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diff --git a/src/include/statistics/statistics.h b/src/include/statistics/statistics.h
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+/*-------------------------------------------------------------------------
+ *
+ * statistics.h
+ *	  Extended statistics and selectivity estimation functions.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/statistics/statistics.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef STATISTICS_H
+#define STATISTICS_H
+
+#include "commands/vacuum.h"
+#include "nodes/pathnodes.h"
+
+#define STATS_MAX_DIMENSIONS	8	/* max number of attributes */
+
+/* Multivariate distinct coefficients */
+#define STATS_NDISTINCT_MAGIC		0xA352BFA4	/* struct identifier */
+#define STATS_NDISTINCT_TYPE_BASIC	1	/* struct version */
+
+/* MVNDistinctItem represents a single combination of columns */
+typedef struct MVNDistinctItem
+{
+	double		ndistinct;		/* ndistinct value for this combination */
+	int			nattributes;	/* number of attributes */
+	AttrNumber *attributes;		/* attribute numbers */
+} MVNDistinctItem;
+
+/* A MVNDistinct object, comprising all possible combinations of columns */
+typedef struct MVNDistinct
+{
+	uint32		magic;			/* magic constant marker */
+	uint32		type;			/* type of ndistinct (BASIC) */
+	uint32		nitems;			/* number of items in the statistic */
+	MVNDistinctItem items[FLEXIBLE_ARRAY_MEMBER];
+} MVNDistinct;
+
+/* Multivariate functional dependencies */
+#define STATS_DEPS_MAGIC		0xB4549A2C	/* marks serialized bytea */
+#define STATS_DEPS_TYPE_BASIC	1	/* basic dependencies type */
+
+/*
+ * Functional dependencies, tracking column-level relationships (values
+ * in one column determine values in another one).
+ */
+typedef struct MVDependency
+{
+	double		degree;			/* degree of validity (0-1) */
+	AttrNumber	nattributes;	/* number of attributes */
+	AttrNumber	attributes[FLEXIBLE_ARRAY_MEMBER];	/* attribute numbers */
+} MVDependency;
+
+typedef struct MVDependencies
+{
+	uint32		magic;			/* magic constant marker */
+	uint32		type;			/* type of MV Dependencies (BASIC) */
+	uint32		ndeps;			/* number of dependencies */
+	MVDependency *deps[FLEXIBLE_ARRAY_MEMBER];	/* dependencies */
+} MVDependencies;
+
+/* used to flag stats serialized to bytea */
+#define STATS_MCV_MAGIC			0xE1A651C2	/* marks serialized bytea */
+#define STATS_MCV_TYPE_BASIC	1	/* basic MCV list type */
+
+/* max items in MCV list (should be equal to max default_statistics_target) */
+#define STATS_MCVLIST_MAX_ITEMS        10000
+
+/*
+ * Multivariate MCV (most-common value) lists
+ *
+ * A straightforward extension of MCV items - i.e. a list (array) of
+ * combinations of attribute values, together with a frequency and null flags.
+ */
+typedef struct MCVItem
+{
+	double		frequency;		/* frequency of this combination */
+	double		base_frequency; /* frequency if independent */
+	bool	   *isnull;			/* NULL flags */
+	Datum	   *values;			/* item values */
+} MCVItem;
+
+/* multivariate MCV list - essentially an array of MCV items */
+typedef struct MCVList
+{
+	uint32		magic;			/* magic constant marker */
+	uint32		type;			/* type of MCV list (BASIC) */
+	uint32		nitems;			/* number of MCV items in the array */
+	AttrNumber	ndimensions;	/* number of dimensions */
+	Oid			types[STATS_MAX_DIMENSIONS];	/* OIDs of data types */
+	MCVItem		items[FLEXIBLE_ARRAY_MEMBER];	/* array of MCV items */
+} MCVList;
+
+extern MVNDistinct *statext_ndistinct_load(Oid mvoid);
+extern MVDependencies *statext_dependencies_load(Oid mvoid);
+extern MCVList *statext_mcv_load(Oid mvoid);
+
+extern void BuildRelationExtStatistics(Relation onerel, double totalrows,
+									   int numrows, HeapTuple *rows,
+									   int natts, VacAttrStats **vacattrstats);
+extern int	ComputeExtStatisticsRows(Relation onerel,
+									 int natts, VacAttrStats **stats);
+extern bool statext_is_kind_built(HeapTuple htup, char kind);
+extern Selectivity dependencies_clauselist_selectivity(PlannerInfo *root,
+													   List *clauses,
+													   int varRelid,
+													   JoinType jointype,
+													   SpecialJoinInfo *sjinfo,
+													   RelOptInfo *rel,
+													   Bitmapset **estimatedclauses);
+extern Selectivity statext_clauselist_selectivity(PlannerInfo *root,
+												  List *clauses,
+												  int varRelid,
+												  JoinType jointype,
+												  SpecialJoinInfo *sjinfo,
+												  RelOptInfo *rel,
+												  Bitmapset **estimatedclauses,
+												  bool is_or);
+extern bool has_stats_of_kind(List *stats, char requiredkind);
+extern StatisticExtInfo *choose_best_statistics(List *stats, char requiredkind,
+												Bitmapset **clause_attnums,
+												List **clause_exprs,
+												int nclauses);
+extern HeapTuple statext_expressions_load(Oid stxoid, int idx);
+
+#endif							/* STATISTICS_H */