statistics.h

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/*-------------------------------------------------------------------------
 *
 * statistics.h
 *    Extended statistics and selectivity estimation functions.
 *
 * Portions Copyright (c) 1996-2020, 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 */
    Bitmapset  *attrs;          /* attr numbers of items */
} 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);
extern bool has_stats_of_kind(List *stats, char requiredkind);
extern StatisticExtInfo *choose_best_statistics(List *stats, char requiredkind,
                                                Bitmapset **clause_attnums,
                                                int nclauses);

#endif                          /* STATISTICS_H */