an abuse of the original meaning
   * of the flag) we set "inh" for subquery RTEs that turn out to be
   * flattenable UNION ALL queries.  This lets us avoid useless searches
   * of append_rel_list.
   *
   * Note: the data structure assumes that append-rel members are single
   * baserels.  This is OK for inheritance, but it prevents us from pulling
   * up a UNION ALL member subquery if it contains a join.  While that could
   * be fixed with a more complex data structure, at present there's not much
   * point because no improvement in the plan could result.
   */
  
  typedef struct AppendRelInfo
  {
  	NodeTag		type;
  
  	/*
  	 * These fields uniquely identify this append relationship.  There can be
  	 * (in fact, always should be) multiple AppendRelInfos for the same
  	 * parent_relid, but never more than one per child_relid, since a given
  	 * RTE cannot be a child of more than one append parent.
  	 */
  	Index		parent_relid;	/* RT index of append parent rel */
  	Index		child_relid;	/* RT index of append child rel */
  
  	/*
  	 * For an inheritance appendrel, the parent and child are both regular
  	 * relations, and we store their rowtype OIDs here for use in translating
  	 * whole-row Vars.  For a UNION-ALL appendrel, the parent and child are
  	 * both subqueries with no named rowtype, and we store InvalidOid here.
  	 */
  	Oid			parent_reltype; /* OID of parent's composite type */
  	Oid			child_reltype;	/* OID of child's composite type */
  
  	/*
  	 * The N'th element of this list is a Var or expression representing the
  	 * child column corresponding to the N'th column of the parent. This is
  	 * used to translate Vars referencing the parent rel into references to
  	 * the child.  A list element is NULL if it corresponds to a dropped
  	 * column of the parent (this is only possible for inheritance cases, not
  	 * UNION ALL).  The list elements are always simple Vars for inheritance
  	 * cases, but can be arbitrary expressions in UNION ALL cases.
  	 *
  	 * Notice we only store entries for user columns (attno > 0).  Whole-row
  	 * Vars are special-cased, and system columns (attno < 0) need no special
  	 * translation since their attnos are the same for all tables.
  	 *
  	 * Caution: the Vars have varlevelsup = 0.  Be careful to adjust as needed
  	 * when copying into a subquery.
  	 */
  	List	   *translated_vars;	/* Expressions in the child's Vars */
  
  	/*
  	 * We store the parent table's OID here for inheritance, or InvalidOid for
  	 * UNION ALL.  This is only needed to help in generating error messages if
  	 * an attempt is made to reference a dropped parent column.
  	 */
  	Oid			parent_reloid;	/* OID of parent relation */
  } AppendRelInfo;
  
  /*
   * For each distinct placeholder expression generated during planning, we
   * store a PlaceHolderInfo node in the PlannerInfo node's placeholder_list.
   * This stores info that is needed centrally rather than in each copy of the
   * PlaceHolderVar.  The phid fields identify which PlaceHolderInfo goes with
   * each PlaceHolderVar.  Note that phid is unique throughout a planner run,
   * not just within a query level --- this is so that we need not reassign ID's
   * when pulling a subquery into its parent.
   *
   * The idea is to evaluate the expression at (only) the ph_eval_at join level,
   * then allow it to bubble up like a Var until the ph_needed join level.
   * ph_needed has the same definition as attr_needed for a regular Var.
   * ph_may_need is an initial estimate of ph_needed, formed using the
   * syntactic locations of references to the PHV.  We need this in order to
   * determine whether the PHV reference forces a join ordering constraint:
   * if the PHV has to be evaluated below the nullable side of an outer join,
   * and then used above that outer join, we must constrain join order to ensure
   * there's a valid place to evaluate the PHV below the join.  The final
   * actual ph_needed level might be lower than ph_may_need, but we can't
   * determine that until later on.  Fortunately this doesn't matter for what
   * we need ph_may_need for: if there's a PHV reference syntactically
   * above the outer join, it's not going to be allowed to drop below the outer
   * join, so we would come to the same conclusions about join order even if
   * we had the final ph_needed value to compare to.
   *
   * The PlaceHolderVar's expression might contain LATERAL references to vars
   * coming from outside its syntactic scope.  If so, those rels are *not*
   * included in ph_eval_at, but they are recorded in ph_lateral.
   *
   * Notice that when ph_eval_at is a join rather than a single baserel, the
   * PlaceHolderInfo may create constraints on join order: the ph_eval_at join
   * has to be formed below any outer joins that should null the PlaceHolderVar.
   *
   * We create a PlaceHolderInfo only after determining that the PlaceHolderVar
   * is actually referenced in the plan tree, so that unreferenced placeholders
   * don't result in unnecessary constraints on join order.
   */
  
  typedef struct PlaceHolderInfo
  {
  	NodeTag		type;
  
  	Index		phid;			/* ID for PH (unique within planner run) */
  	PlaceHolderVar *ph_var;		/* copy of PlaceHolderVar tree */
  	Relids		ph_eval_at;		/* lowest level we can evaluate value at */
  	Relids		ph_lateral;		/* relids of contained lateral refs, if any */
  	Relids		ph_needed;		/* highest level the value is needed at */
  	int32		ph_width;		/* estimated attribute width */
  } PlaceHolderInfo;
  
  /*
   * This struct describes one potentially index-optimizable MIN/MAX aggregate
   * function.  MinMaxAggPath contains a list of these, and if we accept that
   * path, the list is stored into root->minmax_aggs for use during setrefs.c.
   */
  typedef struct MinMaxAggInfo
  {
  	NodeTag		type;
  
  	Oid			aggfnoid;		/* pg_proc Oid of the aggregate */
  	Oid			aggsortop;		/* Oid of its sort operator */
  	Expr	   *target;			/* expression we are aggregating on */
  	PlannerInfo *subroot;		/* modified "root" for planning the subquery */
  	Path	   *path;			/* access path for subquery */
  	Cost		pathcost;		/* estimated cost to fetch first row */
  	Param	   *param;			/* param for subplan's output */
  } MinMaxAggInfo;
  
  /*
   * At runtime, PARAM_EXEC slots are used to pass values around from one plan
   * node to another.  They can be used to pass values down into subqueries (for
   * outer references in subqueries), or up out of subqueries (for the results
   * of a subplan), or from a NestLoop plan node into its inner relation (when
   * the inner scan is parameterized with values from the outer relation).
   * The planner is responsible for assigning nonconflicting PARAM_EXEC IDs to
   * the PARAM_EXEC Params it generates.
   *
   * Outer references are managed via root->plan_params, which is a list of
   * PlannerParamItems.  While planning a subquery, each parent query level's
   * plan_params contains the values required from it by the current subquery.
   * During create_plan(), we use plan_params to track values that must be
   * passed from outer to inner sides of NestLoop plan nodes.
   *
   * The item a PlannerParamItem represents can be one of three kinds:
   *
   * A Var: the slot represents a variable of this level that must be passed
   * down because subqueries have outer references to it, or must be passed
   * from a NestLoop node to its inner scan.  The varlevelsup value in the Var
   * will always be zero.
   *
   * A PlaceHolderVar: this works much like the Var case, except that the
   * entry is a PlaceHolderVar node with a contained expression.  The PHV
   * will have phlevelsup = 0, and the contained expression is adjusted
   * to match in level.
   *
   * An Aggref (with an expression tree representing its argument): the slot
   * represents an aggregate expression that is an outer reference for some
   * subquery.  The Aggref itself has agglevelsup = 0, and its argument tree
   * is adjusted to match in level.
   *
   * Note: we detect duplicate Var and PlaceHolderVar parameters and coalesce
   * them into one slot, but we do not bother to do that for Aggrefs.
   * The scope of duplicate-elimination only extends across the set of
   * parameters passed from one query level into a single subquery, or for
   * nestloop parameters across the set of nestloop parameters used in a single
   * query level.  So there is no possibility of a PARAM_EXEC slot being used
   * for conflicting purposes.
   *
   * In addition, PARAM_EXEC slots are assigned for Params representing outputs
   * from subplans (values that are setParam items for those subplans).  These
   * IDs need not be tracked via PlannerParamItems, since we do not need any
   * duplicate-elimination nor later processing of the represented expressions.
   * Instead, we just record the assignment of the slot number by incrementing
   * root->glob->nParamExec.
   */
  typedef struct PlannerParamItem
  {
  	NodeTag		type;
  
  	Node	   *item;			/* the Var, PlaceHolderVar, or Aggref */
  	int			paramId;		/* its assigned PARAM_EXEC slot number */
  } PlannerParamItem;
  
  /*
   * Partitioning meta data
   */
  
  /*
   * convenient representation of a row of pg_partition -- a partitioning level of
   * a partitioned table or a template for all the partitioning branches at a level.
   */
  typedef struct Partition
  {
  	NodeTag type;
  	Oid partid;			/* OID of row in pg_partition. */
  	Oid parrelid;		/* OID in pg_class of top-level partitioned relation */
  	char parkind;		/* 'r', 'l', or (unsupported) 'h' */
  	int16 parlevel;		/* depth below parent partitioned table */
  	bool paristemplate;	/* just a template, or really a part? */
  	int16 parnatts;		/* number of partitioning attributes */
  	AttrNumber *paratts;/* attribute number vector */ 
  	Oid *parclass;		/* operator class vector */
  } Partition;
  
  struct PartitionNode
  {
  	NodeTag type;
  	Partition *part;
  
  	/* rules for this level */
  	struct PartitionRule *default_part;
  	struct PartitionRule **rules;
  	int			num_rules;		/* excluding default rule */
  };
  
  /* Individual partitioning rule */
  typedef struct PartitionRule
  {
  	NodeTag		 type;
  	Oid			 parruleid;
  	Oid			 paroid;
  	Oid			 parchildrelid;
  	Oid			 parparentoid;
  	bool		 parisdefault;
  	char		*parname;
  	Node		*parrangestart;
  	bool		 parrangestartincl;
  	Node		*parrangeend;
  	bool		 parrangeendincl;
  	Node		*parrangeevery;
  	List		*parlistvalues;
  	int16		 parruleord;
  	List		*parreloptions;
  	Oid			 partemplatespaceId; 	/* the tablespace id for the
  										 * template (or InvalidOid for 
  										 * non-template rules */
  	struct PartitionNode *children; /* sub partition */
  } PartitionRule;
  
  typedef struct PgPartRule
  {
  	NodeTag type;
  	PartitionNode 		*pNode;
  	PartitionRule 		*topRule;	/* the rule for the specified partition */
  
  	/* a textual representation of the partition id (for error msgs) */
  	char		*partIdStr;
  	bool         isName;		/* true if partid is name */
  	int          topRuleRank;	/* rank of topRule */
  	char        *relname; 		/* the error msg formatted "relname" */
  } PgPartRule;
  
  /*
   * A Mapping created by the QD during data loading that maps a
   * relation id to the segfile number that is should be inserting
   * into (in cases of inserting into a partitioned table the QD
   * assigns a segno for each possible partition child relation).
   * 
   * It is a node because it needs to get serialized as a part of 
   * CopyStmt.
   */
  typedef struct SegfileMapNode
  {
  	NodeTag 	type;
  	Oid			relid;
  	int			segno;
  } SegfileMapNode;
  
  /*
   * When making cost estimates for a SEMI or ANTI join, there are some
   * correction factors that are needed in both nestloop and hash joins
   * to account for the fact that the executor can stop scanning inner rows
   * as soon as it finds a match to the current outer row.  These numbers
   * depend only on the selected outer and inner join relations, not on the
   * particular paths used for them, so it's worthwhile to calculate them
   * just once per relation pair not once per considered path.  This struct
   * is filled by compute_semi_anti_join_factors and must be passed along
   * to the join cost estimation functions.
   *
   * outer_match_frac is the fraction of the outer tuples that are
   *		expected to have at least one match.
   * match_count is the average number of matches expected for
   *		outer tuples that have at least one match.
   */
  typedef struct SemiAntiJoinFactors
  {
  	Selectivity outer_match_frac;
  	Selectivity match_count;
  } SemiAntiJoinFactors;
  
  /*
   * Struct for extra information passed to subroutines of add_paths_to_joinrel
   *
   * restrictlist contains all of the RestrictInfo nodes for restriction
   *		clauses that apply to this join
   * mergeclause_list is a list of RestrictInfo nodes for available
   *		mergejoin clauses in this join
   * sjinfo is extra info about special joins for selectivity estimation
   * semifactors is as shown above (only valid for SEMI or ANTI joins)
   * param_source_rels are OK targets for parameterization of result paths
   */
  typedef struct JoinPathExtraData
  {
  	List	   *restrictlist;
  	List	   *mergeclause_list;
  	SpecialJoinInfo *sjinfo;
  	SemiAntiJoinFactors semifactors;
  	Relids		param_source_rels;
  	List	   *redistribution_clauses;
  } JoinPathExtraData;
  
  /*
   * For speed reasons, cost estimation for join paths is performed in two
   * phases: the first phase tries to quickly derive a lower bound for the
   * join cost, and then we check if that's sufficient to reject the path.
   * If not, we come back for a more refined cost estimate.  The first phase
   * fills a JoinCostWorkspace struct with its preliminary cost estimates
   * and possibly additional intermediate values.  The second phase takes
   * these values as inputs to avoid repeating work.
   *
   * (Ideally we'd declare this in cost.h, but it's also needed in pathnode.h,
   * so seems best to put it here.)
   */
  typedef struct JoinCostWorkspace
  {
  	/* Preliminary cost estimates --- must not be larger than final ones! */
  	Cost		startup_cost;	/* cost expended before fetching any tuples */
  	Cost		total_cost;		/* total cost (assuming all tuples fetched) */
  
  	/* Fields below here should be treated as private to costsize.c */
  	Cost		run_cost;		/* non-startup cost components */
  
  	/* private for cost_nestloop code */
  	Cost		inner_run_cost; /* also used by cost_mergejoin code */
  	Cost		inner_rescan_run_cost;
  
  	/* private for cost_mergejoin code */
  	double		outer_rows;
  	double		inner_rows;
  	double		outer_skip_rows;
  	double		inner_skip_rows;
  
  	/* private for cost_hashjoin code */
  	int			numbuckets;
  	int			numbatches;
  } JoinCostWorkspace;
  
  #endif   /* RELATION_H */
  