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1 : : /*------------------------------------------------------------------------
2 : : *
3 : : * geqo_eval.c
4 : : * Routines to evaluate query trees
5 : : *
6 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : : * Portions Copyright (c) 1994, Regents of the University of California
8 : : *
9 : : * src/backend/optimizer/geqo/geqo_eval.c
10 : : *
11 : : *-------------------------------------------------------------------------
12 : : */
13 : :
14 : : /* contributed by:
15 : : =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
16 : : * Martin Utesch * Institute of Automatic Control *
17 : : = = University of Mining and Technology =
18 : : * utesch@aut.tu-freiberg.de * Freiberg, Germany *
19 : : =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
20 : : */
21 : :
22 : : #include "postgres.h"
23 : :
24 : : #include <float.h>
25 : : #include <limits.h>
26 : :
27 : : #include "optimizer/geqo.h"
28 : : #include "optimizer/joininfo.h"
29 : : #include "optimizer/pathnode.h"
30 : : #include "optimizer/paths.h"
31 : : #include "utils/memutils.h"
32 : :
33 : :
34 : : /* A "clump" of already-joined relations within gimme_tree */
35 : : typedef struct
36 : : {
37 : : RelOptInfo *joinrel; /* joinrel for the set of relations */
38 : : int size; /* number of input relations in clump */
39 : : } Clump;
40 : :
41 : : static List *merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump,
42 : : int num_gene, bool force);
43 : : static bool desirable_join(PlannerInfo *root,
44 : : RelOptInfo *outer_rel, RelOptInfo *inner_rel);
45 : :
46 : :
47 : : /*
48 : : * geqo_eval
49 : : *
50 : : * Returns cost of a query tree as an individual of the population.
51 : : *
52 : : * If no legal join order can be extracted from the proposed tour,
53 : : * returns DBL_MAX.
54 : : */
55 : : Cost
56 : 728 : geqo_eval(PlannerInfo *root, Gene *tour, int num_gene)
57 : : {
58 : 728 : MemoryContext mycontext;
59 : 728 : MemoryContext oldcxt;
60 : 728 : RelOptInfo *joinrel;
61 : 728 : Cost fitness;
62 : 728 : int savelength;
63 : 728 : struct HTAB *savehash;
64 : :
65 : : /*
66 : : * Create a private memory context that will hold all temp storage
67 : : * allocated inside gimme_tree().
68 : : *
69 : : * Since geqo_eval() will be called many times, we can't afford to let all
70 : : * that memory go unreclaimed until end of statement. Note we make the
71 : : * temp context a child of the planner's normal context, so that it will
72 : : * be freed even if we abort via ereport(ERROR).
73 : : */
74 : 728 : mycontext = AllocSetContextCreate(CurrentMemoryContext,
75 : : "GEQO",
76 : : ALLOCSET_DEFAULT_SIZES);
77 : 728 : oldcxt = MemoryContextSwitchTo(mycontext);
78 : :
79 : : /*
80 : : * gimme_tree will add entries to root->join_rel_list, which may or may
81 : : * not already contain some entries. The newly added entries will be
82 : : * recycled by the MemoryContextDelete below, so we must ensure that the
83 : : * list is restored to its former state before exiting. We can do this by
84 : : * truncating the list to its original length. NOTE this assumes that any
85 : : * added entries are appended at the end!
86 : : *
87 : : * We also must take care not to mess up the outer join_rel_hash, if there
88 : : * is one. We can do this by just temporarily setting the link to NULL.
89 : : * (If we are dealing with enough join rels, which we very likely are, a
90 : : * new hash table will get built and used locally.)
91 : : *
92 : : * join_rel_level[] shouldn't be in use, so just Assert it isn't.
93 : : */
94 : 728 : savelength = list_length(root->join_rel_list);
95 : 728 : savehash = root->join_rel_hash;
96 [ + - ]: 728 : Assert(root->join_rel_level == NULL);
97 : :
98 : 728 : root->join_rel_hash = NULL;
99 : :
100 : : /* construct the best path for the given combination of relations */
101 : 728 : joinrel = gimme_tree(root, tour, num_gene);
102 : :
103 : : /*
104 : : * compute fitness, if we found a valid join
105 : : *
106 : : * XXX geqo does not currently support optimization for partial result
107 : : * retrieval, nor do we take any cognizance of possible use of
108 : : * parameterized paths --- how to fix?
109 : : */
110 [ + - ]: 728 : if (joinrel)
111 : : {
112 : 728 : Path *best_path = joinrel->cheapest_total_path;
113 : :
114 : 728 : fitness = best_path->total_cost;
115 : 728 : }
116 : : else
117 : 0 : fitness = DBL_MAX;
118 : :
119 : : /*
120 : : * Restore join_rel_list to its former state, and put back original
121 : : * hashtable if any.
122 : : */
123 : 1456 : root->join_rel_list = list_truncate(root->join_rel_list,
124 : 728 : savelength);
125 : 728 : root->join_rel_hash = savehash;
126 : :
127 : : /* release all the memory acquired within gimme_tree */
128 : 728 : MemoryContextSwitchTo(oldcxt);
129 : 728 : MemoryContextDelete(mycontext);
130 : :
131 : 1456 : return fitness;
132 : 728 : }
133 : :
134 : : /*
135 : : * gimme_tree
136 : : * Form planner estimates for a join tree constructed in the specified
137 : : * order.
138 : : *
139 : : * 'tour' is the proposed join order, of length 'num_gene'
140 : : *
141 : : * Returns a new join relation whose cheapest path is the best plan for
142 : : * this join order. NB: will return NULL if join order is invalid and
143 : : * we can't modify it into a valid order.
144 : : *
145 : : * The original implementation of this routine always joined in the specified
146 : : * order, and so could only build left-sided plans (and right-sided and
147 : : * mixtures, as a byproduct of the fact that make_join_rel() is symmetric).
148 : : * It could never produce a "bushy" plan. This had a couple of big problems,
149 : : * of which the worst was that there are situations involving join order
150 : : * restrictions where the only valid plans are bushy.
151 : : *
152 : : * The present implementation takes the given tour as a guideline, but
153 : : * postpones joins that are illegal or seem unsuitable according to some
154 : : * heuristic rules. This allows correct bushy plans to be generated at need,
155 : : * and as a nice side-effect it seems to materially improve the quality of the
156 : : * generated plans. Note however that since it's just a heuristic, it can
157 : : * still fail in some cases. (In particular, we might clump together
158 : : * relations that actually mustn't be joined yet due to LATERAL restrictions;
159 : : * since there's no provision for un-clumping, this must lead to failure.)
160 : : */
161 : : RelOptInfo *
162 : 735 : gimme_tree(PlannerInfo *root, Gene *tour, int num_gene)
163 : : {
164 : 735 : GeqoPrivateData *private = GetGeqoPrivateData(root);
165 : 735 : List *clumps;
166 : 735 : int rel_count;
167 : :
168 : : /*
169 : : * Sometimes, a relation can't yet be joined to others due to heuristics
170 : : * or actual semantic restrictions. We maintain a list of "clumps" of
171 : : * successfully joined relations, with larger clumps at the front. Each
172 : : * new relation from the tour is added to the first clump it can be joined
173 : : * to; if there is none then it becomes a new clump of its own. When we
174 : : * enlarge an existing clump we check to see if it can now be merged with
175 : : * any other clumps. After the tour is all scanned, we forget about the
176 : : * heuristics and try to forcibly join any remaining clumps. If we are
177 : : * unable to merge all the clumps into one, fail.
178 : : */
179 : 735 : clumps = NIL;
180 : :
181 [ + + ]: 2592 : for (rel_count = 0; rel_count < num_gene; rel_count++)
182 : : {
183 : 1857 : int cur_rel_index;
184 : 1857 : RelOptInfo *cur_rel;
185 : 1857 : Clump *cur_clump;
186 : :
187 : : /* Get the next input relation */
188 : 1857 : cur_rel_index = (int) tour[rel_count];
189 : 3714 : cur_rel = (RelOptInfo *) list_nth(private->initial_rels,
190 : 1857 : cur_rel_index - 1);
191 : :
192 : : /* Make it into a single-rel clump */
193 : 1857 : cur_clump = palloc_object(Clump);
194 : 1857 : cur_clump->joinrel = cur_rel;
195 : 1857 : cur_clump->size = 1;
196 : :
197 : : /* Merge it into the clumps list, using only desirable joins */
198 : 1857 : clumps = merge_clump(root, clumps, cur_clump, num_gene, false);
199 : 1857 : }
200 : :
201 [ + - ]: 735 : if (list_length(clumps) > 1)
202 : : {
203 : : /* Force-join the remaining clumps in some legal order */
204 : 0 : List *fclumps;
205 : 0 : ListCell *lc;
206 : :
207 : 0 : fclumps = NIL;
208 [ # # # # : 0 : foreach(lc, clumps)
# # ]
209 : : {
210 : 0 : Clump *clump = (Clump *) lfirst(lc);
211 : :
212 : 0 : fclumps = merge_clump(root, fclumps, clump, num_gene, true);
213 : 0 : }
214 : 0 : clumps = fclumps;
215 : 0 : }
216 : :
217 : : /* Did we succeed in forming a single join relation? */
218 [ - + ]: 735 : if (list_length(clumps) != 1)
219 : 0 : return NULL;
220 : :
221 : 735 : return ((Clump *) linitial(clumps))->joinrel;
222 : 735 : }
223 : :
224 : : /*
225 : : * Merge a "clump" into the list of existing clumps for gimme_tree.
226 : : *
227 : : * We try to merge the clump into some existing clump, and repeat if
228 : : * successful. When no more merging is possible, insert the clump
229 : : * into the list, preserving the list ordering rule (namely, that
230 : : * clumps of larger size appear earlier).
231 : : *
232 : : * If force is true, merge anywhere a join is legal, even if it causes
233 : : * a cartesian join to be performed. When force is false, do only
234 : : * "desirable" joins.
235 : : */
236 : : static List *
237 : 2979 : merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, int num_gene,
238 : : bool force)
239 : : {
240 : 2979 : ListCell *lc;
241 : 2979 : int pos;
242 : :
243 : : /* Look for a clump that new_clump can join to */
244 [ + + + + : 4757 : foreach(lc, clumps)
+ + + + ]
245 : : {
246 : 1778 : Clump *old_clump = (Clump *) lfirst(lc);
247 : :
248 [ + - + + ]: 1778 : if (force ||
249 : 1778 : desirable_join(root, old_clump->joinrel, new_clump->joinrel))
250 : : {
251 : 1398 : RelOptInfo *joinrel;
252 : :
253 : : /*
254 : : * Construct a RelOptInfo representing the join of these two input
255 : : * relations. Note that we expect the joinrel not to exist in
256 : : * root->join_rel_list yet, and so the paths constructed for it
257 : : * will only include the ones we want.
258 : : */
259 : 2796 : joinrel = make_join_rel(root,
260 : 1398 : old_clump->joinrel,
261 : 1398 : new_clump->joinrel);
262 : :
263 : : /* Keep searching if join order is not valid */
264 [ + + ]: 1398 : if (joinrel)
265 : : {
266 : 2244 : bool is_top_rel = bms_equal(joinrel->relids,
267 : 1122 : root->all_query_rels);
268 : :
269 : : /* Create paths for partitionwise joins. */
270 : 1122 : generate_partitionwise_join_paths(root, joinrel);
271 : :
272 : : /*
273 : : * Except for the topmost scan/join rel, consider gathering
274 : : * partial paths. We'll do the same for the topmost scan/join
275 : : * rel once we know the final targetlist (see
276 : : * grouping_planner).
277 : : */
278 [ + + ]: 1122 : if (!is_top_rel)
279 : 387 : generate_useful_gather_paths(root, joinrel, false);
280 : :
281 : : /* Find and save the cheapest paths for this joinrel */
282 : 1122 : set_cheapest(joinrel);
283 : :
284 : : /*
285 : : * Except for the topmost scan/join rel, consider generating
286 : : * partial aggregation paths for the grouped relation on top
287 : : * of the paths of this rel. After that, we're done creating
288 : : * paths for the grouped relation, so run set_cheapest().
289 : : */
290 [ + + + - ]: 1122 : if (joinrel->grouped_rel != NULL && !is_top_rel)
291 : : {
292 : 0 : RelOptInfo *grouped_rel = joinrel->grouped_rel;
293 : :
294 [ # # ]: 0 : Assert(IS_GROUPED_REL(grouped_rel));
295 : :
296 : 0 : generate_grouped_paths(root, grouped_rel, joinrel);
297 : 0 : set_cheapest(grouped_rel);
298 : 0 : }
299 : :
300 : : /* Absorb new clump into old */
301 : 1122 : old_clump->joinrel = joinrel;
302 : 1122 : old_clump->size += new_clump->size;
303 : 1122 : pfree(new_clump);
304 : :
305 : : /* Remove old_clump from list */
306 : 1122 : clumps = foreach_delete_current(clumps, lc);
307 : :
308 : : /*
309 : : * Recursively try to merge the enlarged old_clump with
310 : : * others. When no further merge is possible, we'll reinsert
311 : : * it into the list.
312 : : */
313 : 1122 : return merge_clump(root, clumps, old_clump, num_gene, force);
314 : 1122 : }
315 [ + + ]: 1398 : }
316 [ + + ]: 1778 : }
317 : :
318 : : /*
319 : : * No merging is possible, so add new_clump as an independent clump, in
320 : : * proper order according to size. We can be fast for the common case
321 : : * where it has size 1 --- it should always go at the end.
322 : : */
323 [ + + + + ]: 1857 : if (clumps == NIL || new_clump->size == 1)
324 : 1712 : return lappend(clumps, new_clump);
325 : :
326 : : /* Else search for the place to insert it */
327 [ + + ]: 170 : for (pos = 0; pos < list_length(clumps); pos++)
328 : : {
329 : 145 : Clump *old_clump = (Clump *) list_nth(clumps, pos);
330 : :
331 [ + + ]: 145 : if (new_clump->size > old_clump->size)
332 : 120 : break; /* new_clump belongs before old_clump */
333 [ - + + ]: 145 : }
334 : 145 : clumps = list_insert_nth(clumps, pos, new_clump);
335 : :
336 : 145 : return clumps;
337 : 2979 : }
338 : :
339 : : /*
340 : : * Heuristics for gimme_tree: do we want to join these two relations?
341 : : */
342 : : static bool
343 : 1778 : desirable_join(PlannerInfo *root,
344 : : RelOptInfo *outer_rel, RelOptInfo *inner_rel)
345 : : {
346 : : /*
347 : : * Join if there is an applicable join clause, or if there is a join order
348 : : * restriction forcing these rels to be joined.
349 : : */
350 [ + + - + ]: 1778 : if (have_relevant_joinclause(root, outer_rel, inner_rel) ||
351 : 380 : have_join_order_restriction(root, outer_rel, inner_rel))
352 : 1398 : return true;
353 : :
354 : : /* Otherwise postpone the join till later. */
355 : 380 : return false;
356 : 1778 : }
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