selfuncs.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * selfuncs.h
 *    Selectivity functions for standard operators, and assorted
 *    infrastructure for selectivity and cost estimation.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/selfuncs.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SELFUNCS_H
#define SELFUNCS_H
 
#include "access/htup.h"
#include "fmgr.h"
#include "nodes/pathnodes.h"
 
 
/*
 * Note: the default selectivity estimates are not chosen entirely at random.
 * We want them to be small enough to ensure that indexscans will be used if
 * available, for typical table densities of ~100 tuples/page.  Thus, for
 * example, 0.01 is not quite small enough, since that makes it appear that
 * nearly all pages will be hit anyway.  Also, since we sometimes estimate
 * eqsel as 1/num_distinct, we probably want DEFAULT_NUM_DISTINCT to equal
 * 1/DEFAULT_EQ_SEL.
 */
 
/* default selectivity estimate for equalities such as "A = b" */
#define DEFAULT_EQ_SEL  0.005
 
/* default selectivity estimate for inequalities such as "A < b" */
#define DEFAULT_INEQ_SEL  0.3333333333333333
 
/* default selectivity estimate for range inequalities "A > b AND A < c" */
#define DEFAULT_RANGE_INEQ_SEL  0.005
 
/* default selectivity estimate for multirange inequalities "A > b AND A < c" */
#define DEFAULT_MULTIRANGE_INEQ_SEL 0.005
 
/* default selectivity estimate for pattern-match operators such as LIKE */
#define DEFAULT_MATCH_SEL   0.005
 
/* default selectivity estimate for other matching operators */
#define DEFAULT_MATCHING_SEL    0.010
 
/* default number of distinct values in a table */
#define DEFAULT_NUM_DISTINCT  200
 
/* default selectivity estimate for boolean and null test nodes */
#define DEFAULT_UNK_SEL         0.005
#define DEFAULT_NOT_UNK_SEL     (1.0 - DEFAULT_UNK_SEL)
 
 
/*
 * Clamp a computed probability estimate (which may suffer from roundoff or
 * estimation errors) to valid range.  Argument must be a float variable.
 */
#define CLAMP_PROBABILITY(p) \
    do { \
        if (p < 0.0) \
            p = 0.0; \
        else if (p > 1.0) \
            p = 1.0; \
    } while (0)
 
/*
 * A set of flags which some selectivity estimation functions can pass back to
 * callers to provide further details about some assumptions which were made
 * during the estimation.
 */
#define SELFLAG_USED_DEFAULT        (1 << 0)    /* Estimation fell back on one
                                                 * of the DEFAULTs as defined
                                                 * above. */
 
typedef struct EstimationInfo
{
    uint32      flags;          /* Flags, as defined above to mark special
                                 * properties of the estimation. */
} EstimationInfo;
 
/* Return data from examine_variable and friends */
typedef struct VariableStatData
{
    Node       *var;            /* the Var or expression tree */
    RelOptInfo *rel;            /* Relation, or NULL if not identifiable */
    HeapTuple   statsTuple;     /* pg_statistic tuple, or NULL if none */
    /* NB: if statsTuple!=NULL, it must be freed when caller is done */
    void        (*freefunc) (HeapTuple tuple);  /* how to free statsTuple */
    Oid         vartype;        /* exposed type of expression */
    Oid         atttype;        /* actual type (after stripping relabel) */
    int32       atttypmod;      /* actual typmod (after stripping relabel) */
    bool        isunique;       /* matches unique index or DISTINCT clause */
    bool        acl_ok;         /* result of ACL check on table or column */
} VariableStatData;
 
#define ReleaseVariableStats(vardata)  \
    do { \
        if (HeapTupleIsValid((vardata).statsTuple)) \
            (vardata).freefunc((vardata).statsTuple); \
    } while(0)
 
 
/*
 * genericcostestimate is a general-purpose estimator that can be used for
 * most index types.  In some cases we use genericcostestimate as the base
 * code and then incorporate additional index-type-specific knowledge in
 * the type-specific calling function.  To avoid code duplication, we make
 * genericcostestimate return a number of intermediate values as well as
 * its preliminary estimates of the output cost values.  The GenericCosts
 * struct includes all these values.
 *
 * Callers should initialize all fields of GenericCosts to zero.  In addition,
 * they can set numIndexTuples to some positive value if they have a better
 * than default way of estimating the number of leaf index tuples visited.
 */
typedef struct
{
    /* These are the values the cost estimator must return to the planner */
    Cost        indexStartupCost;   /* index-related startup cost */
    Cost        indexTotalCost; /* total index-related scan cost */
    Selectivity indexSelectivity;   /* selectivity of index */
    double      indexCorrelation;   /* order correlation of index */
 
    /* Intermediate values we obtain along the way */
    double      numIndexPages;  /* number of leaf pages visited */
    double      numIndexTuples; /* number of leaf tuples visited */
    double      spc_random_page_cost;   /* relevant random_page_cost value */
    double      num_sa_scans;   /* # indexscans from ScalarArrayOpExprs */
} GenericCosts;
 
/* Hooks for plugins to get control when we ask for stats */
typedef bool (*get_relation_stats_hook_type) (PlannerInfo *root,
                                              RangeTblEntry *rte,
                                              AttrNumber attnum,
                                              VariableStatData *vardata);
extern PGDLLIMPORT get_relation_stats_hook_type get_relation_stats_hook;
typedef bool (*get_index_stats_hook_type) (PlannerInfo *root,
                                           Oid indexOid,
                                           AttrNumber indexattnum,
                                           VariableStatData *vardata);
extern PGDLLIMPORT get_index_stats_hook_type get_index_stats_hook;
 
/* Functions in selfuncs.c */
 
extern void examine_variable(PlannerInfo *root, Node *node, int varRelid,
                             VariableStatData *vardata);
extern bool statistic_proc_security_check(VariableStatData *vardata, Oid func_oid);
extern bool get_restriction_variable(PlannerInfo *root, List *args,
                                     int varRelid,
                                     VariableStatData *vardata, Node **other,
                                     bool *varonleft);
extern void get_join_variables(PlannerInfo *root, List *args,
                               SpecialJoinInfo *sjinfo,
                               VariableStatData *vardata1,
                               VariableStatData *vardata2,
                               bool *join_is_reversed);
extern double get_variable_numdistinct(VariableStatData *vardata,
                                       bool *isdefault);
extern double mcv_selectivity(VariableStatData *vardata,
                              FmgrInfo *opproc, Oid collation,
                              Datum constval, bool varonleft,
                              double *sumcommonp);
extern double histogram_selectivity(VariableStatData *vardata,
                                    FmgrInfo *opproc, Oid collation,
                                    Datum constval, bool varonleft,
                                    int min_hist_size, int n_skip,
                                    int *hist_size);
extern double generic_restriction_selectivity(PlannerInfo *root,
                                              Oid oproid, Oid collation,
                                              List *args, int varRelid,
                                              double default_selectivity);
extern double ineq_histogram_selectivity(PlannerInfo *root,
                                         VariableStatData *vardata,
                                         Oid opoid, FmgrInfo *opproc,
                                         bool isgt, bool iseq,
                                         Oid collation,
                                         Datum constval, Oid consttype);
extern double var_eq_const(VariableStatData *vardata,
                           Oid oproid, Oid collation,
                           Datum constval, bool constisnull,
                           bool varonleft, bool negate);
extern double var_eq_non_const(VariableStatData *vardata,
                               Oid oproid, Oid collation,
                               Node *other,
                               bool varonleft, bool negate);
 
extern Selectivity boolvarsel(PlannerInfo *root, Node *arg, int varRelid);
extern Selectivity booltestsel(PlannerInfo *root, BoolTestType booltesttype,
                               Node *arg, int varRelid,
                               JoinType jointype, SpecialJoinInfo *sjinfo);
extern Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
                               Node *arg, int varRelid,
                               JoinType jointype, SpecialJoinInfo *sjinfo);
extern Selectivity scalararraysel(PlannerInfo *root,
                                  ScalarArrayOpExpr *clause,
                                  bool is_join_clause,
                                  int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo);
extern int  estimate_array_length(Node *arrayexpr);
extern Selectivity rowcomparesel(PlannerInfo *root,
                                 RowCompareExpr *clause,
                                 int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo);
 
extern void mergejoinscansel(PlannerInfo *root, Node *clause,
                             Oid opfamily, int strategy, bool nulls_first,
                             Selectivity *leftstart, Selectivity *leftend,
                             Selectivity *rightstart, Selectivity *rightend);
 
extern double estimate_num_groups(PlannerInfo *root, List *groupExprs,
                                  double input_rows, List **pgset,
                                  EstimationInfo *estinfo);
 
extern void estimate_hash_bucket_stats(PlannerInfo *root,
                                       Node *hashkey, double nbuckets,
                                       Selectivity *mcv_freq,
                                       Selectivity *bucketsize_frac);
extern double estimate_hashagg_tablesize(PlannerInfo *root, Path *path,
                                         const AggClauseCosts *agg_costs,
                                         double dNumGroups);
 
extern List *get_quals_from_indexclauses(List *indexclauses);
extern Cost index_other_operands_eval_cost(PlannerInfo *root,
                                           List *indexquals);
extern List *add_predicate_to_index_quals(IndexOptInfo *index,
                                          List *indexQuals);
extern void genericcostestimate(PlannerInfo *root, IndexPath *path,
                                double loop_count,
                                GenericCosts *costs);
 
/* Functions in array_selfuncs.c */
 
extern Selectivity scalararraysel_containment(PlannerInfo *root,
                                              Node *leftop, Node *rightop,
                                              Oid elemtype, bool isEquality, bool useOr,
                                              int varRelid);
 
#endif                          /* SELFUNCS_H */