core.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * core.c
   4  *        Routines copied from PostgreSQL core distribution.
   5  *
   6  * src/backend/optimizer/path/allpaths.c
   7  *     set_append_rel_pathlist()
   8  *     generate_mergeappend_paths()
   9  *     get_cheapest_parameterized_child_path()
  10  *     accumulate_append_subpath()
  11  *     standard_join_search()
  12  *
  13  * src/backend/optimizer/path/joinrels.c
  14  *     join_search_one_level()
  15  *     make_rels_by_clause_joins()
  16  *     make_rels_by_clauseless_joins()
  17  *     join_is_legal()
  18  *     has_join_restriction()
  19  *     is_dummy_rel()
  20  *     mark_dummy_rel()
  21  *     restriction_is_constant_false()
  22  *
  23  * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
  24  * Portions Copyright (c) 1994, Regents of the University of California
  25  *
  26  *-------------------------------------------------------------------------
  27  */
  28
  29 /*
  30  * set_append_rel_pathlist
  31  *        Build access paths for an "append relation"
  32  */
  33 static void
  34 set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
  35                                                 Index rti, RangeTblEntry *rte)
  36 {
  37         int                     parentRTindex = rti;
  38         List       *live_childrels = NIL;
  39         List       *subpaths = NIL;
  40         bool            subpaths_valid = true;
  41         List       *all_child_pathkeys = NIL;
  42         List       *all_child_outers = NIL;
  43         ListCell   *l;
  44
  45         /*
  46          * Generate access paths for each member relation, and remember the
  47          * cheapest path for each one.  Also, identify all pathkeys (orderings)
  48          * and parameterizations (required_outer sets) available for the member
  49          * relations.
  50          */
  51         foreach(l, root->append_rel_list)
  52         {
  53                 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
  54                 int                     childRTindex;
  55                 RangeTblEntry *childRTE;
  56                 RelOptInfo *childrel;
  57                 ListCell   *lcp;
  58
  59                 /* append_rel_list contains all append rels; ignore others */
  60                 if (appinfo->parent_relid != parentRTindex)
  61                         continue;
  62
  63                 /* Re-locate the child RTE and RelOptInfo */
  64                 childRTindex = appinfo->child_relid;
  65                 childRTE = root->simple_rte_array[childRTindex];
  66                 childrel = root->simple_rel_array[childRTindex];
  67
  68                 /*
  69                  * Compute the child's access paths.
  70                  */
  71                 set_rel_pathlist(root, childrel, childRTindex, childRTE);
  72
  73                 /*
  74                  * If child is dummy, ignore it.
  75                  */
  76                 if (IS_DUMMY_REL(childrel))
  77                         continue;
  78
  79                 /*
  80                  * Child is live, so add it to the live_childrels list for use below.
  81                  */
  82                 live_childrels = lappend(live_childrels, childrel);
  83
  84                 /*
  85                  * If child has an unparameterized cheapest-total path, add that to
  86                  * the unparameterized Append path we are constructing for the parent.
  87                  * If not, there's no workable unparameterized path.
  88                  */
  89                 if (childrel->cheapest_total_path->param_info == NULL)
  90                         subpaths = accumulate_append_subpath(subpaths,
  91                                                                                           childrel->cheapest_total_path);
  92                 else
  93                         subpaths_valid = false;
  94
  95                 /*
  96                  * Collect lists of all the available path orderings and
  97                  * parameterizations for all the children.  We use these as a
  98                  * heuristic to indicate which sort orderings and parameterizations we
  99                  * should build Append and MergeAppend paths for.
 100                  */
 101                 foreach(lcp, childrel->pathlist)
 102                 {
 103                         Path       *childpath = (Path *) lfirst(lcp);
 104                         List       *childkeys = childpath->pathkeys;
 105                         Relids          childouter = PATH_REQ_OUTER(childpath);
 106
 107                         /* Unsorted paths don't contribute to pathkey list */
 108                         if (childkeys != NIL)
 109                         {
 110                                 ListCell   *lpk;
 111                                 bool            found = false;
 112
 113                                 /* Have we already seen this ordering? */
 114                                 foreach(lpk, all_child_pathkeys)
 115                                 {
 116                                         List       *existing_pathkeys = (List *) lfirst(lpk);
 117
 118                                         if (compare_pathkeys(existing_pathkeys,
 119                                                                                  childkeys) == PATHKEYS_EQUAL)
 120                                         {
 121                                                 found = true;
 122                                                 break;
 123                                         }
 124                                 }
 125                                 if (!found)
 126                                 {
 127                                         /* No, so add it to all_child_pathkeys */
 128                                         all_child_pathkeys = lappend(all_child_pathkeys,
 129                                                                                                  childkeys);
 130                                 }
 131                         }
 132
 133                         /* Unparameterized paths don't contribute to param-set list */
 134                         if (childouter)
 135                         {
 136                                 ListCell   *lco;
 137                                 bool            found = false;
 138
 139                                 /* Have we already seen this param set? */
 140                                 foreach(lco, all_child_outers)
 141                                 {
 142                                         Relids          existing_outers = (Relids) lfirst(lco);
 143
 144                                         if (bms_equal(existing_outers, childouter))
 145                                         {
 146                                                 found = true;
 147                                                 break;
 148                                         }
 149                                 }
 150                                 if (!found)
 151                                 {
 152                                         /* No, so add it to all_child_outers */
 153                                         all_child_outers = lappend(all_child_outers,
 154                                                                                            childouter);
 155                                 }
 156                         }
 157                 }
 158         }
 159
 160         /*
 161          * If we found unparameterized paths for all children, build an unordered,
 162          * unparameterized Append path for the rel.  (Note: this is correct even
 163          * if we have zero or one live subpath due to constraint exclusion.)
 164          */
 165         if (subpaths_valid)
 166                 add_path(rel, (Path *) create_append_path(rel, subpaths, NULL));
 167
 168         /*
 169          * Also build unparameterized MergeAppend paths based on the collected
 170          * list of child pathkeys.
 171          */
 172         if (subpaths_valid)
 173                 generate_mergeappend_paths(root, rel, live_childrels,
 174                                                                    all_child_pathkeys);
 175
 176         /*
 177          * Build Append paths for each parameterization seen among the child rels.
 178          * (This may look pretty expensive, but in most cases of practical
 179          * interest, the child rels will expose mostly the same parameterizations,
 180          * so that not that many cases actually get considered here.)
 181          *
 182          * The Append node itself cannot enforce quals, so all qual checking must
 183          * be done in the child paths.  This means that to have a parameterized
 184          * Append path, we must have the exact same parameterization for each
 185          * child path; otherwise some children might be failing to check the
 186          * moved-down quals.  To make them match up, we can try to increase the
 187          * parameterization of lesser-parameterized paths.
 188          */
 189         foreach(l, all_child_outers)
 190         {
 191                 Relids          required_outer = (Relids) lfirst(l);
 192                 ListCell   *lcr;
 193
 194                 /* Select the child paths for an Append with this parameterization */
 195                 subpaths = NIL;
 196                 subpaths_valid = true;
 197                 foreach(lcr, live_childrels)
 198                 {
 199                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 200                         Path       *subpath;
 201
 202                         subpath = get_cheapest_parameterized_child_path(root,
 203                                                                                                                         childrel,
 204                                                                                                                         required_outer);
 205                         if (subpath == NULL)
 206                         {
 207                                 /* failed to make a suitable path for this child */
 208                                 subpaths_valid = false;
 209                                 break;
 210                         }
 211                         subpaths = accumulate_append_subpath(subpaths, subpath);
 212                 }
 213
 214                 if (subpaths_valid)
 215                         add_path(rel, (Path *)
 216                                          create_append_path(rel, subpaths, required_outer));
 217         }
 218 }
 219
 220 /*
 221  * generate_mergeappend_paths
 222  *              Generate MergeAppend paths for an append relation
 223  *
 224  * Generate a path for each ordering (pathkey list) appearing in
 225  * all_child_pathkeys.
 226  *
 227  * We consider both cheapest-startup and cheapest-total cases, ie, for each
 228  * interesting ordering, collect all the cheapest startup subpaths and all the
 229  * cheapest total paths, and build a MergeAppend path for each case.
 230  *
 231  * We don't currently generate any parameterized MergeAppend paths.  While
 232  * it would not take much more code here to do so, it's very unclear that it
 233  * is worth the planning cycles to investigate such paths: there's little
 234  * use for an ordered path on the inside of a nestloop.  In fact, it's likely
 235  * that the current coding of add_path would reject such paths out of hand,
 236  * because add_path gives no credit for sort ordering of parameterized paths,
 237  * and a parameterized MergeAppend is going to be more expensive than the
 238  * corresponding parameterized Append path.  If we ever try harder to support
 239  * parameterized mergejoin plans, it might be worth adding support for
 240  * parameterized MergeAppends to feed such joins.  (See notes in
 241  * optimizer/README for why that might not ever happen, though.)
 242  */
 243 static void
 244 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
 245                                                    List *live_childrels,
 246                                                    List *all_child_pathkeys)
 247 {
 248         ListCell   *lcp;
 249
 250         foreach(lcp, all_child_pathkeys)
 251         {
 252                 List       *pathkeys = (List *) lfirst(lcp);
 253                 List       *startup_subpaths = NIL;
 254                 List       *total_subpaths = NIL;
 255                 bool            startup_neq_total = false;
 256                 ListCell   *lcr;
 257
 258                 /* Select the child paths for this ordering... */
 259                 foreach(lcr, live_childrels)
 260                 {
 261                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 262                         Path       *cheapest_startup,
 263                                            *cheapest_total;
 264
 265                         /* Locate the right paths, if they are available. */
 266                         cheapest_startup =
 267                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 268                                                                                            pathkeys,
 269                                                                                            NULL,
 270                                                                                            STARTUP_COST);
 271                         cheapest_total =
 272                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 273                                                                                            pathkeys,
 274                                                                                            NULL,
 275                                                                                            TOTAL_COST);
 276
 277                         /*
 278                          * If we can't find any paths with the right order just use the
 279                          * cheapest-total path; we'll have to sort it later.
 280                          */
 281                         if (cheapest_startup == NULL || cheapest_total == NULL)
 282                         {
 283                                 cheapest_startup = cheapest_total =
 284                                         childrel->cheapest_total_path;
 285                                 /* Assert we do have an unparameterized path for this child */
 286                                 Assert(cheapest_total->param_info == NULL);
 287                         }
 288
 289                         /*
 290                          * Notice whether we actually have different paths for the
 291                          * "cheapest" and "total" cases; frequently there will be no point
 292                          * in two create_merge_append_path() calls.
 293                          */
 294                         if (cheapest_startup != cheapest_total)
 295                                 startup_neq_total = true;
 296
 297                         startup_subpaths =
 298                                 accumulate_append_subpath(startup_subpaths, cheapest_startup);
 299                         total_subpaths =
 300                                 accumulate_append_subpath(total_subpaths, cheapest_total);
 301                 }
 302
 303                 /* ... and build the MergeAppend paths */
 304                 add_path(rel, (Path *) create_merge_append_path(root,
 305                                                                                                                 rel,
 306                                                                                                                 startup_subpaths,
 307                                                                                                                 pathkeys,
 308                                                                                                                 NULL));
 309                 if (startup_neq_total)
 310                         add_path(rel, (Path *) create_merge_append_path(root,
 311                                                                                                                         rel,
 312                                                                                                                         total_subpaths,
 313                                                                                                                         pathkeys,
 314                                                                                                                         NULL));
 315         }
 316 }
 317
 318 /*
 319  * get_cheapest_parameterized_child_path
 320  *              Get cheapest path for this relation that has exactly the requested
 321  *              parameterization.
 322  *
 323  * Returns NULL if unable to create such a path.
 324  */
 325 static Path *
 326 get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
 327                                                                           Relids required_outer)
 328 {
 329         Path       *cheapest;
 330         ListCell   *lc;
 331
 332         /*
 333          * Look up the cheapest existing path with no more than the needed
 334          * parameterization.  If it has exactly the needed parameterization, we're
 335          * done.
 336          */
 337         cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
 338                                                                                           NIL,
 339                                                                                           required_outer,
 340                                                                                           TOTAL_COST);
 341         Assert(cheapest != NULL);
 342         if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
 343                 return cheapest;
 344
 345         /*
 346          * Otherwise, we can "reparameterize" an existing path to match the given
 347          * parameterization, which effectively means pushing down additional
 348          * joinquals to be checked within the path's scan.  However, some existing
 349          * paths might check the available joinquals already while others don't;
 350          * therefore, it's not clear which existing path will be cheapest after
 351          * reparameterization.  We have to go through them all and find out.
 352          */
 353         cheapest = NULL;
 354         foreach(lc, rel->pathlist)
 355         {
 356                 Path       *path = (Path *) lfirst(lc);
 357
 358                 /* Can't use it if it needs more than requested parameterization */
 359                 if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
 360                         continue;
 361
 362                 /*
 363                  * Reparameterization can only increase the path's cost, so if it's
 364                  * already more expensive than the current cheapest, forget it.
 365                  */
 366                 if (cheapest != NULL &&
 367                         compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
 368                         continue;
 369
 370                 /* Reparameterize if needed, then recheck cost */
 371                 if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
 372                 {
 373                         path = reparameterize_path(root, path, required_outer, 1.0);
 374                         if (path == NULL)
 375                                 continue;               /* failed to reparameterize this one */
 376                         Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));
 377
 378                         if (cheapest != NULL &&
 379                                 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
 380                                 continue;
 381                 }
 382
 383                 /* We have a new best path */
 384                 cheapest = path;
 385         }
 386
 387         /* Return the best path, or NULL if we found no suitable candidate */
 388         return cheapest;
 389 }
 390
 391 /*
 392  * accumulate_append_subpath
 393  *              Add a subpath to the list being built for an Append or MergeAppend
 394  *
 395  * It's possible that the child is itself an Append or MergeAppend path, in
 396  * which case we can "cut out the middleman" and just add its child paths to
 397  * our own list.  (We don't try to do this earlier because we need to apply
 398  * both levels of transformation to the quals.)
 399  *
 400  * Note that if we omit a child MergeAppend in this way, we are effectively
 401  * omitting a sort step, which seems fine: if the parent is to be an Append,
 402  * its result would be unsorted anyway, while if the parent is to be a
 403  * MergeAppend, there's no point in a separate sort on a child.
 404  */
 405 static List *
 406 accumulate_append_subpath(List *subpaths, Path *path)
 407 {
 408         if (IsA(path, AppendPath))
 409         {
 410                 AppendPath *apath = (AppendPath *) path;
 411
 412                 /* list_copy is important here to avoid sharing list substructure */
 413                 return list_concat(subpaths, list_copy(apath->subpaths));
 414         }
 415         else if (IsA(path, MergeAppendPath))
 416         {
 417                 MergeAppendPath *mpath = (MergeAppendPath *) path;
 418
 419                 /* list_copy is important here to avoid sharing list substructure */
 420                 return list_concat(subpaths, list_copy(mpath->subpaths));
 421         }
 422         else
 423                 return lappend(subpaths, path);
 424 }
 425
 426 /*
 427  * standard_join_search
 428  *        Find possible joinpaths for a query by successively finding ways
 429  *        to join component relations into join relations.
 430  *
 431  * 'levels_needed' is the number of iterations needed, ie, the number of
 432  *              independent jointree items in the query.  This is > 1.
 433  *
 434  * 'initial_rels' is a list of RelOptInfo nodes for each independent
 435  *              jointree item.  These are the components to be joined together.
 436  *              Note that levels_needed == list_length(initial_rels).
 437  *
 438  * Returns the final level of join relations, i.e., the relation that is
 439  * the result of joining all the original relations together.
 440  * At least one implementation path must be provided for this relation and
 441  * all required sub-relations.
 442  *
 443  * To support loadable plugins that modify planner behavior by changing the
 444  * join searching algorithm, we provide a hook variable that lets a plugin
 445  * replace or supplement this function.  Any such hook must return the same
 446  * final join relation as the standard code would, but it might have a
 447  * different set of implementation paths attached, and only the sub-joinrels
 448  * needed for these paths need have been instantiated.
 449  *
 450  * Note to plugin authors: the functions invoked during standard_join_search()
 451  * modify root->join_rel_list and root->join_rel_hash.  If you want to do more
 452  * than one join-order search, you'll probably need to save and restore the
 453  * original states of those data structures.  See geqo_eval() for an example.
 454  */
 455 RelOptInfo *
 456 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
 457 {
 458         int                     lev;
 459         RelOptInfo *rel;
 460
 461         /*
 462          * This function cannot be invoked recursively within any one planning
 463          * problem, so join_rel_level[] can't be in use already.
 464          */
 465         Assert(root->join_rel_level == NULL);
 466
 467         /*
 468          * We employ a simple "dynamic programming" algorithm: we first find all
 469          * ways to build joins of two jointree items, then all ways to build joins
 470          * of three items (from two-item joins and single items), then four-item
 471          * joins, and so on until we have considered all ways to join all the
 472          * items into one rel.
 473          *
 474          * root->join_rel_level[j] is a list of all the j-item rels.  Initially we
 475          * set root->join_rel_level[1] to represent all the single-jointree-item
 476          * relations.
 477          */
 478         root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
 479
 480         root->join_rel_level[1] = initial_rels;
 481
 482         for (lev = 2; lev <= levels_needed; lev++)
 483         {
 484                 ListCell   *lc;
 485
 486                 /*
 487                  * Determine all possible pairs of relations to be joined at this
 488                  * level, and build paths for making each one from every available
 489                  * pair of lower-level relations.
 490                  */
 491                 join_search_one_level(root, lev);
 492
 493                 /*
 494                  * Do cleanup work on each just-processed rel.
 495                  */
 496                 foreach(lc, root->join_rel_level[lev])
 497                 {
 498                         rel = (RelOptInfo *) lfirst(lc);
 499
 500                         /* Find and save the cheapest paths for this rel */
 501                         set_cheapest(rel);
 502
 503 #ifdef OPTIMIZER_DEBUG
 504                         debug_print_rel(root, rel);
 505 #endif
 506                 }
 507         }
 508
 509         /*
 510          * We should have a single rel at the final level.
 511          */
 512         if (root->join_rel_level[levels_needed] == NIL)
 513                 elog(ERROR, "failed to build any %d-way joins", levels_needed);
 514         Assert(list_length(root->join_rel_level[levels_needed]) == 1);
 515
 516         rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
 517
 518         root->join_rel_level = NULL;
 519
 520         return rel;
 521 }
 522
 523 /*
 524  * join_search_one_level
 525  *        Consider ways to produce join relations containing exactly 'level'
 526  *        jointree items.  (This is one step of the dynamic-programming method
 527  *        embodied in standard_join_search.)  Join rel nodes for each feasible
 528  *        combination of lower-level rels are created and returned in a list.
 529  *        Implementation paths are created for each such joinrel, too.
 530  *
 531  * level: level of rels we want to make this time
 532  * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
 533  *
 534  * The result is returned in root->join_rel_level[level].
 535  */
 536 void
 537 join_search_one_level(PlannerInfo *root, int level)
 538 {
 539         List      **joinrels = root->join_rel_level;
 540         ListCell   *r;
 541         int                     k;
 542
 543         Assert(joinrels[level] == NIL);
 544
 545         /* Set join_cur_level so that new joinrels are added to proper list */
 546         root->join_cur_level = level;
 547
 548         /*
 549          * First, consider left-sided and right-sided plans, in which rels of
 550          * exactly level-1 member relations are joined against initial relations.
 551          * We prefer to join using join clauses, but if we find a rel of level-1
 552          * members that has no join clauses, we will generate Cartesian-product
 553          * joins against all initial rels not already contained in it.
 554          */
 555         foreach(r, joinrels[level - 1])
 556         {
 557                 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 558
 559                 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
 560                         has_join_restriction(root, old_rel))
 561                 {
 562                         /*
 563                          * There are join clauses or join order restrictions relevant to
 564                          * this rel, so consider joins between this rel and (only) those
 565                          * initial rels it is linked to by a clause or restriction.
 566                          *
 567                          * At level 2 this condition is symmetric, so there is no need to
 568                          * look at initial rels before this one in the list; we already
 569                          * considered such joins when we were at the earlier rel.  (The
 570                          * mirror-image joins are handled automatically by make_join_rel.)
 571                          * In later passes (level > 2), we join rels of the previous level
 572                          * to each initial rel they don't already include but have a join
 573                          * clause or restriction with.
 574                          */
 575                         ListCell   *other_rels;
 576
 577                         if (level == 2)         /* consider remaining initial rels */
 578                                 other_rels = lnext(r);
 579                         else    /* consider all initial rels */
 580                                 other_rels = list_head(joinrels[1]);
 581
 582                         make_rels_by_clause_joins(root,
 583                                                                           old_rel,
 584                                                                           other_rels);
 585                 }
 586                 else
 587                 {
 588                         /*
 589                          * Oops, we have a relation that is not joined to any other
 590                          * relation, either directly or by join-order restrictions.
 591                          * Cartesian product time.
 592                          *
 593                          * We consider a cartesian product with each not-already-included
 594                          * initial rel, whether it has other join clauses or not.  At
 595                          * level 2, if there are two or more clauseless initial rels, we
 596                          * will redundantly consider joining them in both directions; but
 597                          * such cases aren't common enough to justify adding complexity to
 598                          * avoid the duplicated effort.
 599                          */
 600                         make_rels_by_clauseless_joins(root,
 601                                                                                   old_rel,
 602                                                                                   list_head(joinrels[1]));
 603                 }
 604         }
 605
 606         /*
 607          * Now, consider "bushy plans" in which relations of k initial rels are
 608          * joined to relations of level-k initial rels, for 2 <= k <= level-2.
 609          *
 610          * We only consider bushy-plan joins for pairs of rels where there is a
 611          * suitable join clause (or join order restriction), in order to avoid
 612          * unreasonable growth of planning time.
 613          */
 614         for (k = 2;; k++)
 615         {
 616                 int                     other_level = level - k;
 617
 618                 /*
 619                  * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
 620                  * need to go as far as the halfway point.
 621                  */
 622                 if (k > other_level)
 623                         break;
 624
 625                 foreach(r, joinrels[k])
 626                 {
 627                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 628                         ListCell   *other_rels;
 629                         ListCell   *r2;
 630
 631                         /*
 632                          * We can ignore relations without join clauses here, unless they
 633                          * participate in join-order restrictions --- then we might have
 634                          * to force a bushy join plan.
 635                          */
 636                         if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
 637                                 !has_join_restriction(root, old_rel))
 638                                 continue;
 639
 640                         if (k == other_level)
 641                                 other_rels = lnext(r);  /* only consider remaining rels */
 642                         else
 643                                 other_rels = list_head(joinrels[other_level]);
 644
 645                         for_each_cell(r2, other_rels)
 646                         {
 647                                 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
 648
 649                                 if (!bms_overlap(old_rel->relids, new_rel->relids))
 650                                 {
 651                                         /*
 652                                          * OK, we can build a rel of the right level from this
 653                                          * pair of rels.  Do so if there is at least one relevant
 654                                          * join clause or join order restriction.
 655                                          */
 656                                         if (have_relevant_joinclause(root, old_rel, new_rel) ||
 657                                                 have_join_order_restriction(root, old_rel, new_rel))
 658                                         {
 659                                                 (void) make_join_rel(root, old_rel, new_rel);
 660                                         }
 661                                 }
 662                         }
 663                 }
 664         }
 665
 666         /*----------
 667          * Last-ditch effort: if we failed to find any usable joins so far, force
 668          * a set of cartesian-product joins to be generated.  This handles the
 669          * special case where all the available rels have join clauses but we
 670          * cannot use any of those clauses yet.  This can only happen when we are
 671          * considering a join sub-problem (a sub-joinlist) and all the rels in the
 672          * sub-problem have only join clauses with rels outside the sub-problem.
 673          * An example is
 674          *
 675          *              SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
 676          *              WHERE a.w = c.x and b.y = d.z;
 677          *
 678          * If the "a INNER JOIN b" sub-problem does not get flattened into the
 679          * upper level, we must be willing to make a cartesian join of a and b;
 680          * but the code above will not have done so, because it thought that both
 681          * a and b have joinclauses.  We consider only left-sided and right-sided
 682          * cartesian joins in this case (no bushy).
 683          *----------
 684          */
 685         if (joinrels[level] == NIL)
 686         {
 687                 /*
 688                  * This loop is just like the first one, except we always call
 689                  * make_rels_by_clauseless_joins().
 690                  */
 691                 foreach(r, joinrels[level - 1])
 692                 {
 693                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 694
 695                         make_rels_by_clauseless_joins(root,
 696                                                                                   old_rel,
 697                                                                                   list_head(joinrels[1]));
 698                 }
 699
 700                 /*----------
 701                  * When special joins are involved, there may be no legal way
 702                  * to make an N-way join for some values of N.  For example consider
 703                  *
 704                  * SELECT ... FROM t1 WHERE
 705                  *       x IN (SELECT ... FROM t2,t3 WHERE ...) AND
 706                  *       y IN (SELECT ... FROM t4,t5 WHERE ...)
 707                  *
 708                  * We will flatten this query to a 5-way join problem, but there are
 709                  * no 4-way joins that join_is_legal() will consider legal.  We have
 710                  * to accept failure at level 4 and go on to discover a workable
 711                  * bushy plan at level 5.
 712                  *
 713                  * However, if there are no special joins and no lateral references
 714                  * then join_is_legal() should never fail, and so the following sanity
 715                  * check is useful.
 716                  *----------
 717                  */
 718                 if (joinrels[level] == NIL &&
 719                         root->join_info_list == NIL &&
 720                         !root->hasLateralRTEs)
 721                         elog(ERROR, "failed to build any %d-way joins", level);
 722         }
 723 }
 724
 725 /*
 726  * make_rels_by_clause_joins
 727  *        Build joins between the given relation 'old_rel' and other relations
 728  *        that participate in join clauses that 'old_rel' also participates in
 729  *        (or participate in join-order restrictions with it).
 730  *        The join rels are returned in root->join_rel_level[join_cur_level].
 731  *
 732  * Note: at levels above 2 we will generate the same joined relation in
 733  * multiple ways --- for example (a join b) join c is the same RelOptInfo as
 734  * (b join c) join a, though the second case will add a different set of Paths
 735  * to it.  This is the reason for using the join_rel_level mechanism, which
 736  * automatically ensures that each new joinrel is only added to the list once.
 737  *
 738  * 'old_rel' is the relation entry for the relation to be joined
 739  * 'other_rels': the first cell in a linked list containing the other
 740  * rels to be considered for joining
 741  *
 742  * Currently, this is only used with initial rels in other_rels, but it
 743  * will work for joining to joinrels too.
 744  */
 745 static void
 746 make_rels_by_clause_joins(PlannerInfo *root,
 747                                                   RelOptInfo *old_rel,
 748                                                   ListCell *other_rels)
 749 {
 750         ListCell   *l;
 751
 752         for_each_cell(l, other_rels)
 753         {
 754                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 755
 756                 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
 757                         (have_relevant_joinclause(root, old_rel, other_rel) ||
 758                          have_join_order_restriction(root, old_rel, other_rel)))
 759                 {
 760                         (void) make_join_rel(root, old_rel, other_rel);
 761                 }
 762         }
 763 }
 764
 765 /*
 766  * make_rels_by_clauseless_joins
 767  *        Given a relation 'old_rel' and a list of other relations
 768  *        'other_rels', create a join relation between 'old_rel' and each
 769  *        member of 'other_rels' that isn't already included in 'old_rel'.
 770  *        The join rels are returned in root->join_rel_level[join_cur_level].
 771  *
 772  * 'old_rel' is the relation entry for the relation to be joined
 773  * 'other_rels': the first cell of a linked list containing the
 774  * other rels to be considered for joining
 775  *
 776  * Currently, this is only used with initial rels in other_rels, but it would
 777  * work for joining to joinrels too.
 778  */
 779 static void
 780 make_rels_by_clauseless_joins(PlannerInfo *root,
 781                                                           RelOptInfo *old_rel,
 782                                                           ListCell *other_rels)
 783 {
 784         ListCell   *l;
 785
 786         for_each_cell(l, other_rels)
 787         {
 788                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 789
 790                 if (!bms_overlap(other_rel->relids, old_rel->relids))
 791                 {
 792                         (void) make_join_rel(root, old_rel, other_rel);
 793                 }
 794         }
 795 }
 796
 797 /*
 798  * join_is_legal
 799  *         Determine whether a proposed join is legal given the query's
 800  *         join order constraints; and if it is, determine the join type.
 801  *
 802  * Caller must supply not only the two rels, but the union of their relids.
 803  * (We could simplify the API by computing joinrelids locally, but this
 804  * would be redundant work in the normal path through make_join_rel.)
 805  *
 806  * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
 807  * else it's set to point to the associated SpecialJoinInfo node.  Also,
 808  * *reversed_p is set TRUE if the given relations need to be swapped to
 809  * match the SpecialJoinInfo node.
 810  */
 811 static bool
 812 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 813                           Relids joinrelids,
 814                           SpecialJoinInfo **sjinfo_p, bool *reversed_p)
 815 {
 816         SpecialJoinInfo *match_sjinfo;
 817         bool            reversed;
 818         bool            unique_ified;
 819         bool            must_be_leftjoin;
 820         ListCell   *l;
 821
 822         /*
 823          * Ensure output params are set on failure return.  This is just to
 824          * suppress uninitialized-variable warnings from overly anal compilers.
 825          */
 826         *sjinfo_p = NULL;
 827         *reversed_p = false;
 828
 829         /*
 830          * If we have any special joins, the proposed join might be illegal; and
 831          * in any case we have to determine its join type.  Scan the join info
 832          * list for matches and conflicts.
 833          */
 834         match_sjinfo = NULL;
 835         reversed = false;
 836         unique_ified = false;
 837         must_be_leftjoin = false;
 838
 839         foreach(l, root->join_info_list)
 840         {
 841                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
 842
 843                 /*
 844                  * This special join is not relevant unless its RHS overlaps the
 845                  * proposed join.  (Check this first as a fast path for dismissing
 846                  * most irrelevant SJs quickly.)
 847                  */
 848                 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
 849                         continue;
 850
 851                 /*
 852                  * Also, not relevant if proposed join is fully contained within RHS
 853                  * (ie, we're still building up the RHS).
 854                  */
 855                 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
 856                         continue;
 857
 858                 /*
 859                  * Also, not relevant if SJ is already done within either input.
 860                  */
 861                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 862                         bms_is_subset(sjinfo->min_righthand, rel1->relids))
 863                         continue;
 864                 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
 865                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
 866                         continue;
 867
 868                 /*
 869                  * If it's a semijoin and we already joined the RHS to any other rels
 870                  * within either input, then we must have unique-ified the RHS at that
 871                  * point (see below).  Therefore the semijoin is no longer relevant in
 872                  * this join path.
 873                  */
 874                 if (sjinfo->jointype == JOIN_SEMI)
 875                 {
 876                         if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
 877                                 !bms_equal(sjinfo->syn_righthand, rel1->relids))
 878                                 continue;
 879                         if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
 880                                 !bms_equal(sjinfo->syn_righthand, rel2->relids))
 881                                 continue;
 882                 }
 883
 884                 /*
 885                  * If one input contains min_lefthand and the other contains
 886                  * min_righthand, then we can perform the SJ at this join.
 887                  *
 888                  * Reject if we get matches to more than one SJ; that implies we're
 889                  * considering something that's not really valid.
 890                  */
 891                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 892                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
 893                 {
 894                         if (match_sjinfo)
 895                                 return false;   /* invalid join path */
 896                         match_sjinfo = sjinfo;
 897                         reversed = false;
 898                 }
 899                 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
 900                                  bms_is_subset(sjinfo->min_righthand, rel1->relids))
 901                 {
 902                         if (match_sjinfo)
 903                                 return false;   /* invalid join path */
 904                         match_sjinfo = sjinfo;
 905                         reversed = true;
 906                 }
 907                 else if (sjinfo->jointype == JOIN_SEMI &&
 908                                  bms_equal(sjinfo->syn_righthand, rel2->relids) &&
 909                                  create_unique_path(root, rel2, rel2->cheapest_total_path,
 910                                                                         sjinfo) != NULL)
 911                 {
 912                         /*----------
 913                          * For a semijoin, we can join the RHS to anything else by
 914                          * unique-ifying the RHS (if the RHS can be unique-ified).
 915                          * We will only get here if we have the full RHS but less
 916                          * than min_lefthand on the LHS.
 917                          *
 918                          * The reason to consider such a join path is exemplified by
 919                          *      SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
 920                          * If we insist on doing this as a semijoin we will first have
 921                          * to form the cartesian product of A*B.  But if we unique-ify
 922                          * C then the semijoin becomes a plain innerjoin and we can join
 923                          * in any order, eg C to A and then to B.  When C is much smaller
 924                          * than A and B this can be a huge win.  So we allow C to be
 925                          * joined to just A or just B here, and then make_join_rel has
 926                          * to handle the case properly.
 927                          *
 928                          * Note that actually we'll allow unique-ified C to be joined to
 929                          * some other relation D here, too.  That is legal, if usually not
 930                          * very sane, and this routine is only concerned with legality not
 931                          * with whether the join is good strategy.
 932                          *----------
 933                          */
 934                         if (match_sjinfo)
 935                                 return false;   /* invalid join path */
 936                         match_sjinfo = sjinfo;
 937                         reversed = false;
 938                         unique_ified = true;
 939                 }
 940                 else if (sjinfo->jointype == JOIN_SEMI &&
 941                                  bms_equal(sjinfo->syn_righthand, rel1->relids) &&
 942                                  create_unique_path(root, rel1, rel1->cheapest_total_path,
 943                                                                         sjinfo) != NULL)
 944                 {
 945                         /* Reversed semijoin case */
 946                         if (match_sjinfo)
 947                                 return false;   /* invalid join path */
 948                         match_sjinfo = sjinfo;
 949                         reversed = true;
 950                         unique_ified = true;
 951                 }
 952                 else
 953                 {
 954                         /*
 955                          * Otherwise, the proposed join overlaps the RHS but isn't a valid
 956                          * implementation of this SJ.  But don't panic quite yet: the RHS
 957                          * violation might have occurred previously, in one or both input
 958                          * relations, in which case we must have previously decided that
 959                          * it was OK to commute some other SJ with this one.  If we need
 960                          * to perform this join to finish building up the RHS, rejecting
 961                          * it could lead to not finding any plan at all.  (This can occur
 962                          * because of the heuristics elsewhere in this file that postpone
 963                          * clauseless joins: we might not consider doing a clauseless join
 964                          * within the RHS until after we've performed other, validly
 965                          * commutable SJs with one or both sides of the clauseless join.)
 966                          * This consideration boils down to the rule that if both inputs
 967                          * overlap the RHS, we can allow the join --- they are either
 968                          * fully within the RHS, or represent previously-allowed joins to
 969                          * rels outside it.
 970                          */
 971                         if (bms_overlap(rel1->relids, sjinfo->min_righthand) &&
 972                                 bms_overlap(rel2->relids, sjinfo->min_righthand))
 973                                 continue;               /* assume valid previous violation of RHS */
 974
 975                         /*
 976                          * The proposed join could still be legal, but only if we're
 977                          * allowed to associate it into the RHS of this SJ.  That means
 978                          * this SJ must be a LEFT join (not SEMI or ANTI, and certainly
 979                          * not FULL) and the proposed join must not overlap the LHS.
 980                          */
 981                         if (sjinfo->jointype != JOIN_LEFT ||
 982                                 bms_overlap(joinrelids, sjinfo->min_lefthand))
 983                                 return false;   /* invalid join path */
 984
 985                         /*
 986                          * To be valid, the proposed join must be a LEFT join; otherwise
 987                          * it can't associate into this SJ's RHS.  But we may not yet have
 988                          * found the SpecialJoinInfo matching the proposed join, so we
 989                          * can't test that yet.  Remember the requirement for later.
 990                          */
 991                         must_be_leftjoin = true;
 992                 }
 993         }
 994
 995         /*
 996          * Fail if violated any SJ's RHS and didn't match to a LEFT SJ: the
 997          * proposed join can't associate into an SJ's RHS.
 998          *
 999          * Also, fail if the proposed join's predicate isn't strict; we're
1000          * essentially checking to see if we can apply outer-join identity 3, and
1001          * that's a requirement.  (This check may be redundant with checks in
1002          * make_outerjoininfo, but I'm not quite sure, and it's cheap to test.)
1003          */
1004         if (must_be_leftjoin &&
1005                 (match_sjinfo == NULL ||
1006                  match_sjinfo->jointype != JOIN_LEFT ||
1007                  !match_sjinfo->lhs_strict))
1008                 return false;                   /* invalid join path */
1009
1010         /*
1011          * We also have to check for constraints imposed by LATERAL references.
1012          */
1013         if (root->hasLateralRTEs)
1014         {
1015                 bool            lateral_fwd;
1016                 bool            lateral_rev;
1017                 Relids          join_lateral_rels;
1018
1019                 /*
1020                  * The proposed rels could each contain lateral references to the
1021                  * other, in which case the join is impossible.  If there are lateral
1022                  * references in just one direction, then the join has to be done with
1023                  * a nestloop with the lateral referencer on the inside.  If the join
1024                  * matches an SJ that cannot be implemented by such a nestloop, the
1025                  * join is impossible.
1026                  *
1027                  * Also, if the lateral reference is only indirect, we should reject
1028                  * the join; whatever rel(s) the reference chain goes through must be
1029                  * joined to first.
1030                  *
1031                  * Another case that might keep us from building a valid plan is the
1032                  * implementation restriction described by have_dangerous_phv().
1033                  */
1034                 lateral_fwd = bms_overlap(rel1->relids, rel2->lateral_relids);
1035                 lateral_rev = bms_overlap(rel2->relids, rel1->lateral_relids);
1036                 if (lateral_fwd && lateral_rev)
1037                         return false;           /* have lateral refs in both directions */
1038                 if (lateral_fwd)
1039                 {
1040                         /* has to be implemented as nestloop with rel1 on left */
1041                         if (match_sjinfo &&
1042                                 (reversed ||
1043                                  unique_ified ||
1044                                  match_sjinfo->jointype == JOIN_FULL))
1045                                 return false;   /* not implementable as nestloop */
1046                         /* check there is a direct reference from rel2 to rel1 */
1047                         if (!bms_overlap(rel1->relids, rel2->direct_lateral_relids))
1048                                 return false;   /* only indirect refs, so reject */
1049                         /* check we won't have a dangerous PHV */
1050                         if (have_dangerous_phv(root, rel1->relids, rel2->lateral_relids))
1051                                 return false;   /* might be unable to handle required PHV */
1052                 }
1053                 else if (lateral_rev)
1054                 {
1055                         /* has to be implemented as nestloop with rel2 on left */
1056                         if (match_sjinfo &&
1057                                 (!reversed ||
1058                                  unique_ified ||
1059                                  match_sjinfo->jointype == JOIN_FULL))
1060                                 return false;   /* not implementable as nestloop */
1061                         /* check there is a direct reference from rel1 to rel2 */
1062                         if (!bms_overlap(rel2->relids, rel1->direct_lateral_relids))
1063                                 return false;   /* only indirect refs, so reject */
1064                         /* check we won't have a dangerous PHV */
1065                         if (have_dangerous_phv(root, rel2->relids, rel1->lateral_relids))
1066                                 return false;   /* might be unable to handle required PHV */
1067                 }
1068
1069                 /*
1070                  * LATERAL references could also cause problems later on if we accept
1071                  * this join: if the join's minimum parameterization includes any rels
1072                  * that would have to be on the inside of an outer join with this join
1073                  * rel, then it's never going to be possible to build the complete
1074                  * query using this join.  We should reject this join not only because
1075                  * it'll save work, but because if we don't, the clauseless-join
1076                  * heuristics might think that legality of this join means that some
1077                  * other join rel need not be formed, and that could lead to failure
1078                  * to find any plan at all.  We have to consider not only rels that
1079                  * are directly on the inner side of an OJ with the joinrel, but also
1080                  * ones that are indirectly so, so search to find all such rels.
1081                  */
1082                 join_lateral_rels = min_join_parameterization(root, joinrelids,
1083                                                                                                           rel1, rel2);
1084                 if (join_lateral_rels)
1085                 {
1086                         Relids          join_plus_rhs = bms_copy(joinrelids);
1087                         bool            more;
1088
1089                         do
1090                         {
1091                                 more = false;
1092                                 foreach(l, root->join_info_list)
1093                                 {
1094                                         SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1095
1096                                         if (bms_overlap(sjinfo->min_lefthand, join_plus_rhs) &&
1097                                                 !bms_is_subset(sjinfo->min_righthand, join_plus_rhs))
1098                                         {
1099                                                 join_plus_rhs = bms_add_members(join_plus_rhs,
1100                                                                                                           sjinfo->min_righthand);
1101                                                 more = true;
1102                                         }
1103                                         /* full joins constrain both sides symmetrically */
1104                                         if (sjinfo->jointype == JOIN_FULL &&
1105                                                 bms_overlap(sjinfo->min_righthand, join_plus_rhs) &&
1106                                                 !bms_is_subset(sjinfo->min_lefthand, join_plus_rhs))
1107                                         {
1108                                                 join_plus_rhs = bms_add_members(join_plus_rhs,
1109                                                                                                                 sjinfo->min_lefthand);
1110                                                 more = true;
1111                                         }
1112                                 }
1113                         } while (more);
1114                         if (bms_overlap(join_plus_rhs, join_lateral_rels))
1115                                 return false;   /* will not be able to join to some RHS rel */
1116                 }
1117         }
1118
1119         /* Otherwise, it's a valid join */
1120         *sjinfo_p = match_sjinfo;
1121         *reversed_p = reversed;
1122         return true;
1123 }
1124
1125 /*
1126  * has_join_restriction
1127  *              Detect whether the specified relation has join-order restrictions,
1128  *              due to being inside an outer join or an IN (sub-SELECT),
1129  *              or participating in any LATERAL references or multi-rel PHVs.
1130  *
1131  * Essentially, this tests whether have_join_order_restriction() could
1132  * succeed with this rel and some other one.  It's OK if we sometimes
1133  * say "true" incorrectly.  (Therefore, we don't bother with the relatively
1134  * expensive has_legal_joinclause test.)
1135  */
1136 static bool
1137 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
1138 {
1139         ListCell   *l;
1140
1141         if (rel->lateral_relids != NULL || rel->lateral_referencers != NULL)
1142                 return true;
1143
1144         foreach(l, root->placeholder_list)
1145         {
1146                 PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
1147
1148                 if (bms_is_subset(rel->relids, phinfo->ph_eval_at) &&
1149                         !bms_equal(rel->relids, phinfo->ph_eval_at))
1150                         return true;
1151         }
1152
1153         foreach(l, root->join_info_list)
1154         {
1155                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1156
1157                 /* ignore full joins --- other mechanisms preserve their ordering */
1158                 if (sjinfo->jointype == JOIN_FULL)
1159                         continue;
1160
1161                 /* ignore if SJ is already contained in rel */
1162                 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
1163                         bms_is_subset(sjinfo->min_righthand, rel->relids))
1164                         continue;
1165
1166                 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
1167                 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
1168                         bms_overlap(sjinfo->min_righthand, rel->relids))
1169                         return true;
1170         }
1171
1172         return false;
1173 }
1174
1175 /*
1176  * is_dummy_rel --- has relation been proven empty?
1177  */
1178 static bool
1179 is_dummy_rel(RelOptInfo *rel)
1180 {
1181         return IS_DUMMY_REL(rel);
1182 }
1183
1184 /*
1185  * Mark a relation as proven empty.
1186  *
1187  * During GEQO planning, this can get invoked more than once on the same
1188  * baserel struct, so it's worth checking to see if the rel is already marked
1189  * dummy.
1190  *
1191  * Also, when called during GEQO join planning, we are in a short-lived
1192  * memory context.  We must make sure that the dummy path attached to a
1193  * baserel survives the GEQO cycle, else the baserel is trashed for future
1194  * GEQO cycles.  On the other hand, when we are marking a joinrel during GEQO,
1195  * we don't want the dummy path to clutter the main planning context.  Upshot
1196  * is that the best solution is to explicitly make the dummy path in the same
1197  * context the given RelOptInfo is in.
1198  */
1199 static void
1200 mark_dummy_rel(RelOptInfo *rel)
1201 {
1202         MemoryContext oldcontext;
1203
1204         /* Already marked? */
1205         if (is_dummy_rel(rel))
1206                 return;
1207
1208         /* No, so choose correct context to make the dummy path in */
1209         oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
1210
1211         /* Set dummy size estimate */
1212         rel->rows = 0;
1213
1214         /* Evict any previously chosen paths */
1215         rel->pathlist = NIL;
1216
1217         /* Set up the dummy path */
1218         add_path(rel, (Path *) create_append_path(rel, NIL, NULL));
1219
1220         /* Set or update cheapest_total_path and related fields */
1221         set_cheapest(rel);
1222
1223         MemoryContextSwitchTo(oldcontext);
1224 }
1225
1226 /*
1227  * restriction_is_constant_false --- is a restrictlist just FALSE?
1228  *
1229  * In cases where a qual is provably constant FALSE, eval_const_expressions
1230  * will generally have thrown away anything that's ANDed with it.  In outer
1231  * join situations this will leave us computing cartesian products only to
1232  * decide there's no match for an outer row, which is pretty stupid.  So,
1233  * we need to detect the case.
1234  *
1235  * If only_pushed_down is TRUE, then consider only pushed-down quals.
1236  */
1237 static bool
1238 restriction_is_constant_false(List *restrictlist, bool only_pushed_down)
1239 {
1240         ListCell   *lc;
1241
1242         /*
1243          * Despite the above comment, the restriction list we see here might
1244          * possibly have other members besides the FALSE constant, since other
1245          * quals could get "pushed down" to the outer join level.  So we check
1246          * each member of the list.
1247          */
1248         foreach(lc, restrictlist)
1249         {
1250                 RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
1251
1252                 Assert(IsA(rinfo, RestrictInfo));
1253                 if (only_pushed_down && !rinfo->is_pushed_down)
1254                         continue;
1255
1256                 if (rinfo->clause && IsA(rinfo->clause, Const))
1257                 {
1258                         Const      *con = (Const *) rinfo->clause;
1259
1260                         /* constant NULL is as good as constant FALSE for our purposes */
1261                         if (con->constisnull)
1262                                 return true;
1263                         if (!DatumGetBool(con->constvalue))
1264                                 return true;
1265                 }
1266         }
1267         return false;
1268 }