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equivclass.c
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1 /*-------------------------------------------------------------------------
2  *
3  * equivclass.c
4  * Routines for managing EquivalenceClasses
5  *
6  * See src/backend/optimizer/README for discussion of EquivalenceClasses.
7  *
8  *
9  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
10  * Portions Copyright (c) 1994, Regents of the University of California
11  *
12  * IDENTIFICATION
13  * src/backend/optimizer/path/equivclass.c
14  *
15  *-------------------------------------------------------------------------
16  */
17 #include "postgres.h"
18 
19 #include <limits.h>
20 
21 #include "access/stratnum.h"
22 #include "catalog/pg_type.h"
23 #include "nodes/makefuncs.h"
24 #include "nodes/nodeFuncs.h"
25 #include "optimizer/clauses.h"
26 #include "optimizer/pathnode.h"
27 #include "optimizer/paths.h"
28 #include "optimizer/planmain.h"
29 #include "optimizer/prep.h"
30 #include "optimizer/restrictinfo.h"
31 #include "optimizer/var.h"
32 #include "utils/lsyscache.h"
33 
34 
35 static EquivalenceMember *add_eq_member(EquivalenceClass *ec,
36  Expr *expr, Relids relids, Relids nullable_relids,
37  bool is_child, Oid datatype);
38 static void generate_base_implied_equalities_const(PlannerInfo *root,
39  EquivalenceClass *ec);
40 static void generate_base_implied_equalities_no_const(PlannerInfo *root,
41  EquivalenceClass *ec);
42 static void generate_base_implied_equalities_broken(PlannerInfo *root,
43  EquivalenceClass *ec);
44 static List *generate_join_implied_equalities_normal(PlannerInfo *root,
45  EquivalenceClass *ec,
46  Relids join_relids,
47  Relids outer_relids,
48  Relids inner_relids);
49 static List *generate_join_implied_equalities_broken(PlannerInfo *root,
50  EquivalenceClass *ec,
51  Relids nominal_join_relids,
52  Relids outer_relids,
53  Relids nominal_inner_relids,
54  RelOptInfo *inner_rel);
55 static Oid select_equality_operator(EquivalenceClass *ec,
56  Oid lefttype, Oid righttype);
57 static RestrictInfo *create_join_clause(PlannerInfo *root,
58  EquivalenceClass *ec, Oid opno,
59  EquivalenceMember *leftem,
60  EquivalenceMember *rightem,
61  EquivalenceClass *parent_ec);
62 static bool reconsider_outer_join_clause(PlannerInfo *root,
63  RestrictInfo *rinfo,
64  bool outer_on_left);
65 static bool reconsider_full_join_clause(PlannerInfo *root,
66  RestrictInfo *rinfo);
67 
68 
69 /*
70  * process_equivalence
71  * The given clause has a mergejoinable operator and can be applied without
72  * any delay by an outer join, so its two sides can be considered equal
73  * anywhere they are both computable; moreover that equality can be
74  * extended transitively. Record this knowledge in the EquivalenceClass
75  * data structure, if applicable. Returns true if successful, false if not
76  * (in which case caller should treat the clause as ordinary, not an
77  * equivalence).
78  *
79  * In some cases, although we cannot convert a clause into EquivalenceClass
80  * knowledge, we can still modify it to a more useful form than the original.
81  * Then, *p_restrictinfo will be replaced by a new RestrictInfo, which is what
82  * the caller should use for further processing.
83  *
84  * If below_outer_join is true, then the clause was found below the nullable
85  * side of an outer join, so its sides might validly be both NULL rather than
86  * strictly equal. We can still deduce equalities in such cases, but we take
87  * care to mark an EquivalenceClass if it came from any such clauses. Also,
88  * we have to check that both sides are either pseudo-constants or strict
89  * functions of Vars, else they might not both go to NULL above the outer
90  * join. (This is the main reason why we need a failure return. It's more
91  * convenient to check this case here than at the call sites...)
92  *
93  * We also reject proposed equivalence clauses if they contain leaky functions
94  * and have security_level above zero. The EC evaluation rules require us to
95  * apply certain tests at certain joining levels, and we can't tolerate
96  * delaying any test on security_level grounds. By rejecting candidate clauses
97  * that might require security delays, we ensure it's safe to apply an EC
98  * clause as soon as it's supposed to be applied.
99  *
100  * On success return, we have also initialized the clause's left_ec/right_ec
101  * fields to point to the EquivalenceClass representing it. This saves lookup
102  * effort later.
103  *
104  * Note: constructing merged EquivalenceClasses is a standard UNION-FIND
105  * problem, for which there exist better data structures than simple lists.
106  * If this code ever proves to be a bottleneck then it could be sped up ---
107  * but for now, simple is beautiful.
108  *
109  * Note: this is only called during planner startup, not during GEQO
110  * exploration, so we need not worry about whether we're in the right
111  * memory context.
112  */
113 bool
114 process_equivalence(PlannerInfo *root,
115  RestrictInfo **p_restrictinfo,
116  bool below_outer_join)
117 {
118  RestrictInfo *restrictinfo = *p_restrictinfo;
119  Expr *clause = restrictinfo->clause;
120  Oid opno,
121  collation,
122  item1_type,
123  item2_type;
124  Expr *item1;
125  Expr *item2;
126  Relids item1_relids,
127  item2_relids,
128  item1_nullable_relids,
129  item2_nullable_relids;
130  List *opfamilies;
131  EquivalenceClass *ec1,
132  *ec2;
133  EquivalenceMember *em1,
134  *em2;
135  ListCell *lc1;
136 
137  /* Should not already be marked as having generated an eclass */
138  Assert(restrictinfo->left_ec == NULL);
139  Assert(restrictinfo->right_ec == NULL);
140 
141  /* Reject if it is potentially postponable by security considerations */
142  if (restrictinfo->security_level > 0 && !restrictinfo->leakproof)
143  return false;
144 
145  /* Extract info from given clause */
146  Assert(is_opclause(clause));
147  opno = ((OpExpr *) clause)->opno;
148  collation = ((OpExpr *) clause)->inputcollid;
149  item1 = (Expr *) get_leftop(clause);
150  item2 = (Expr *) get_rightop(clause);
151  item1_relids = restrictinfo->left_relids;
152  item2_relids = restrictinfo->right_relids;
153 
154  /*
155  * Ensure both input expressions expose the desired collation (their types
156  * should be OK already); see comments for canonicalize_ec_expression.
157  */
158  item1 = canonicalize_ec_expression(item1,
159  exprType((Node *) item1),
160  collation);
161  item2 = canonicalize_ec_expression(item2,
162  exprType((Node *) item2),
163  collation);
164 
165  /*
166  * Clauses of the form X=X cannot be translated into EquivalenceClasses.
167  * We'd either end up with a single-entry EC, losing the knowledge that
168  * the clause was present at all, or else make an EC with duplicate
169  * entries, causing other issues.
170  */
171  if (equal(item1, item2))
172  {
173  /*
174  * If the operator is strict, then the clause can be treated as just
175  * "X IS NOT NULL". (Since we know we are considering a top-level
176  * qual, we can ignore the difference between FALSE and NULL results.)
177  * It's worth making the conversion because we'll typically get a much
178  * better selectivity estimate than we would for X=X.
179  *
180  * If the operator is not strict, we can't be sure what it will do
181  * with NULLs, so don't attempt to optimize it.
182  */
183  set_opfuncid((OpExpr *) clause);
184  if (func_strict(((OpExpr *) clause)->opfuncid))
185  {
186  NullTest *ntest = makeNode(NullTest);
187 
188  ntest->arg = item1;
189  ntest->nulltesttype = IS_NOT_NULL;
190  ntest->argisrow = false; /* correct even if composite arg */
191  ntest->location = -1;
192 
193  *p_restrictinfo =
194  make_restrictinfo((Expr *) ntest,
195  restrictinfo->is_pushed_down,
196  restrictinfo->outerjoin_delayed,
197  restrictinfo->pseudoconstant,
198  restrictinfo->security_level,
199  NULL,
200  restrictinfo->outer_relids,
201  restrictinfo->nullable_relids);
202  }
203  return false;
204  }
205 
206  /*
207  * If below outer join, check for strictness, else reject.
208  */
209  if (below_outer_join)
210  {
211  if (!bms_is_empty(item1_relids) &&
212  contain_nonstrict_functions((Node *) item1))
213  return false; /* LHS is non-strict but not constant */
214  if (!bms_is_empty(item2_relids) &&
215  contain_nonstrict_functions((Node *) item2))
216  return false; /* RHS is non-strict but not constant */
217  }
218 
219  /* Calculate nullable-relid sets for each side of the clause */
220  item1_nullable_relids = bms_intersect(item1_relids,
221  restrictinfo->nullable_relids);
222  item2_nullable_relids = bms_intersect(item2_relids,
223  restrictinfo->nullable_relids);
224 
225  /*
226  * We use the declared input types of the operator, not exprType() of the
227  * inputs, as the nominal datatypes for opfamily lookup. This presumes
228  * that btree operators are always registered with amoplefttype and
229  * amoprighttype equal to their declared input types. We will need this
230  * info anyway to build EquivalenceMember nodes, and by extracting it now
231  * we can use type comparisons to short-circuit some equal() tests.
232  */
233  op_input_types(opno, &item1_type, &item2_type);
234 
235  opfamilies = restrictinfo->mergeopfamilies;
236 
237  /*
238  * Sweep through the existing EquivalenceClasses looking for matches to
239  * item1 and item2. These are the possible outcomes:
240  *
241  * 1. We find both in the same EC. The equivalence is already known, so
242  * there's nothing to do.
243  *
244  * 2. We find both in different ECs. Merge the two ECs together.
245  *
246  * 3. We find just one. Add the other to its EC.
247  *
248  * 4. We find neither. Make a new, two-entry EC.
249  *
250  * Note: since all ECs are built through this process or the similar
251  * search in get_eclass_for_sort_expr(), it's impossible that we'd match
252  * an item in more than one existing nonvolatile EC. So it's okay to stop
253  * at the first match.
254  */
255  ec1 = ec2 = NULL;
256  em1 = em2 = NULL;
257  foreach(lc1, root->eq_classes)
258  {
259  EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
260  ListCell *lc2;
261 
262  /* Never match to a volatile EC */
263  if (cur_ec->ec_has_volatile)
264  continue;
265 
266  /*
267  * The collation has to match; check this first since it's cheaper
268  * than the opfamily comparison.
269  */
270  if (collation != cur_ec->ec_collation)
271  continue;
272 
273  /*
274  * A "match" requires matching sets of btree opfamilies. Use of
275  * equal() for this test has implications discussed in the comments
276  * for get_mergejoin_opfamilies().
277  */
278  if (!equal(opfamilies, cur_ec->ec_opfamilies))
279  continue;
280 
281  foreach(lc2, cur_ec->ec_members)
282  {
283  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
284 
285  Assert(!cur_em->em_is_child); /* no children yet */
286 
287  /*
288  * If below an outer join, don't match constants: they're not as
289  * constant as they look.
290  */
291  if ((below_outer_join || cur_ec->ec_below_outer_join) &&
292  cur_em->em_is_const)
293  continue;
294 
295  if (!ec1 &&
296  item1_type == cur_em->em_datatype &&
297  equal(item1, cur_em->em_expr))
298  {
299  ec1 = cur_ec;
300  em1 = cur_em;
301  if (ec2)
302  break;
303  }
304 
305  if (!ec2 &&
306  item2_type == cur_em->em_datatype &&
307  equal(item2, cur_em->em_expr))
308  {
309  ec2 = cur_ec;
310  em2 = cur_em;
311  if (ec1)
312  break;
313  }
314  }
315 
316  if (ec1 && ec2)
317  break;
318  }
319 
320  /* Sweep finished, what did we find? */
321 
322  if (ec1 && ec2)
323  {
324  /* If case 1, nothing to do, except add to sources */
325  if (ec1 == ec2)
326  {
327  ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
328  ec1->ec_below_outer_join |= below_outer_join;
329  ec1->ec_min_security = Min(ec1->ec_min_security,
330  restrictinfo->security_level);
331  ec1->ec_max_security = Max(ec1->ec_max_security,
332  restrictinfo->security_level);
333  /* mark the RI as associated with this eclass */
334  restrictinfo->left_ec = ec1;
335  restrictinfo->right_ec = ec1;
336  /* mark the RI as usable with this pair of EMs */
337  restrictinfo->left_em = em1;
338  restrictinfo->right_em = em2;
339  return true;
340  }
341 
342  /*
343  * Case 2: need to merge ec1 and ec2. This should never happen after
344  * we've built any canonical pathkeys; if it did, those pathkeys might
345  * be rendered non-canonical by the merge.
346  */
347  if (root->canon_pathkeys != NIL)
348  elog(ERROR, "too late to merge equivalence classes");
349 
350  /*
351  * We add ec2's items to ec1, then set ec2's ec_merged link to point
352  * to ec1 and remove ec2 from the eq_classes list. We cannot simply
353  * delete ec2 because that could leave dangling pointers in existing
354  * PathKeys. We leave it behind with a link so that the merged EC can
355  * be found.
356  */
357  ec1->ec_members = list_concat(ec1->ec_members, ec2->ec_members);
358  ec1->ec_sources = list_concat(ec1->ec_sources, ec2->ec_sources);
359  ec1->ec_derives = list_concat(ec1->ec_derives, ec2->ec_derives);
360  ec1->ec_relids = bms_join(ec1->ec_relids, ec2->ec_relids);
361  ec1->ec_has_const |= ec2->ec_has_const;
362  /* can't need to set has_volatile */
363  ec1->ec_below_outer_join |= ec2->ec_below_outer_join;
364  ec1->ec_min_security = Min(ec1->ec_min_security,
365  ec2->ec_min_security);
366  ec1->ec_max_security = Max(ec1->ec_max_security,
367  ec2->ec_max_security);
368  ec2->ec_merged = ec1;
369  root->eq_classes = list_delete_ptr(root->eq_classes, ec2);
370  /* just to avoid debugging confusion w/ dangling pointers: */
371  ec2->ec_members = NIL;
372  ec2->ec_sources = NIL;
373  ec2->ec_derives = NIL;
374  ec2->ec_relids = NULL;
375  ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
376  ec1->ec_below_outer_join |= below_outer_join;
377  ec1->ec_min_security = Min(ec1->ec_min_security,
378  restrictinfo->security_level);
379  ec1->ec_max_security = Max(ec1->ec_max_security,
380  restrictinfo->security_level);
381  /* mark the RI as associated with this eclass */
382  restrictinfo->left_ec = ec1;
383  restrictinfo->right_ec = ec1;
384  /* mark the RI as usable with this pair of EMs */
385  restrictinfo->left_em = em1;
386  restrictinfo->right_em = em2;
387  }
388  else if (ec1)
389  {
390  /* Case 3: add item2 to ec1 */
391  em2 = add_eq_member(ec1, item2, item2_relids, item2_nullable_relids,
392  false, item2_type);
393  ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
394  ec1->ec_below_outer_join |= below_outer_join;
395  ec1->ec_min_security = Min(ec1->ec_min_security,
396  restrictinfo->security_level);
397  ec1->ec_max_security = Max(ec1->ec_max_security,
398  restrictinfo->security_level);
399  /* mark the RI as associated with this eclass */
400  restrictinfo->left_ec = ec1;
401  restrictinfo->right_ec = ec1;
402  /* mark the RI as usable with this pair of EMs */
403  restrictinfo->left_em = em1;
404  restrictinfo->right_em = em2;
405  }
406  else if (ec2)
407  {
408  /* Case 3: add item1 to ec2 */
409  em1 = add_eq_member(ec2, item1, item1_relids, item1_nullable_relids,
410  false, item1_type);
411  ec2->ec_sources = lappend(ec2->ec_sources, restrictinfo);
412  ec2->ec_below_outer_join |= below_outer_join;
413  ec2->ec_min_security = Min(ec2->ec_min_security,
414  restrictinfo->security_level);
415  ec2->ec_max_security = Max(ec2->ec_max_security,
416  restrictinfo->security_level);
417  /* mark the RI as associated with this eclass */
418  restrictinfo->left_ec = ec2;
419  restrictinfo->right_ec = ec2;
420  /* mark the RI as usable with this pair of EMs */
421  restrictinfo->left_em = em1;
422  restrictinfo->right_em = em2;
423  }
424  else
425  {
426  /* Case 4: make a new, two-entry EC */
427  EquivalenceClass *ec = makeNode(EquivalenceClass);
428 
429  ec->ec_opfamilies = opfamilies;
430  ec->ec_collation = collation;
431  ec->ec_members = NIL;
432  ec->ec_sources = list_make1(restrictinfo);
433  ec->ec_derives = NIL;
434  ec->ec_relids = NULL;
435  ec->ec_has_const = false;
436  ec->ec_has_volatile = false;
437  ec->ec_below_outer_join = below_outer_join;
438  ec->ec_broken = false;
439  ec->ec_sortref = 0;
440  ec->ec_min_security = restrictinfo->security_level;
441  ec->ec_max_security = restrictinfo->security_level;
442  ec->ec_merged = NULL;
443  em1 = add_eq_member(ec, item1, item1_relids, item1_nullable_relids,
444  false, item1_type);
445  em2 = add_eq_member(ec, item2, item2_relids, item2_nullable_relids,
446  false, item2_type);
447 
448  root->eq_classes = lappend(root->eq_classes, ec);
449 
450  /* mark the RI as associated with this eclass */
451  restrictinfo->left_ec = ec;
452  restrictinfo->right_ec = ec;
453  /* mark the RI as usable with this pair of EMs */
454  restrictinfo->left_em = em1;
455  restrictinfo->right_em = em2;
456  }
457 
458  return true;
459 }
460 
461 /*
462  * canonicalize_ec_expression
463  *
464  * This function ensures that the expression exposes the expected type and
465  * collation, so that it will be equal() to other equivalence-class expressions
466  * that it ought to be equal() to.
467  *
468  * The rule for datatypes is that the exposed type should match what it would
469  * be for an input to an operator of the EC's opfamilies; which is usually
470  * the declared input type of the operator, but in the case of polymorphic
471  * operators no relabeling is wanted (compare the behavior of parse_coerce.c).
472  * Expressions coming in from quals will generally have the right type
473  * already, but expressions coming from indexkeys may not (because they are
474  * represented without any explicit relabel in pg_index), and the same problem
475  * occurs for sort expressions (because the parser is likewise cavalier about
476  * putting relabels on them). Such cases will be binary-compatible with the
477  * real operators, so adding a RelabelType is sufficient.
478  *
479  * Also, the expression's exposed collation must match the EC's collation.
480  * This is important because in comparisons like "foo < bar COLLATE baz",
481  * only one of the expressions has the correct exposed collation as we receive
482  * it from the parser. Forcing both of them to have it ensures that all
483  * variant spellings of such a construct behave the same. Again, we can
484  * stick on a RelabelType to force the right exposed collation. (It might
485  * work to not label the collation at all in EC members, but this is risky
486  * since some parts of the system expect exprCollation() to deliver the
487  * right answer for a sort key.)
488  *
489  * Note this code assumes that the expression has already been through
490  * eval_const_expressions, so there are no CollateExprs and no redundant
491  * RelabelTypes.
492  */
493 Expr *
494 canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
495 {
496  Oid expr_type = exprType((Node *) expr);
497 
498  /*
499  * For a polymorphic-input-type opclass, just keep the same exposed type.
500  * RECORD opclasses work like polymorphic-type ones for this purpose.
501  */
502  if (IsPolymorphicType(req_type) || req_type == RECORDOID)
503  req_type = expr_type;
504 
505  /*
506  * No work if the expression exposes the right type/collation already.
507  */
508  if (expr_type != req_type ||
509  exprCollation((Node *) expr) != req_collation)
510  {
511  /*
512  * Strip any existing RelabelType, then add a new one if needed. This
513  * is to preserve the invariant of no redundant RelabelTypes.
514  *
515  * If we have to change the exposed type of the stripped expression,
516  * set typmod to -1 (since the new type may not have the same typmod
517  * interpretation). If we only have to change collation, preserve the
518  * exposed typmod.
519  */
520  while (expr && IsA(expr, RelabelType))
521  expr = (Expr *) ((RelabelType *) expr)->arg;
522 
523  if (exprType((Node *) expr) != req_type)
524  expr = (Expr *) makeRelabelType(expr,
525  req_type,
526  -1,
527  req_collation,
528  COERCE_IMPLICIT_CAST);
529  else if (exprCollation((Node *) expr) != req_collation)
530  expr = (Expr *) makeRelabelType(expr,
531  req_type,
532  exprTypmod((Node *) expr),
533  req_collation,
534  COERCE_IMPLICIT_CAST);
535  }
536 
537  return expr;
538 }
539 
540 /*
541  * add_eq_member - build a new EquivalenceMember and add it to an EC
542  */
543 static EquivalenceMember *
544 add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
545  Relids nullable_relids, bool is_child, Oid datatype)
546 {
547  EquivalenceMember *em = makeNode(EquivalenceMember);
548 
549  em->em_expr = expr;
550  em->em_relids = relids;
551  em->em_nullable_relids = nullable_relids;
552  em->em_is_const = false;
553  em->em_is_child = is_child;
554  em->em_datatype = datatype;
555 
556  if (bms_is_empty(relids))
557  {
558  /*
559  * No Vars, assume it's a pseudoconstant. This is correct for entries
560  * generated from process_equivalence(), because a WHERE clause can't
561  * contain aggregates or SRFs, and non-volatility was checked before
562  * process_equivalence() ever got called. But
563  * get_eclass_for_sort_expr() has to work harder. We put the tests
564  * there not here to save cycles in the equivalence case.
565  */
566  Assert(!is_child);
567  em->em_is_const = true;
568  ec->ec_has_const = true;
569  /* it can't affect ec_relids */
570  }
571  else if (!is_child) /* child members don't add to ec_relids */
572  {
573  ec->ec_relids = bms_add_members(ec->ec_relids, relids);
574  }
575  ec->ec_members = lappend(ec->ec_members, em);
576 
577  return em;
578 }
579 
580 
581 /*
582  * get_eclass_for_sort_expr
583  * Given an expression and opfamily/collation info, find an existing
584  * equivalence class it is a member of; if none, optionally build a new
585  * single-member EquivalenceClass for it.
586  *
587  * expr is the expression, and nullable_relids is the set of base relids
588  * that are potentially nullable below it. We actually only care about
589  * the set of such relids that are used in the expression; but for caller
590  * convenience, we perform that intersection step here. The caller need
591  * only be sure that nullable_relids doesn't omit any nullable rels that
592  * might appear in the expr.
593  *
594  * sortref is the SortGroupRef of the originating SortGroupClause, if any,
595  * or zero if not. (It should never be zero if the expression is volatile!)
596  *
597  * If rel is not NULL, it identifies a specific relation we're considering
598  * a path for, and indicates that child EC members for that relation can be
599  * considered. Otherwise child members are ignored. (Note: since child EC
600  * members aren't guaranteed unique, a non-NULL value means that there could
601  * be more than one EC that matches the expression; if so it's order-dependent
602  * which one you get. This is annoying but it only happens in corner cases,
603  * so for now we live with just reporting the first match. See also
604  * generate_implied_equalities_for_column and match_pathkeys_to_index.)
605  *
606  * If create_it is true, we'll build a new EquivalenceClass when there is no
607  * match. If create_it is false, we just return NULL when no match.
608  *
609  * This can be used safely both before and after EquivalenceClass merging;
610  * since it never causes merging it does not invalidate any existing ECs
611  * or PathKeys. However, ECs added after path generation has begun are
612  * of limited usefulness, so usually it's best to create them beforehand.
613  *
614  * Note: opfamilies must be chosen consistently with the way
615  * process_equivalence() would do; that is, generated from a mergejoinable
616  * equality operator. Else we might fail to detect valid equivalences,
617  * generating poor (but not incorrect) plans.
618  */
619 EquivalenceClass *
620 get_eclass_for_sort_expr(PlannerInfo *root,
621  Expr *expr,
622  Relids nullable_relids,
623  List *opfamilies,
624  Oid opcintype,
625  Oid collation,
626  Index sortref,
627  Relids rel,
628  bool create_it)
629 {
630  Relids expr_relids;
631  EquivalenceClass *newec;
632  EquivalenceMember *newem;
633  ListCell *lc1;
634  MemoryContext oldcontext;
635 
636  /*
637  * Ensure the expression exposes the correct type and collation.
638  */
639  expr = canonicalize_ec_expression(expr, opcintype, collation);
640 
641  /*
642  * Get the precise set of nullable relids appearing in the expression.
643  */
644  expr_relids = pull_varnos((Node *) expr);
645  nullable_relids = bms_intersect(nullable_relids, expr_relids);
646 
647  /*
648  * Scan through the existing EquivalenceClasses for a match
649  */
650  foreach(lc1, root->eq_classes)
651  {
652  EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
653  ListCell *lc2;
654 
655  /*
656  * Never match to a volatile EC, except when we are looking at another
657  * reference to the same volatile SortGroupClause.
658  */
659  if (cur_ec->ec_has_volatile &&
660  (sortref == 0 || sortref != cur_ec->ec_sortref))
661  continue;
662 
663  if (collation != cur_ec->ec_collation)
664  continue;
665  if (!equal(opfamilies, cur_ec->ec_opfamilies))
666  continue;
667 
668  foreach(lc2, cur_ec->ec_members)
669  {
670  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
671 
672  /*
673  * Ignore child members unless they match the request.
674  */
675  if (cur_em->em_is_child &&
676  !bms_equal(cur_em->em_relids, rel))
677  continue;
678 
679  /*
680  * If below an outer join, don't match constants: they're not as
681  * constant as they look.
682  */
683  if (cur_ec->ec_below_outer_join &&
684  cur_em->em_is_const)
685  continue;
686 
687  if (opcintype == cur_em->em_datatype &&
688  equal(expr, cur_em->em_expr))
689  return cur_ec; /* Match! */
690  }
691  }
692 
693  /* No match; does caller want a NULL result? */
694  if (!create_it)
695  return NULL;
696 
697  /*
698  * OK, build a new single-member EC
699  *
700  * Here, we must be sure that we construct the EC in the right context.
701  */
702  oldcontext = MemoryContextSwitchTo(root->planner_cxt);
703 
704  newec = makeNode(EquivalenceClass);
705  newec->ec_opfamilies = list_copy(opfamilies);
706  newec->ec_collation = collation;
707  newec->ec_members = NIL;
708  newec->ec_sources = NIL;
709  newec->ec_derives = NIL;
710  newec->ec_relids = NULL;
711  newec->ec_has_const = false;
712  newec->ec_has_volatile = contain_volatile_functions((Node *) expr);
713  newec->ec_below_outer_join = false;
714  newec->ec_broken = false;
715  newec->ec_sortref = sortref;
716  newec->ec_min_security = UINT_MAX;
717  newec->ec_max_security = 0;
718  newec->ec_merged = NULL;
719 
720  if (newec->ec_has_volatile && sortref == 0) /* should not happen */
721  elog(ERROR, "volatile EquivalenceClass has no sortref");
722 
723  newem = add_eq_member(newec, copyObject(expr), expr_relids,
724  nullable_relids, false, opcintype);
725 
726  /*
727  * add_eq_member doesn't check for volatile functions, set-returning
728  * functions, aggregates, or window functions, but such could appear in
729  * sort expressions; so we have to check whether its const-marking was
730  * correct.
731  */
732  if (newec->ec_has_const)
733  {
734  if (newec->ec_has_volatile ||
735  expression_returns_set((Node *) expr) ||
736  contain_agg_clause((Node *) expr) ||
737  contain_window_function((Node *) expr))
738  {
739  newec->ec_has_const = false;
740  newem->em_is_const = false;
741  }
742  }
743 
744  root->eq_classes = lappend(root->eq_classes, newec);
745 
746  MemoryContextSwitchTo(oldcontext);
747 
748  return newec;
749 }
750 
751 
752 /*
753  * generate_base_implied_equalities
754  * Generate any restriction clauses that we can deduce from equivalence
755  * classes.
756  *
757  * When an EC contains pseudoconstants, our strategy is to generate
758  * "member = const1" clauses where const1 is the first constant member, for
759  * every other member (including other constants). If we are able to do this
760  * then we don't need any "var = var" comparisons because we've successfully
761  * constrained all the vars at their points of creation. If we fail to
762  * generate any of these clauses due to lack of cross-type operators, we fall
763  * back to the "ec_broken" strategy described below. (XXX if there are
764  * multiple constants of different types, it's possible that we might succeed
765  * in forming all the required clauses if we started from a different const
766  * member; but this seems a sufficiently hokey corner case to not be worth
767  * spending lots of cycles on.)
768  *
769  * For ECs that contain no pseudoconstants, we generate derived clauses
770  * "member1 = member2" for each pair of members belonging to the same base
771  * relation (actually, if there are more than two for the same base relation,
772  * we only need enough clauses to link each to each other). This provides
773  * the base case for the recursion: each row emitted by a base relation scan
774  * will constrain all computable members of the EC to be equal. As each
775  * join path is formed, we'll add additional derived clauses on-the-fly
776  * to maintain this invariant (see generate_join_implied_equalities).
777  *
778  * If the opfamilies used by the EC do not provide complete sets of cross-type
779  * equality operators, it is possible that we will fail to generate a clause
780  * that must be generated to maintain the invariant. (An example: given
781  * "WHERE a.x = b.y AND b.y = a.z", the scheme breaks down if we cannot
782  * generate "a.x = a.z" as a restriction clause for A.) In this case we mark
783  * the EC "ec_broken" and fall back to regurgitating its original source
784  * RestrictInfos at appropriate times. We do not try to retract any derived
785  * clauses already generated from the broken EC, so the resulting plan could
786  * be poor due to bad selectivity estimates caused by redundant clauses. But
787  * the correct solution to that is to fix the opfamilies ...
788  *
789  * Equality clauses derived by this function are passed off to
790  * process_implied_equality (in plan/initsplan.c) to be inserted into the
791  * restrictinfo datastructures. Note that this must be called after initial
792  * scanning of the quals and before Path construction begins.
793  *
794  * We make no attempt to avoid generating duplicate RestrictInfos here: we
795  * don't search ec_sources for matches, nor put the created RestrictInfos
796  * into ec_derives. Doing so would require some slightly ugly changes in
797  * initsplan.c's API, and there's no real advantage, because the clauses
798  * generated here can't duplicate anything we will generate for joins anyway.
799  */
800 void
801 generate_base_implied_equalities(PlannerInfo *root)
802 {
803  ListCell *lc;
804  Index rti;
805 
806  foreach(lc, root->eq_classes)
807  {
808  EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
809 
810  Assert(ec->ec_merged == NULL); /* else shouldn't be in list */
811  Assert(!ec->ec_broken); /* not yet anyway... */
812 
813  /* Single-member ECs won't generate any deductions */
814  if (list_length(ec->ec_members) <= 1)
815  continue;
816 
817  if (ec->ec_has_const)
818  generate_base_implied_equalities_const(root, ec);
819  else
820  generate_base_implied_equalities_no_const(root, ec);
821 
822  /* Recover if we failed to generate required derived clauses */
823  if (ec->ec_broken)
824  generate_base_implied_equalities_broken(root, ec);
825  }
826 
827  /*
828  * This is also a handy place to mark base rels (which should all exist by
829  * now) with flags showing whether they have pending eclass joins.
830  */
831  for (rti = 1; rti < root->simple_rel_array_size; rti++)
832  {
833  RelOptInfo *brel = root->simple_rel_array[rti];
834 
835  if (brel == NULL)
836  continue;
837 
838  brel->has_eclass_joins = has_relevant_eclass_joinclause(root, brel);
839  }
840 }
841 
842 /*
843  * generate_base_implied_equalities when EC contains pseudoconstant(s)
844  */
845 static void
846 generate_base_implied_equalities_const(PlannerInfo *root,
847  EquivalenceClass *ec)
848 {
849  EquivalenceMember *const_em = NULL;
850  ListCell *lc;
851 
852  /*
853  * In the trivial case where we just had one "var = const" clause, push
854  * the original clause back into the main planner machinery. There is
855  * nothing to be gained by doing it differently, and we save the effort to
856  * re-build and re-analyze an equality clause that will be exactly
857  * equivalent to the old one.
858  */
859  if (list_length(ec->ec_members) == 2 &&
860  list_length(ec->ec_sources) == 1)
861  {
862  RestrictInfo *restrictinfo = (RestrictInfo *) linitial(ec->ec_sources);
863 
864  if (bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
865  {
866  distribute_restrictinfo_to_rels(root, restrictinfo);
867  return;
868  }
869  }
870 
871  /*
872  * Find the constant member to use. We prefer an actual constant to
873  * pseudo-constants (such as Params), because the constraint exclusion
874  * machinery might be able to exclude relations on the basis of generated
875  * "var = const" equalities, but "var = param" won't work for that.
876  */
877  foreach(lc, ec->ec_members)
878  {
879  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
880 
881  if (cur_em->em_is_const)
882  {
883  const_em = cur_em;
884  if (IsA(cur_em->em_expr, Const))
885  break;
886  }
887  }
888  Assert(const_em != NULL);
889 
890  /* Generate a derived equality against each other member */
891  foreach(lc, ec->ec_members)
892  {
893  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
894  Oid eq_op;
895 
896  Assert(!cur_em->em_is_child); /* no children yet */
897  if (cur_em == const_em)
898  continue;
899  eq_op = select_equality_operator(ec,
900  cur_em->em_datatype,
901  const_em->em_datatype);
902  if (!OidIsValid(eq_op))
903  {
904  /* failed... */
905  ec->ec_broken = true;
906  break;
907  }
908  process_implied_equality(root, eq_op, ec->ec_collation,
909  cur_em->em_expr, const_em->em_expr,
910  bms_copy(ec->ec_relids),
911  bms_union(cur_em->em_nullable_relids,
912  const_em->em_nullable_relids),
913  ec->ec_min_security,
914  ec->ec_below_outer_join,
915  cur_em->em_is_const);
916  }
917 }
918 
919 /*
920  * generate_base_implied_equalities when EC contains no pseudoconstants
921  */
922 static void
923 generate_base_implied_equalities_no_const(PlannerInfo *root,
924  EquivalenceClass *ec)
925 {
926  EquivalenceMember **prev_ems;
927  ListCell *lc;
928 
929  /*
930  * We scan the EC members once and track the last-seen member for each
931  * base relation. When we see another member of the same base relation,
932  * we generate "prev_mem = cur_mem". This results in the minimum number
933  * of derived clauses, but it's possible that it will fail when a
934  * different ordering would succeed. XXX FIXME: use a UNION-FIND
935  * algorithm similar to the way we build merged ECs. (Use a list-of-lists
936  * for each rel.)
937  */
938  prev_ems = (EquivalenceMember **)
939  palloc0(root->simple_rel_array_size * sizeof(EquivalenceMember *));
940 
941  foreach(lc, ec->ec_members)
942  {
943  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
944  int relid;
945 
946  Assert(!cur_em->em_is_child); /* no children yet */
947  if (!bms_get_singleton_member(cur_em->em_relids, &relid))
948  continue;
949  Assert(relid < root->simple_rel_array_size);
950 
951  if (prev_ems[relid] != NULL)
952  {
953  EquivalenceMember *prev_em = prev_ems[relid];
954  Oid eq_op;
955 
956  eq_op = select_equality_operator(ec,
957  prev_em->em_datatype,
958  cur_em->em_datatype);
959  if (!OidIsValid(eq_op))
960  {
961  /* failed... */
962  ec->ec_broken = true;
963  break;
964  }
965  process_implied_equality(root, eq_op, ec->ec_collation,
966  prev_em->em_expr, cur_em->em_expr,
967  bms_copy(ec->ec_relids),
968  bms_union(prev_em->em_nullable_relids,
969  cur_em->em_nullable_relids),
970  ec->ec_min_security,
971  ec->ec_below_outer_join,
972  false);
973  }
974  prev_ems[relid] = cur_em;
975  }
976 
977  pfree(prev_ems);
978 
979  /*
980  * We also have to make sure that all the Vars used in the member clauses
981  * will be available at any join node we might try to reference them at.
982  * For the moment we force all the Vars to be available at all join nodes
983  * for this eclass. Perhaps this could be improved by doing some
984  * pre-analysis of which members we prefer to join, but it's no worse than
985  * what happened in the pre-8.3 code.
986  */
987  foreach(lc, ec->ec_members)
988  {
989  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
990  List *vars = pull_var_clause((Node *) cur_em->em_expr,
991  PVC_RECURSE_AGGREGATES |
992  PVC_RECURSE_WINDOWFUNCS |
993  PVC_INCLUDE_PLACEHOLDERS);
994 
995  add_vars_to_targetlist(root, vars, ec->ec_relids, false);
996  list_free(vars);
997  }
998 }
999 
1000 /*
1001  * generate_base_implied_equalities cleanup after failure
1002  *
1003  * What we must do here is push any zero- or one-relation source RestrictInfos
1004  * of the EC back into the main restrictinfo datastructures. Multi-relation
1005  * clauses will be regurgitated later by generate_join_implied_equalities().
1006  * (We do it this way to maintain continuity with the case that ec_broken
1007  * becomes set only after we've gone up a join level or two.) However, for
1008  * an EC that contains constants, we can adopt a simpler strategy and just
1009  * throw back all the source RestrictInfos immediately; that works because
1010  * we know that such an EC can't become broken later. (This rule justifies
1011  * ignoring ec_has_const ECs in generate_join_implied_equalities, even when
1012  * they are broken.)
1013  */
1014 static void
1015 generate_base_implied_equalities_broken(PlannerInfo *root,
1016  EquivalenceClass *ec)
1017 {
1018  ListCell *lc;
1019 
1020  foreach(lc, ec->ec_sources)
1021  {
1022  RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
1023 
1024  if (ec->ec_has_const ||
1025  bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
1026  distribute_restrictinfo_to_rels(root, restrictinfo);
1027  }
1028 }
1029 
1030 
1031 /*
1032  * generate_join_implied_equalities
1033  * Generate any join clauses that we can deduce from equivalence classes.
1034  *
1035  * At a join node, we must enforce restriction clauses sufficient to ensure
1036  * that all equivalence-class members computable at that node are equal.
1037  * Since the set of clauses to enforce can vary depending on which subset
1038  * relations are the inputs, we have to compute this afresh for each join
1039  * relation pair. Hence a fresh List of RestrictInfo nodes is built and
1040  * passed back on each call.
1041  *
1042  * In addition to its use at join nodes, this can be applied to generate
1043  * eclass-based join clauses for use in a parameterized scan of a base rel.
1044  * The reason for the asymmetry of specifying the inner rel as a RelOptInfo
1045  * and the outer rel by Relids is that this usage occurs before we have
1046  * built any join RelOptInfos.
1047  *
1048  * An annoying special case for parameterized scans is that the inner rel can
1049  * be an appendrel child (an "other rel"). In this case we must generate
1050  * appropriate clauses using child EC members. add_child_rel_equivalences
1051  * must already have been done for the child rel.
1052  *
1053  * The results are sufficient for use in merge, hash, and plain nestloop join
1054  * methods. We do not worry here about selecting clauses that are optimal
1055  * for use in a parameterized indexscan. indxpath.c makes its own selections
1056  * of clauses to use, and if the ones we pick here are redundant with those,
1057  * the extras will be eliminated at createplan time, using the parent_ec
1058  * markers that we provide (see is_redundant_derived_clause()).
1059  *
1060  * Because the same join clauses are likely to be needed multiple times as
1061  * we consider different join paths, we avoid generating multiple copies:
1062  * whenever we select a particular pair of EquivalenceMembers to join,
1063  * we check to see if the pair matches any original clause (in ec_sources)
1064  * or previously-built clause (in ec_derives). This saves memory and allows
1065  * re-use of information cached in RestrictInfos.
1066  *
1067  * join_relids should always equal bms_union(outer_relids, inner_rel->relids).
1068  * We could simplify this function's API by computing it internally, but in
1069  * most current uses, the caller has the value at hand anyway.
1070  */
1071 List *
1072 generate_join_implied_equalities(PlannerInfo *root,
1073  Relids join_relids,
1074  Relids outer_relids,
1075  RelOptInfo *inner_rel)
1076 {
1077  return generate_join_implied_equalities_for_ecs(root,
1078  root->eq_classes,
1079  join_relids,
1080  outer_relids,
1081  inner_rel);
1082 }
1083 
1084 /*
1085  * generate_join_implied_equalities_for_ecs
1086  * As above, but consider only the listed ECs.
1087  */
1088 List *
1089 generate_join_implied_equalities_for_ecs(PlannerInfo *root,
1090  List *eclasses,
1091  Relids join_relids,
1092  Relids outer_relids,
1093  RelOptInfo *inner_rel)
1094 {
1095  List *result = NIL;
1096  Relids inner_relids = inner_rel->relids;
1097  Relids nominal_inner_relids;
1098  Relids nominal_join_relids;
1099  ListCell *lc;
1100 
1101  /* If inner rel is a child, extra setup work is needed */
1102  if (IS_OTHER_REL(inner_rel))
1103  {
1104  Assert(!bms_is_empty(inner_rel->top_parent_relids));
1105 
1106  /* Fetch relid set for the topmost parent rel */
1107  nominal_inner_relids = inner_rel->top_parent_relids;
1108  /* ECs will be marked with the parent's relid, not the child's */
1109  nominal_join_relids = bms_union(outer_relids, nominal_inner_relids);
1110  }
1111  else
1112  {
1113  nominal_inner_relids = inner_relids;
1114  nominal_join_relids = join_relids;
1115  }
1116 
1117  foreach(lc, eclasses)
1118  {
1119  EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
1120  List *sublist = NIL;
1121 
1122  /* ECs containing consts do not need any further enforcement */
1123  if (ec->ec_has_const)
1124  continue;
1125 
1126  /* Single-member ECs won't generate any deductions */
1127  if (list_length(ec->ec_members) <= 1)
1128  continue;
1129 
1130  /* We can quickly ignore any that don't overlap the join, too */
1131  if (!bms_overlap(ec->ec_relids, nominal_join_relids))
1132  continue;
1133 
1134  if (!ec->ec_broken)
1135  sublist = generate_join_implied_equalities_normal(root,
1136  ec,
1137  join_relids,
1138  outer_relids,
1139  inner_relids);
1140 
1141  /* Recover if we failed to generate required derived clauses */
1142  if (ec->ec_broken)
1143  sublist = generate_join_implied_equalities_broken(root,
1144  ec,
1145  nominal_join_relids,
1146  outer_relids,
1147  nominal_inner_relids,
1148  inner_rel);
1149 
1150  result = list_concat(result, sublist);
1151  }
1152 
1153  return result;
1154 }
1155 
1156 /*
1157  * generate_join_implied_equalities for a still-valid EC
1158  */
1159 static List *
1160 generate_join_implied_equalities_normal(PlannerInfo *root,
1161  EquivalenceClass *ec,
1162  Relids join_relids,
1163  Relids outer_relids,
1164  Relids inner_relids)
1165 {
1166  List *result = NIL;
1167  List *new_members = NIL;
1168  List *outer_members = NIL;
1169  List *inner_members = NIL;
1170  ListCell *lc1;
1171 
1172  /*
1173  * First, scan the EC to identify member values that are computable at the
1174  * outer rel, at the inner rel, or at this relation but not in either
1175  * input rel. The outer-rel members should already be enforced equal,
1176  * likewise for the inner-rel members. We'll need to create clauses to
1177  * enforce that any newly computable members are all equal to each other
1178  * as well as to at least one input member, plus enforce at least one
1179  * outer-rel member equal to at least one inner-rel member.
1180  */
1181  foreach(lc1, ec->ec_members)
1182  {
1183  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc1);
1184 
1185  /*
1186  * We don't need to check explicitly for child EC members. This test
1187  * against join_relids will cause them to be ignored except when
1188  * considering a child inner rel, which is what we want.
1189  */
1190  if (!bms_is_subset(cur_em->em_relids, join_relids))
1191  continue; /* not computable yet, or wrong child */
1192 
1193  if (bms_is_subset(cur_em->em_relids, outer_relids))
1194  outer_members = lappend(outer_members, cur_em);
1195  else if (bms_is_subset(cur_em->em_relids, inner_relids))
1196  inner_members = lappend(inner_members, cur_em);
1197  else
1198  new_members = lappend(new_members, cur_em);
1199  }
1200 
1201  /*
1202  * First, select the joinclause if needed. We can equate any one outer
1203  * member to any one inner member, but we have to find a datatype
1204  * combination for which an opfamily member operator exists. If we have
1205  * choices, we prefer simple Var members (possibly with RelabelType) since
1206  * these are (a) cheapest to compute at runtime and (b) most likely to
1207  * have useful statistics. Also, prefer operators that are also
1208  * hashjoinable.
1209  */
1210  if (outer_members && inner_members)
1211  {
1212  EquivalenceMember *best_outer_em = NULL;
1213  EquivalenceMember *best_inner_em = NULL;
1214  Oid best_eq_op = InvalidOid;
1215  int best_score = -1;
1216  RestrictInfo *rinfo;
1217 
1218  foreach(lc1, outer_members)
1219  {
1220  EquivalenceMember *outer_em = (EquivalenceMember *) lfirst(lc1);
1221  ListCell *lc2;
1222 
1223  foreach(lc2, inner_members)
1224  {
1225  EquivalenceMember *inner_em = (EquivalenceMember *) lfirst(lc2);
1226  Oid eq_op;
1227  int score;
1228 
1229  eq_op = select_equality_operator(ec,
1230  outer_em->em_datatype,
1231  inner_em->em_datatype);
1232  if (!OidIsValid(eq_op))
1233  continue;
1234  score = 0;
1235  if (IsA(outer_em->em_expr, Var) ||
1236  (IsA(outer_em->em_expr, RelabelType) &&
1237  IsA(((RelabelType *) outer_em->em_expr)->arg, Var)))
1238  score++;
1239  if (IsA(inner_em->em_expr, Var) ||
1240  (IsA(inner_em->em_expr, RelabelType) &&
1241  IsA(((RelabelType *) inner_em->em_expr)->arg, Var)))
1242  score++;
1243  if (op_hashjoinable(eq_op,
1244  exprType((Node *) outer_em->em_expr)))
1245  score++;
1246  if (score > best_score)
1247  {
1248  best_outer_em = outer_em;
1249  best_inner_em = inner_em;
1250  best_eq_op = eq_op;
1251  best_score = score;
1252  if (best_score == 3)
1253  break; /* no need to look further */
1254  }
1255  }
1256  if (best_score == 3)
1257  break; /* no need to look further */
1258  }
1259  if (best_score < 0)
1260  {
1261  /* failed... */
1262  ec->ec_broken = true;
1263  return NIL;
1264  }
1265 
1266  /*
1267  * Create clause, setting parent_ec to mark it as redundant with other
1268  * joinclauses
1269  */
1270  rinfo = create_join_clause(root, ec, best_eq_op,
1271  best_outer_em, best_inner_em,
1272  ec);
1273 
1274  result = lappend(result, rinfo);
1275  }
1276 
1277  /*
1278  * Now deal with building restrictions for any expressions that involve
1279  * Vars from both sides of the join. We have to equate all of these to
1280  * each other as well as to at least one old member (if any).
1281  *
1282  * XXX as in generate_base_implied_equalities_no_const, we could be a lot
1283  * smarter here to avoid unnecessary failures in cross-type situations.
1284  * For now, use the same left-to-right method used there.
1285  */
1286  if (new_members)
1287  {
1288  List *old_members = list_concat(outer_members, inner_members);
1289  EquivalenceMember *prev_em = NULL;
1290  RestrictInfo *rinfo;
1291 
1292  /* For now, arbitrarily take the first old_member as the one to use */
1293  if (old_members)
1294  new_members = lappend(new_members, linitial(old_members));
1295 
1296  foreach(lc1, new_members)
1297  {
1298  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc1);
1299 
1300  if (prev_em != NULL)
1301  {
1302  Oid eq_op;
1303 
1304  eq_op = select_equality_operator(ec,
1305  prev_em->em_datatype,
1306  cur_em->em_datatype);
1307  if (!OidIsValid(eq_op))
1308  {
1309  /* failed... */
1310  ec->ec_broken = true;
1311  return NIL;
1312  }
1313  /* do NOT set parent_ec, this qual is not redundant! */
1314  rinfo = create_join_clause(root, ec, eq_op,
1315  prev_em, cur_em,
1316  NULL);
1317 
1318  result = lappend(result, rinfo);
1319  }
1320  prev_em = cur_em;
1321  }
1322  }
1323 
1324  return result;
1325 }
1326 
1327 /*
1328  * generate_join_implied_equalities cleanup after failure
1329  *
1330  * Return any original RestrictInfos that are enforceable at this join.
1331  *
1332  * In the case of a child inner relation, we have to translate the
1333  * original RestrictInfos from parent to child Vars.
1334  */
1335 static List *
1336 generate_join_implied_equalities_broken(PlannerInfo *root,
1337  EquivalenceClass *ec,
1338  Relids nominal_join_relids,
1339  Relids outer_relids,
1340  Relids nominal_inner_relids,
1341  RelOptInfo *inner_rel)
1342 {
1343  List *result = NIL;
1344  ListCell *lc;
1345 
1346  foreach(lc, ec->ec_sources)
1347  {
1348  RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
1349  Relids clause_relids = restrictinfo->required_relids;
1350 
1351  if (bms_is_subset(clause_relids, nominal_join_relids) &&
1352  !bms_is_subset(clause_relids, outer_relids) &&
1353  !bms_is_subset(clause_relids, nominal_inner_relids))
1354  result = lappend(result, restrictinfo);
1355  }
1356 
1357  /*
1358  * If we have to translate, just brute-force apply adjust_appendrel_attrs
1359  * to all the RestrictInfos at once. This will result in returning
1360  * RestrictInfos that are not listed in ec_derives, but there shouldn't be
1361  * any duplication, and it's a sufficiently narrow corner case that we
1362  * shouldn't sweat too much over it anyway.
1363  *
1364  * Since inner_rel might be an indirect descendant of the baserel
1365  * mentioned in the ec_sources clauses, we have to be prepared to apply
1366  * multiple levels of Var translation.
1367  */
1368  if (IS_OTHER_REL(inner_rel) && result != NIL)
1369  result = (List *) adjust_appendrel_attrs_multilevel(root,
1370  (Node *) result,
1371  inner_rel->relids,
1372  inner_rel->top_parent_relids);
1373 
1374  return result;
1375 }
1376 
1377 
1378 /*
1379  * select_equality_operator
1380  * Select a suitable equality operator for comparing two EC members
1381  *
1382  * Returns InvalidOid if no operator can be found for this datatype combination
1383  */
1384 static Oid
1385 select_equality_operator(EquivalenceClass *ec, Oid lefttype, Oid righttype)
1386 {
1387  ListCell *lc;
1388 
1389  foreach(lc, ec->ec_opfamilies)
1390  {
1391  Oid opfamily = lfirst_oid(lc);
1392  Oid opno;
1393 
1394  opno = get_opfamily_member(opfamily, lefttype, righttype,
1395  BTEqualStrategyNumber);
1396  if (!OidIsValid(opno))
1397  continue;
1398  /* If no barrier quals in query, don't worry about leaky operators */
1399  if (ec->ec_max_security == 0)
1400  return opno;
1401  /* Otherwise, insist that selected operators be leakproof */
1402  if (get_func_leakproof(get_opcode(opno)))
1403  return opno;
1404  }
1405  return InvalidOid;
1406 }
1407 
1408 
1409 /*
1410  * create_join_clause
1411  * Find or make a RestrictInfo comparing the two given EC members
1412  * with the given operator.
1413  *
1414  * parent_ec is either equal to ec (if the clause is a potentially-redundant
1415  * join clause) or NULL (if not). We have to treat this as part of the
1416  * match requirements --- it's possible that a clause comparing the same two
1417  * EMs is a join clause in one join path and a restriction clause in another.
1418  */
1419 static RestrictInfo *
1420 create_join_clause(PlannerInfo *root,
1421  EquivalenceClass *ec, Oid opno,
1422  EquivalenceMember *leftem,
1423  EquivalenceMember *rightem,
1424  EquivalenceClass *parent_ec)
1425 {
1426  RestrictInfo *rinfo;
1427  ListCell *lc;
1428  MemoryContext oldcontext;
1429 
1430  /*
1431  * Search to see if we already built a RestrictInfo for this pair of
1432  * EquivalenceMembers. We can use either original source clauses or
1433  * previously-derived clauses. The check on opno is probably redundant,
1434  * but be safe ...
1435  */
1436  foreach(lc, ec->ec_sources)
1437  {
1438  rinfo = (RestrictInfo *) lfirst(lc);
1439  if (rinfo->left_em == leftem &&
1440  rinfo->right_em == rightem &&
1441  rinfo->parent_ec == parent_ec &&
1442  opno == ((OpExpr *) rinfo->clause)->opno)
1443  return rinfo;
1444  }
1445 
1446  foreach(lc, ec->ec_derives)
1447  {
1448  rinfo = (RestrictInfo *) lfirst(lc);
1449  if (rinfo->left_em == leftem &&
1450  rinfo->right_em == rightem &&
1451  rinfo->parent_ec == parent_ec &&
1452  opno == ((OpExpr *) rinfo->clause)->opno)
1453  return rinfo;
1454  }
1455 
1456  /*
1457  * Not there, so build it, in planner context so we can re-use it. (Not
1458  * important in normal planning, but definitely so in GEQO.)
1459  */
1460  oldcontext = MemoryContextSwitchTo(root->planner_cxt);
1461 
1462  rinfo = build_implied_join_equality(opno,
1463  ec->ec_collation,
1464  leftem->em_expr,
1465  rightem->em_expr,
1466  bms_union(leftem->em_relids,
1467  rightem->em_relids),
1468  bms_union(leftem->em_nullable_relids,
1469  rightem->em_nullable_relids),
1470  ec->ec_min_security);
1471 
1472  /* Mark the clause as redundant, or not */
1473  rinfo->parent_ec = parent_ec;
1474 
1475  /*
1476  * We know the correct values for left_ec/right_ec, ie this particular EC,
1477  * so we can just set them directly instead of forcing another lookup.
1478  */
1479  rinfo->left_ec = ec;
1480  rinfo->right_ec = ec;
1481 
1482  /* Mark it as usable with these EMs */
1483  rinfo->left_em = leftem;
1484  rinfo->right_em = rightem;
1485  /* and save it for possible re-use */
1486  ec->ec_derives = lappend(ec->ec_derives, rinfo);
1487 
1488  MemoryContextSwitchTo(oldcontext);
1489 
1490  return rinfo;
1491 }
1492 
1493 
1494 /*
1495  * reconsider_outer_join_clauses
1496  * Re-examine any outer-join clauses that were set aside by
1497  * distribute_qual_to_rels(), and see if we can derive any
1498  * EquivalenceClasses from them. Then, if they were not made
1499  * redundant, push them out into the regular join-clause lists.
1500  *
1501  * When we have mergejoinable clauses A = B that are outer-join clauses,
1502  * we can't blindly combine them with other clauses A = C to deduce B = C,
1503  * since in fact the "equality" A = B won't necessarily hold above the
1504  * outer join (one of the variables might be NULL instead). Nonetheless
1505  * there are cases where we can add qual clauses using transitivity.
1506  *
1507  * One case that we look for here is an outer-join clause OUTERVAR = INNERVAR
1508  * for which there is also an equivalence clause OUTERVAR = CONSTANT.
1509  * It is safe and useful to push a clause INNERVAR = CONSTANT into the
1510  * evaluation of the inner (nullable) relation, because any inner rows not
1511  * meeting this condition will not contribute to the outer-join result anyway.
1512  * (Any outer rows they could join to will be eliminated by the pushed-down
1513  * equivalence clause.)
1514  *
1515  * Note that the above rule does not work for full outer joins; nor is it
1516  * very interesting to consider cases where the generated equivalence clause
1517  * would involve relations outside the outer join, since such clauses couldn't
1518  * be pushed into the inner side's scan anyway. So the restriction to
1519  * outervar = pseudoconstant is not really giving up anything.
1520  *
1521  * For full-join cases, we can only do something useful if it's a FULL JOIN
1522  * USING and a merged column has an equivalence MERGEDVAR = CONSTANT.
1523  * By the time it gets here, the merged column will look like
1524  * COALESCE(LEFTVAR, RIGHTVAR)
1525  * and we will have a full-join clause LEFTVAR = RIGHTVAR that we can match
1526  * the COALESCE expression to. In this situation we can push LEFTVAR = CONSTANT
1527  * and RIGHTVAR = CONSTANT into the input relations, since any rows not
1528  * meeting these conditions cannot contribute to the join result.
1529  *
1530  * Again, there isn't any traction to be gained by trying to deal with
1531  * clauses comparing a mergedvar to a non-pseudoconstant. So we can make
1532  * use of the EquivalenceClasses to search for matching variables that were
1533  * equivalenced to constants. The interesting outer-join clauses were
1534  * accumulated for us by distribute_qual_to_rels.
1535  *
1536  * When we find one of these cases, we implement the changes we want by
1537  * generating a new equivalence clause INNERVAR = CONSTANT (or LEFTVAR, etc)
1538  * and pushing it into the EquivalenceClass structures. This is because we
1539  * may already know that INNERVAR is equivalenced to some other var(s), and
1540  * we'd like the constant to propagate to them too. Note that it would be
1541  * unsafe to merge any existing EC for INNERVAR with the OUTERVAR's EC ---
1542  * that could result in propagating constant restrictions from
1543  * INNERVAR to OUTERVAR, which would be very wrong.
1544  *
1545  * It's possible that the INNERVAR is also an OUTERVAR for some other
1546  * outer-join clause, in which case the process can be repeated. So we repeat
1547  * looping over the lists of clauses until no further deductions can be made.
1548  * Whenever we do make a deduction, we remove the generating clause from the
1549  * lists, since we don't want to make the same deduction twice.
1550  *
1551  * If we don't find any match for a set-aside outer join clause, we must
1552  * throw it back into the regular joinclause processing by passing it to
1553  * distribute_restrictinfo_to_rels(). If we do generate a derived clause,
1554  * however, the outer-join clause is redundant. We still throw it back,
1555  * because otherwise the join will be seen as a clauseless join and avoided
1556  * during join order searching; but we mark it as redundant to keep from
1557  * messing up the joinrel's size estimate. (This behavior means that the
1558  * API for this routine is uselessly complex: we could have just put all
1559  * the clauses into the regular processing initially. We keep it because
1560  * someday we might want to do something else, such as inserting "dummy"
1561  * joinclauses instead of real ones.)
1562  *
1563  * Outer join clauses that are marked outerjoin_delayed are special: this
1564  * condition means that one or both VARs might go to null due to a lower
1565  * outer join. We can still push a constant through the clause, but only
1566  * if its operator is strict; and we *have to* throw the clause back into
1567  * regular joinclause processing. By keeping the strict join clause,
1568  * we ensure that any null-extended rows that are mistakenly generated due
1569  * to suppressing rows not matching the constant will be rejected at the
1570  * upper outer join. (This doesn't work for full-join clauses.)
1571  */
1572 void
1573 reconsider_outer_join_clauses(PlannerInfo *root)
1574 {
1575  bool found;
1576  ListCell *cell;
1577  ListCell *prev;
1578  ListCell *next;
1579 
1580  /* Outer loop repeats until we find no more deductions */
1581  do
1582  {
1583  found = false;
1584 
1585  /* Process the LEFT JOIN clauses */
1586  prev = NULL;
1587  for (cell = list_head(root->left_join_clauses); cell; cell = next)
1588  {
1589  RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
1590 
1591  next = lnext(cell);
1592  if (reconsider_outer_join_clause(root, rinfo, true))
1593  {
1594  found = true;
1595  /* remove it from the list */
1596  root->left_join_clauses =
1597  list_delete_cell(root->left_join_clauses, cell, prev);
1598  /* we throw it back anyway (see notes above) */
1599  /* but the thrown-back clause has no extra selectivity */
1600  rinfo->norm_selec = 2.0;
1601  rinfo->outer_selec = 1.0;
1602  distribute_restrictinfo_to_rels(root, rinfo);
1603  }
1604  else
1605  prev = cell;
1606  }
1607 
1608  /* Process the RIGHT JOIN clauses */
1609  prev = NULL;
1610  for (cell = list_head(root->right_join_clauses); cell; cell = next)
1611  {
1612  RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
1613 
1614  next = lnext(cell);
1615  if (reconsider_outer_join_clause(root, rinfo, false))
1616  {
1617  found = true;
1618  /* remove it from the list */
1619  root->right_join_clauses =
1620  list_delete_cell(root->right_join_clauses, cell, prev);
1621  /* we throw it back anyway (see notes above) */
1622  /* but the thrown-back clause has no extra selectivity */
1623  rinfo->norm_selec = 2.0;
1624  rinfo->outer_selec = 1.0;
1625  distribute_restrictinfo_to_rels(root, rinfo);
1626  }
1627  else
1628  prev = cell;
1629  }
1630 
1631  /* Process the FULL JOIN clauses */
1632  prev = NULL;
1633  for (cell = list_head(root->full_join_clauses); cell; cell = next)
1634  {
1635  RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
1636 
1637  next = lnext(cell);
1638  if (reconsider_full_join_clause(root, rinfo))
1639  {
1640  found = true;
1641  /* remove it from the list */
1642  root->full_join_clauses =
1643  list_delete_cell(root->full_join_clauses, cell, prev);
1644  /* we throw it back anyway (see notes above) */
1645  /* but the thrown-back clause has no extra selectivity */
1646  rinfo->norm_selec = 2.0;
1647  rinfo->outer_selec = 1.0;
1648  distribute_restrictinfo_to_rels(root, rinfo);
1649  }
1650  else
1651  prev = cell;
1652  }
1653  } while (found);
1654 
1655  /* Now, any remaining clauses have to be thrown back */
1656  foreach(cell, root->left_join_clauses)
1657  {
1658  RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
1659 
1660  distribute_restrictinfo_to_rels(root, rinfo);
1661  }
1662  foreach(cell, root->right_join_clauses)
1663  {
1664  RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
1665 
1666  distribute_restrictinfo_to_rels(root, rinfo);
1667  }
1668  foreach(cell, root->full_join_clauses)
1669  {
1670  RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
1671 
1672  distribute_restrictinfo_to_rels(root, rinfo);
1673  }
1674 }
1675 
1676 /*
1677  * reconsider_outer_join_clauses for a single LEFT/RIGHT JOIN clause
1678  *
1679  * Returns true if we were able to propagate a constant through the clause.
1680  */
1681 static bool
1682 reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
1683  bool outer_on_left)
1684 {
1685  Expr *outervar,
1686  *innervar;
1687  Oid opno,
1688  collation,
1689  left_type,
1690  right_type,
1691  inner_datatype;
1692  Relids inner_relids,
1693  inner_nullable_relids;
1694  ListCell *lc1;
1695 
1696  Assert(is_opclause(rinfo->clause));
1697  opno = ((OpExpr *) rinfo->clause)->opno;
1698  collation = ((OpExpr *) rinfo->clause)->inputcollid;
1699 
1700  /* If clause is outerjoin_delayed, operator must be strict */
1701  if (rinfo->outerjoin_delayed && !op_strict(opno))
1702  return false;
1703 
1704  /* Extract needed info from the clause */
1705  op_input_types(opno, &left_type, &right_type);
1706  if (outer_on_left)
1707  {
1708  outervar = (Expr *) get_leftop(rinfo->clause);
1709  innervar = (Expr *) get_rightop(rinfo->clause);
1710  inner_datatype = right_type;
1711  inner_relids = rinfo->right_relids;
1712  }
1713  else
1714  {
1715  outervar = (Expr *) get_rightop(rinfo->clause);
1716  innervar = (Expr *) get_leftop(rinfo->clause);
1717  inner_datatype = left_type;
1718  inner_relids = rinfo->left_relids;
1719  }
1720  inner_nullable_relids = bms_intersect(inner_relids,
1721  rinfo->nullable_relids);
1722 
1723  /* Scan EquivalenceClasses for a match to outervar */
1724  foreach(lc1, root->eq_classes)
1725  {
1726  EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
1727  bool match;
1728  ListCell *lc2;
1729 
1730  /* Ignore EC unless it contains pseudoconstants */
1731  if (!cur_ec->ec_has_const)
1732  continue;
1733  /* Never match to a volatile EC */
1734  if (cur_ec->ec_has_volatile)
1735  continue;
1736  /* It has to match the outer-join clause as to semantics, too */
1737  if (collation != cur_ec->ec_collation)
1738  continue;
1739  if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
1740  continue;
1741  /* Does it contain a match to outervar? */
1742  match = false;
1743  foreach(lc2, cur_ec->ec_members)
1744  {
1745  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
1746 
1747  Assert(!cur_em->em_is_child); /* no children yet */
1748  if (equal(outervar, cur_em->em_expr))
1749  {
1750  match = true;
1751  break;
1752  }
1753  }
1754  if (!match)
1755  continue; /* no match, so ignore this EC */
1756 
1757  /*
1758  * Yes it does! Try to generate a clause INNERVAR = CONSTANT for each
1759  * CONSTANT in the EC. Note that we must succeed with at least one
1760  * constant before we can decide to throw away the outer-join clause.
1761  */
1762  match = false;
1763  foreach(lc2, cur_ec->ec_members)
1764  {
1765  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
1766  Oid eq_op;
1767  RestrictInfo *newrinfo;
1768 
1769  if (!cur_em->em_is_const)
1770  continue; /* ignore non-const members */
1771  eq_op = select_equality_operator(cur_ec,
1772  inner_datatype,
1773  cur_em->em_datatype);
1774  if (!OidIsValid(eq_op))
1775  continue; /* can't generate equality */
1776  newrinfo = build_implied_join_equality(eq_op,
1777  cur_ec->ec_collation,
1778  innervar,
1779  cur_em->em_expr,
1780  bms_copy(inner_relids),
1781  bms_copy(inner_nullable_relids),
1782  cur_ec->ec_min_security);
1783  if (process_equivalence(root, &newrinfo, true))
1784  match = true;
1785  }
1786 
1787  /*
1788  * If we were able to equate INNERVAR to any constant, report success.
1789  * Otherwise, fall out of the search loop, since we know the OUTERVAR
1790  * appears in at most one EC.
1791  */
1792  if (match)
1793  return true;
1794  else
1795  break;
1796  }
1797 
1798  return false; /* failed to make any deduction */
1799 }
1800 
1801 /*
1802  * reconsider_outer_join_clauses for a single FULL JOIN clause
1803  *
1804  * Returns true if we were able to propagate a constant through the clause.
1805  */
1806 static bool
1807 reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
1808 {
1809  Expr *leftvar;
1810  Expr *rightvar;
1811  Oid opno,
1812  collation,
1813  left_type,
1814  right_type;
1815  Relids left_relids,
1816  right_relids,
1817  left_nullable_relids,
1818  right_nullable_relids;
1819  ListCell *lc1;
1820 
1821  /* Can't use an outerjoin_delayed clause here */
1822  if (rinfo->outerjoin_delayed)
1823  return false;
1824 
1825  /* Extract needed info from the clause */
1826  Assert(is_opclause(rinfo->clause));
1827  opno = ((OpExpr *) rinfo->clause)->opno;
1828  collation = ((OpExpr *) rinfo->clause)->inputcollid;
1829  op_input_types(opno, &left_type, &right_type);
1830  leftvar = (Expr *) get_leftop(rinfo->clause);
1831  rightvar = (Expr *) get_rightop(rinfo->clause);
1832  left_relids = rinfo->left_relids;
1833  right_relids = rinfo->right_relids;
1834  left_nullable_relids = bms_intersect(left_relids,
1835  rinfo->nullable_relids);
1836  right_nullable_relids = bms_intersect(right_relids,
1837  rinfo->nullable_relids);
1838 
1839  foreach(lc1, root->eq_classes)
1840  {
1841  EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
1842  EquivalenceMember *coal_em = NULL;
1843  bool match;
1844  bool matchleft;
1845  bool matchright;
1846  ListCell *lc2;
1847 
1848  /* Ignore EC unless it contains pseudoconstants */
1849  if (!cur_ec->ec_has_const)
1850  continue;
1851  /* Never match to a volatile EC */
1852  if (cur_ec->ec_has_volatile)
1853  continue;
1854  /* It has to match the outer-join clause as to semantics, too */
1855  if (collation != cur_ec->ec_collation)
1856  continue;
1857  if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
1858  continue;
1859 
1860  /*
1861  * Does it contain a COALESCE(leftvar, rightvar) construct?
1862  *
1863  * We can assume the COALESCE() inputs are in the same order as the
1864  * join clause, since both were automatically generated in the cases
1865  * we care about.
1866  *
1867  * XXX currently this may fail to match in cross-type cases because
1868  * the COALESCE will contain typecast operations while the join clause
1869  * may not (if there is a cross-type mergejoin operator available for
1870  * the two column types). Is it OK to strip implicit coercions from
1871  * the COALESCE arguments?
1872  */
1873  match = false;
1874  foreach(lc2, cur_ec->ec_members)
1875  {
1876  coal_em = (EquivalenceMember *) lfirst(lc2);
1877  Assert(!coal_em->em_is_child); /* no children yet */
1878  if (IsA(coal_em->em_expr, CoalesceExpr))
1879  {
1880  CoalesceExpr *cexpr = (CoalesceExpr *) coal_em->em_expr;
1881  Node *cfirst;
1882  Node *csecond;
1883 
1884  if (list_length(cexpr->args) != 2)
1885  continue;
1886  cfirst = (Node *) linitial(cexpr->args);
1887  csecond = (Node *) lsecond(cexpr->args);
1888 
1889  if (equal(leftvar, cfirst) && equal(rightvar, csecond))
1890  {
1891  match = true;
1892  break;
1893  }
1894  }
1895  }
1896  if (!match)
1897  continue; /* no match, so ignore this EC */
1898 
1899  /*
1900  * Yes it does! Try to generate clauses LEFTVAR = CONSTANT and
1901  * RIGHTVAR = CONSTANT for each CONSTANT in the EC. Note that we must
1902  * succeed with at least one constant for each var before we can
1903  * decide to throw away the outer-join clause.
1904  */
1905  matchleft = matchright = false;
1906  foreach(lc2, cur_ec->ec_members)
1907  {
1908  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
1909  Oid eq_op;
1910  RestrictInfo *newrinfo;
1911 
1912  if (!cur_em->em_is_const)
1913  continue; /* ignore non-const members */
1914  eq_op = select_equality_operator(cur_ec,
1915  left_type,
1916  cur_em->em_datatype);
1917  if (OidIsValid(eq_op))
1918  {
1919  newrinfo = build_implied_join_equality(eq_op,
1920  cur_ec->ec_collation,
1921  leftvar,
1922  cur_em->em_expr,
1923  bms_copy(left_relids),
1924  bms_copy(left_nullable_relids),
1925  cur_ec->ec_min_security);
1926  if (process_equivalence(root, &newrinfo, true))
1927  matchleft = true;
1928  }
1929  eq_op = select_equality_operator(cur_ec,
1930  right_type,
1931  cur_em->em_datatype);
1932  if (OidIsValid(eq_op))
1933  {
1934  newrinfo = build_implied_join_equality(eq_op,
1935  cur_ec->ec_collation,
1936  rightvar,
1937  cur_em->em_expr,
1938  bms_copy(right_relids),
1939  bms_copy(right_nullable_relids),
1940  cur_ec->ec_min_security);
1941  if (process_equivalence(root, &newrinfo, true))
1942  matchright = true;
1943  }
1944  }
1945 
1946  /*
1947  * If we were able to equate both vars to constants, we're done, and
1948  * we can throw away the full-join clause as redundant. Moreover, we
1949  * can remove the COALESCE entry from the EC, since the added
1950  * restrictions ensure it will always have the expected value. (We
1951  * don't bother trying to update ec_relids or ec_sources.)
1952  */
1953  if (matchleft && matchright)
1954  {
1955  cur_ec->ec_members = list_delete_ptr(cur_ec->ec_members, coal_em);
1956  return true;
1957  }
1958 
1959  /*
1960  * Otherwise, fall out of the search loop, since we know the COALESCE
1961  * appears in at most one EC (XXX might stop being true if we allow
1962  * stripping of coercions above?)
1963  */
1964  break;
1965  }
1966 
1967  return false; /* failed to make any deduction */
1968 }
1969 
1970 
1971 /*
1972  * exprs_known_equal
1973  * Detect whether two expressions are known equal due to equivalence
1974  * relationships.
1975  *
1976  * Actually, this only shows that the expressions are equal according
1977  * to some opfamily's notion of equality --- but we only use it for
1978  * selectivity estimation, so a fuzzy idea of equality is OK.
1979  *
1980  * Note: does not bother to check for "equal(item1, item2)"; caller must
1981  * check that case if it's possible to pass identical items.
1982  */
1983 bool
1984 exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2)
1985 {
1986  ListCell *lc1;
1987 
1988  foreach(lc1, root->eq_classes)
1989  {
1990  EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
1991  bool item1member = false;
1992  bool item2member = false;
1993  ListCell *lc2;
1994 
1995  /* Never match to a volatile EC */
1996  if (ec->ec_has_volatile)
1997  continue;
1998 
1999  foreach(lc2, ec->ec_members)
2000  {
2001  EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
2002 
2003  if (em->em_is_child)
2004  continue; /* ignore children here */
2005  if (equal(item1, em->em_expr))
2006  item1member = true;
2007  else if (equal(item2, em->em_expr))
2008  item2member = true;
2009  /* Exit as soon as equality is proven */
2010  if (item1member && item2member)
2011  return true;
2012  }
2013  }
2014  return false;
2015 }
2016 
2017 
2018 /*
2019  * match_eclasses_to_foreign_key_col
2020  * See whether a foreign key column match is proven by any eclass.
2021  *
2022  * If the referenced and referencing Vars of the fkey's colno'th column are
2023  * known equal due to any eclass, return that eclass; otherwise return NULL.
2024  * (In principle there might be more than one matching eclass if multiple
2025  * collations are involved, but since collation doesn't matter for equality,
2026  * we ignore that fine point here.) This is much like exprs_known_equal,
2027  * except that we insist on the comparison operator matching the eclass, so
2028  * that the result is definite not approximate.
2029  */
2030 EquivalenceClass *
2031 match_eclasses_to_foreign_key_col(PlannerInfo *root,
2032  ForeignKeyOptInfo *fkinfo,
2033  int colno)
2034 {
2035  Index var1varno = fkinfo->con_relid;
2036  AttrNumber var1attno = fkinfo->conkey[colno];
2037  Index var2varno = fkinfo->ref_relid;
2038  AttrNumber var2attno = fkinfo->confkey[colno];
2039  Oid eqop = fkinfo->conpfeqop[colno];
2040  List *opfamilies = NIL; /* compute only if needed */
2041  ListCell *lc1;
2042 
2043  foreach(lc1, root->eq_classes)
2044  {
2045  EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
2046  bool item1member = false;
2047  bool item2member = false;
2048  ListCell *lc2;
2049 
2050  /* Never match to a volatile EC */
2051  if (ec->ec_has_volatile)
2052  continue;
2053  /* Note: it seems okay to match to "broken" eclasses here */
2054 
2055  foreach(lc2, ec->ec_members)
2056  {
2057  EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
2058  Var *var;
2059 
2060  if (em->em_is_child)
2061  continue; /* ignore children here */
2062 
2063  /* EM must be a Var, possibly with RelabelType */
2064  var = (Var *) em->em_expr;
2065  while (var && IsA(var, RelabelType))
2066  var = (Var *) ((RelabelType *) var)->arg;
2067  if (!(var && IsA(var, Var)))
2068  continue;
2069 
2070  /* Match? */
2071  if (var->varno == var1varno && var->varattno == var1attno)
2072  item1member = true;
2073  else if (var->varno == var2varno && var->varattno == var2attno)
2074  item2member = true;
2075 
2076  /* Have we found both PK and FK column in this EC? */
2077  if (item1member && item2member)
2078  {
2079  /*
2080  * Succeed if eqop matches EC's opfamilies. We could test
2081  * this before scanning the members, but it's probably cheaper
2082  * to test for member matches first.
2083  */
2084  if (opfamilies == NIL) /* compute if we didn't already */
2085  opfamilies = get_mergejoin_opfamilies(eqop);
2086  if (equal(opfamilies, ec->ec_opfamilies))
2087  return ec;
2088  /* Otherwise, done with this EC, move on to the next */
2089  break;
2090  }
2091  }
2092  }
2093  return NULL;
2094 }
2095 
2096 
2097 /*
2098  * add_child_rel_equivalences
2099  * Search for EC members that reference the parent_rel, and
2100  * add transformed members referencing the child_rel.
2101  *
2102  * Note that this function won't be called at all unless we have at least some
2103  * reason to believe that the EC members it generates will be useful.
2104  *
2105  * parent_rel and child_rel could be derived from appinfo, but since the
2106  * caller has already computed them, we might as well just pass them in.
2107  */
2108 void
2109 add_child_rel_equivalences(PlannerInfo *root,
2110  AppendRelInfo *appinfo,
2111  RelOptInfo *parent_rel,
2112  RelOptInfo *child_rel)
2113 {
2114  ListCell *lc1;
2115 
2116  foreach(lc1, root->eq_classes)
2117  {
2118  EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
2119  ListCell *lc2;
2120 
2121  /*
2122  * If this EC contains a volatile expression, then generating child
2123  * EMs would be downright dangerous, so skip it. We rely on a
2124  * volatile EC having only one EM.
2125  */
2126  if (cur_ec->ec_has_volatile)
2127  continue;
2128 
2129  /*
2130  * No point in searching if parent rel not mentioned in eclass; but we
2131  * can't tell that for sure if parent rel is itself a child.
2132  */
2133  if (parent_rel->reloptkind == RELOPT_BASEREL &&
2134  !bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
2135  continue;
2136 
2137  foreach(lc2, cur_ec->ec_members)
2138  {
2139  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
2140 
2141  if (cur_em->em_is_const)
2142  continue; /* ignore consts here */
2143 
2144  /* Does it reference parent_rel? */
2145  if (bms_overlap(cur_em->em_relids, parent_rel->relids))
2146  {
2147  /* Yes, generate transformed child version */
2148  Expr *child_expr;
2149  Relids new_relids;
2150  Relids new_nullable_relids;
2151 
2152  child_expr = (Expr *)
2153  adjust_appendrel_attrs(root,
2154  (Node *) cur_em->em_expr,
2155  1, &appinfo);
2156 
2157  /*
2158  * Transform em_relids to match. Note we do *not* do
2159  * pull_varnos(child_expr) here, as for example the
2160  * transformation might have substituted a constant, but we
2161  * don't want the child member to be marked as constant.
2162  */
2163  new_relids = bms_difference(cur_em->em_relids,
2164  parent_rel->relids);
2165  new_relids = bms_add_members(new_relids, child_rel->relids);
2166 
2167  /*
2168  * And likewise for nullable_relids. Note this code assumes
2169  * parent and child relids are singletons.
2170  */
2171  new_nullable_relids = cur_em->em_nullable_relids;
2172  if (bms_overlap(new_nullable_relids, parent_rel->relids))
2173  {
2174  new_nullable_relids = bms_difference(new_nullable_relids,
2175  parent_rel->relids);
2176  new_nullable_relids = bms_add_members(new_nullable_relids,
2177  child_rel->relids);
2178  }
2179 
2180  (void) add_eq_member(cur_ec, child_expr,
2181  new_relids, new_nullable_relids,
2182  true, cur_em->em_datatype);
2183  }
2184  }
2185  }
2186 }
2187 
2188 
2189 /*
2190  * generate_implied_equalities_for_column
2191  * Create EC-derived joinclauses usable with a specific column.
2192  *
2193  * This is used by indxpath.c to extract potentially indexable joinclauses
2194  * from ECs, and can be used by foreign data wrappers for similar purposes.
2195  * We assume that only expressions in Vars of a single table are of interest,
2196  * but the caller provides a callback function to identify exactly which
2197  * such expressions it would like to know about.
2198  *
2199  * We assume that any given table/index column could appear in only one EC.
2200  * (This should be true in all but the most pathological cases, and if it
2201  * isn't, we stop on the first match anyway.) Therefore, what we return
2202  * is a redundant list of clauses equating the table/index column to each of
2203  * the other-relation values it is known to be equal to. Any one of
2204  * these clauses can be used to create a parameterized path, and there
2205  * is no value in using more than one. (But it *is* worthwhile to create
2206  * a separate parameterized path for each one, since that leads to different
2207  * join orders.)
2208  *
2209  * The caller can pass a Relids set of rels we aren't interested in joining
2210  * to, so as to save the work of creating useless clauses.
2211  */
2212 List *
2213 generate_implied_equalities_for_column(PlannerInfo *root,
2214  RelOptInfo *rel,
2215  ec_matches_callback_type callback,
2216  void *callback_arg,
2217  Relids prohibited_rels)
2218 {
2219  List *result = NIL;
2220  bool is_child_rel = (rel->reloptkind == RELOPT_OTHER_MEMBER_REL);
2221  Relids parent_relids;
2222  ListCell *lc1;
2223 
2224  /* Indexes are available only on base or "other" member relations. */
2225  Assert(IS_SIMPLE_REL(rel));
2226 
2227  /* If it's a child rel, we'll need to know what its parent(s) are */
2228  if (is_child_rel)
2229  parent_relids = find_childrel_parents(root, rel);
2230  else
2231  parent_relids = NULL; /* not used, but keep compiler quiet */
2232 
2233  foreach(lc1, root->eq_classes)
2234  {
2235  EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
2236  EquivalenceMember *cur_em;
2237  ListCell *lc2;
2238 
2239  /*
2240  * Won't generate joinclauses if const or single-member (the latter
2241  * test covers the volatile case too)
2242  */
2243  if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1)
2244  continue;
2245 
2246  /*
2247  * No point in searching if rel not mentioned in eclass (but we can't
2248  * tell that for a child rel).
2249  */
2250  if (!is_child_rel &&
2251  !bms_is_subset(rel->relids, cur_ec->ec_relids))
2252  continue;
2253 
2254  /*
2255  * Scan members, looking for a match to the target column. Note that
2256  * child EC members are considered, but only when they belong to the
2257  * target relation. (Unlike regular members, the same expression
2258  * could be a child member of more than one EC. Therefore, it's
2259  * potentially order-dependent which EC a child relation's target
2260  * column gets matched to. This is annoying but it only happens in
2261  * corner cases, so for now we live with just reporting the first
2262  * match. See also get_eclass_for_sort_expr.)
2263  */
2264  cur_em = NULL;
2265  foreach(lc2, cur_ec->ec_members)
2266  {
2267  cur_em = (EquivalenceMember *) lfirst(lc2);
2268  if (bms_equal(cur_em->em_relids, rel->relids) &&
2269  callback(root, rel, cur_ec, cur_em, callback_arg))
2270  break;
2271  cur_em = NULL;
2272  }
2273 
2274  if (!cur_em)
2275  continue;
2276 
2277  /*
2278  * Found our match. Scan the other EC members and attempt to generate
2279  * joinclauses.
2280  */
2281  foreach(lc2, cur_ec->ec_members)
2282  {
2283  EquivalenceMember *other_em = (EquivalenceMember *) lfirst(lc2);
2284  Oid eq_op;
2285  RestrictInfo *rinfo;
2286 
2287  if (other_em->em_is_child)
2288  continue; /* ignore children here */
2289 
2290  /* Make sure it'll be a join to a different rel */
2291  if (other_em == cur_em ||
2292  bms_overlap(other_em->em_relids, rel->relids))
2293  continue;
2294 
2295  /* Forget it if caller doesn't want joins to this rel */
2296  if (bms_overlap(other_em->em_relids, prohibited_rels))
2297  continue;
2298 
2299  /*
2300  * Also, if this is a child rel, avoid generating a useless join
2301  * to its parent rel(s).
2302  */
2303  if (is_child_rel &&
2304  bms_overlap(parent_relids, other_em->em_relids))
2305  continue;
2306 
2307  eq_op = select_equality_operator(cur_ec,
2308  cur_em->em_datatype,
2309  other_em->em_datatype);
2310  if (!OidIsValid(eq_op))
2311  continue;
2312 
2313  /* set parent_ec to mark as redundant with other joinclauses */
2314  rinfo = create_join_clause(root, cur_ec, eq_op,
2315  cur_em, other_em,
2316  cur_ec);
2317 
2318  result = lappend(result, rinfo);
2319  }
2320 
2321  /*
2322  * If somehow we failed to create any join clauses, we might as well
2323  * keep scanning the ECs for another match. But if we did make any,
2324  * we're done, because we don't want to return non-redundant clauses.
2325  */
2326  if (result)
2327  break;
2328  }
2329 
2330  return result;
2331 }
2332 
2333 /*
2334  * have_relevant_eclass_joinclause
2335  * Detect whether there is an EquivalenceClass that could produce
2336  * a joinclause involving the two given relations.
2337  *
2338  * This is essentially a very cut-down version of
2339  * generate_join_implied_equalities(). Note it's OK to occasionally say "yes"
2340  * incorrectly. Hence we don't bother with details like whether the lack of a
2341  * cross-type operator might prevent the clause from actually being generated.
2342  */
2343 bool
2344 have_relevant_eclass_joinclause(PlannerInfo *root,
2345  RelOptInfo *rel1, RelOptInfo *rel2)
2346 {
2347  ListCell *lc1;
2348 
2349  foreach(lc1, root->eq_classes)
2350  {
2351  EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
2352 
2353  /*
2354  * Won't generate joinclauses if single-member (this test covers the
2355  * volatile case too)
2356  */
2357  if (list_length(ec->ec_members) <= 1)
2358  continue;
2359 
2360  /*
2361  * We do not need to examine the individual members of the EC, because
2362  * all that we care about is whether each rel overlaps the relids of
2363  * at least one member, and a test on ec_relids is sufficient to prove
2364  * that. (As with have_relevant_joinclause(), it is not necessary
2365  * that the EC be able to form a joinclause relating exactly the two
2366  * given rels, only that it be able to form a joinclause mentioning
2367  * both, and this will surely be true if both of them overlap
2368  * ec_relids.)
2369  *
2370  * Note we don't test ec_broken; if we did, we'd need a separate code
2371  * path to look through ec_sources. Checking the membership anyway is
2372  * OK as a possibly-overoptimistic heuristic.
2373  *
2374  * We don't test ec_has_const either, even though a const eclass won't
2375  * generate real join clauses. This is because if we had "WHERE a.x =
2376  * b.y and a.x = 42", it is worth considering a join between a and b,
2377  * since the join result is likely to be small even though it'll end
2378  * up being an unqualified nestloop.
2379  */
2380  if (bms_overlap(rel1->relids, ec->ec_relids) &&
2381  bms_overlap(rel2->relids, ec->ec_relids))
2382  return true;
2383  }
2384 
2385  return false;
2386 }
2387 
2388 
2389 /*
2390  * has_relevant_eclass_joinclause
2391  * Detect whether there is an EquivalenceClass that could produce
2392  * a joinclause involving the given relation and anything else.
2393  *
2394  * This is the same as have_relevant_eclass_joinclause with the other rel
2395  * implicitly defined as "everything else in the query".
2396  */
2397 bool
2398 has_relevant_eclass_joinclause(PlannerInfo *root, RelOptInfo *rel1)
2399 {
2400  ListCell *lc1;
2401 
2402  foreach(lc1, root->eq_classes)
2403  {
2404  EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
2405 
2406  /*
2407  * Won't generate joinclauses if single-member (this test covers the
2408  * volatile case too)
2409  */
2410  if (list_length(ec->ec_members) <= 1)
2411  continue;
2412 
2413  /*
2414  * Per the comment in have_relevant_eclass_joinclause, it's sufficient
2415  * to find an EC that mentions both this rel and some other rel.
2416  */
2417  if (bms_overlap(rel1->relids, ec->ec_relids) &&
2418  !bms_is_subset(ec->ec_relids, rel1->relids))
2419  return true;
2420  }
2421 
2422  return false;
2423 }
2424 
2425 
2426 /*
2427  * eclass_useful_for_merging
2428  * Detect whether the EC could produce any mergejoinable join clauses
2429  * against the specified relation.
2430  *
2431  * This is just a heuristic test and doesn't have to be exact; it's better
2432  * to say "yes" incorrectly than "no". Hence we don't bother with details
2433  * like whether the lack of a cross-type operator might prevent the clause
2434  * from actually being generated.
2435  */
2436 bool
2437 eclass_useful_for_merging(PlannerInfo *root,
2438  EquivalenceClass *eclass,
2439  RelOptInfo *rel)
2440 {
2441  Relids relids;
2442  ListCell *lc;
2443 
2444  Assert(!eclass->ec_merged);
2445 
2446  /*
2447  * Won't generate joinclauses if const or single-member (the latter test
2448  * covers the volatile case too)
2449  */
2450  if (eclass->ec_has_const || list_length(eclass->ec_members) <= 1)
2451  return false;
2452 
2453  /*
2454  * Note we don't test ec_broken; if we did, we'd need a separate code path
2455  * to look through ec_sources. Checking the members anyway is OK as a
2456  * possibly-overoptimistic heuristic.
2457  */
2458 
2459  /* If specified rel is a child, we must consider the topmost parent rel */
2460  if (IS_OTHER_REL(rel))
2461  {
2462  Assert(!bms_is_empty(rel->top_parent_relids));
2463  relids = rel->top_parent_relids;
2464  }
2465  else
2466  relids = rel->relids;
2467 
2468  /* If rel already includes all members of eclass, no point in searching */
2469  if (bms_is_subset(eclass->ec_relids, relids))
2470  return false;
2471 
2472  /* To join, we need a member not in the given rel */
2473  foreach(lc, eclass->ec_members)
2474  {
2475  EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
2476 
2477  if (cur_em->em_is_child)
2478  continue; /* ignore children here */
2479 
2480  if (!bms_overlap(cur_em->em_relids, relids))
2481  return true;
2482  }
2483 
2484  return false;
2485 }
2486 
2487 
2488 /*
2489  * is_redundant_derived_clause
2490  * Test whether rinfo is derived from same EC as any clause in clauselist;
2491  * if so, it can be presumed to represent a condition that's redundant
2492  * with that member of the list.
2493  */
2494 bool
2495 is_redundant_derived_clause(RestrictInfo *rinfo, List *clauselist)
2496 {
2497  EquivalenceClass *parent_ec = rinfo->parent_ec;
2498  ListCell *lc;
2499 
2500  /* Fail if it's not a potentially-redundant clause from some EC */
2501  if (parent_ec == NULL)
2502  return false;
2503 
2504  foreach(lc, clauselist)
2505  {
2506  RestrictInfo *otherrinfo = (RestrictInfo *) lfirst(lc);
2507 
2508  if (otherrinfo->parent_ec == parent_ec)
2509  return true;
2510  }
2511 
2512  return false;
2513 }
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