Add Cardinality typedef

Similar to Cost and Selectivity, this is just a double, which can be
used in path and plan nodes to give some hint about the meaning of a
field.

Discussion: https://www.postgresql.org/message-id/c091e5cd-45f8-69ee-6a9b-de86912cc7e7@enterprisedb.com

src/include/nodes/nodes.h

@@ -668,6 +668,7 @@ extern bool equal(const void *a, const void *b);
  */
 typedef double Selectivity;		/* fraction of tuples a qualifier will pass */
 typedef double Cost;			/* execution cost (in page-access units) */
+typedef double Cardinality;		/* (estimated) number of rows or other integer count */
 
 
 /*

src/include/nodes/parsenodes.h

@@ -1144,7 +1144,7 @@ typedef struct RangeTblEntry
 	 * Fields valid for ENR RTEs (else NULL/zero):
 	 */
 	char	   *enrname;		/* name of ephemeral named relation */
-	double		enrtuples;		/* estimated or actual from caller */
+	Cardinality	enrtuples;		/* estimated or actual from caller */
 
 	/*
 	 * Fields valid in all RTEs:

src/include/nodes/pathnodes.h

@@ -334,11 +334,11 @@ struct PlannerInfo
 
 	MemoryContext planner_cxt;	/* context holding PlannerInfo */
 
-	double		total_table_pages;	/* # of pages in all non-dummy tables of
+	Cardinality	total_table_pages;	/* # of pages in all non-dummy tables of
 									 * query */
 
-	double		tuple_fraction; /* tuple_fraction passed to query_planner */
-	double		limit_tuples;	/* limit_tuples passed to query_planner */
+	Selectivity	tuple_fraction; /* tuple_fraction passed to query_planner */
+	Cardinality	limit_tuples;	/* limit_tuples passed to query_planner */
 
 	Index		qual_security_level;	/* minimum security_level for quals */
 	/* Note: qual_security_level is zero if there are no securityQuals */
@@ -681,7 +681,7 @@ typedef struct RelOptInfo
 	Relids		relids;			/* set of base relids (rangetable indexes) */
 
 	/* size estimates generated by planner */
-	double		rows;			/* estimated number of result tuples */
+	Cardinality	rows;			/* estimated number of result tuples */
 
 	/* per-relation planner control flags */
 	bool		consider_startup;	/* keep cheap-startup-cost paths? */
@@ -718,7 +718,7 @@ typedef struct RelOptInfo
 	List	   *indexlist;		/* list of IndexOptInfo */
 	List	   *statlist;		/* list of StatisticExtInfo */
 	BlockNumber pages;			/* size estimates derived from pg_class */
-	double		tuples;
+	Cardinality	tuples;
 	double		allvisfrac;
 	Bitmapset  *eclass_indexes; /* Indexes in PlannerInfo's eq_classes list of
 								 * ECs that mention this rel */
@@ -841,7 +841,7 @@ struct IndexOptInfo
 
 	/* index-size statistics (from pg_class and elsewhere) */
 	BlockNumber pages;			/* number of disk pages in index */
-	double		tuples;			/* number of index tuples in index */
+	Cardinality	tuples;			/* number of index tuples in index */
 	int			tree_height;	/* index tree height, or -1 if unknown */
 
 	/* index descriptor information */
@@ -1139,7 +1139,7 @@ typedef struct ParamPathInfo
 	NodeTag		type;
 
 	Relids		ppi_req_outer;	/* rels supplying parameters used by path */
-	double		ppi_rows;		/* estimated number of result tuples */
+	Cardinality	ppi_rows;		/* estimated number of result tuples */
 	List	   *ppi_clauses;	/* join clauses available from outer rels */
 } ParamPathInfo;
 
@@ -1189,7 +1189,7 @@ typedef struct Path
 	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 */
+	Cardinality	rows;			/* estimated number of result tuples */
 	Cost		startup_cost;	/* cost expended before fetching any tuples */
 	Cost		total_cost;		/* total cost (assuming all tuples fetched) */
 
@@ -1452,7 +1452,7 @@ typedef struct AppendPath
 	List	   *subpaths;		/* list of component Paths */
 	/* Index of first partial path in subpaths; list_length(subpaths) if none */
 	int			first_partial_path;
-	double		limit_tuples;	/* hard limit on output tuples, or -1 */
+	Cardinality	limit_tuples;	/* hard limit on output tuples, or -1 */
 } AppendPath;
 
 #define IS_DUMMY_APPEND(p) \
@@ -1474,7 +1474,7 @@ typedef struct MergeAppendPath
 {
 	Path		path;
 	List	   *subpaths;		/* list of component Paths */
-	double		limit_tuples;	/* hard limit on output tuples, or -1 */
+	Cardinality	limit_tuples;	/* hard limit on output tuples, or -1 */
 } MergeAppendPath;
 
 /*
@@ -1515,7 +1515,7 @@ typedef struct MemoizePath
 	List	   *param_exprs;	/* cache keys */
 	bool		singlerow;		/* true if the cache entry is to be marked as
 								 * complete after caching the first record. */
-	double		calls;			/* expected number of rescans */
+	Cardinality	calls;			/* expected number of rescans */
 	uint32		est_entries;	/* The maximum number of entries that the
 								 * planner expects will fit in the cache, or 0
 								 * if unknown */
@@ -1667,7 +1667,7 @@ typedef struct HashPath
 	JoinPath	jpath;
 	List	   *path_hashclauses;	/* join clauses used for hashing */
 	int			num_batches;	/* number of batches expected */
-	double		inner_rows_total;	/* total inner rows expected */
+	Cardinality	inner_rows_total;	/* total inner rows expected */
 } HashPath;
 
 /*
@@ -1770,7 +1770,7 @@ typedef struct AggPath
 	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 */
+	Cardinality	numGroups;		/* estimated number of groups in input */
 	uint64		transitionSpace;	/* for pass-by-ref transition data */
 	List	   *groupClause;	/* a list of SortGroupClause's */
 	List	   *qual;			/* quals (HAVING quals), if any */
@@ -1784,7 +1784,7 @@ typedef struct GroupingSetData
 {
 	NodeTag		type;
 	List	   *set;			/* grouping set as list of sortgrouprefs */
-	double		numGroups;		/* est. number of result groups */
+	Cardinality	numGroups;		/* est. number of result groups */
 } GroupingSetData;
 
 typedef struct RollupData
@@ -1793,7 +1793,7 @@ typedef struct RollupData
 	List	   *groupClause;	/* applicable subset of parse->groupClause */
 	List	   *gsets;			/* lists of integer indexes into groupClause */
 	List	   *gsets_data;		/* list of GroupingSetData */
-	double		numGroups;		/* est. number of result groups */
+	Cardinality	numGroups;		/* est. number of result groups */
 	bool		hashable;		/* can be hashed */
 	bool		is_hashed;		/* to be implemented as a hashagg */
 } RollupData;
@@ -1844,7 +1844,7 @@ typedef struct SetOpPath
 	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 */
+	Cardinality	numGroups;		/* estimated number of groups in input */
 } SetOpPath;
 
 /*
@@ -1857,7 +1857,7 @@ typedef struct RecursiveUnionPath
 	Path	   *rightpath;
 	List	   *distinctList;	/* SortGroupClauses identifying target cols */
 	int			wtParam;		/* ID of Param representing work table */
-	double		numGroups;		/* estimated number of groups in input */
+	Cardinality	numGroups;		/* estimated number of groups in input */
 } RecursiveUnionPath;
 
 /*
@@ -2612,7 +2612,7 @@ typedef struct
 typedef struct
 {
 	bool		limit_needed;
-	double		limit_tuples;
+	Cardinality	limit_tuples;
 	int64		count_est;
 	int64		offset_est;
 } FinalPathExtraData;
@@ -2643,15 +2643,15 @@ typedef struct JoinCostWorkspace
 	Cost		inner_rescan_run_cost;
 
 	/* private for cost_mergejoin code */
-	double		outer_rows;
-	double		inner_rows;
-	double		outer_skip_rows;
-	double		inner_skip_rows;
+	Cardinality	outer_rows;
+	Cardinality	inner_rows;
+	Cardinality	outer_skip_rows;
+	Cardinality	inner_skip_rows;
 
 	/* private for cost_hashjoin code */
 	int			numbuckets;
 	int			numbatches;
-	double		inner_rows_total;
+	Cardinality	inner_rows_total;
 } JoinCostWorkspace;
 
 /*

src/include/nodes/plannodes.h

@@ -120,7 +120,7 @@ typedef struct Plan
 	/*
 	 * planner's estimate of result size of this plan step
 	 */
-	double		plan_rows;		/* number of rows plan is expected to emit */
+	Cardinality	plan_rows;		/* number of rows plan is expected to emit */
 	int			plan_width;		/* average row width in bytes */
 
 	/*
@@ -976,7 +976,7 @@ typedef struct Hash
 	AttrNumber	skewColumn;		/* outer join key's column #, or zero */
 	bool		skewInherit;	/* is outer join rel an inheritance tree? */
 	/* all other info is in the parent HashJoin node */
-	double		rows_total;		/* estimate total rows if parallel_aware */
+	Cardinality	rows_total;		/* estimate total rows if parallel_aware */
 } Hash;
 
 /* ----------------