1 /*-------------------------------------------------------------------------
4 * Routines to plan a single query
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.)
12 * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
13 * Portions Copyright (c) 1994, Regents of the University of California
17 * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planmain.c,v 1.56 2000/07/24 03:11:01 tgl Exp $
19 *-------------------------------------------------------------------------
23 #include <sys/types.h>
25 #include "optimizer/clauses.h"
26 #include "optimizer/cost.h"
27 #include "optimizer/pathnode.h"
28 #include "optimizer/paths.h"
29 #include "optimizer/planmain.h"
30 #include "optimizer/tlist.h"
33 static Plan *subplanner(Query *root, List *flat_tlist, List *qual,
34 double tuple_fraction);
37 /*--------------------
39 * Generate a plan for a basic query, which may involve joins but
40 * not any fancier features.
42 * tlist is the target list the query should produce (NOT root->targetList!)
43 * qual is the qualification of the query (likewise!)
44 * tuple_fraction is the fraction of tuples we expect will be retrieved
46 * qual must already have been converted to implicit-AND form.
48 * Note: the Query node now also includes a query_pathkeys field, which
49 * is both an input and an output of query_planner(). The input value
50 * signals query_planner that the indicated sort order is wanted in the
51 * final output plan. The output value is the actual pathkeys of the
52 * selected path. This might not be the same as what the caller requested;
53 * the caller must do pathkeys_contained_in() to decide whether an
54 * explicit sort is still needed. (The main reason query_pathkeys is a
55 * Query field and not a passed parameter is that the low-level routines
56 * in indxpath.c need to see it.) The pathkeys value passed to query_planner
57 * has not yet been "canonicalized", since the necessary info does not get
58 * computed until subplanner() scans the qual clauses. We canonicalize it
59 * inside subplanner() as soon as that task is done. The output value
60 * will be in canonical form as well.
62 * tuple_fraction is interpreted as follows:
63 * 0 (or less): expect all tuples to be retrieved (normal case)
64 * 0 < tuple_fraction < 1: expect the given fraction of tuples available
65 * from the plan to be retrieved
66 * tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
67 * expected to be retrieved (ie, a LIMIT specification)
68 * Note that while this routine and its subroutines treat a negative
69 * tuple_fraction the same as 0, union_planner has a different interpretation.
71 * Returns a query plan.
75 query_planner(Query *root,
78 double tuple_fraction)
80 List *constant_qual = NIL;
85 * If the query contains no relation references at all, it must be
86 * something like "SELECT 2+2;". Build a trivial "Result" plan.
88 if (root->rtable == NIL)
90 /* If it's not a select, it should have had a target relation... */
91 if (root->commandType != CMD_SELECT)
92 elog(ERROR, "Empty range table for non-SELECT query");
94 root->query_pathkeys = NIL; /* signal unordered result */
96 /* Make childless Result node to evaluate given tlist. */
97 return (Plan *) make_result(tlist, (Node *) qual, (Plan *) NULL);
101 * Pull out any non-variable qual clauses so these can be put in a
102 * toplevel "Result" node, where they will gate execution of the whole
103 * plan (the Result will not invoke its descendant plan unless the
104 * quals are true). Note that any *really* non-variable quals will
105 * have been optimized away by eval_const_expressions(). What we're
106 * mostly interested in here is quals that depend only on outer-level
107 * vars, although if the qual reduces to "WHERE FALSE" this path will
110 qual = pull_constant_clauses(qual, &constant_qual);
113 * Create a target list that consists solely of (resdom var) target
114 * list entries, i.e., contains no arbitrary expressions.
116 * All subplan nodes will have "flat" (var-only) tlists.
118 * This implies that all expression evaluations are done at the root of
119 * the plan tree. Once upon a time there was code to try to push
120 * expensive function calls down to lower plan nodes, but that's dead
121 * code and has been for a long time...
123 var_only_tlist = flatten_tlist(tlist);
126 * Choose the best access path and build a plan for it.
128 subplan = subplanner(root, var_only_tlist, qual, tuple_fraction);
131 * Build a result node to control the plan if we have constant quals.
137 * The result node will also be responsible for evaluating the
138 * originally requested tlist.
140 subplan = (Plan *) make_result(tlist,
141 (Node *) constant_qual,
148 * Replace the toplevel plan node's flattened target list with the
149 * targetlist given by my caller, so that expressions are
152 subplan->targetlist = tlist;
161 * Subplanner creates an entire plan consisting of joins and scans
162 * for processing a single level of attributes.
164 * flat_tlist is the flattened target list
165 * qual is the qualification to be satisfied
166 * tuple_fraction is the fraction of tuples we expect will be retrieved
168 * See query_planner() comments about the interpretation of tuple_fraction.
173 subplanner(Query *root,
176 double tuple_fraction)
178 RelOptInfo *final_rel;
183 * Initialize the targetlist and qualification, adding entries to
184 * base_rel_list as relation references are found (e.g., in the
185 * qualification, the targetlist, etc.). Restrict and join clauses
186 * are added to appropriate lists belonging to the mentioned
187 * relations. We also build lists of equijoined keys for pathkey
190 root->base_rel_list = NIL;
191 root->join_rel_list = NIL;
192 root->equi_key_list = NIL;
194 make_var_only_tlist(root, flat_tlist);
195 add_restrict_and_join_to_rels(root, qual);
198 * Make sure we have RelOptInfo nodes for all relations used.
200 add_missing_rels_to_query(root);
203 * Use the completed lists of equijoined keys to deduce any implied
204 * but unstated equalities (for example, A=B and B=C imply A=C).
206 generate_implied_equalities(root);
209 * We should now have all the pathkey equivalence sets built, so it's
210 * now possible to convert the requested query_pathkeys to canonical
213 root->query_pathkeys = canonicalize_pathkeys(root, root->query_pathkeys);
216 * Ready to do the primary planning.
218 final_rel = make_one_rel(root);
224 * We expect to end up here for a trivial INSERT ... VALUES query
225 * (which will have a target relation, so it gets past
226 * query_planner's check for empty range table; but the target rel
227 * is unreferenced and not marked inJoinSet, so we find there is
230 * It's also possible to get here if the query was rewritten by the
231 * rule processor (creating rangetable entries not marked
232 * inJoinSet) but the rules either did nothing or were simplified
233 * to nothing by constant-expression folding. So, don't complain.
235 root->query_pathkeys = NIL; /* signal unordered result */
237 /* Make childless Result node to evaluate given tlist. */
238 return (Plan *) make_result(flat_tlist, (Node *) qual, (Plan *) NULL);
241 #ifdef NOT_USED /* fix xfunc */
244 * Perform Predicate Migration on each path, to optimize and correctly
245 * assess the cost of each before choosing the cheapest one. -- JMH,
248 * Needn't do so if the top rel is pruneable: that means there's no
249 * expensive functions left to pull up. -- JMH, 11/22/92
251 if (XfuncMode != XFUNC_OFF && XfuncMode != XFUNC_NOPM &&
252 XfuncMode != XFUNC_NOPULL && !final_rel->pruneable)
256 foreach(pathnode, final_rel->pathlist)
258 if (xfunc_do_predmig((Path *) lfirst(pathnode)))
259 set_cheapest(final_rel);
265 * Now that we have an estimate of the final rel's size, we can
266 * convert a tuple_fraction specified as an absolute count (ie, a
267 * LIMIT option) into a fraction of the total tuples.
269 if (tuple_fraction >= 1.0)
270 tuple_fraction /= final_rel->rows;
273 * Determine the cheapest path, independently of any ordering
274 * considerations. We do, however, take into account whether the
275 * whole plan is expected to be evaluated or not.
277 if (tuple_fraction <= 0.0 || tuple_fraction >= 1.0)
278 cheapestpath = final_rel->cheapest_total_path;
281 get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
285 Assert(cheapestpath != NULL);
288 * Select the best path and create a subplan to execute it.
290 * If no special sort order is wanted, or if the cheapest path is already
291 * appropriately ordered, we use the cheapest path found above.
293 if (root->query_pathkeys == NIL ||
294 pathkeys_contained_in(root->query_pathkeys,
295 cheapestpath->pathkeys))
297 root->query_pathkeys = cheapestpath->pathkeys;
298 return create_plan(root, cheapestpath);
302 * Otherwise, look to see if we have an already-ordered path that is
303 * cheaper than doing an explicit sort on the cheapest-total-cost
306 cheapestpath = final_rel->cheapest_total_path;
308 get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
309 root->query_pathkeys,
313 Path sort_path; /* dummy for result of cost_sort */
315 cost_sort(&sort_path, root->query_pathkeys,
316 final_rel->rows, final_rel->width);
317 sort_path.startup_cost += cheapestpath->total_cost;
318 sort_path.total_cost += cheapestpath->total_cost;
319 if (compare_fractional_path_costs(presortedpath, &sort_path,
320 tuple_fraction) <= 0)
322 /* Presorted path is cheaper, use it */
323 root->query_pathkeys = presortedpath->pathkeys;
324 return create_plan(root, presortedpath);
326 /* otherwise, doing it the hard way is still cheaper */
330 * Nothing for it but to sort the cheapest-total-cost path --- but we
331 * let the caller do that. union_planner has to be able to add a sort
332 * node anyway, so no need for extra code here. (Furthermore, the
333 * given pathkeys might involve something we can't compute here, such
334 * as an aggregate function...)
336 root->query_pathkeys = cheapestpath->pathkeys;
337 return create_plan(root, cheapestpath);