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) 1996-2026, 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 285041 : query_planner(PlannerInfo *root,
55 : query_pathkeys_callback qp_callback, void *qp_extra)
56 : {
57 285041 : 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 285041 : root->join_rel_list = NIL;
68 285041 : root->join_rel_hash = NULL;
69 285041 : root->join_rel_level = NULL;
70 285041 : root->join_cur_level = 0;
71 285041 : root->canon_pathkeys = NIL;
72 285041 : root->left_join_clauses = NIL;
73 285041 : root->right_join_clauses = NIL;
74 285041 : root->full_join_clauses = NIL;
75 285041 : root->join_info_list = NIL;
76 285041 : root->placeholder_list = NIL;
77 285041 : root->placeholder_array = NULL;
78 285041 : root->placeholder_array_size = 0;
79 285041 : root->agg_clause_list = NIL;
80 285041 : root->group_expr_list = NIL;
81 285041 : root->tlist_vars = NIL;
82 285041 : root->fkey_list = NIL;
83 285041 : root->initial_rels = NIL;
84 :
85 : /*
86 : * Set up arrays for accessing base relations and AppendRelInfos.
87 : */
88 285041 : setup_simple_rel_arrays(root);
89 :
90 : /*
91 : * In the trivial case where the jointree is a single RTE_RESULT relation,
92 : * bypass all the rest of this function and just make a RelOptInfo and its
93 : * one access path. This is worth optimizing because it applies for
94 : * common cases like "SELECT expression" and "INSERT ... VALUES()".
95 : */
96 : Assert(parse->jointree->fromlist != NIL);
97 285041 : if (list_length(parse->jointree->fromlist) == 1)
98 : {
99 262438 : Node *jtnode = (Node *) linitial(parse->jointree->fromlist);
100 :
101 262438 : if (IsA(jtnode, RangeTblRef))
102 : {
103 223287 : int varno = ((RangeTblRef *) jtnode)->rtindex;
104 223287 : RangeTblEntry *rte = root->simple_rte_array[varno];
105 :
106 : Assert(rte != NULL);
107 223287 : if (rte->rtekind == RTE_RESULT)
108 : {
109 : /* Make the RelOptInfo for it directly */
110 101968 : final_rel = build_simple_rel(root, varno, NULL);
111 :
112 : /*
113 : * If query allows parallelism in general, check whether the
114 : * quals are parallel-restricted. (We need not check
115 : * final_rel->reltarget because it's empty at this point.
116 : * Anything parallel-restricted in the query tlist will be
117 : * dealt with later.) We should always do this in a subquery,
118 : * since it might be useful to use the subquery in parallel
119 : * paths in the parent level. At top level this is normally
120 : * not worth the cycles, because a Result-only plan would
121 : * never be interesting to parallelize. However, if
122 : * debug_parallel_query is on, then we want to execute the
123 : * Result in a parallel worker if possible, so we must check.
124 : */
125 101968 : if (root->glob->parallelModeOK &&
126 52275 : (root->query_level > 1 ||
127 49133 : debug_parallel_query != DEBUG_PARALLEL_OFF))
128 3190 : final_rel->consider_parallel =
129 3190 : is_parallel_safe(root, parse->jointree->quals);
130 :
131 : /*
132 : * The only path for it is a trivial Result path. We cheat a
133 : * bit here by using a GroupResultPath, because that way we
134 : * can just jam the quals into it without preprocessing them.
135 : * (But, if you hold your head at the right angle, a FROM-less
136 : * SELECT is a kind of degenerate-grouping case, so it's not
137 : * that much of a cheat.)
138 : */
139 101968 : add_path(final_rel, (Path *)
140 101968 : create_group_result_path(root, final_rel,
141 101968 : final_rel->reltarget,
142 101968 : (List *) parse->jointree->quals));
143 :
144 : /* Select cheapest path (pretty easy in this case...) */
145 101968 : set_cheapest(final_rel);
146 :
147 : /*
148 : * We don't need to run generate_base_implied_equalities, but
149 : * we do need to pretend that EC merging is complete.
150 : */
151 101968 : root->ec_merging_done = true;
152 :
153 : /*
154 : * We still are required to call qp_callback, in case it's
155 : * something like "SELECT 2+2 ORDER BY 1".
156 : */
157 101968 : (*qp_callback) (root, qp_extra);
158 :
159 101968 : return final_rel;
160 : }
161 : }
162 : }
163 :
164 : /*
165 : * Construct RelOptInfo nodes for all base relations used in the query.
166 : * Appendrel member relations ("other rels") will be added later.
167 : *
168 : * Note: the reason we find the baserels by searching the jointree, rather
169 : * than scanning the rangetable, is that the rangetable may contain RTEs
170 : * for rels not actively part of the query, for example views. We don't
171 : * want to make RelOptInfos for them.
172 : */
173 183073 : add_base_rels_to_query(root, (Node *) parse->jointree);
174 :
175 : /* Remove any redundant GROUP BY columns */
176 183064 : remove_useless_groupby_columns(root);
177 :
178 : /*
179 : * Examine the targetlist and join tree, adding entries to baserel
180 : * targetlists for all referenced Vars, and generating PlaceHolderInfo
181 : * entries for all referenced PlaceHolderVars. Restrict and join clauses
182 : * are added to appropriate lists belonging to the mentioned relations. We
183 : * also build EquivalenceClasses for provably equivalent expressions. The
184 : * SpecialJoinInfo list is also built to hold information about join order
185 : * restrictions. Finally, we form a target joinlist for make_one_rel() to
186 : * work from.
187 : */
188 183064 : build_base_rel_tlists(root, root->processed_tlist);
189 :
190 183064 : find_placeholders_in_jointree(root);
191 :
192 183064 : find_lateral_references(root);
193 :
194 183064 : joinlist = deconstruct_jointree(root);
195 :
196 : /*
197 : * Reconsider any postponed outer-join quals now that we have built up
198 : * equivalence classes. (This could result in further additions or
199 : * mergings of classes.)
200 : */
201 183064 : reconsider_outer_join_clauses(root);
202 :
203 : /*
204 : * If we formed any equivalence classes, generate additional restriction
205 : * clauses as appropriate. (Implied join clauses are formed on-the-fly
206 : * later.)
207 : */
208 183064 : generate_base_implied_equalities(root);
209 :
210 : /*
211 : * We have completed merging equivalence sets, so it's now possible to
212 : * generate pathkeys in canonical form; so compute query_pathkeys and
213 : * other pathkeys fields in PlannerInfo.
214 : */
215 183064 : (*qp_callback) (root, qp_extra);
216 :
217 : /*
218 : * Examine any "placeholder" expressions generated during subquery pullup.
219 : * Make sure that the Vars they need are marked as needed at the relevant
220 : * join level. This must be done before join removal because it might
221 : * cause Vars or placeholders to be needed above a join when they weren't
222 : * so marked before.
223 : */
224 183064 : fix_placeholder_input_needed_levels(root);
225 :
226 : /*
227 : * Remove any useless outer joins. Ideally this would be done during
228 : * jointree preprocessing, but the necessary information isn't available
229 : * until we've built baserel data structures and classified qual clauses.
230 : */
231 183064 : joinlist = remove_useless_joins(root, joinlist);
232 :
233 : /*
234 : * Also, reduce any semijoins with unique inner rels to plain inner joins.
235 : * Likewise, this can't be done until now for lack of needed info.
236 : */
237 183064 : reduce_unique_semijoins(root);
238 :
239 : /*
240 : * Remove self joins on a unique column.
241 : */
242 183064 : joinlist = remove_useless_self_joins(root, joinlist);
243 :
244 : /*
245 : * Now distribute "placeholders" to base rels as needed. This has to be
246 : * done after join removal because removal could change whether a
247 : * placeholder is evaluable at a base rel.
248 : */
249 183064 : add_placeholders_to_base_rels(root);
250 :
251 : /*
252 : * Construct the lateral reference sets now that we have finalized
253 : * PlaceHolderVar eval levels.
254 : */
255 183064 : create_lateral_join_info(root);
256 :
257 : /*
258 : * Match foreign keys to equivalence classes and join quals. This must be
259 : * done after finalizing equivalence classes, and it's useful to wait till
260 : * after join removal so that we can skip processing foreign keys
261 : * involving removed relations.
262 : */
263 183064 : match_foreign_keys_to_quals(root);
264 :
265 : /*
266 : * Look for join OR clauses that we can extract single-relation
267 : * restriction OR clauses from.
268 : */
269 183064 : extract_restriction_or_clauses(root);
270 :
271 : /*
272 : * Check if eager aggregation is applicable, and if so, set up
273 : * root->agg_clause_list and root->group_expr_list.
274 : */
275 183064 : setup_eager_aggregation(root);
276 :
277 : /*
278 : * Now expand appendrels by adding "otherrels" for their children. We
279 : * delay this to the end so that we have as much information as possible
280 : * available for each baserel, including all restriction clauses. That
281 : * let us prune away partitions that don't satisfy a restriction clause.
282 : * Also note that some information such as lateral_relids is propagated
283 : * from baserels to otherrels here, so we must have computed it already.
284 : */
285 183064 : add_other_rels_to_query(root);
286 :
287 : /*
288 : * Distribute any UPDATE/DELETE/MERGE row identity variables to the target
289 : * relations. This can't be done till we've finished expansion of
290 : * appendrels.
291 : */
292 183063 : distribute_row_identity_vars(root);
293 :
294 : /*
295 : * Ready to do the primary planning.
296 : */
297 183063 : final_rel = make_one_rel(root, joinlist);
298 :
299 : /* Check that we got at least one usable path */
300 183046 : if (!final_rel || !final_rel->cheapest_total_path ||
301 183046 : final_rel->cheapest_total_path->param_info != NULL)
302 0 : elog(ERROR, "failed to construct the join relation");
303 :
304 183046 : return final_rel;
305 : }
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