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) 1996-2013, 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         /* Select cheapest paths */
 220         set_cheapest(rel);
 221 }
 222
 223 /*
 224  * generate_mergeappend_paths
 225  *              Generate MergeAppend paths for an append relation
 226  *
 227  * Generate a path for each ordering (pathkey list) appearing in
 228  * all_child_pathkeys.
 229  *
 230  * We consider both cheapest-startup and cheapest-total cases, ie, for each
 231  * interesting ordering, collect all the cheapest startup subpaths and all the
 232  * cheapest total paths, and build a MergeAppend path for each case.
 233  *
 234  * We don't currently generate any parameterized MergeAppend paths.  While
 235  * it would not take much more code here to do so, it's very unclear that it
 236  * is worth the planning cycles to investigate such paths: there's little
 237  * use for an ordered path on the inside of a nestloop.  In fact, it's likely
 238  * that the current coding of add_path would reject such paths out of hand,
 239  * because add_path gives no credit for sort ordering of parameterized paths,
 240  * and a parameterized MergeAppend is going to be more expensive than the
 241  * corresponding parameterized Append path.  If we ever try harder to support
 242  * parameterized mergejoin plans, it might be worth adding support for
 243  * parameterized MergeAppends to feed such joins.  (See notes in
 244  * optimizer/README for why that might not ever happen, though.)
 245  */
 246 static void
 247 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
 248                                                    List *live_childrels,
 249                                                    List *all_child_pathkeys)
 250 {
 251         ListCell   *lcp;
 252
 253         foreach(lcp, all_child_pathkeys)
 254         {
 255                 List       *pathkeys = (List *) lfirst(lcp);
 256                 List       *startup_subpaths = NIL;
 257                 List       *total_subpaths = NIL;
 258                 bool            startup_neq_total = false;
 259                 ListCell   *lcr;
 260
 261                 /* Select the child paths for this ordering... */
 262                 foreach(lcr, live_childrels)
 263                 {
 264                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 265                         Path       *cheapest_startup,
 266                                            *cheapest_total;
 267
 268                         /* Locate the right paths, if they are available. */
 269                         cheapest_startup =
 270                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 271                                                                                            pathkeys,
 272                                                                                            NULL,
 273                                                                                            STARTUP_COST);
 274                         cheapest_total =
 275                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 276                                                                                            pathkeys,
 277                                                                                            NULL,
 278                                                                                            TOTAL_COST);
 279
 280                         /*
 281                          * If we can't find any paths with the right order just use the
 282                          * cheapest-total path; we'll have to sort it later.
 283                          */
 284                         if (cheapest_startup == NULL || cheapest_total == NULL)
 285                         {
 286                                 cheapest_startup = cheapest_total =
 287                                         childrel->cheapest_total_path;
 288                                 /* Assert we do have an unparameterized path for this child */
 289                                 Assert(cheapest_total->param_info == NULL);
 290                         }
 291
 292                         /*
 293                          * Notice whether we actually have different paths for the
 294                          * "cheapest" and "total" cases; frequently there will be no point
 295                          * in two create_merge_append_path() calls.
 296                          */
 297                         if (cheapest_startup != cheapest_total)
 298                                 startup_neq_total = true;
 299
 300                         startup_subpaths =
 301                                 accumulate_append_subpath(startup_subpaths, cheapest_startup);
 302                         total_subpaths =
 303                                 accumulate_append_subpath(total_subpaths, cheapest_total);
 304                 }
 305
 306                 /* ... and build the MergeAppend paths */
 307                 add_path(rel, (Path *) create_merge_append_path(root,
 308                                                                                                                 rel,
 309                                                                                                                 startup_subpaths,
 310                                                                                                                 pathkeys,
 311                                                                                                                 NULL));
 312                 if (startup_neq_total)
 313                         add_path(rel, (Path *) create_merge_append_path(root,
 314                                                                                                                         rel,
 315                                                                                                                         total_subpaths,
 316                                                                                                                         pathkeys,
 317                                                                                                                         NULL));
 318         }
 319 }
 320
 321 /*
 322  * get_cheapest_parameterized_child_path
 323  *              Get cheapest path for this relation that has exactly the requested
 324  *              parameterization.
 325  *
 326  * Returns NULL if unable to create such a path.
 327  */
 328 static Path *
 329 get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
 330                                                                           Relids required_outer)
 331 {
 332         Path       *cheapest;
 333         ListCell   *lc;
 334
 335         /*
 336          * Look up the cheapest existing path with no more than the needed
 337          * parameterization.  If it has exactly the needed parameterization, we're
 338          * done.
 339          */
 340         cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
 341                                                                                           NIL,
 342                                                                                           required_outer,
 343                                                                                           TOTAL_COST);
 344         Assert(cheapest != NULL);
 345         if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
 346                 return cheapest;
 347
 348         /*
 349          * Otherwise, we can "reparameterize" an existing path to match the given
 350          * parameterization, which effectively means pushing down additional
 351          * joinquals to be checked within the path's scan.  However, some existing
 352          * paths might check the available joinquals already while others don't;
 353          * therefore, it's not clear which existing path will be cheapest after
 354          * reparameterization.  We have to go through them all and find out.
 355          */
 356         cheapest = NULL;
 357         foreach(lc, rel->pathlist)
 358         {
 359                 Path       *path = (Path *) lfirst(lc);
 360
 361                 /* Can't use it if it needs more than requested parameterization */
 362                 if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
 363                         continue;
 364
 365                 /*
 366                  * Reparameterization can only increase the path's cost, so if it's
 367                  * already more expensive than the current cheapest, forget it.
 368                  */
 369                 if (cheapest != NULL &&
 370                         compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
 371                         continue;
 372
 373                 /* Reparameterize if needed, then recheck cost */
 374                 if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
 375                 {
 376                         path = reparameterize_path(root, path, required_outer, 1.0);
 377                         if (path == NULL)
 378                                 continue;               /* failed to reparameterize this one */
 379                         Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));
 380
 381                         if (cheapest != NULL &&
 382                                 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
 383                                 continue;
 384                 }
 385
 386                 /* We have a new best path */
 387                 cheapest = path;
 388         }
 389
 390         /* Return the best path, or NULL if we found no suitable candidate */
 391         return cheapest;
 392 }
 393
 394 /*
 395  * accumulate_append_subpath
 396  *              Add a subpath to the list being built for an Append or MergeAppend
 397  *
 398  * It's possible that the child is itself an Append or MergeAppend path, in
 399  * which case we can "cut out the middleman" and just add its child paths to
 400  * our own list.  (We don't try to do this earlier because we need to apply
 401  * both levels of transformation to the quals.)
 402  *
 403  * Note that if we omit a child MergeAppend in this way, we are effectively
 404  * omitting a sort step, which seems fine: if the parent is to be an Append,
 405  * its result would be unsorted anyway, while if the parent is to be a
 406  * MergeAppend, there's no point in a separate sort on a child.
 407  */
 408 static List *
 409 accumulate_append_subpath(List *subpaths, Path *path)
 410 {
 411         if (IsA(path, AppendPath))
 412         {
 413                 AppendPath *apath = (AppendPath *) path;
 414
 415                 /* list_copy is important here to avoid sharing list substructure */
 416                 return list_concat(subpaths, list_copy(apath->subpaths));
 417         }
 418         else if (IsA(path, MergeAppendPath))
 419         {
 420                 MergeAppendPath *mpath = (MergeAppendPath *) path;
 421
 422                 /* list_copy is important here to avoid sharing list substructure */
 423                 return list_concat(subpaths, list_copy(mpath->subpaths));
 424         }
 425         else
 426                 return lappend(subpaths, path);
 427 }
 428
 429 /*
 430  * standard_join_search
 431  *        Find possible joinpaths for a query by successively finding ways
 432  *        to join component relations into join relations.
 433  *
 434  * 'levels_needed' is the number of iterations needed, ie, the number of
 435  *              independent jointree items in the query.  This is > 1.
 436  *
 437  * 'initial_rels' is a list of RelOptInfo nodes for each independent
 438  *              jointree item.  These are the components to be joined together.
 439  *              Note that levels_needed == list_length(initial_rels).
 440  *
 441  * Returns the final level of join relations, i.e., the relation that is
 442  * the result of joining all the original relations together.
 443  * At least one implementation path must be provided for this relation and
 444  * all required sub-relations.
 445  *
 446  * To support loadable plugins that modify planner behavior by changing the
 447  * join searching algorithm, we provide a hook variable that lets a plugin
 448  * replace or supplement this function.  Any such hook must return the same
 449  * final join relation as the standard code would, but it might have a
 450  * different set of implementation paths attached, and only the sub-joinrels
 451  * needed for these paths need have been instantiated.
 452  *
 453  * Note to plugin authors: the functions invoked during standard_join_search()
 454  * modify root->join_rel_list and root->join_rel_hash.  If you want to do more
 455  * than one join-order search, you'll probably need to save and restore the
 456  * original states of those data structures.  See geqo_eval() for an example.
 457  */
 458 RelOptInfo *
 459 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
 460 {
 461         int                     lev;
 462         RelOptInfo *rel;
 463
 464         /*
 465          * This function cannot be invoked recursively within any one planning
 466          * problem, so join_rel_level[] can't be in use already.
 467          */
 468         Assert(root->join_rel_level == NULL);
 469
 470         /*
 471          * We employ a simple "dynamic programming" algorithm: we first find all
 472          * ways to build joins of two jointree items, then all ways to build joins
 473          * of three items (from two-item joins and single items), then four-item
 474          * joins, and so on until we have considered all ways to join all the
 475          * items into one rel.
 476          *
 477          * root->join_rel_level[j] is a list of all the j-item rels.  Initially we
 478          * set root->join_rel_level[1] to represent all the single-jointree-item
 479          * relations.
 480          */
 481         root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
 482
 483         root->join_rel_level[1] = initial_rels;
 484
 485         for (lev = 2; lev <= levels_needed; lev++)
 486         {
 487                 ListCell   *lc;
 488
 489                 /*
 490                  * Determine all possible pairs of relations to be joined at this
 491                  * level, and build paths for making each one from every available
 492                  * pair of lower-level relations.
 493                  */
 494                 join_search_one_level(root, lev);
 495
 496                 /*
 497                  * Do cleanup work on each just-processed rel.
 498                  */
 499                 foreach(lc, root->join_rel_level[lev])
 500                 {
 501                         rel = (RelOptInfo *) lfirst(lc);
 502
 503                         /* Find and save the cheapest paths for this rel */
 504                         set_cheapest(rel);
 505
 506 #ifdef OPTIMIZER_DEBUG
 507                         debug_print_rel(root, rel);
 508 #endif
 509                 }
 510         }
 511
 512         /*
 513          * We should have a single rel at the final level.
 514          */
 515         if (root->join_rel_level[levels_needed] == NIL)
 516                 elog(ERROR, "failed to build any %d-way joins", levels_needed);
 517         Assert(list_length(root->join_rel_level[levels_needed]) == 1);
 518
 519         rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
 520
 521         root->join_rel_level = NULL;
 522
 523         return rel;
 524 }
 525
 526 /*
 527  * join_search_one_level
 528  *        Consider ways to produce join relations containing exactly 'level'
 529  *        jointree items.  (This is one step of the dynamic-programming method
 530  *        embodied in standard_join_search.)  Join rel nodes for each feasible
 531  *        combination of lower-level rels are created and returned in a list.
 532  *        Implementation paths are created for each such joinrel, too.
 533  *
 534  * level: level of rels we want to make this time
 535  * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
 536  *
 537  * The result is returned in root->join_rel_level[level].
 538  */
 539 void
 540 join_search_one_level(PlannerInfo *root, int level)
 541 {
 542         List      **joinrels = root->join_rel_level;
 543         ListCell   *r;
 544         int                     k;
 545
 546         Assert(joinrels[level] == NIL);
 547
 548         /* Set join_cur_level so that new joinrels are added to proper list */
 549         root->join_cur_level = level;
 550
 551         /*
 552          * First, consider left-sided and right-sided plans, in which rels of
 553          * exactly level-1 member relations are joined against initial relations.
 554          * We prefer to join using join clauses, but if we find a rel of level-1
 555          * members that has no join clauses, we will generate Cartesian-product
 556          * joins against all initial rels not already contained in it.
 557          */
 558         foreach(r, joinrels[level - 1])
 559         {
 560                 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 561
 562                 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
 563                         has_join_restriction(root, old_rel))
 564                 {
 565                         /*
 566                          * There are join clauses or join order restrictions relevant to
 567                          * this rel, so consider joins between this rel and (only) those
 568                          * initial rels it is linked to by a clause or restriction.
 569                          *
 570                          * At level 2 this condition is symmetric, so there is no need to
 571                          * look at initial rels before this one in the list; we already
 572                          * considered such joins when we were at the earlier rel.  (The
 573                          * mirror-image joins are handled automatically by make_join_rel.)
 574                          * In later passes (level > 2), we join rels of the previous level
 575                          * to each initial rel they don't already include but have a join
 576                          * clause or restriction with.
 577                          */
 578                         ListCell   *other_rels;
 579
 580                         if (level == 2)         /* consider remaining initial rels */
 581                                 other_rels = lnext(r);
 582                         else    /* consider all initial rels */
 583                                 other_rels = list_head(joinrels[1]);
 584
 585                         make_rels_by_clause_joins(root,
 586                                                                           old_rel,
 587                                                                           other_rels);
 588                 }
 589                 else
 590                 {
 591                         /*
 592                          * Oops, we have a relation that is not joined to any other
 593                          * relation, either directly or by join-order restrictions.
 594                          * Cartesian product time.
 595                          *
 596                          * We consider a cartesian product with each not-already-included
 597                          * initial rel, whether it has other join clauses or not.  At
 598                          * level 2, if there are two or more clauseless initial rels, we
 599                          * will redundantly consider joining them in both directions; but
 600                          * such cases aren't common enough to justify adding complexity to
 601                          * avoid the duplicated effort.
 602                          */
 603                         make_rels_by_clauseless_joins(root,
 604                                                                                   old_rel,
 605                                                                                   list_head(joinrels[1]));
 606                 }
 607         }
 608
 609         /*
 610          * Now, consider "bushy plans" in which relations of k initial rels are
 611          * joined to relations of level-k initial rels, for 2 <= k <= level-2.
 612          *
 613          * We only consider bushy-plan joins for pairs of rels where there is a
 614          * suitable join clause (or join order restriction), in order to avoid
 615          * unreasonable growth of planning time.
 616          */
 617         for (k = 2;; k++)
 618         {
 619                 int                     other_level = level - k;
 620
 621                 /*
 622                  * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
 623                  * need to go as far as the halfway point.
 624                  */
 625                 if (k > other_level)
 626                         break;
 627
 628                 foreach(r, joinrels[k])
 629                 {
 630                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 631                         ListCell   *other_rels;
 632                         ListCell   *r2;
 633
 634                         /*
 635                          * We can ignore relations without join clauses here, unless they
 636                          * participate in join-order restrictions --- then we might have
 637                          * to force a bushy join plan.
 638                          */
 639                         if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
 640                                 !has_join_restriction(root, old_rel))
 641                                 continue;
 642
 643                         if (k == other_level)
 644                                 other_rels = lnext(r);  /* only consider remaining rels */
 645                         else
 646                                 other_rels = list_head(joinrels[other_level]);
 647
 648                         for_each_cell(r2, other_rels)
 649                         {
 650                                 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
 651
 652                                 if (!bms_overlap(old_rel->relids, new_rel->relids))
 653                                 {
 654                                         /*
 655                                          * OK, we can build a rel of the right level from this
 656                                          * pair of rels.  Do so if there is at least one relevant
 657                                          * join clause or join order restriction.
 658                                          */
 659                                         if (have_relevant_joinclause(root, old_rel, new_rel) ||
 660                                                 have_join_order_restriction(root, old_rel, new_rel))
 661                                         {
 662                                                 (void) make_join_rel(root, old_rel, new_rel);
 663                                         }
 664                                 }
 665                         }
 666                 }
 667         }
 668
 669         /*----------
 670          * Last-ditch effort: if we failed to find any usable joins so far, force
 671          * a set of cartesian-product joins to be generated.  This handles the
 672          * special case where all the available rels have join clauses but we
 673          * cannot use any of those clauses yet.  This can only happen when we are
 674          * considering a join sub-problem (a sub-joinlist) and all the rels in the
 675          * sub-problem have only join clauses with rels outside the sub-problem.
 676          * An example is
 677          *
 678          *              SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
 679          *              WHERE a.w = c.x and b.y = d.z;
 680          *
 681          * If the "a INNER JOIN b" sub-problem does not get flattened into the
 682          * upper level, we must be willing to make a cartesian join of a and b;
 683          * but the code above will not have done so, because it thought that both
 684          * a and b have joinclauses.  We consider only left-sided and right-sided
 685          * cartesian joins in this case (no bushy).
 686          *----------
 687          */
 688         if (joinrels[level] == NIL)
 689         {
 690                 /*
 691                  * This loop is just like the first one, except we always call
 692                  * make_rels_by_clauseless_joins().
 693                  */
 694                 foreach(r, joinrels[level - 1])
 695                 {
 696                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 697
 698                         make_rels_by_clauseless_joins(root,
 699                                                                                   old_rel,
 700                                                                                   list_head(joinrels[1]));
 701                 }
 702
 703                 /*----------
 704                  * When special joins are involved, there may be no legal way
 705                  * to make an N-way join for some values of N.  For example consider
 706                  *
 707                  * SELECT ... FROM t1 WHERE
 708                  *       x IN (SELECT ... FROM t2,t3 WHERE ...) AND
 709                  *       y IN (SELECT ... FROM t4,t5 WHERE ...)
 710                  *
 711                  * We will flatten this query to a 5-way join problem, but there are
 712                  * no 4-way joins that join_is_legal() will consider legal.  We have
 713                  * to accept failure at level 4 and go on to discover a workable
 714                  * bushy plan at level 5.
 715                  *
 716                  * However, if there are no special joins and no lateral references
 717                  * then join_is_legal() should never fail, and so the following sanity
 718                  * check is useful.
 719                  *----------
 720                  */
 721                 if (joinrels[level] == NIL &&
 722                         root->join_info_list == NIL &&
 723                         root->lateral_info_list == NIL)
 724                         elog(ERROR, "failed to build any %d-way joins", level);
 725         }
 726 }
 727
 728 /*
 729  * make_rels_by_clause_joins
 730  *        Build joins between the given relation 'old_rel' and other relations
 731  *        that participate in join clauses that 'old_rel' also participates in
 732  *        (or participate in join-order restrictions with it).
 733  *        The join rels are returned in root->join_rel_level[join_cur_level].
 734  *
 735  * Note: at levels above 2 we will generate the same joined relation in
 736  * multiple ways --- for example (a join b) join c is the same RelOptInfo as
 737  * (b join c) join a, though the second case will add a different set of Paths
 738  * to it.  This is the reason for using the join_rel_level mechanism, which
 739  * automatically ensures that each new joinrel is only added to the list once.
 740  *
 741  * 'old_rel' is the relation entry for the relation to be joined
 742  * 'other_rels': the first cell in a linked list containing the other
 743  * rels to be considered for joining
 744  *
 745  * Currently, this is only used with initial rels in other_rels, but it
 746  * will work for joining to joinrels too.
 747  */
 748 static void
 749 make_rels_by_clause_joins(PlannerInfo *root,
 750                                                   RelOptInfo *old_rel,
 751                                                   ListCell *other_rels)
 752 {
 753         ListCell   *l;
 754
 755         for_each_cell(l, other_rels)
 756         {
 757                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 758
 759                 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
 760                         (have_relevant_joinclause(root, old_rel, other_rel) ||
 761                          have_join_order_restriction(root, old_rel, other_rel)))
 762                 {
 763                         (void) make_join_rel(root, old_rel, other_rel);
 764                 }
 765         }
 766 }
 767
 768 /*
 769  * make_rels_by_clauseless_joins
 770  *        Given a relation 'old_rel' and a list of other relations
 771  *        'other_rels', create a join relation between 'old_rel' and each
 772  *        member of 'other_rels' that isn't already included in 'old_rel'.
 773  *        The join rels are returned in root->join_rel_level[join_cur_level].
 774  *
 775  * 'old_rel' is the relation entry for the relation to be joined
 776  * 'other_rels': the first cell of a linked list containing the
 777  * other rels to be considered for joining
 778  *
 779  * Currently, this is only used with initial rels in other_rels, but it would
 780  * work for joining to joinrels too.
 781  */
 782 static void
 783 make_rels_by_clauseless_joins(PlannerInfo *root,
 784                                                           RelOptInfo *old_rel,
 785                                                           ListCell *other_rels)
 786 {
 787         ListCell   *l;
 788
 789         for_each_cell(l, other_rels)
 790         {
 791                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 792
 793                 if (!bms_overlap(other_rel->relids, old_rel->relids))
 794                 {
 795                         (void) make_join_rel(root, old_rel, other_rel);
 796                 }
 797         }
 798 }
 799
 800 /*
 801  * join_is_legal
 802  *         Determine whether a proposed join is legal given the query's
 803  *         join order constraints; and if it is, determine the join type.
 804  *
 805  * Caller must supply not only the two rels, but the union of their relids.
 806  * (We could simplify the API by computing joinrelids locally, but this
 807  * would be redundant work in the normal path through make_join_rel.)
 808  *
 809  * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
 810  * else it's set to point to the associated SpecialJoinInfo node.  Also,
 811  * *reversed_p is set TRUE if the given relations need to be swapped to
 812  * match the SpecialJoinInfo node.
 813  */
 814 static bool
 815 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 816                           Relids joinrelids,
 817                           SpecialJoinInfo **sjinfo_p, bool *reversed_p)
 818 {
 819         SpecialJoinInfo *match_sjinfo;
 820         bool            reversed;
 821         bool            unique_ified;
 822         bool            must_be_leftjoin;
 823         ListCell   *l;
 824
 825         /*
 826          * Ensure output params are set on failure return.  This is just to
 827          * suppress uninitialized-variable warnings from overly anal compilers.
 828          */
 829         *sjinfo_p = NULL;
 830         *reversed_p = false;
 831
 832         /*
 833          * If we have any special joins, the proposed join might be illegal; and
 834          * in any case we have to determine its join type.  Scan the join info
 835          * list for matches and conflicts.
 836          */
 837         match_sjinfo = NULL;
 838         reversed = false;
 839         unique_ified = false;
 840         must_be_leftjoin = false;
 841
 842         foreach(l, root->join_info_list)
 843         {
 844                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
 845
 846                 /*
 847                  * This special join is not relevant unless its RHS overlaps the
 848                  * proposed join.  (Check this first as a fast path for dismissing
 849                  * most irrelevant SJs quickly.)
 850                  */
 851                 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
 852                         continue;
 853
 854                 /*
 855                  * Also, not relevant if proposed join is fully contained within RHS
 856                  * (ie, we're still building up the RHS).
 857                  */
 858                 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
 859                         continue;
 860
 861                 /*
 862                  * Also, not relevant if SJ is already done within either input.
 863                  */
 864                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 865                         bms_is_subset(sjinfo->min_righthand, rel1->relids))
 866                         continue;
 867                 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
 868                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
 869                         continue;
 870
 871                 /*
 872                  * If it's a semijoin and we already joined the RHS to any other rels
 873                  * within either input, then we must have unique-ified the RHS at that
 874                  * point (see below).  Therefore the semijoin is no longer relevant in
 875                  * this join path.
 876                  */
 877                 if (sjinfo->jointype == JOIN_SEMI)
 878                 {
 879                         if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
 880                                 !bms_equal(sjinfo->syn_righthand, rel1->relids))
 881                                 continue;
 882                         if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
 883                                 !bms_equal(sjinfo->syn_righthand, rel2->relids))
 884                                 continue;
 885                 }
 886
 887                 /*
 888                  * If one input contains min_lefthand and the other contains
 889                  * min_righthand, then we can perform the SJ at this join.
 890                  *
 891                  * Reject if we get matches to more than one SJ; that implies we're
 892                  * considering something that's not really valid.
 893                  */
 894                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 895                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
 896                 {
 897                         if (match_sjinfo)
 898                                 return false;   /* invalid join path */
 899                         match_sjinfo = sjinfo;
 900                         reversed = false;
 901                 }
 902                 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
 903                                  bms_is_subset(sjinfo->min_righthand, rel1->relids))
 904                 {
 905                         if (match_sjinfo)
 906                                 return false;   /* invalid join path */
 907                         match_sjinfo = sjinfo;
 908                         reversed = true;
 909                 }
 910                 else if (sjinfo->jointype == JOIN_SEMI &&
 911                                  bms_equal(sjinfo->syn_righthand, rel2->relids) &&
 912                                  create_unique_path(root, rel2, rel2->cheapest_total_path,
 913                                                                         sjinfo) != NULL)
 914                 {
 915                         /*----------
 916                          * For a semijoin, we can join the RHS to anything else by
 917                          * unique-ifying the RHS (if the RHS can be unique-ified).
 918                          * We will only get here if we have the full RHS but less
 919                          * than min_lefthand on the LHS.
 920                          *
 921                          * The reason to consider such a join path is exemplified by
 922                          *      SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
 923                          * If we insist on doing this as a semijoin we will first have
 924                          * to form the cartesian product of A*B.  But if we unique-ify
 925                          * C then the semijoin becomes a plain innerjoin and we can join
 926                          * in any order, eg C to A and then to B.  When C is much smaller
 927                          * than A and B this can be a huge win.  So we allow C to be
 928                          * joined to just A or just B here, and then make_join_rel has
 929                          * to handle the case properly.
 930                          *
 931                          * Note that actually we'll allow unique-ified C to be joined to
 932                          * some other relation D here, too.  That is legal, if usually not
 933                          * very sane, and this routine is only concerned with legality not
 934                          * with whether the join is good strategy.
 935                          *----------
 936                          */
 937                         if (match_sjinfo)
 938                                 return false;   /* invalid join path */
 939                         match_sjinfo = sjinfo;
 940                         reversed = false;
 941                         unique_ified = true;
 942                 }
 943                 else if (sjinfo->jointype == JOIN_SEMI &&
 944                                  bms_equal(sjinfo->syn_righthand, rel1->relids) &&
 945                                  create_unique_path(root, rel1, rel1->cheapest_total_path,
 946                                                                         sjinfo) != NULL)
 947                 {
 948                         /* Reversed semijoin case */
 949                         if (match_sjinfo)
 950                                 return false;   /* invalid join path */
 951                         match_sjinfo = sjinfo;
 952                         reversed = true;
 953                         unique_ified = true;
 954                 }
 955                 else
 956                 {
 957                         /*
 958                          * Otherwise, the proposed join overlaps the RHS but isn't a valid
 959                          * implementation of this SJ.  But don't panic quite yet: the RHS
 960                          * violation might have occurred previously, in one or both input
 961                          * relations, in which case we must have previously decided that
 962                          * it was OK to commute some other SJ with this one.  If we need
 963                          * to perform this join to finish building up the RHS, rejecting
 964                          * it could lead to not finding any plan at all.  (This can occur
 965                          * because of the heuristics elsewhere in this file that postpone
 966                          * clauseless joins: we might not consider doing a clauseless join
 967                          * within the RHS until after we've performed other, validly
 968                          * commutable SJs with one or both sides of the clauseless join.)
 969                          * This consideration boils down to the rule that if both inputs
 970                          * overlap the RHS, we can allow the join --- they are either
 971                          * fully within the RHS, or represent previously-allowed joins to
 972                          * rels outside it.
 973                          */
 974                         if (bms_overlap(rel1->relids, sjinfo->min_righthand) &&
 975                                 bms_overlap(rel2->relids, sjinfo->min_righthand))
 976                                 continue;               /* assume valid previous violation of RHS */
 977
 978                         /*
 979                          * The proposed join could still be legal, but only if we're
 980                          * allowed to associate it into the RHS of this SJ.  That means
 981                          * this SJ must be a LEFT join (not SEMI or ANTI, and certainly
 982                          * not FULL) and the proposed join must not overlap the LHS.
 983                          */
 984                         if (sjinfo->jointype != JOIN_LEFT ||
 985                                 bms_overlap(joinrelids, sjinfo->min_lefthand))
 986                                 return false;   /* invalid join path */
 987
 988                         /*
 989                          * To be valid, the proposed join must be a LEFT join; otherwise
 990                          * it can't associate into this SJ's RHS.  But we may not yet have
 991                          * found the SpecialJoinInfo matching the proposed join, so we
 992                          * can't test that yet.  Remember the requirement for later.
 993                          */
 994                         must_be_leftjoin = true;
 995                 }
 996         }
 997
 998         /*
 999          * Fail if violated any SJ's RHS and didn't match to a LEFT SJ: the
1000          * proposed join can't associate into an SJ's RHS.
1001          *
1002          * Also, fail if the proposed join's predicate isn't strict; we're
1003          * essentially checking to see if we can apply outer-join identity 3, and
1004          * that's a requirement.  (This check may be redundant with checks in
1005          * make_outerjoininfo, but I'm not quite sure, and it's cheap to test.)
1006          */
1007         if (must_be_leftjoin &&
1008                 (match_sjinfo == NULL ||
1009                  match_sjinfo->jointype != JOIN_LEFT ||
1010                  !match_sjinfo->lhs_strict))
1011                 return false;                   /* invalid join path */
1012
1013         /*
1014          * We also have to check for constraints imposed by LATERAL references.
1015          */
1016         if (root->hasLateralRTEs)
1017         {
1018                 bool            lateral_fwd;
1019                 bool            lateral_rev;
1020                 Relids          join_lateral_rels;
1021
1022                 /*
1023                  * The proposed rels could each contain lateral references to the
1024                  * other, in which case the join is impossible.  If there are lateral
1025                  * references in just one direction, then the join has to be done with
1026                  * a nestloop with the lateral referencer on the inside.  If the join
1027                  * matches an SJ that cannot be implemented by such a nestloop, the
1028                  * join is impossible.
1029                  *
1030                  * Also, if the lateral reference is only indirect, we should reject
1031                  * the join; whatever rel(s) the reference chain goes through must be
1032                  * joined to first.
1033                  *
1034                  * Another case that might keep us from building a valid plan is the
1035                  * implementation restriction described by have_dangerous_phv().
1036                  */
1037                 lateral_fwd = bms_overlap(rel1->relids, rel2->lateral_relids);
1038                 lateral_rev = bms_overlap(rel2->relids, rel1->lateral_relids);
1039                 if (lateral_fwd && lateral_rev)
1040                         return false;           /* have lateral refs in both directions */
1041                 if (lateral_fwd)
1042                 {
1043                         /* has to be implemented as nestloop with rel1 on left */
1044                         if (match_sjinfo &&
1045                                 (reversed ||
1046                                  unique_ified ||
1047                                  match_sjinfo->jointype == JOIN_FULL))
1048                                 return false;   /* not implementable as nestloop */
1049                         /* check there is a direct reference from rel2 to rel1 */
1050                         foreach(l, root->lateral_info_list)
1051                         {
1052                                 LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
1053
1054                                 if (bms_is_subset(ljinfo->lateral_rhs, rel2->relids) &&
1055                                         bms_is_subset(ljinfo->lateral_lhs, rel1->relids))
1056                                         break;
1057                         }
1058                         if (l == NULL)
1059                                 return false;   /* only indirect refs, so reject */
1060                         /* check we won't have a dangerous PHV */
1061                         if (have_dangerous_phv(root, rel1->relids, rel2->lateral_relids))
1062                                 return false;   /* might be unable to handle required PHV */
1063                 }
1064                 else if (lateral_rev)
1065                 {
1066                         /* has to be implemented as nestloop with rel2 on left */
1067                         if (match_sjinfo &&
1068                                 (!reversed ||
1069                                  unique_ified ||
1070                                  match_sjinfo->jointype == JOIN_FULL))
1071                                 return false;   /* not implementable as nestloop */
1072                         /* check there is a direct reference from rel1 to rel2 */
1073                         foreach(l, root->lateral_info_list)
1074                         {
1075                                 LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
1076
1077                                 if (bms_is_subset(ljinfo->lateral_rhs, rel1->relids) &&
1078                                         bms_is_subset(ljinfo->lateral_lhs, rel2->relids))
1079                                         break;
1080                         }
1081                         if (l == NULL)
1082                                 return false;   /* only indirect refs, so reject */
1083                         /* check we won't have a dangerous PHV */
1084                         if (have_dangerous_phv(root, rel2->relids, rel1->lateral_relids))
1085                                 return false;   /* might be unable to handle required PHV */
1086                 }
1087
1088                 /*
1089                  * LATERAL references could also cause problems later on if we accept
1090                  * this join: if the join's minimum parameterization includes any rels
1091                  * that would have to be on the inside of an outer join with this join
1092                  * rel, then it's never going to be possible to build the complete
1093                  * query using this join.  We should reject this join not only because
1094                  * it'll save work, but because if we don't, the clauseless-join
1095                  * heuristics might think that legality of this join means that some
1096                  * other join rel need not be formed, and that could lead to failure
1097                  * to find any plan at all.  We have to consider not only rels that
1098                  * are directly on the inner side of an OJ with the joinrel, but also
1099                  * ones that are indirectly so, so search to find all such rels.
1100                  */
1101                 join_lateral_rels = min_join_parameterization(root, joinrelids,
1102                                                                                                           rel1, rel2);
1103                 if (join_lateral_rels)
1104                 {
1105                         Relids          join_plus_rhs = bms_copy(joinrelids);
1106                         bool            more;
1107
1108                         do
1109                         {
1110                                 more = false;
1111                                 foreach(l, root->join_info_list)
1112                                 {
1113                                         SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1114
1115                                         if (bms_overlap(sjinfo->min_lefthand, join_plus_rhs) &&
1116                                                 !bms_is_subset(sjinfo->min_righthand, join_plus_rhs))
1117                                         {
1118                                                 join_plus_rhs = bms_add_members(join_plus_rhs,
1119                                                                                                           sjinfo->min_righthand);
1120                                                 more = true;
1121                                         }
1122                                         /* full joins constrain both sides symmetrically */
1123                                         if (sjinfo->jointype == JOIN_FULL &&
1124                                                 bms_overlap(sjinfo->min_righthand, join_plus_rhs) &&
1125                                                 !bms_is_subset(sjinfo->min_lefthand, join_plus_rhs))
1126                                         {
1127                                                 join_plus_rhs = bms_add_members(join_plus_rhs,
1128                                                                                                                 sjinfo->min_lefthand);
1129                                                 more = true;
1130                                         }
1131                                 }
1132                         } while (more);
1133                         if (bms_overlap(join_plus_rhs, join_lateral_rels))
1134                                 return false;   /* will not be able to join to some RHS rel */
1135                 }
1136         }
1137
1138         /* Otherwise, it's a valid join */
1139         *sjinfo_p = match_sjinfo;
1140         *reversed_p = reversed;
1141         return true;
1142 }
1143
1144 /*
1145  * has_join_restriction
1146  *              Detect whether the specified relation has join-order restrictions,
1147  *              due to being inside an outer join or an IN (sub-SELECT),
1148  *              or participating in any LATERAL references or multi-rel PHVs.
1149  *
1150  * Essentially, this tests whether have_join_order_restriction() could
1151  * succeed with this rel and some other one.  It's OK if we sometimes
1152  * say "true" incorrectly.  (Therefore, we don't bother with the relatively
1153  * expensive has_legal_joinclause test.)
1154  */
1155 static bool
1156 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
1157 {
1158         ListCell   *l;
1159
1160         if (rel->lateral_relids != NULL || rel->lateral_referencers != NULL)
1161                 return true;
1162
1163         foreach(l, root->placeholder_list)
1164         {
1165                 PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
1166
1167                 if (bms_is_subset(rel->relids, phinfo->ph_eval_at) &&
1168                         !bms_equal(rel->relids, phinfo->ph_eval_at))
1169                         return true;
1170         }
1171
1172         foreach(l, root->join_info_list)
1173         {
1174                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1175
1176                 /* ignore full joins --- other mechanisms preserve their ordering */
1177                 if (sjinfo->jointype == JOIN_FULL)
1178                         continue;
1179
1180                 /* ignore if SJ is already contained in rel */
1181                 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
1182                         bms_is_subset(sjinfo->min_righthand, rel->relids))
1183                         continue;
1184
1185                 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
1186                 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
1187                         bms_overlap(sjinfo->min_righthand, rel->relids))
1188                         return true;
1189         }
1190
1191         return false;
1192 }
1193
1194 /*
1195  * is_dummy_rel --- has relation been proven empty?
1196  */
1197 static bool
1198 is_dummy_rel(RelOptInfo *rel)
1199 {
1200         return IS_DUMMY_REL(rel);
1201 }
1202
1203 /*
1204  * Mark a relation as proven empty.
1205  *
1206  * During GEQO planning, this can get invoked more than once on the same
1207  * baserel struct, so it's worth checking to see if the rel is already marked
1208  * dummy.
1209  *
1210  * Also, when called during GEQO join planning, we are in a short-lived
1211  * memory context.  We must make sure that the dummy path attached to a
1212  * baserel survives the GEQO cycle, else the baserel is trashed for future
1213  * GEQO cycles.  On the other hand, when we are marking a joinrel during GEQO,
1214  * we don't want the dummy path to clutter the main planning context.  Upshot
1215  * is that the best solution is to explicitly make the dummy path in the same
1216  * context the given RelOptInfo is in.
1217  */
1218 static void
1219 mark_dummy_rel(RelOptInfo *rel)
1220 {
1221         MemoryContext oldcontext;
1222
1223         /* Already marked? */
1224         if (is_dummy_rel(rel))
1225                 return;
1226
1227         /* No, so choose correct context to make the dummy path in */
1228         oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
1229
1230         /* Set dummy size estimate */
1231         rel->rows = 0;
1232
1233         /* Evict any previously chosen paths */
1234         rel->pathlist = NIL;
1235
1236         /* Set up the dummy path */
1237         add_path(rel, (Path *) create_append_path(rel, NIL, NULL));
1238
1239         /* Set or update cheapest_total_path and related fields */
1240         set_cheapest(rel);
1241
1242         MemoryContextSwitchTo(oldcontext);
1243 }
1244
1245 /*
1246  * restriction_is_constant_false --- is a restrictlist just false?
1247  *
1248  * In cases where a qual is provably constant false, eval_const_expressions
1249  * will generally have thrown away anything that's ANDed with it.  In outer
1250  * join situations this will leave us computing cartesian products only to
1251  * decide there's no match for an outer row, which is pretty stupid.  So,
1252  * we need to detect the case.
1253  *
1254  * If only_pushed_down is true, then consider only quals that are pushed-down
1255  * from the point of view of the joinrel.
1256  */
1257 static bool
1258 restriction_is_constant_false(List *restrictlist,
1259                                                           RelOptInfo *joinrel,
1260                                                           bool only_pushed_down)
1261 {
1262         ListCell   *lc;
1263
1264         /*
1265          * Despite the above comment, the restriction list we see here might
1266          * possibly have other members besides the FALSE constant, since other
1267          * quals could get "pushed down" to the outer join level.  So we check
1268          * each member of the list.
1269          */
1270         foreach(lc, restrictlist)
1271         {
1272                 RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
1273
1274                 Assert(IsA(rinfo, RestrictInfo));
1275                 if (only_pushed_down && !RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
1276                         continue;
1277
1278                 if (rinfo->clause && IsA(rinfo->clause, Const))
1279                 {
1280                         Const      *con = (Const *) rinfo->clause;
1281
1282                         /* constant NULL is as good as constant FALSE for our purposes */
1283                         if (con->constisnull)
1284                                 return true;
1285                         if (!DatumGetBool(con->constvalue))
1286                                 return true;
1287                 }
1288         }
1289         return false;
1290 }