postgresql/src/include/utils/selfuncs.h

/*-------------------------------------------------------------------------
 *
 * selfuncs.h
 *	  Selectivity functions for standard operators, and assorted
 *	  infrastructure for selectivity and cost estimation.
 *
 *
 * Portions Copyright (c) 1996-2017, 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 "fmgr.h"
#include "access/htup.h"
#include "nodes/relation.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 pattern-match operators such as LIKE */
#define DEFAULT_MATCH_SEL	0.005

/* 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)


/* 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;		/* type to pass to get_attstatsslot */
	int32		atttypmod;		/* typmod to pass to get_attstatsslot */
	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)


typedef enum
{
	Pattern_Type_Like, Pattern_Type_Like_IC,
	Pattern_Type_Regex, Pattern_Type_Regex_IC
} Pattern_Type;

typedef enum
{
	Pattern_Prefix_None, Pattern_Prefix_Partial, Pattern_Prefix_Exact
} Pattern_Prefix_Status;

/*
 * deconstruct_indexquals is a simple function to examine the indexquals
 * attached to a proposed IndexPath.  It returns a list of IndexQualInfo
 * structs, one per qual expression.
 */
typedef struct
{
	RestrictInfo *rinfo;		/* the indexqual itself */
	int			indexcol;		/* zero-based index column number */
	bool		varonleft;		/* true if index column is on left of qual */
	Oid			clause_op;		/* qual's operator OID, if relevant */
	Node	   *other_operand;	/* non-index operand of qual's operator */
} IndexQualInfo;

/*
 * 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 ScalarArrayOps */
} 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,
				Datum constval, bool varonleft,
				double *sumcommonp);
extern double histogram_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
					  Datum constval, bool varonleft,
					  int min_hist_size, int n_skip,
					  int *hist_size);

extern Pattern_Prefix_Status pattern_fixed_prefix(Const *patt,
					 Pattern_Type ptype,
					 Oid collation,
					 Const **prefix,
					 Selectivity *rest_selec);
extern Const *make_greater_string(const Const *str_const, FmgrInfo *ltproc,
					Oid collation);

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);

extern Selectivity estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey,
						 double nbuckets);

extern List *deconstruct_indexquals(IndexPath *path);
extern void genericcostestimate(PlannerInfo *root, IndexPath *path,
					double loop_count,
					List *qinfos,
					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 */