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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. The name is now something of a misnomer,
10 * since some of the call sites are in the executor not the planner,
11 * but "function support function" would be a confusing name so we
12 * stick with "planner support function".
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) 1996-2025, 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/plannodes.h"
37
38struct PlannerInfo; /* avoid including pathnodes.h here */
39struct IndexOptInfo;
40struct SpecialJoinInfo;
41struct WindowClause;
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 */
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 */
131typedef 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 */
158typedef 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/* ----------
243 * To support more efficient query execution of any monotonically increasing
244 * and/or monotonically decreasing window functions, we support calling the
245 * window function's prosupport function passing along this struct whenever
246 * the planner sees an OpExpr qual directly reference a window function in a
247 * subquery. When the planner encounters this, we populate this struct and
248 * pass it along to the window function's prosupport function so that it can
249 * evaluate if the given WindowFunc is;
250 *
251 * a) monotonically increasing, or
252 * b) monotonically decreasing, or
253 * c) both monotonically increasing and decreasing, or
254 * d) none of the above.
255 *
256 * A function that is monotonically increasing can never return a value that
257 * is lower than a value returned in a "previous call". A monotonically
258 * decreasing function can never return a value higher than a value returned
259 * in a previous call. A function that is both must return the same value
260 * each time.
261 *
262 * We define "previous call" to mean a previous call to the same WindowFunc
263 * struct in the same window partition.
264 *
265 * row_number() is an example of a monotonically increasing function. The
266 * return value will be reset back to 1 in each new partition. An example of
267 * a monotonically increasing and decreasing function is COUNT(*) OVER ().
268 * Since there is no ORDER BY clause in this example, all rows in the
269 * partition are peers and all rows within the partition will be within the
270 * frame bound. Likewise for COUNT(*) OVER(ORDER BY a ROWS BETWEEN UNBOUNDED
271 * PRECEDING AND UNBOUNDED FOLLOWING).
272 *
273 * COUNT(*) OVER (ORDER BY a ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)
274 * is an example of a monotonically decreasing function.
275 *
276 * Implementations must only concern themselves with the given WindowFunc
277 * being monotonic in a single partition.
278 *
279 * Inputs:
280 * 'window_func' is the pointer to the window function being called.
281 *
282 * 'window_clause' pointer to the WindowClause data. Support functions can
283 * use this to check frame bounds, etc.
284 *
285 * Outputs:
286 * 'monotonic' the resulting MonotonicFunction value for the given input
287 * window function and window clause.
288 * ----------
289 */
291{
293
294 /* Input fields: */
295 WindowFunc *window_func; /* Pointer to the window function data */
296 struct WindowClause *window_clause; /* Pointer to the window clause data */
297
298 /* Output fields: */
301
302/*
303 * Some WindowFunc behavior might not be affected by certain variations in
304 * the WindowClause's frameOptions. For example, row_number() is coded in
305 * such a way that the frame options don't change the returned row number.
306 * nodeWindowAgg.c will have less work to do if the ROWS option is used
307 * instead of the RANGE option as no check needs to be done for peer rows.
308 * Since RANGE is included in the default frame options, window functions
309 * such as row_number() might want to change that to ROW.
310 *
311 * Here we allow a WindowFunc's support function to determine which, if
312 * anything, can be changed about the WindowClause which the WindowFunc
313 * belongs to. Currently only the frameOptions can be modified. However,
314 * we may want to allow more optimizations in the future.
315 *
316 * The support function is responsible for ensuring the optimized version of
317 * the frameOptions doesn't affect the result of the window function. The
318 * planner is responsible for only changing the frame options when all
319 * WindowFuncs using this particular WindowClause agree on what the optimized
320 * version of the frameOptions are. If a particular WindowFunc being used
321 * does not have a support function then the planner will not make any changes
322 * to the WindowClause's frameOptions.
323 *
324 * 'window_func' and 'window_clause' are set by the planner before calling the
325 * support function so that the support function has these fields available.
326 * These may be required in order to determine which optimizations are
327 * possible.
328 *
329 * 'frameOptions' is set by the planner to WindowClause.frameOptions. The
330 * support function must only adjust this if optimizations are possible for
331 * the given WindowFunc.
332 */
334{
336
337 /* Input fields: */
338 WindowFunc *window_func; /* Pointer to the window function data */
339 struct WindowClause *window_clause; /* Pointer to the window clause data */
340
341 /* Input/Output fields: */
342 int frameOptions; /* New frameOptions, or left untouched if no
343 * optimizations are possible. */
345
346/*
347 * The ModifyInPlace request allows the support function to detect whether
348 * a call to its target function can be allowed to modify a read/write
349 * expanded object in-place. The context is that we are considering a
350 * PL/pgSQL (or similar PL) assignment of the form "x := f(x, ...)" where
351 * the variable x is of a type that can be represented as an expanded object
352 * (see utils/expandeddatum.h). If f() can usefully optimize by modifying
353 * the passed-in object in-place, then this request can be implemented to
354 * instruct PL/pgSQL to pass a read-write expanded pointer to the variable's
355 * value. (Note that there is no guarantee that later calls to f() will
356 * actually do so. If f() receives a read-only pointer, or a pointer to a
357 * non-expanded object, it must follow the usual convention of not modifying
358 * the pointed-to object.) There are two requirements that must be met
359 * to make this safe:
360 * 1. f() must guarantee that it will not have modified the object if it
361 * fails. Otherwise the variable's value might change unexpectedly.
362 * 2. If the other arguments to f() ("..." in the above example) contain
363 * references to x, f() must be able to cope with that; or if that's not
364 * safe, the support function must scan the other arguments to verify that
365 * there are no other references to x. An example of the concern here is
366 * that in "arr := array_append(arr, arr[1])", if the array element type
367 * is pass-by-reference then array_append would receive a second argument
368 * that points into the array object it intends to modify. array_append is
369 * coded to make that safe, but other functions might not be able to cope.
370 *
371 * "args" is a node tree list representing the function's arguments.
372 * One or more nodes within the node tree will be PARAM_EXTERN Params
373 * with ID "paramid", which represent the assignment target variable.
374 * (Note that such references are not necessarily at top level in the list,
375 * for example we might have "x := f(x, g(x))". Generally it's only safe
376 * to optimize a reference that is at top level, else we're making promises
377 * about the behavior of g() as well as f().)
378 *
379 * If modify-in-place is safe, the support function should return the
380 * address of the Param node that is to return a read-write pointer.
381 * (At most one of the references is allowed to do so.) Otherwise,
382 * return NULL.
383 */
385{
387
388 Oid funcid; /* PG_PROC OID of the target function */
389 List *args; /* Arguments to the function */
390 int paramid; /* ID of Param(s) representing variable */
392
393#endif /* SUPPORTNODES_H */
double Cost
Definition: nodes.h:257
NodeTag
Definition: nodes.h:27
double Selectivity
Definition: nodes.h:256
JoinType
Definition: nodes.h:294
MonotonicFunction
Definition: plannodes.h:1767
unsigned int Oid
Definition: postgres_ext.h:30
Definition: pg_list.h:54
Definition: nodes.h:135
struct PlannerInfo * root
Definition: supportnodes.h:136
struct IndexOptInfo * index
Definition: supportnodes.h:232
struct PlannerInfo * root
Definition: supportnodes.h:228
struct WindowClause * window_clause
Definition: supportnodes.h:339
struct PlannerInfo * root
Definition: supportnodes.h:163
struct PlannerInfo * root
Definition: supportnodes.h:96
struct SpecialJoinInfo * sjinfo
Definition: supportnodes.h:103
struct PlannerInfo * root
Definition: supportnodes.h:68
struct WindowClause * window_clause
Definition: supportnodes.h:296
MonotonicFunction monotonic
Definition: supportnodes.h:299
struct SupportRequestModifyInPlace SupportRequestModifyInPlace
struct SupportRequestSimplify SupportRequestSimplify
struct SupportRequestCost SupportRequestCost
struct SupportRequestIndexCondition SupportRequestIndexCondition
struct SupportRequestOptimizeWindowClause SupportRequestOptimizeWindowClause
struct SupportRequestSelectivity SupportRequestSelectivity
struct SupportRequestRows SupportRequestRows
struct SupportRequestWFuncMonotonic SupportRequestWFuncMonotonic