Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * planmain.c
4 : * Routines to plan a single query
5 : *
6 : * What's in a name, anyway? The top-level entry point of the planner/
7 : * optimizer is over in planner.c, not here as you might think from the
8 : * file name. But this is the main code for planning a basic join operation,
9 : * shorn of features like subselects, inheritance, aggregates, grouping,
10 : * and so on. (Those are the things planner.c deals with.)
11 : *
12 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
13 : * Portions Copyright (c) 1994, Regents of the University of California
14 : *
15 : *
16 : * IDENTIFICATION
17 : * src/backend/optimizer/plan/planmain.c
18 : *
19 : *-------------------------------------------------------------------------
20 : */
21 : #include "postgres.h"
22 :
23 : #include "optimizer/appendinfo.h"
24 : #include "optimizer/clauses.h"
25 : #include "optimizer/optimizer.h"
26 : #include "optimizer/orclauses.h"
27 : #include "optimizer/pathnode.h"
28 : #include "optimizer/paths.h"
29 : #include "optimizer/placeholder.h"
30 : #include "optimizer/planmain.h"
31 :
32 :
33 : /*
34 : * query_planner
35 : * Generate a path (that is, a simplified plan) for a basic query,
36 : * which may involve joins but not any fancier features.
37 : *
38 : * Since query_planner does not handle the toplevel processing (grouping,
39 : * sorting, etc) it cannot select the best path by itself. Instead, it
40 : * returns the RelOptInfo for the top level of joining, and the caller
41 : * (grouping_planner) can choose among the surviving paths for the rel.
42 : *
43 : * root describes the query to plan
44 : * qp_callback is a function to compute query_pathkeys once it's safe to do so
45 : * qp_extra is optional extra data to pass to qp_callback
46 : *
47 : * Note: the PlannerInfo node also includes a query_pathkeys field, which
48 : * tells query_planner the sort order that is desired in the final output
49 : * plan. This value is *not* available at call time, but is computed by
50 : * qp_callback once we have completed merging the query's equivalence classes.
51 : * (We cannot construct canonical pathkeys until that's done.)
52 : */
53 : RelOptInfo *
54 551296 : query_planner(PlannerInfo *root,
55 : query_pathkeys_callback qp_callback, void *qp_extra)
56 : {
57 551296 : Query *parse = root->parse;
58 : List *joinlist;
59 : RelOptInfo *final_rel;
60 :
61 : /*
62 : * Init planner lists to empty.
63 : *
64 : * NOTE: append_rel_list was set up by subquery_planner, so do not touch
65 : * here.
66 : */
67 551296 : root->join_rel_list = NIL;
68 551296 : root->join_rel_hash = NULL;
69 551296 : root->join_rel_level = NULL;
70 551296 : root->join_cur_level = 0;
71 551296 : root->canon_pathkeys = NIL;
72 551296 : root->left_join_clauses = NIL;
73 551296 : root->right_join_clauses = NIL;
74 551296 : root->full_join_clauses = NIL;
75 551296 : root->join_info_list = NIL;
76 551296 : root->placeholder_list = NIL;
77 551296 : root->placeholder_array = NULL;
78 551296 : root->placeholder_array_size = 0;
79 551296 : root->fkey_list = NIL;
80 551296 : root->initial_rels = NIL;
81 :
82 : /*
83 : * Set up arrays for accessing base relations and AppendRelInfos.
84 : */
85 551296 : setup_simple_rel_arrays(root);
86 :
87 : /*
88 : * In the trivial case where the jointree is a single RTE_RESULT relation,
89 : * bypass all the rest of this function and just make a RelOptInfo and its
90 : * one access path. This is worth optimizing because it applies for
91 : * common cases like "SELECT expression" and "INSERT ... VALUES()".
92 : */
93 : Assert(parse->jointree->fromlist != NIL);
94 551296 : if (list_length(parse->jointree->fromlist) == 1)
95 : {
96 508296 : Node *jtnode = (Node *) linitial(parse->jointree->fromlist);
97 :
98 508296 : if (IsA(jtnode, RangeTblRef))
99 : {
100 419884 : int varno = ((RangeTblRef *) jtnode)->rtindex;
101 419884 : RangeTblEntry *rte = root->simple_rte_array[varno];
102 :
103 : Assert(rte != NULL);
104 419884 : if (rte->rtekind == RTE_RESULT)
105 : {
106 : /* Make the RelOptInfo for it directly */
107 215148 : final_rel = build_simple_rel(root, varno, NULL);
108 :
109 : /*
110 : * If query allows parallelism in general, check whether the
111 : * quals are parallel-restricted. (We need not check
112 : * final_rel->reltarget because it's empty at this point.
113 : * Anything parallel-restricted in the query tlist will be
114 : * dealt with later.) We should always do this in a subquery,
115 : * since it might be useful to use the subquery in parallel
116 : * paths in the parent level. At top level this is normally
117 : * not worth the cycles, because a Result-only plan would
118 : * never be interesting to parallelize. However, if
119 : * debug_parallel_query is on, then we want to execute the
120 : * Result in a parallel worker if possible, so we must check.
121 : */
122 215148 : if (root->glob->parallelModeOK &&
123 109328 : (root->query_level > 1 ||
124 106328 : debug_parallel_query != DEBUG_PARALLEL_OFF))
125 3060 : final_rel->consider_parallel =
126 3060 : is_parallel_safe(root, parse->jointree->quals);
127 :
128 : /*
129 : * The only path for it is a trivial Result path. We cheat a
130 : * bit here by using a GroupResultPath, because that way we
131 : * can just jam the quals into it without preprocessing them.
132 : * (But, if you hold your head at the right angle, a FROM-less
133 : * SELECT is a kind of degenerate-grouping case, so it's not
134 : * that much of a cheat.)
135 : */
136 215148 : add_path(final_rel, (Path *)
137 215148 : create_group_result_path(root, final_rel,
138 215148 : final_rel->reltarget,
139 215148 : (List *) parse->jointree->quals));
140 :
141 : /* Select cheapest path (pretty easy in this case...) */
142 215148 : set_cheapest(final_rel);
143 :
144 : /*
145 : * We don't need to run generate_base_implied_equalities, but
146 : * we do need to pretend that EC merging is complete.
147 : */
148 215148 : root->ec_merging_done = true;
149 :
150 : /*
151 : * We still are required to call qp_callback, in case it's
152 : * something like "SELECT 2+2 ORDER BY 1".
153 : */
154 215148 : (*qp_callback) (root, qp_extra);
155 :
156 215148 : return final_rel;
157 : }
158 : }
159 : }
160 :
161 : /*
162 : * Construct RelOptInfo nodes for all base relations used in the query.
163 : * Appendrel member relations ("other rels") will be added later.
164 : *
165 : * Note: the reason we find the baserels by searching the jointree, rather
166 : * than scanning the rangetable, is that the rangetable may contain RTEs
167 : * for rels not actively part of the query, for example views. We don't
168 : * want to make RelOptInfos for them.
169 : */
170 336148 : add_base_rels_to_query(root, (Node *) parse->jointree);
171 :
172 : /* Remove any redundant GROUP BY columns */
173 336130 : remove_useless_groupby_columns(root);
174 :
175 : /*
176 : * Examine the targetlist and join tree, adding entries to baserel
177 : * targetlists for all referenced Vars, and generating PlaceHolderInfo
178 : * entries for all referenced PlaceHolderVars. Restrict and join clauses
179 : * are added to appropriate lists belonging to the mentioned relations. We
180 : * also build EquivalenceClasses for provably equivalent expressions. The
181 : * SpecialJoinInfo list is also built to hold information about join order
182 : * restrictions. Finally, we form a target joinlist for make_one_rel() to
183 : * work from.
184 : */
185 336130 : build_base_rel_tlists(root, root->processed_tlist);
186 :
187 336130 : find_placeholders_in_jointree(root);
188 :
189 336130 : find_lateral_references(root);
190 :
191 336130 : joinlist = deconstruct_jointree(root);
192 :
193 : /*
194 : * Reconsider any postponed outer-join quals now that we have built up
195 : * equivalence classes. (This could result in further additions or
196 : * mergings of classes.)
197 : */
198 336130 : reconsider_outer_join_clauses(root);
199 :
200 : /*
201 : * If we formed any equivalence classes, generate additional restriction
202 : * clauses as appropriate. (Implied join clauses are formed on-the-fly
203 : * later.)
204 : */
205 336130 : generate_base_implied_equalities(root);
206 :
207 : /*
208 : * We have completed merging equivalence sets, so it's now possible to
209 : * generate pathkeys in canonical form; so compute query_pathkeys and
210 : * other pathkeys fields in PlannerInfo.
211 : */
212 336130 : (*qp_callback) (root, qp_extra);
213 :
214 : /*
215 : * Examine any "placeholder" expressions generated during subquery pullup.
216 : * Make sure that the Vars they need are marked as needed at the relevant
217 : * join level. This must be done before join removal because it might
218 : * cause Vars or placeholders to be needed above a join when they weren't
219 : * so marked before.
220 : */
221 336130 : fix_placeholder_input_needed_levels(root);
222 :
223 : /*
224 : * Remove any useless outer joins. Ideally this would be done during
225 : * jointree preprocessing, but the necessary information isn't available
226 : * until we've built baserel data structures and classified qual clauses.
227 : */
228 336130 : joinlist = remove_useless_joins(root, joinlist);
229 :
230 : /*
231 : * Also, reduce any semijoins with unique inner rels to plain inner joins.
232 : * Likewise, this can't be done until now for lack of needed info.
233 : */
234 336130 : reduce_unique_semijoins(root);
235 :
236 : /*
237 : * Remove self joins on a unique column.
238 : */
239 336130 : joinlist = remove_useless_self_joins(root, joinlist);
240 :
241 : /*
242 : * Now distribute "placeholders" to base rels as needed. This has to be
243 : * done after join removal because removal could change whether a
244 : * placeholder is evaluable at a base rel.
245 : */
246 336130 : add_placeholders_to_base_rels(root);
247 :
248 : /*
249 : * Construct the lateral reference sets now that we have finalized
250 : * PlaceHolderVar eval levels.
251 : */
252 336130 : create_lateral_join_info(root);
253 :
254 : /*
255 : * Match foreign keys to equivalence classes and join quals. This must be
256 : * done after finalizing equivalence classes, and it's useful to wait till
257 : * after join removal so that we can skip processing foreign keys
258 : * involving removed relations.
259 : */
260 336130 : match_foreign_keys_to_quals(root);
261 :
262 : /*
263 : * Look for join OR clauses that we can extract single-relation
264 : * restriction OR clauses from.
265 : */
266 336130 : extract_restriction_or_clauses(root);
267 :
268 : /*
269 : * Now expand appendrels by adding "otherrels" for their children. We
270 : * delay this to the end so that we have as much information as possible
271 : * available for each baserel, including all restriction clauses. That
272 : * let us prune away partitions that don't satisfy a restriction clause.
273 : * Also note that some information such as lateral_relids is propagated
274 : * from baserels to otherrels here, so we must have computed it already.
275 : */
276 336130 : add_other_rels_to_query(root);
277 :
278 : /*
279 : * Distribute any UPDATE/DELETE/MERGE row identity variables to the target
280 : * relations. This can't be done till we've finished expansion of
281 : * appendrels.
282 : */
283 336128 : distribute_row_identity_vars(root);
284 :
285 : /*
286 : * Ready to do the primary planning.
287 : */
288 336128 : final_rel = make_one_rel(root, joinlist);
289 :
290 : /* Check that we got at least one usable path */
291 336100 : if (!final_rel || !final_rel->cheapest_total_path ||
292 336100 : final_rel->cheapest_total_path->param_info != NULL)
293 0 : elog(ERROR, "failed to construct the join relation");
294 :
295 336100 : return final_rel;
296 : }
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