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supportnodes.h
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1 /*-------------------------------------------------------------------------
2  *
3  * supportnodes.h
4  * Definitions for planner support functions.
5  *
6  * This file defines the API for "planner support functions", which
7  * are SQL functions (normally written in C) that can be attached to
8  * another "target" function to give the system additional knowledge
9  * about the target function. All the current capabilities have to do
10  * with planning queries that use the target function, though it is
11  * possible that future extensions will add functionality to be invoked
12  * by the parser or executor.
13  *
14  * A support function must have the SQL signature
15  * supportfn(internal) returns internal
16  * The argument is a pointer to one of the Node types defined in this file.
17  * The result is usually also a Node pointer, though its type depends on
18  * which capability is being invoked. In all cases, a NULL pointer result
19  * (that's PG_RETURN_POINTER(NULL), not PG_RETURN_NULL()) indicates that
20  * the support function cannot do anything useful for the given request.
21  * Support functions must return a NULL pointer, not fail, if they do not
22  * recognize the request node type or cannot handle the given case; this
23  * allows for future extensions of the set of request cases.
24  *
25  *
26  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
27  * Portions Copyright (c) 1994, Regents of the University of California
28  *
29  * src/include/nodes/supportnodes.h
30  *
31  *-------------------------------------------------------------------------
32  */
33 #ifndef SUPPORTNODES_H
34 #define SUPPORTNODES_H
35 
36 #include "nodes/primnodes.h"
37 
38 struct PlannerInfo; /* avoid including pathnodes.h here */
39 struct IndexOptInfo;
40 struct SpecialJoinInfo;
41 
42 
43 /*
44  * The Simplify request allows the support function to perform plan-time
45  * simplification of a call to its target function. For example, a varchar
46  * length coercion that does not decrease the allowed length of its argument
47  * could be replaced by a RelabelType node, or "x + 0" could be replaced by
48  * "x". This is invoked during the planner's constant-folding pass, so the
49  * function's arguments can be presumed already simplified.
50  *
51  * The planner's PlannerInfo "root" is typically not needed, but can be
52  * consulted if it's necessary to obtain info about Vars present in
53  * the given node tree. Beware that root could be NULL in some usages.
54  *
55  * "fcall" will be a FuncExpr invoking the support function's target
56  * function. (This is true even if the original parsetree node was an
57  * operator call; a FuncExpr is synthesized for this purpose.)
58  *
59  * The result should be a semantically-equivalent transformed node tree,
60  * or NULL if no simplification could be performed. Do *not* return or
61  * modify *fcall, as it isn't really a separately allocated Node. But
62  * it's okay to use fcall->args, or parts of it, in the result tree.
63  */
64 typedef struct SupportRequestSimplify
65 {
67 
68  struct PlannerInfo *root; /* Planner's infrastructure */
69  FuncExpr *fcall; /* Function call to be simplified */
71 
72 /*
73  * The Selectivity request allows the support function to provide a
74  * selectivity estimate for a function appearing at top level of a WHERE
75  * clause (so it applies only to functions returning boolean).
76  *
77  * The input arguments are the same as are supplied to operator restriction
78  * and join estimators, except that we unify those two APIs into just one
79  * request type. See clause_selectivity() for the details.
80  *
81  * If an estimate can be made, store it into the "selectivity" field and
82  * return the address of the SupportRequestSelectivity node; the estimate
83  * must be between 0 and 1 inclusive. Return NULL if no estimate can be
84  * made (in which case the planner will fall back to a default estimate,
85  * traditionally 1/3).
86  *
87  * If the target function is being used as the implementation of an operator,
88  * the support function will not be used for this purpose; the operator's
89  * restriction or join estimator is consulted instead.
90  */
92 {
94 
95  /* Input fields: */
96  struct PlannerInfo *root; /* Planner's infrastructure */
97  Oid funcid; /* function we are inquiring about */
98  List *args; /* pre-simplified arguments to function */
99  Oid inputcollid; /* function's input collation */
100  bool is_join; /* is this a join or restriction case? */
101  int varRelid; /* if restriction, RTI of target relation */
102  JoinType jointype; /* if join, outer join type */
103  struct SpecialJoinInfo *sjinfo; /* if outer join, info about join */
104 
105  /* Output fields: */
106  Selectivity selectivity; /* returned selectivity estimate */
108 
109 /*
110  * The Cost request allows the support function to provide an execution
111  * cost estimate for its target function. The cost estimate can include
112  * both a one-time (query startup) component and a per-execution component.
113  * The estimate should *not* include the costs of evaluating the target
114  * function's arguments, only the target function itself.
115  *
116  * The "node" argument is normally the parse node that is invoking the
117  * target function. This is a FuncExpr in the simplest case, but it could
118  * also be an OpExpr, DistinctExpr, NullIfExpr, or WindowFunc, or possibly
119  * other cases in future. NULL is passed if the function cannot presume
120  * its arguments to be equivalent to what the calling node presents as
121  * arguments; that happens for, e.g., aggregate support functions and
122  * per-column comparison operators used by RowExprs.
123  *
124  * If an estimate can be made, store it into the cost fields and return the
125  * address of the SupportRequestCost node. Return NULL if no estimate can be
126  * made, in which case the planner will rely on the target function's procost
127  * field. (Note: while procost is automatically scaled by cpu_operator_cost,
128  * this is not the case for the outputs of the Cost request; the support
129  * function must scale its results appropriately on its own.)
130  */
131 typedef struct SupportRequestCost
132 {
134 
135  /* Input fields: */
136  struct PlannerInfo *root; /* Planner's infrastructure (could be NULL) */
137  Oid funcid; /* function we are inquiring about */
138  Node *node; /* parse node invoking function, or NULL */
139 
140  /* Output fields: */
141  Cost startup; /* one-time cost */
142  Cost per_tuple; /* per-evaluation cost */
144 
145 /*
146  * The Rows request allows the support function to provide an output rowcount
147  * estimate for its target function (so it applies only to set-returning
148  * functions).
149  *
150  * The "node" argument is the parse node that is invoking the target function;
151  * currently this will always be a FuncExpr or OpExpr.
152  *
153  * If an estimate can be made, store it into the rows field and return the
154  * address of the SupportRequestRows node. Return NULL if no estimate can be
155  * made, in which case the planner will rely on the target function's prorows
156  * field.
157  */
158 typedef struct SupportRequestRows
159 {
161 
162  /* Input fields: */
163  struct PlannerInfo *root; /* Planner's infrastructure (could be NULL) */
164  Oid funcid; /* function we are inquiring about */
165  Node *node; /* parse node invoking function */
166 
167  /* Output fields: */
168  double rows; /* number of rows expected to be returned */
170 
171 /*
172  * The IndexCondition request allows the support function to generate
173  * a directly-indexable condition based on a target function call that is
174  * not itself indexable. The target function call must appear at the top
175  * level of WHERE or JOIN/ON, so this applies only to functions returning
176  * boolean.
177  *
178  * The "node" argument is the parse node that is invoking the target function;
179  * currently this will always be a FuncExpr or OpExpr. The call is made
180  * only if at least one function argument matches an index column's variable
181  * or expression. "indexarg" identifies the matching argument (it's the
182  * argument's zero-based index in the node's args list).
183  *
184  * If the transformation is possible, return a List of directly-indexable
185  * condition expressions, else return NULL. (A List is used because it's
186  * sometimes useful to generate more than one indexable condition, such as
187  * when a LIKE with constant prefix gives rise to both >= and < conditions.)
188  *
189  * "Directly indexable" means that the condition must be directly executable
190  * by the index machinery. Typically this means that it is a binary OpExpr
191  * with the index column value on the left, a pseudo-constant on the right,
192  * and an operator that is in the index column's operator family. Other
193  * possibilities include RowCompareExpr, ScalarArrayOpExpr, and NullTest,
194  * depending on the index type; but those seem less likely to be useful for
195  * derived index conditions. "Pseudo-constant" means that the right-hand
196  * expression must not contain any volatile functions, nor any Vars of the
197  * table the index is for; use is_pseudo_constant_for_index() to check this.
198  * (Note: if the passed "node" is an OpExpr, the core planner already verified
199  * that the non-indexkey operand is pseudo-constant; but when the "node"
200  * is a FuncExpr, it does not check, since it doesn't know which of the
201  * function's arguments you might need to use in an index comparison value.)
202  *
203  * In many cases, an index condition can be generated but it is weaker than
204  * the function condition itself; for example, a LIKE with a constant prefix
205  * can produce an index range check based on the prefix, but we still need
206  * to execute the LIKE operator to verify the rest of the pattern. We say
207  * that such an index condition is "lossy". When returning an index condition,
208  * you should set the "lossy" request field to true if the condition is lossy,
209  * or false if it is an exact equivalent of the function's result. The core
210  * code will initialize that field to true, which is the common case.
211  *
212  * It is important to verify that the index operator family is the correct
213  * one for the condition you want to generate. Core support functions tend
214  * to use the known OID of a built-in opfamily for this, but extensions need
215  * to work harder, since their OIDs aren't fixed. A possibly workable
216  * answer for an index on an extension datatype is to verify the index AM's
217  * OID instead, and then assume that there's only one relevant opclass for
218  * your datatype so the opfamily must be the right one. Generating OpExpr
219  * nodes may also require knowing extension datatype OIDs (often you can
220  * find these out by applying exprType() to a function argument) and
221  * operator OIDs (which you can look up using get_opfamily_member).
222  */
224 {
226 
227  /* Input fields: */
228  struct PlannerInfo *root; /* Planner's infrastructure */
229  Oid funcid; /* function we are inquiring about */
230  Node *node; /* parse node invoking function */
231  int indexarg; /* index of function arg matching indexcol */
232  struct IndexOptInfo *index; /* planner's info about target index */
233  int indexcol; /* index of target index column (0-based) */
234  Oid opfamily; /* index column's operator family */
235  Oid indexcollation; /* index column's collation */
236 
237  /* Output fields: */
238  bool lossy; /* set to false if index condition is an exact
239  * equivalent of the function call */
241 
242 #endif /* SUPPORTNODES_H */
struct PlannerInfo * root
Definition: supportnodes.h:68
Definition: nodes.h:525
struct SupportRequestRows SupportRequestRows
double Selectivity
Definition: nodes.h:658
unsigned int Oid
Definition: postgres_ext.h:31
NodeTag
Definition: nodes.h:26
JoinType
Definition: nodes.h:692
struct PlannerInfo * root
Definition: supportnodes.h:163
struct SupportRequestSimplify SupportRequestSimplify
struct IndexOptInfo * index
Definition: supportnodes.h:232
struct PlannerInfo * root
Definition: supportnodes.h:96
struct SpecialJoinInfo * sjinfo
Definition: supportnodes.h:103
struct SupportRequestCost SupportRequestCost
struct SupportRequestIndexCondition SupportRequestIndexCondition
struct SupportRequestSelectivity SupportRequestSelectivity
struct PlannerInfo * root
Definition: supportnodes.h:136
Definition: pg_list.h:50
double Cost
Definition: nodes.h:659
struct PlannerInfo * root
Definition: supportnodes.h:228