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022cd0bfd3
Commit 5e0928005 changed the planner so that, instead of blindly using
DEFAULT_COLLATION_OID when invoking operators for selectivity estimation,
it would use the collation of the column whose statistics we're
considering. This was recognized as still being not quite the right
thing, but it seemed like a good incremental improvement. However,
shortly thereafter we introduced nondeterministic collations, and that
creates cases where operators can fail if they're passed the wrong
collation. We don't want planning to fail in cases where the query itself
would work, so this means that we *must* use the query's collation when
invoking operators for estimation purposes.
The only real problem this creates is in ineq_histogram_selectivity, where
the binary search might produce a garbage answer if we perform comparisons
using a different collation than the column's histogram is ordered with.
However, when the query's collation is significantly different from the
column's default collation, the estimate we previously generated would be
pretty irrelevant anyway; so it's not clear that this will result in
noticeably worse estimates in practice. (A follow-on patch will improve
this situation in HEAD, but it seems too invasive for back-patch.)
The patch requires changing the signatures of mcv_selectivity and allied
functions, which are exported and very possibly are used by extensions.
In HEAD, I just did that, but an API/ABI break of this sort isn't
acceptable in stable branches. Therefore, in v12 the patch introduces
"mcv_selectivity_ext" and so on, with signatures matching HEAD, and makes
the old functions into wrappers that assume DEFAULT_COLLATION_OID should
be used. That does not match the prior behavior, but it should avoid risk
of failure in most cases. (In practice, I think most extension datatypes
aren't collation-aware, so the change probably doesn't matter to them.)
Per report from James Lucas. Back-patch to v12 where the problem was
introduced.
Discussion: https://postgr.es/m/CAAFmbbOvfi=wMM=3qRsPunBSLb8BFREno2oOzSBS=mzfLPKABw@mail.gmail.com
228 lines
9 KiB
C
228 lines
9 KiB
C
/*-------------------------------------------------------------------------
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*
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* selfuncs.h
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* Selectivity functions for standard operators, and assorted
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* infrastructure for selectivity and cost estimation.
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*
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/selfuncs.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SELFUNCS_H
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#define SELFUNCS_H
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#include "access/htup.h"
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#include "nodes/pathnodes.h"
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/*
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* Note: the default selectivity estimates are not chosen entirely at random.
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* We want them to be small enough to ensure that indexscans will be used if
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* available, for typical table densities of ~100 tuples/page. Thus, for
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* example, 0.01 is not quite small enough, since that makes it appear that
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* nearly all pages will be hit anyway. Also, since we sometimes estimate
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* eqsel as 1/num_distinct, we probably want DEFAULT_NUM_DISTINCT to equal
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* 1/DEFAULT_EQ_SEL.
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*/
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/* default selectivity estimate for equalities such as "A = b" */
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#define DEFAULT_EQ_SEL 0.005
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/* default selectivity estimate for inequalities such as "A < b" */
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#define DEFAULT_INEQ_SEL 0.3333333333333333
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/* default selectivity estimate for range inequalities "A > b AND A < c" */
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#define DEFAULT_RANGE_INEQ_SEL 0.005
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/* default selectivity estimate for pattern-match operators such as LIKE */
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#define DEFAULT_MATCH_SEL 0.005
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/* default number of distinct values in a table */
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#define DEFAULT_NUM_DISTINCT 200
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/* default selectivity estimate for boolean and null test nodes */
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#define DEFAULT_UNK_SEL 0.005
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#define DEFAULT_NOT_UNK_SEL (1.0 - DEFAULT_UNK_SEL)
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/*
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* Clamp a computed probability estimate (which may suffer from roundoff or
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* estimation errors) to valid range. Argument must be a float variable.
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*/
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#define CLAMP_PROBABILITY(p) \
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do { \
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if (p < 0.0) \
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p = 0.0; \
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else if (p > 1.0) \
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p = 1.0; \
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} while (0)
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/* Return data from examine_variable and friends */
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typedef struct VariableStatData
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{
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Node *var; /* the Var or expression tree */
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RelOptInfo *rel; /* Relation, or NULL if not identifiable */
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HeapTuple statsTuple; /* pg_statistic tuple, or NULL if none */
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/* NB: if statsTuple!=NULL, it must be freed when caller is done */
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void (*freefunc) (HeapTuple tuple); /* how to free statsTuple */
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Oid vartype; /* exposed type of expression */
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Oid atttype; /* actual type (after stripping relabel) */
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int32 atttypmod; /* actual typmod (after stripping relabel) */
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bool isunique; /* matches unique index or DISTINCT clause */
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bool acl_ok; /* result of ACL check on table or column */
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} VariableStatData;
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#define ReleaseVariableStats(vardata) \
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do { \
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if (HeapTupleIsValid((vardata).statsTuple)) \
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(vardata).freefunc((vardata).statsTuple); \
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} while(0)
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/*
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* genericcostestimate is a general-purpose estimator that can be used for
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* most index types. In some cases we use genericcostestimate as the base
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* code and then incorporate additional index-type-specific knowledge in
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* the type-specific calling function. To avoid code duplication, we make
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* genericcostestimate return a number of intermediate values as well as
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* its preliminary estimates of the output cost values. The GenericCosts
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* struct includes all these values.
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*
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* Callers should initialize all fields of GenericCosts to zero. In addition,
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* they can set numIndexTuples to some positive value if they have a better
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* than default way of estimating the number of leaf index tuples visited.
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*/
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typedef struct
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{
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/* These are the values the cost estimator must return to the planner */
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Cost indexStartupCost; /* index-related startup cost */
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Cost indexTotalCost; /* total index-related scan cost */
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Selectivity indexSelectivity; /* selectivity of index */
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double indexCorrelation; /* order correlation of index */
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/* Intermediate values we obtain along the way */
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double numIndexPages; /* number of leaf pages visited */
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double numIndexTuples; /* number of leaf tuples visited */
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double spc_random_page_cost; /* relevant random_page_cost value */
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double num_sa_scans; /* # indexscans from ScalarArrayOps */
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} GenericCosts;
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/* Hooks for plugins to get control when we ask for stats */
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typedef bool (*get_relation_stats_hook_type) (PlannerInfo *root,
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RangeTblEntry *rte,
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AttrNumber attnum,
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VariableStatData *vardata);
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extern PGDLLIMPORT get_relation_stats_hook_type get_relation_stats_hook;
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typedef bool (*get_index_stats_hook_type) (PlannerInfo *root,
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Oid indexOid,
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AttrNumber indexattnum,
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VariableStatData *vardata);
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extern PGDLLIMPORT get_index_stats_hook_type get_index_stats_hook;
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/* Functions in selfuncs.c */
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extern void examine_variable(PlannerInfo *root, Node *node, int varRelid,
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VariableStatData *vardata);
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extern bool statistic_proc_security_check(VariableStatData *vardata, Oid func_oid);
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extern bool get_restriction_variable(PlannerInfo *root, List *args,
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int varRelid,
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VariableStatData *vardata, Node **other,
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bool *varonleft);
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extern void get_join_variables(PlannerInfo *root, List *args,
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SpecialJoinInfo *sjinfo,
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VariableStatData *vardata1,
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VariableStatData *vardata2,
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bool *join_is_reversed);
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extern double get_variable_numdistinct(VariableStatData *vardata,
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bool *isdefault);
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extern double mcv_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
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Datum constval, bool varonleft,
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double *sumcommonp);
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extern double mcv_selectivity_ext(VariableStatData *vardata,
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FmgrInfo *opproc, Oid collation,
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Datum constval, bool varonleft,
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double *sumcommonp);
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extern double histogram_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
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Datum constval, bool varonleft,
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int min_hist_size, int n_skip,
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int *hist_size);
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extern double histogram_selectivity_ext(VariableStatData *vardata,
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FmgrInfo *opproc, Oid collation,
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Datum constval, bool varonleft,
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int min_hist_size, int n_skip,
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int *hist_size);
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extern double ineq_histogram_selectivity(PlannerInfo *root,
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VariableStatData *vardata,
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FmgrInfo *opproc, bool isgt, bool iseq,
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Datum constval, Oid consttype);
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extern double ineq_histogram_selectivity_ext(PlannerInfo *root,
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VariableStatData *vardata,
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FmgrInfo *opproc,
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bool isgt, bool iseq,
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Oid collation,
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Datum constval, Oid consttype);
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extern double var_eq_const(VariableStatData *vardata, Oid oproid,
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Datum constval, bool constisnull,
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bool varonleft, bool negate);
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extern double var_eq_const_ext(VariableStatData *vardata,
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Oid oproid, Oid collation,
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Datum constval, bool constisnull,
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bool varonleft, bool negate);
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extern double var_eq_non_const(VariableStatData *vardata, Oid oproid,
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Node *other,
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bool varonleft, bool negate);
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extern Selectivity boolvarsel(PlannerInfo *root, Node *arg, int varRelid);
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extern Selectivity booltestsel(PlannerInfo *root, BoolTestType booltesttype,
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Node *arg, int varRelid,
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JoinType jointype, SpecialJoinInfo *sjinfo);
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extern Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
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Node *arg, int varRelid,
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JoinType jointype, SpecialJoinInfo *sjinfo);
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extern Selectivity scalararraysel(PlannerInfo *root,
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ScalarArrayOpExpr *clause,
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bool is_join_clause,
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int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo);
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extern int estimate_array_length(Node *arrayexpr);
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extern Selectivity rowcomparesel(PlannerInfo *root,
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RowCompareExpr *clause,
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int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo);
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extern void mergejoinscansel(PlannerInfo *root, Node *clause,
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Oid opfamily, int strategy, bool nulls_first,
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Selectivity *leftstart, Selectivity *leftend,
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Selectivity *rightstart, Selectivity *rightend);
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extern double estimate_num_groups(PlannerInfo *root, List *groupExprs,
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double input_rows, List **pgset);
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extern void estimate_hash_bucket_stats(PlannerInfo *root,
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Node *hashkey, double nbuckets,
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Selectivity *mcv_freq,
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Selectivity *bucketsize_frac);
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extern double estimate_hashagg_tablesize(Path *path,
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const AggClauseCosts *agg_costs,
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double dNumGroups);
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extern List *get_quals_from_indexclauses(List *indexclauses);
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extern Cost index_other_operands_eval_cost(PlannerInfo *root,
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List *indexquals);
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extern List *add_predicate_to_index_quals(IndexOptInfo *index,
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List *indexQuals);
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extern void genericcostestimate(PlannerInfo *root, IndexPath *path,
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double loop_count,
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GenericCosts *costs);
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/* Functions in array_selfuncs.c */
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extern Selectivity scalararraysel_containment(PlannerInfo *root,
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Node *leftop, Node *rightop,
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Oid elemtype, bool isEquality, bool useOr,
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int varRelid);
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#endif /* SELFUNCS_H */
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