Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * planagg.c
4 : * Special planning for aggregate queries.
5 : *
6 : * This module tries to replace MIN/MAX aggregate functions by subqueries
7 : * of the form
8 : * (SELECT col FROM tab
9 : * WHERE col IS NOT NULL AND existing-quals
10 : * ORDER BY col ASC/DESC
11 : * LIMIT 1)
12 : * Given a suitable index on tab.col, this can be much faster than the
13 : * generic scan-all-the-rows aggregation plan. We can handle multiple
14 : * MIN/MAX aggregates by generating multiple subqueries, and their
15 : * orderings can be different. However, if the query contains any
16 : * non-optimizable aggregates, there's no point since we'll have to
17 : * scan all the rows anyway.
18 : *
19 : *
20 : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
21 : * Portions Copyright (c) 1994, Regents of the University of California
22 : *
23 : *
24 : * IDENTIFICATION
25 : * src/backend/optimizer/plan/planagg.c
26 : *
27 : *-------------------------------------------------------------------------
28 : */
29 : #include "postgres.h"
30 :
31 : #include "access/htup_details.h"
32 : #include "catalog/pg_aggregate.h"
33 : #include "catalog/pg_type.h"
34 : #include "nodes/makefuncs.h"
35 : #include "nodes/nodeFuncs.h"
36 : #include "optimizer/cost.h"
37 : #include "optimizer/optimizer.h"
38 : #include "optimizer/pathnode.h"
39 : #include "optimizer/paths.h"
40 : #include "optimizer/planmain.h"
41 : #include "optimizer/planner.h"
42 : #include "optimizer/subselect.h"
43 : #include "optimizer/tlist.h"
44 : #include "parser/parse_clause.h"
45 : #include "parser/parsetree.h"
46 : #include "rewrite/rewriteManip.h"
47 : #include "utils/lsyscache.h"
48 : #include "utils/syscache.h"
49 :
50 : static bool can_minmax_aggs(PlannerInfo *root, List **context);
51 : static bool build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
52 : Oid eqop, Oid sortop, bool reverse_sort,
53 : bool nulls_first);
54 : static void minmax_qp_callback(PlannerInfo *root, void *extra);
55 : static Oid fetch_agg_sort_op(Oid aggfnoid);
56 :
57 :
58 : /*
59 : * preprocess_minmax_aggregates - preprocess MIN/MAX aggregates
60 : *
61 : * Check to see whether the query contains MIN/MAX aggregate functions that
62 : * might be optimizable via indexscans. If it does, and all the aggregates
63 : * are potentially optimizable, then create a MinMaxAggPath and add it to
64 : * the (UPPERREL_GROUP_AGG, NULL) upperrel.
65 : *
66 : * This should be called by grouping_planner() just before it's ready to call
67 : * query_planner(), because we generate indexscan paths by cloning the
68 : * planner's state and invoking query_planner() on a modified version of
69 : * the query parsetree. Thus, all preprocessing needed before query_planner()
70 : * must already be done. This relies on the list of aggregates in
71 : * root->agginfos, so preprocess_aggrefs() must have been called already, too.
72 : */
73 : void
74 33127 : preprocess_minmax_aggregates(PlannerInfo *root)
75 : {
76 33127 : Query *parse = root->parse;
77 : FromExpr *jtnode;
78 : RangeTblRef *rtr;
79 : RangeTblEntry *rte;
80 : List *aggs_list;
81 : RelOptInfo *grouped_rel;
82 : ListCell *lc;
83 :
84 : /* minmax_aggs list should be empty at this point */
85 : Assert(root->minmax_aggs == NIL);
86 :
87 : /* Nothing to do if query has no aggregates */
88 33127 : if (!parse->hasAggs)
89 32800 : return;
90 :
91 : Assert(!parse->setOperations); /* shouldn't get here if a setop */
92 : Assert(parse->rowMarks == NIL); /* nor if FOR UPDATE */
93 :
94 : /*
95 : * Reject unoptimizable cases.
96 : *
97 : * We don't handle GROUP BY or windowing, because our current
98 : * implementations of grouping require looking at all the rows anyway, and
99 : * so there's not much point in optimizing MIN/MAX.
100 : */
101 33127 : if (parse->groupClause || list_length(parse->groupingSets) > 1 ||
102 29638 : parse->hasWindowFuncs)
103 3494 : return;
104 :
105 : /*
106 : * Reject if query contains any CTEs; there's no way to build an indexscan
107 : * on one so we couldn't succeed here. (If the CTEs are unreferenced,
108 : * that's not true, but it doesn't seem worth expending cycles to check.)
109 : */
110 29633 : if (parse->cteList)
111 61 : return;
112 :
113 : /*
114 : * We also restrict the query to reference exactly one table, since join
115 : * conditions can't be handled reasonably. (We could perhaps handle a
116 : * query containing cartesian-product joins, but it hardly seems worth the
117 : * trouble.) However, the single table could be buried in several levels
118 : * of FromExpr due to subqueries. Note the "single" table could be an
119 : * inheritance parent, too, including the case of a UNION ALL subquery
120 : * that's been flattened to an appendrel.
121 : */
122 29572 : jtnode = parse->jointree;
123 56110 : while (IsA(jtnode, FromExpr))
124 : {
125 29607 : if (list_length(jtnode->fromlist) != 1)
126 3069 : return;
127 26538 : jtnode = linitial(jtnode->fromlist);
128 : }
129 26503 : if (!IsA(jtnode, RangeTblRef))
130 1206 : return;
131 25297 : rtr = (RangeTblRef *) jtnode;
132 25297 : rte = planner_rt_fetch(rtr->rtindex, root);
133 25297 : if (rte->rtekind == RTE_RELATION)
134 : /* ordinary relation, ok */ ;
135 7010 : else if (rte->rtekind == RTE_SUBQUERY && rte->inh)
136 : /* flattened UNION ALL subquery, ok */ ;
137 : else
138 6940 : return;
139 :
140 : /*
141 : * Examine all the aggregates and verify all are MIN/MAX aggregates. Stop
142 : * as soon as we find one that isn't.
143 : */
144 18357 : aggs_list = NIL;
145 18357 : if (!can_minmax_aggs(root, &aggs_list))
146 17765 : return;
147 :
148 : /*
149 : * OK, there is at least the possibility of performing the optimization.
150 : * Build an access path for each aggregate. If any of the aggregates
151 : * prove to be non-indexable, give up; there is no point in optimizing
152 : * just some of them.
153 : */
154 949 : foreach(lc, aggs_list)
155 : {
156 622 : MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
157 : Oid eqop;
158 : bool reverse;
159 :
160 : /*
161 : * We'll need the equality operator that goes with the aggregate's
162 : * ordering operator.
163 : */
164 622 : eqop = get_equality_op_for_ordering_op(mminfo->aggsortop, &reverse);
165 622 : if (!OidIsValid(eqop)) /* shouldn't happen */
166 0 : elog(ERROR, "could not find equality operator for ordering operator %u",
167 : mminfo->aggsortop);
168 :
169 : /*
170 : * We can use either an ordering that gives NULLS FIRST or one that
171 : * gives NULLS LAST; furthermore there's unlikely to be much
172 : * performance difference between them, so it doesn't seem worth
173 : * costing out both ways if we get a hit on the first one. NULLS
174 : * FIRST is more likely to be available if the operator is a
175 : * reverse-sort operator, so try that first if reverse.
176 : */
177 622 : if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse, reverse))
178 357 : continue;
179 265 : if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse, !reverse))
180 0 : continue;
181 :
182 : /* No indexable path for this aggregate, so fail */
183 265 : return;
184 : }
185 :
186 : /*
187 : * OK, we can do the query this way. Prepare to create a MinMaxAggPath
188 : * node.
189 : *
190 : * First, create an output Param node for each agg. (If we end up not
191 : * using the MinMaxAggPath, we'll waste a PARAM_EXEC slot for each agg,
192 : * which is not worth worrying about. We can't wait till create_plan time
193 : * to decide whether to make the Param, unfortunately.)
194 : */
195 684 : foreach(lc, aggs_list)
196 : {
197 357 : MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
198 :
199 357 : mminfo->param =
200 357 : SS_make_initplan_output_param(root,
201 357 : exprType((Node *) mminfo->target),
202 : -1,
203 357 : exprCollation((Node *) mminfo->target));
204 : }
205 :
206 : /*
207 : * Create a MinMaxAggPath node with the appropriate estimated costs and
208 : * other needed data, and add it to the UPPERREL_GROUP_AGG upperrel, where
209 : * it will compete against the standard aggregate implementation. (It
210 : * will likely always win, but we need not assume that here.)
211 : *
212 : * Note: grouping_planner won't have created this upperrel yet, but it's
213 : * fine for us to create it first. We will not have inserted the correct
214 : * consider_parallel value in it, but MinMaxAggPath paths are currently
215 : * never parallel-safe anyway, so that doesn't matter. Likewise, it
216 : * doesn't matter that we haven't filled FDW-related fields in the rel.
217 : * Also, because there are no rowmarks, we know that the processed_tlist
218 : * doesn't need to change anymore, so making the pathtarget now is safe.
219 : */
220 327 : grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG, NULL);
221 327 : add_path(grouped_rel, (Path *)
222 327 : create_minmaxagg_path(root, grouped_rel,
223 : create_pathtarget(root,
224 : root->processed_tlist),
225 : aggs_list,
226 327 : (List *) parse->havingQual));
227 : }
228 :
229 : /*
230 : * can_minmax_aggs
231 : * Examine all the aggregates in the query, and check if they are
232 : * all MIN/MAX aggregates. If so, build a list of MinMaxAggInfo
233 : * nodes for them.
234 : *
235 : * Returns false if a non-MIN/MAX aggregate is found, true otherwise.
236 : */
237 : static bool
238 18357 : can_minmax_aggs(PlannerInfo *root, List **context)
239 : {
240 : ListCell *lc;
241 :
242 : /*
243 : * This function used to have to scan the query for itself, but now we can
244 : * just thumb through the AggInfo list made by preprocess_aggrefs.
245 : */
246 19259 : foreach(lc, root->agginfos)
247 : {
248 18667 : AggInfo *agginfo = lfirst_node(AggInfo, lc);
249 18667 : Aggref *aggref = linitial_node(Aggref, agginfo->aggrefs);
250 : Oid aggsortop;
251 : TargetEntry *curTarget;
252 : MinMaxAggInfo *mminfo;
253 :
254 : Assert(aggref->agglevelsup == 0);
255 18667 : if (list_length(aggref->args) != 1)
256 17765 : return false; /* it couldn't be MIN/MAX */
257 :
258 : /*
259 : * ORDER BY is usually irrelevant for MIN/MAX, but it can change the
260 : * outcome if the aggsortop's operator class recognizes non-identical
261 : * values as equal. For example, 4.0 and 4.00 are equal according to
262 : * numeric_ops, yet distinguishable. If MIN() receives more than one
263 : * value equal to 4.0 and no value less than 4.0, it is unspecified
264 : * which of those equal values MIN() returns. An ORDER BY expression
265 : * that differs for each of those equal values of the argument
266 : * expression makes the result predictable once again. This is a
267 : * niche requirement, and we do not implement it with subquery paths.
268 : * In any case, this test lets us reject ordered-set aggregates
269 : * quickly.
270 : */
271 11030 : if (aggref->aggorder != NIL)
272 394 : return false;
273 : /* note: we do not care if DISTINCT is mentioned ... */
274 :
275 : /*
276 : * We might implement the optimization when a FILTER clause is present
277 : * by adding the filter to the quals of the generated subquery. For
278 : * now, just punt.
279 : */
280 10636 : if (aggref->aggfilter != NULL)
281 31 : return false;
282 :
283 10605 : aggsortop = fetch_agg_sort_op(aggref->aggfnoid);
284 10605 : if (!OidIsValid(aggsortop))
285 9680 : return false; /* not a MIN/MAX aggregate */
286 :
287 925 : curTarget = (TargetEntry *) linitial(aggref->args);
288 :
289 925 : if (contain_mutable_functions((Node *) curTarget->expr))
290 3 : return false; /* not potentially indexable */
291 :
292 922 : if (type_is_rowtype(exprType((Node *) curTarget->expr)))
293 20 : return false; /* IS NOT NULL would have weird semantics */
294 :
295 902 : mminfo = makeNode(MinMaxAggInfo);
296 902 : mminfo->aggfnoid = aggref->aggfnoid;
297 902 : mminfo->aggsortop = aggsortop;
298 902 : mminfo->target = curTarget->expr;
299 902 : mminfo->subroot = NULL; /* don't compute path yet */
300 902 : mminfo->path = NULL;
301 902 : mminfo->pathcost = 0;
302 902 : mminfo->param = NULL;
303 :
304 902 : *context = lappend(*context, mminfo);
305 : }
306 592 : return true;
307 : }
308 :
309 : /*
310 : * build_minmax_path
311 : * Given a MIN/MAX aggregate, try to build an indexscan Path it can be
312 : * optimized with.
313 : *
314 : * If successful, stash the best path in *mminfo and return true.
315 : * Otherwise, return false.
316 : */
317 : static bool
318 887 : build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
319 : Oid eqop, Oid sortop, bool reverse_sort, bool nulls_first)
320 : {
321 : PlannerInfo *subroot;
322 : Query *parse;
323 : TargetEntry *tle;
324 : List *tlist;
325 : NullTest *ntest;
326 : SortGroupClause *sortcl;
327 : RelOptInfo *final_rel;
328 : Path *sorted_path;
329 : Cost path_cost;
330 : double path_fraction;
331 :
332 : /*
333 : * We are going to construct what is effectively a sub-SELECT query, so
334 : * clone the current query level's state and adjust it to make it look
335 : * like a subquery. Any outer references will now be one level higher
336 : * than before. (This means that when we are done, there will be no Vars
337 : * of level 1, which is why the subquery can become an initplan.)
338 : */
339 887 : subroot = palloc_object(PlannerInfo);
340 887 : memcpy(subroot, root, sizeof(PlannerInfo));
341 887 : subroot->query_level++;
342 887 : subroot->parent_root = root;
343 887 : subroot->plan_name = choose_plan_name(root->glob, "minmax", true);
344 887 : subroot->alternative_plan_name = root->plan_name;
345 :
346 : /* reset subplan-related stuff */
347 887 : subroot->plan_params = NIL;
348 887 : subroot->outer_params = NULL;
349 887 : subroot->init_plans = NIL;
350 887 : subroot->agginfos = NIL;
351 887 : subroot->aggtransinfos = NIL;
352 :
353 887 : subroot->parse = parse = copyObject(root->parse);
354 887 : IncrementVarSublevelsUp((Node *) parse, 1, 1);
355 :
356 : /* append_rel_list might contain outer Vars? */
357 887 : subroot->append_rel_list = copyObject(root->append_rel_list);
358 887 : IncrementVarSublevelsUp((Node *) subroot->append_rel_list, 1, 1);
359 : /* There shouldn't be any OJ info to translate, as yet */
360 : Assert(subroot->join_info_list == NIL);
361 : /* and we haven't made equivalence classes, either */
362 : Assert(subroot->eq_classes == NIL);
363 : /* and we haven't created PlaceHolderInfos, either */
364 : Assert(subroot->placeholder_list == NIL);
365 :
366 : /*----------
367 : * Generate modified query of the form
368 : * (SELECT col FROM tab
369 : * WHERE col IS NOT NULL AND existing-quals
370 : * ORDER BY col ASC/DESC
371 : * LIMIT 1)
372 : *----------
373 : */
374 : /* single tlist entry that is the aggregate target */
375 887 : tle = makeTargetEntry(copyObject(mminfo->target),
376 : (AttrNumber) 1,
377 : pstrdup("agg_target"),
378 : false);
379 887 : tlist = list_make1(tle);
380 887 : subroot->processed_tlist = parse->targetList = tlist;
381 :
382 : /* No HAVING, no DISTINCT, no aggregates anymore */
383 887 : parse->havingQual = NULL;
384 887 : subroot->hasHavingQual = false;
385 887 : parse->distinctClause = NIL;
386 887 : parse->hasDistinctOn = false;
387 887 : parse->hasAggs = false;
388 :
389 : /* Build "target IS NOT NULL" expression */
390 887 : ntest = makeNode(NullTest);
391 887 : ntest->nulltesttype = IS_NOT_NULL;
392 887 : ntest->arg = copyObject(mminfo->target);
393 : /* we checked it wasn't a rowtype in can_minmax_aggs */
394 887 : ntest->argisrow = false;
395 887 : ntest->location = -1;
396 :
397 : /* User might have had that in WHERE already */
398 887 : if (!list_member((List *) parse->jointree->quals, ntest))
399 887 : parse->jointree->quals = (Node *)
400 887 : lcons(ntest, (List *) parse->jointree->quals);
401 :
402 : /* Build suitable ORDER BY clause */
403 887 : sortcl = makeNode(SortGroupClause);
404 887 : sortcl->tleSortGroupRef = assignSortGroupRef(tle, subroot->processed_tlist);
405 887 : sortcl->eqop = eqop;
406 887 : sortcl->sortop = sortop;
407 887 : sortcl->reverse_sort = reverse_sort;
408 887 : sortcl->nulls_first = nulls_first;
409 887 : sortcl->hashable = false; /* no need to make this accurate */
410 887 : parse->sortClause = list_make1(sortcl);
411 :
412 : /* set up expressions for LIMIT 1 */
413 887 : parse->limitOffset = NULL;
414 887 : parse->limitCount = (Node *) makeConst(INT8OID, -1, InvalidOid,
415 : sizeof(int64),
416 : Int64GetDatum(1), false,
417 : true);
418 :
419 : /*
420 : * Generate the best paths for this query, telling query_planner that we
421 : * have LIMIT 1.
422 : */
423 887 : subroot->tuple_fraction = 1.0;
424 887 : subroot->limit_tuples = 1.0;
425 :
426 887 : final_rel = query_planner(subroot, minmax_qp_callback, NULL);
427 :
428 : /*
429 : * Since we didn't go through subquery_planner() to handle the subquery,
430 : * we have to do some of the same cleanup it would do, in particular cope
431 : * with params and initplans used within this subquery. (This won't
432 : * matter if we end up not using the subplan.)
433 : */
434 887 : SS_identify_outer_params(subroot);
435 887 : SS_charge_for_initplans(subroot, final_rel);
436 :
437 : /*
438 : * Get the best presorted path, that being the one that's cheapest for
439 : * fetching just one row. If there's no such path, fail.
440 : */
441 887 : if (final_rel->rows > 1.0)
442 857 : path_fraction = 1.0 / final_rel->rows;
443 : else
444 30 : path_fraction = 1.0;
445 :
446 : sorted_path =
447 887 : get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
448 : subroot->query_pathkeys,
449 : NULL,
450 : path_fraction);
451 887 : if (!sorted_path)
452 530 : return false;
453 :
454 : /*
455 : * The path might not return exactly what we want, so fix that. (We
456 : * assume that this won't change any conclusions about which was the
457 : * cheapest path.)
458 : */
459 357 : sorted_path = apply_projection_to_path(subroot, final_rel, sorted_path,
460 : create_pathtarget(subroot,
461 : subroot->processed_tlist));
462 :
463 : /*
464 : * Determine cost to get just the first row of the presorted path.
465 : *
466 : * Note: cost calculation here should match
467 : * compare_fractional_path_costs().
468 : */
469 357 : path_cost = sorted_path->startup_cost +
470 357 : path_fraction * (sorted_path->total_cost - sorted_path->startup_cost);
471 :
472 : /* Save state for further processing */
473 357 : mminfo->subroot = subroot;
474 357 : mminfo->path = sorted_path;
475 357 : mminfo->pathcost = path_cost;
476 :
477 357 : return true;
478 : }
479 :
480 : /*
481 : * Compute query_pathkeys and other pathkeys during query_planner()
482 : */
483 : static void
484 887 : minmax_qp_callback(PlannerInfo *root, void *extra)
485 : {
486 887 : root->group_pathkeys = NIL;
487 887 : root->window_pathkeys = NIL;
488 887 : root->distinct_pathkeys = NIL;
489 :
490 887 : root->sort_pathkeys =
491 887 : make_pathkeys_for_sortclauses(root,
492 887 : root->parse->sortClause,
493 887 : root->parse->targetList);
494 :
495 887 : root->query_pathkeys = root->sort_pathkeys;
496 887 : }
497 :
498 : /*
499 : * Get the OID of the sort operator, if any, associated with an aggregate.
500 : * Returns InvalidOid if there is no such operator.
501 : */
502 : static Oid
503 10605 : fetch_agg_sort_op(Oid aggfnoid)
504 : {
505 : HeapTuple aggTuple;
506 : Form_pg_aggregate aggform;
507 : Oid aggsortop;
508 :
509 : /* fetch aggregate entry from pg_aggregate */
510 10605 : aggTuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(aggfnoid));
511 10605 : if (!HeapTupleIsValid(aggTuple))
512 0 : return InvalidOid;
513 10605 : aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
514 10605 : aggsortop = aggform->aggsortop;
515 10605 : ReleaseSysCache(aggTuple);
516 :
517 10605 : return aggsortop;
518 : }
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