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) 1996-2024, 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 483382 : query_planner(PlannerInfo *root,
55 : query_pathkeys_callback qp_callback, void *qp_extra)
56 : {
57 483382 : 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 483382 : root->join_rel_list = NIL;
68 483382 : root->join_rel_hash = NULL;
69 483382 : root->join_rel_level = NULL;
70 483382 : root->join_cur_level = 0;
71 483382 : root->canon_pathkeys = NIL;
72 483382 : root->left_join_clauses = NIL;
73 483382 : root->right_join_clauses = NIL;
74 483382 : root->full_join_clauses = NIL;
75 483382 : root->join_info_list = NIL;
76 483382 : root->placeholder_list = NIL;
77 483382 : root->placeholder_array = NULL;
78 483382 : root->placeholder_array_size = 0;
79 483382 : root->fkey_list = NIL;
80 483382 : root->initial_rels = NIL;
81 :
82 : /*
83 : * Set up arrays for accessing base relations and AppendRelInfos.
84 : */
85 483382 : 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 483382 : if (list_length(parse->jointree->fromlist) == 1)
95 : {
96 444196 : Node *jtnode = (Node *) linitial(parse->jointree->fromlist);
97 :
98 444196 : if (IsA(jtnode, RangeTblRef))
99 : {
100 395002 : int varno = ((RangeTblRef *) jtnode)->rtindex;
101 395002 : RangeTblEntry *rte = root->simple_rte_array[varno];
102 :
103 : Assert(rte != NULL);
104 395002 : if (rte->rtekind == RTE_RESULT)
105 : {
106 : /* Make the RelOptInfo for it directly */
107 206102 : 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 206102 : if (root->glob->parallelModeOK &&
123 102724 : (root->query_level > 1 ||
124 99876 : debug_parallel_query != DEBUG_PARALLEL_OFF))
125 2860 : final_rel->consider_parallel =
126 2860 : 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 206102 : add_path(final_rel, (Path *)
137 206102 : create_group_result_path(root, final_rel,
138 206102 : final_rel->reltarget,
139 206102 : (List *) parse->jointree->quals));
140 :
141 : /* Select cheapest path (pretty easy in this case...) */
142 206102 : 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 206102 : 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 206102 : (*qp_callback) (root, qp_extra);
155 :
156 206102 : 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 277280 : add_base_rels_to_query(root, (Node *) parse->jointree);
171 :
172 : /*
173 : * Examine the targetlist and join tree, adding entries to baserel
174 : * targetlists for all referenced Vars, and generating PlaceHolderInfo
175 : * entries for all referenced PlaceHolderVars. Restrict and join clauses
176 : * are added to appropriate lists belonging to the mentioned relations. We
177 : * also build EquivalenceClasses for provably equivalent expressions. The
178 : * SpecialJoinInfo list is also built to hold information about join order
179 : * restrictions. Finally, we form a target joinlist for make_one_rel() to
180 : * work from.
181 : */
182 277266 : build_base_rel_tlists(root, root->processed_tlist);
183 :
184 277266 : find_placeholders_in_jointree(root);
185 :
186 277266 : find_lateral_references(root);
187 :
188 277266 : joinlist = deconstruct_jointree(root);
189 :
190 : /*
191 : * Reconsider any postponed outer-join quals now that we have built up
192 : * equivalence classes. (This could result in further additions or
193 : * mergings of classes.)
194 : */
195 277266 : reconsider_outer_join_clauses(root);
196 :
197 : /*
198 : * If we formed any equivalence classes, generate additional restriction
199 : * clauses as appropriate. (Implied join clauses are formed on-the-fly
200 : * later.)
201 : */
202 277266 : generate_base_implied_equalities(root);
203 :
204 : /*
205 : * We have completed merging equivalence sets, so it's now possible to
206 : * generate pathkeys in canonical form; so compute query_pathkeys and
207 : * other pathkeys fields in PlannerInfo.
208 : */
209 277266 : (*qp_callback) (root, qp_extra);
210 :
211 : /*
212 : * Examine any "placeholder" expressions generated during subquery pullup.
213 : * Make sure that the Vars they need are marked as needed at the relevant
214 : * join level. This must be done before join removal because it might
215 : * cause Vars or placeholders to be needed above a join when they weren't
216 : * so marked before.
217 : */
218 277266 : fix_placeholder_input_needed_levels(root);
219 :
220 : /*
221 : * Remove any useless outer joins. Ideally this would be done during
222 : * jointree preprocessing, but the necessary information isn't available
223 : * until we've built baserel data structures and classified qual clauses.
224 : */
225 277266 : joinlist = remove_useless_joins(root, joinlist);
226 :
227 : /*
228 : * Also, reduce any semijoins with unique inner rels to plain inner joins.
229 : * Likewise, this can't be done until now for lack of needed info.
230 : */
231 277266 : reduce_unique_semijoins(root);
232 :
233 : /*
234 : * Now distribute "placeholders" to base rels as needed. This has to be
235 : * done after join removal because removal could change whether a
236 : * placeholder is evaluable at a base rel.
237 : */
238 277266 : add_placeholders_to_base_rels(root);
239 :
240 : /*
241 : * Construct the lateral reference sets now that we have finalized
242 : * PlaceHolderVar eval levels.
243 : */
244 277266 : create_lateral_join_info(root);
245 :
246 : /*
247 : * Match foreign keys to equivalence classes and join quals. This must be
248 : * done after finalizing equivalence classes, and it's useful to wait till
249 : * after join removal so that we can skip processing foreign keys
250 : * involving removed relations.
251 : */
252 277266 : match_foreign_keys_to_quals(root);
253 :
254 : /*
255 : * Look for join OR clauses that we can extract single-relation
256 : * restriction OR clauses from.
257 : */
258 277266 : extract_restriction_or_clauses(root);
259 :
260 : /*
261 : * Now expand appendrels by adding "otherrels" for their children. We
262 : * delay this to the end so that we have as much information as possible
263 : * available for each baserel, including all restriction clauses. That
264 : * let us prune away partitions that don't satisfy a restriction clause.
265 : * Also note that some information such as lateral_relids is propagated
266 : * from baserels to otherrels here, so we must have computed it already.
267 : */
268 277266 : add_other_rels_to_query(root);
269 :
270 : /*
271 : * Distribute any UPDATE/DELETE/MERGE row identity variables to the target
272 : * relations. This can't be done till we've finished expansion of
273 : * appendrels.
274 : */
275 277264 : distribute_row_identity_vars(root);
276 :
277 : /*
278 : * Ready to do the primary planning.
279 : */
280 277264 : final_rel = make_one_rel(root, joinlist);
281 :
282 : /* Check that we got at least one usable path */
283 277236 : if (!final_rel || !final_rel->cheapest_total_path ||
284 277236 : final_rel->cheapest_total_path->param_info != NULL)
285 0 : elog(ERROR, "failed to construct the join relation");
286 :
287 277236 : return final_rel;
288 : }
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