Branch data 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 : 4926 : preprocess_minmax_aggregates(PlannerInfo *root)
75 : : {
76 : 4926 : Query *parse = root->parse;
77 : 4926 : FromExpr *jtnode;
78 : 4926 : RangeTblRef *rtr;
79 : 4926 : RangeTblEntry *rte;
80 : 4926 : List *aggs_list;
81 : 4926 : RelOptInfo *grouped_rel;
82 : 4926 : ListCell *lc;
83 : :
84 : : /* minmax_aggs list should be empty at this point */
85 [ + - ]: 4926 : Assert(root->minmax_aggs == NIL);
86 : :
87 : : /* Nothing to do if query has no aggregates */
88 [ + - ]: 4926 : if (!parse->hasAggs)
89 : 0 : return;
90 : :
91 [ + - ]: 4926 : Assert(!parse->setOperations); /* shouldn't get here if a setop */
92 [ + - ]: 4926 : 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 [ + + + + : 4926 : if (parse->groupClause || list_length(parse->groupingSets) > 1 ||
+ + ]
102 : 4295 : parse->hasWindowFuncs)
103 : 632 : 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 [ + + ]: 4294 : if (parse->cteList)
111 : 12 : 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 : 4282 : jtnode = parse->jointree;
123 [ + + ]: 8021 : while (IsA(jtnode, FromExpr))
124 : : {
125 [ + + ]: 4287 : if (list_length(jtnode->fromlist) != 1)
126 : 548 : return;
127 : 3739 : jtnode = linitial(jtnode->fromlist);
128 : : }
129 [ + + ]: 3734 : if (!IsA(jtnode, RangeTblRef))
130 : 151 : return;
131 : 3583 : rtr = (RangeTblRef *) jtnode;
132 [ + - ]: 3583 : rte = planner_rt_fetch(rtr->rtindex, root);
133 [ + + ]: 3583 : if (rte->rtekind == RTE_RELATION)
134 : : /* ordinary relation, ok */ ;
135 [ + + + + ]: 529 : else if (rte->rtekind == RTE_SUBQUERY && rte->inh)
136 : : /* flattened UNION ALL subquery, ok */ ;
137 : : else
138 : 520 : 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 : 3063 : aggs_list = NIL;
145 [ + + ]: 3063 : if (!can_minmax_aggs(root, &aggs_list))
146 : 2956 : 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 [ + - + + : 220 : foreach(lc, aggs_list)
+ + + + ]
155 : : {
156 : 113 : MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
157 : 113 : Oid eqop;
158 : 113 : bool reverse;
159 : :
160 : : /*
161 : : * We'll need the equality operator that goes with the aggregate's
162 : : * ordering operator.
163 : : */
164 : 113 : eqop = get_equality_op_for_ordering_op(mminfo->aggsortop, &reverse);
165 [ + - ]: 113 : 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 [ + + ]: 113 : if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse, reverse))
178 : 64 : continue;
179 [ - + ]: 49 : 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 : 49 : return;
184 [ + + ]: 113 : }
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 [ + - + + : 122 : foreach(lc, aggs_list)
+ + ]
196 : : {
197 : 64 : MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
198 : :
199 : 64 : mminfo->param =
200 : 128 : SS_make_initplan_output_param(root,
201 : 64 : exprType((Node *) mminfo->target),
202 : : -1,
203 : 64 : exprCollation((Node *) mminfo->target));
204 : 64 : }
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 : 58 : grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG, NULL);
221 : 116 : add_path(grouped_rel, (Path *)
222 : 116 : create_minmaxagg_path(root, grouped_rel,
223 : 58 : create_pathtarget(root,
224 : : root->processed_tlist),
225 : 58 : aggs_list,
226 : 58 : (List *) parse->havingQual));
227 [ - + ]: 4926 : }
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 : 3063 : can_minmax_aggs(PlannerInfo *root, List **context)
239 : : {
240 : 3063 : 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 [ + - + + : 6188 : foreach(lc, root->agginfos)
+ + + + ]
247 : : {
248 : 3125 : AggInfo *agginfo = lfirst_node(AggInfo, lc);
249 : 3125 : Aggref *aggref = linitial_node(Aggref, agginfo->aggrefs);
250 : 3125 : Oid aggsortop;
251 : 3125 : TargetEntry *curTarget;
252 : 3125 : MinMaxAggInfo *mminfo;
253 : :
254 [ + - ]: 3125 : Assert(aggref->agglevelsup == 0);
255 [ + + ]: 3125 : if (list_length(aggref->args) != 1)
256 : 1078 : 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 [ + + ]: 2047 : if (aggref->aggorder != NIL)
272 : 27 : 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 [ + + ]: 2020 : if (aggref->aggfilter != NULL)
281 : 6 : return false;
282 : :
283 : 2014 : aggsortop = fetch_agg_sort_op(aggref->aggfnoid);
284 [ + + ]: 2014 : if (!OidIsValid(aggsortop))
285 : 1841 : return false; /* not a MIN/MAX aggregate */
286 : :
287 : 173 : curTarget = (TargetEntry *) linitial(aggref->args);
288 : :
289 [ - + ]: 173 : if (contain_mutable_functions((Node *) curTarget->expr))
290 : 0 : return false; /* not potentially indexable */
291 : :
292 [ + + ]: 173 : if (type_is_rowtype(exprType((Node *) curTarget->expr)))
293 : 4 : return false; /* IS NOT NULL would have weird semantics */
294 : :
295 : 169 : mminfo = makeNode(MinMaxAggInfo);
296 : 169 : mminfo->aggfnoid = aggref->aggfnoid;
297 : 169 : mminfo->aggsortop = aggsortop;
298 : 169 : mminfo->target = curTarget->expr;
299 : 169 : mminfo->subroot = NULL; /* don't compute path yet */
300 : 169 : mminfo->path = NULL;
301 : 169 : mminfo->pathcost = 0;
302 : 169 : mminfo->param = NULL;
303 : :
304 : 169 : *context = lappend(*context, mminfo);
305 [ + + ]: 3125 : }
306 : 107 : return true;
307 : 3063 : }
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 : 162 : build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
319 : : Oid eqop, Oid sortop, bool reverse_sort, bool nulls_first)
320 : : {
321 : 162 : PlannerInfo *subroot;
322 : 162 : Query *parse;
323 : 162 : TargetEntry *tle;
324 : 162 : List *tlist;
325 : 162 : NullTest *ntest;
326 : 162 : SortGroupClause *sortcl;
327 : 162 : RelOptInfo *final_rel;
328 : 162 : Path *sorted_path;
329 : 162 : Cost path_cost;
330 : 162 : 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 : 162 : subroot = palloc_object(PlannerInfo);
340 : 162 : memcpy(subroot, root, sizeof(PlannerInfo));
341 : 162 : subroot->query_level++;
342 : 162 : subroot->parent_root = root;
343 : 162 : subroot->plan_name = choose_plan_name(root->glob, "minmax", true);
344 : :
345 : : /* reset subplan-related stuff */
346 : 162 : subroot->plan_params = NIL;
347 : 162 : subroot->outer_params = NULL;
348 : 162 : subroot->init_plans = NIL;
349 : 162 : subroot->agginfos = NIL;
350 : 162 : subroot->aggtransinfos = NIL;
351 : :
352 : 162 : subroot->parse = parse = copyObject(root->parse);
353 : 162 : IncrementVarSublevelsUp((Node *) parse, 1, 1);
354 : :
355 : : /* append_rel_list might contain outer Vars? */
356 : 162 : subroot->append_rel_list = copyObject(root->append_rel_list);
357 : 162 : IncrementVarSublevelsUp((Node *) subroot->append_rel_list, 1, 1);
358 : : /* There shouldn't be any OJ info to translate, as yet */
359 [ + - ]: 162 : Assert(subroot->join_info_list == NIL);
360 : : /* and we haven't made equivalence classes, either */
361 [ + - ]: 162 : Assert(subroot->eq_classes == NIL);
362 : : /* and we haven't created PlaceHolderInfos, either */
363 [ + - ]: 162 : Assert(subroot->placeholder_list == NIL);
364 : :
365 : : /*----------
366 : : * Generate modified query of the form
367 : : * (SELECT col FROM tab
368 : : * WHERE col IS NOT NULL AND existing-quals
369 : : * ORDER BY col ASC/DESC
370 : : * LIMIT 1)
371 : : *----------
372 : : */
373 : : /* single tlist entry that is the aggregate target */
374 : 324 : tle = makeTargetEntry(copyObject(mminfo->target),
375 : : (AttrNumber) 1,
376 : 162 : pstrdup("agg_target"),
377 : : false);
378 : 162 : tlist = list_make1(tle);
379 : 162 : subroot->processed_tlist = parse->targetList = tlist;
380 : :
381 : : /* No HAVING, no DISTINCT, no aggregates anymore */
382 : 162 : parse->havingQual = NULL;
383 : 162 : subroot->hasHavingQual = false;
384 : 162 : parse->distinctClause = NIL;
385 : 162 : parse->hasDistinctOn = false;
386 : 162 : parse->hasAggs = false;
387 : :
388 : : /* Build "target IS NOT NULL" expression */
389 : 162 : ntest = makeNode(NullTest);
390 : 162 : ntest->nulltesttype = IS_NOT_NULL;
391 : 162 : ntest->arg = copyObject(mminfo->target);
392 : : /* we checked it wasn't a rowtype in can_minmax_aggs */
393 : 162 : ntest->argisrow = false;
394 : 162 : ntest->location = -1;
395 : :
396 : : /* User might have had that in WHERE already */
397 [ - + ]: 162 : if (!list_member((List *) parse->jointree->quals, ntest))
398 : 162 : parse->jointree->quals = (Node *)
399 : 162 : lcons(ntest, (List *) parse->jointree->quals);
400 : :
401 : : /* Build suitable ORDER BY clause */
402 : 162 : sortcl = makeNode(SortGroupClause);
403 : 162 : sortcl->tleSortGroupRef = assignSortGroupRef(tle, subroot->processed_tlist);
404 : 162 : sortcl->eqop = eqop;
405 : 162 : sortcl->sortop = sortop;
406 : 162 : sortcl->reverse_sort = reverse_sort;
407 : 162 : sortcl->nulls_first = nulls_first;
408 : 162 : sortcl->hashable = false; /* no need to make this accurate */
409 : 162 : parse->sortClause = list_make1(sortcl);
410 : :
411 : : /* set up expressions for LIMIT 1 */
412 : 162 : parse->limitOffset = NULL;
413 : 162 : parse->limitCount = (Node *) makeConst(INT8OID, -1, InvalidOid,
414 : : sizeof(int64),
415 : 162 : Int64GetDatum(1), false,
416 : : true);
417 : :
418 : : /*
419 : : * Generate the best paths for this query, telling query_planner that we
420 : : * have LIMIT 1.
421 : : */
422 : 162 : subroot->tuple_fraction = 1.0;
423 : 162 : subroot->limit_tuples = 1.0;
424 : :
425 : 162 : final_rel = query_planner(subroot, minmax_qp_callback, NULL);
426 : :
427 : : /*
428 : : * Since we didn't go through subquery_planner() to handle the subquery,
429 : : * we have to do some of the same cleanup it would do, in particular cope
430 : : * with params and initplans used within this subquery. (This won't
431 : : * matter if we end up not using the subplan.)
432 : : */
433 : 162 : SS_identify_outer_params(subroot);
434 : 162 : SS_charge_for_initplans(subroot, final_rel);
435 : :
436 : : /*
437 : : * Get the best presorted path, that being the one that's cheapest for
438 : : * fetching just one row. If there's no such path, fail.
439 : : */
440 [ + + ]: 162 : if (final_rel->rows > 1.0)
441 : 156 : path_fraction = 1.0 / final_rel->rows;
442 : : else
443 : 6 : path_fraction = 1.0;
444 : :
445 : 162 : sorted_path =
446 : 324 : get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
447 : 162 : subroot->query_pathkeys,
448 : : NULL,
449 : 162 : path_fraction);
450 [ + + ]: 162 : if (!sorted_path)
451 : 98 : return false;
452 : :
453 : : /*
454 : : * The path might not return exactly what we want, so fix that. (We
455 : : * assume that this won't change any conclusions about which was the
456 : : * cheapest path.)
457 : : */
458 : 128 : sorted_path = apply_projection_to_path(subroot, final_rel, sorted_path,
459 : 64 : create_pathtarget(subroot,
460 : : subroot->processed_tlist));
461 : :
462 : : /*
463 : : * Determine cost to get just the first row of the presorted path.
464 : : *
465 : : * Note: cost calculation here should match
466 : : * compare_fractional_path_costs().
467 : : */
468 : 128 : path_cost = sorted_path->startup_cost +
469 : 64 : path_fraction * (sorted_path->total_cost - sorted_path->startup_cost);
470 : :
471 : : /* Save state for further processing */
472 : 64 : mminfo->subroot = subroot;
473 : 64 : mminfo->path = sorted_path;
474 : 64 : mminfo->pathcost = path_cost;
475 : :
476 : 64 : return true;
477 : 162 : }
478 : :
479 : : /*
480 : : * Compute query_pathkeys and other pathkeys during query_planner()
481 : : */
482 : : static void
483 : 162 : minmax_qp_callback(PlannerInfo *root, void *extra)
484 : : {
485 : 162 : root->group_pathkeys = NIL;
486 : 162 : root->window_pathkeys = NIL;
487 : 162 : root->distinct_pathkeys = NIL;
488 : :
489 : 162 : root->sort_pathkeys =
490 : 324 : make_pathkeys_for_sortclauses(root,
491 : 162 : root->parse->sortClause,
492 : 162 : root->parse->targetList);
493 : :
494 : 162 : root->query_pathkeys = root->sort_pathkeys;
495 : 162 : }
496 : :
497 : : /*
498 : : * Get the OID of the sort operator, if any, associated with an aggregate.
499 : : * Returns InvalidOid if there is no such operator.
500 : : */
501 : : static Oid
502 : 2014 : fetch_agg_sort_op(Oid aggfnoid)
503 : : {
504 : 2014 : HeapTuple aggTuple;
505 : 2014 : Form_pg_aggregate aggform;
506 : 2014 : Oid aggsortop;
507 : :
508 : : /* fetch aggregate entry from pg_aggregate */
509 : 2014 : aggTuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(aggfnoid));
510 [ + - ]: 2014 : if (!HeapTupleIsValid(aggTuple))
511 : 0 : return InvalidOid;
512 : 2014 : aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
513 : 2014 : aggsortop = aggform->aggsortop;
514 : 2014 : ReleaseSysCache(aggTuple);
515 : :
516 : 2014 : return aggsortop;
517 : 2014 : }
|
