mirror of
https://github.com/postgres/postgres.git
synced 2026-05-22 00:25:21 -04:00
Tom Lane
0ee5a39862
the number of rows likely to be produced by a query such as SELECT * FROM t1 LEFT JOIN t2 USING (key) WHERE t2.key IS NULL; What this is doing is selecting for t1 rows with no match in t2, and thus it may produce a significant number of rows even if the t2.key table column contains no nulls at all. 8.2 thinks the table column's null fraction is relevant and thus may estimate no rows out, which results in terrible plans if there are more joins above this one. A proper fix for this will involve passing much more information about the context of a clause to the selectivity estimator functions than we ever have. There's no time left to write such a patch for 8.3, and it wouldn't be back-patchable into 8.2 anyway. Instead, put in an ad-hoc test to defeat the normal table-stats-based estimation when an IS NULL test is evaluated at an outer join, and just use a constant estimate instead --- I went with 0.5 for lack of a better idea. This won't catch every case but it will catch the typical ways of writing such queries, and it seems unlikely to make things worse for other queries.
179 lines
6.1 KiB
C
179 lines
6.1 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* selfuncs.h
|
|
* Selectivity functions and index cost estimation functions for
|
|
* standard operators and index access methods.
|
|
*
|
|
*
|
|
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
* $PostgreSQL: pgsql/src/include/utils/selfuncs.h,v 1.40 2007/08/31 23:35:22 tgl Exp $
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#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
|
|
{
|
|
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 */
|
|
Oid vartype; /* exposed type of expression */
|
|
Oid atttype; /* type to pass to get_attstatsslot */
|
|
int32 atttypmod; /* typmod to pass to get_attstatsslot */
|
|
bool isunique; /* true if matched to a unique index */
|
|
} VariableStatData;
|
|
|
|
#define ReleaseVariableStats(vardata) \
|
|
do { \
|
|
if (HeapTupleIsValid((vardata).statsTuple)) \
|
|
ReleaseSysCache((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;
|
|
|
|
|
|
/* selfuncs.c */
|
|
|
|
extern void examine_variable(PlannerInfo *root, Node *node, int varRelid,
|
|
VariableStatData *vardata);
|
|
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,
|
|
VariableStatData *vardata1,
|
|
VariableStatData *vardata2);
|
|
extern double get_variable_numdistinct(VariableStatData *vardata);
|
|
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);
|
|
|
|
extern Pattern_Prefix_Status pattern_fixed_prefix(Const *patt,
|
|
Pattern_Type ptype,
|
|
Const **prefix,
|
|
Const **rest);
|
|
extern Const *make_greater_string(const Const *str_const);
|
|
|
|
extern Datum eqsel(PG_FUNCTION_ARGS);
|
|
extern Datum neqsel(PG_FUNCTION_ARGS);
|
|
extern Datum scalarltsel(PG_FUNCTION_ARGS);
|
|
extern Datum scalargtsel(PG_FUNCTION_ARGS);
|
|
extern Datum regexeqsel(PG_FUNCTION_ARGS);
|
|
extern Datum icregexeqsel(PG_FUNCTION_ARGS);
|
|
extern Datum likesel(PG_FUNCTION_ARGS);
|
|
extern Datum iclikesel(PG_FUNCTION_ARGS);
|
|
extern Datum regexnesel(PG_FUNCTION_ARGS);
|
|
extern Datum icregexnesel(PG_FUNCTION_ARGS);
|
|
extern Datum nlikesel(PG_FUNCTION_ARGS);
|
|
extern Datum icnlikesel(PG_FUNCTION_ARGS);
|
|
|
|
extern Datum eqjoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum neqjoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum scalarltjoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum scalargtjoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum regexeqjoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum icregexeqjoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum likejoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum iclikejoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum regexnejoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum icregexnejoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum nlikejoinsel(PG_FUNCTION_ARGS);
|
|
extern Datum icnlikejoinsel(PG_FUNCTION_ARGS);
|
|
|
|
extern Selectivity booltestsel(PlannerInfo *root, BoolTestType booltesttype,
|
|
Node *arg, int varRelid, JoinType jointype);
|
|
extern Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
|
|
Node *arg, int varRelid, JoinType jointype);
|
|
extern Selectivity scalararraysel(PlannerInfo *root,
|
|
ScalarArrayOpExpr *clause,
|
|
bool is_join_clause,
|
|
int varRelid, JoinType jointype);
|
|
extern int estimate_array_length(Node *arrayexpr);
|
|
extern Selectivity rowcomparesel(PlannerInfo *root,
|
|
RowCompareExpr *clause,
|
|
int varRelid, JoinType jointype);
|
|
|
|
extern void mergejoinscansel(PlannerInfo *root, Node *clause,
|
|
Oid opfamily, int strategy, bool nulls_first,
|
|
Selectivity *leftscan,
|
|
Selectivity *rightscan);
|
|
|
|
extern double estimate_num_groups(PlannerInfo *root, List *groupExprs,
|
|
double input_rows);
|
|
|
|
extern Selectivity estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey,
|
|
double nbuckets);
|
|
|
|
extern Datum btcostestimate(PG_FUNCTION_ARGS);
|
|
extern Datum hashcostestimate(PG_FUNCTION_ARGS);
|
|
extern Datum gistcostestimate(PG_FUNCTION_ARGS);
|
|
extern Datum gincostestimate(PG_FUNCTION_ARGS);
|
|
|
|
#endif /* SELFUNCS_H */
|