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) 1996-2017, 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/clauses.h"
24 #include "optimizer/orclauses.h"
25 #include "optimizer/pathnode.h"
26 #include "optimizer/paths.h"
27 #include "optimizer/placeholder.h"
28 #include "optimizer/planmain.h"
29
30
31 /*
32 * query_planner
33 * Generate a path (that is, a simplified plan) for a basic query,
34 * which may involve joins but not any fancier features.
35 *
36 * Since query_planner does not handle the toplevel processing (grouping,
37 * sorting, etc) it cannot select the best path by itself. Instead, it
38 * returns the RelOptInfo for the top level of joining, and the caller
39 * (grouping_planner) can choose among the surviving paths for the rel.
40 *
41 * root describes the query to plan
42 * tlist is the target list the query should produce
43 * (this is NOT necessarily root->parse->targetList!)
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 *
query_planner(PlannerInfo * root,List * tlist,query_pathkeys_callback qp_callback,void * qp_extra)54 query_planner(PlannerInfo *root, List *tlist,
55 query_pathkeys_callback qp_callback, void *qp_extra)
56 {
57 Query *parse = root->parse;
58 List *joinlist;
59 RelOptInfo *final_rel;
60 Index rti;
61 double total_pages;
62
63 /*
64 * If the query has an empty join tree, then it's something easy like
65 * "SELECT 2+2;" or "INSERT ... VALUES()". Fall through quickly.
66 */
67 if (parse->jointree->fromlist == NIL)
68 {
69 /* We need a dummy joinrel to describe the empty set of baserels */
70 final_rel = build_empty_join_rel(root);
71
72 /*
73 * If query allows parallelism in general, check whether the quals are
74 * parallel-restricted. (We need not check final_rel->reltarget
75 * because it's empty at this point. Anything parallel-restricted in
76 * the query tlist will be dealt with later.)
77 */
78 if (root->glob->parallelModeOK)
79 final_rel->consider_parallel =
80 is_parallel_safe(root, parse->jointree->quals);
81
82 /* The only path for it is a trivial Result path */
83 add_path(final_rel, (Path *)
84 create_result_path(root, final_rel,
85 final_rel->reltarget,
86 (List *) parse->jointree->quals));
87
88 /* Select cheapest path (pretty easy in this case...) */
89 set_cheapest(final_rel);
90
91 /*
92 * We still are required to call qp_callback, in case it's something
93 * like "SELECT 2+2 ORDER BY 1".
94 */
95 root->canon_pathkeys = NIL;
96 (*qp_callback) (root, qp_extra);
97
98 return final_rel;
99 }
100
101 /*
102 * Init planner lists to empty.
103 *
104 * NOTE: append_rel_list was set up by subquery_planner, so do not touch
105 * here.
106 */
107 root->join_rel_list = NIL;
108 root->join_rel_hash = NULL;
109 root->join_rel_level = NULL;
110 root->join_cur_level = 0;
111 root->canon_pathkeys = NIL;
112 root->left_join_clauses = NIL;
113 root->right_join_clauses = NIL;
114 root->full_join_clauses = NIL;
115 root->join_info_list = NIL;
116 root->placeholder_list = NIL;
117 root->fkey_list = NIL;
118 root->initial_rels = NIL;
119
120 /*
121 * Make a flattened version of the rangetable for faster access (this is
122 * OK because the rangetable won't change any more), and set up an empty
123 * array for indexing base relations.
124 */
125 setup_simple_rel_arrays(root);
126
127 /*
128 * Construct RelOptInfo nodes for all base relations in query, and
129 * indirectly for all appendrel member relations ("other rels"). This
130 * will give us a RelOptInfo for every "simple" (non-join) rel involved in
131 * the query.
132 *
133 * Note: the reason we find the rels by searching the jointree and
134 * appendrel list, rather than just scanning the rangetable, is that the
135 * rangetable may contain RTEs for rels not actively part of the query,
136 * for example views. We don't want to make RelOptInfos for them.
137 */
138 add_base_rels_to_query(root, (Node *) parse->jointree);
139
140 /*
141 * Examine the targetlist and join tree, adding entries to baserel
142 * targetlists for all referenced Vars, and generating PlaceHolderInfo
143 * entries for all referenced PlaceHolderVars. Restrict and join clauses
144 * are added to appropriate lists belonging to the mentioned relations. We
145 * also build EquivalenceClasses for provably equivalent expressions. The
146 * SpecialJoinInfo list is also built to hold information about join order
147 * restrictions. Finally, we form a target joinlist for make_one_rel() to
148 * work from.
149 */
150 build_base_rel_tlists(root, tlist);
151
152 find_placeholders_in_jointree(root);
153
154 find_lateral_references(root);
155
156 joinlist = deconstruct_jointree(root);
157
158 /*
159 * Reconsider any postponed outer-join quals now that we have built up
160 * equivalence classes. (This could result in further additions or
161 * mergings of classes.)
162 */
163 reconsider_outer_join_clauses(root);
164
165 /*
166 * If we formed any equivalence classes, generate additional restriction
167 * clauses as appropriate. (Implied join clauses are formed on-the-fly
168 * later.)
169 */
170 generate_base_implied_equalities(root);
171
172 /*
173 * We have completed merging equivalence sets, so it's now possible to
174 * generate pathkeys in canonical form; so compute query_pathkeys and
175 * other pathkeys fields in PlannerInfo.
176 */
177 (*qp_callback) (root, qp_extra);
178
179 /*
180 * Examine any "placeholder" expressions generated during subquery pullup.
181 * Make sure that the Vars they need are marked as needed at the relevant
182 * join level. This must be done before join removal because it might
183 * cause Vars or placeholders to be needed above a join when they weren't
184 * so marked before.
185 */
186 fix_placeholder_input_needed_levels(root);
187
188 /*
189 * Remove any useless outer joins. Ideally this would be done during
190 * jointree preprocessing, but the necessary information isn't available
191 * until we've built baserel data structures and classified qual clauses.
192 */
193 joinlist = remove_useless_joins(root, joinlist);
194
195 /*
196 * Also, reduce any semijoins with unique inner rels to plain inner joins.
197 * Likewise, this can't be done until now for lack of needed info.
198 */
199 reduce_unique_semijoins(root);
200
201 /*
202 * Now distribute "placeholders" to base rels as needed. This has to be
203 * done after join removal because removal could change whether a
204 * placeholder is evaluable at a base rel.
205 */
206 add_placeholders_to_base_rels(root);
207
208 /*
209 * Construct the lateral reference sets now that we have finalized
210 * PlaceHolderVar eval levels.
211 */
212 create_lateral_join_info(root);
213
214 /*
215 * Match foreign keys to equivalence classes and join quals. This must be
216 * done after finalizing equivalence classes, and it's useful to wait till
217 * after join removal so that we can skip processing foreign keys
218 * involving removed relations.
219 */
220 match_foreign_keys_to_quals(root);
221
222 /*
223 * Look for join OR clauses that we can extract single-relation
224 * restriction OR clauses from.
225 */
226 extract_restriction_or_clauses(root);
227
228 /*
229 * We should now have size estimates for every actual table involved in
230 * the query, and we also know which if any have been deleted from the
231 * query by join removal; so we can compute total_table_pages.
232 *
233 * Note that appendrels are not double-counted here, even though we don't
234 * bother to distinguish RelOptInfos for appendrel parents, because the
235 * parents will still have size zero.
236 *
237 * XXX if a table is self-joined, we will count it once per appearance,
238 * which perhaps is the wrong thing ... but that's not completely clear,
239 * and detecting self-joins here is difficult, so ignore it for now.
240 */
241 total_pages = 0;
242 for (rti = 1; rti < root->simple_rel_array_size; rti++)
243 {
244 RelOptInfo *brel = root->simple_rel_array[rti];
245
246 if (brel == NULL)
247 continue;
248
249 Assert(brel->relid == rti); /* sanity check on array */
250
251 if (IS_SIMPLE_REL(brel))
252 total_pages += (double) brel->pages;
253 }
254 root->total_table_pages = total_pages;
255
256 /*
257 * Ready to do the primary planning.
258 */
259 final_rel = make_one_rel(root, joinlist);
260
261 /* Check that we got at least one usable path */
262 if (!final_rel || !final_rel->cheapest_total_path ||
263 final_rel->cheapest_total_path->param_info != NULL)
264 elog(ERROR, "failed to construct the join relation");
265
266 return final_rel;
267 }
268