core.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * core.c
   4  *        Routines copied from PostgreSQL core distribution.
   5  *
   6
   7  * The main purpose of this files is having access to static functions in core.
   8  * Another purpose is tweaking functions behavior by replacing part of them by
   9  * macro definitions. See at the end of pg_hint_plan.c for details. Anyway,
  10  * this file *must* contain required functions without making any change.
  11  *
  12  * This file contains the following functions from corresponding files.
  13  *
  14  * src/backend/optimizer/path/allpaths.c
  15  *
  16  *      static functions:
  17  *         set_plain_rel_pathlist()
  18  *     set_append_rel_pathlist()
  19  *     generate_mergeappend_paths()
  20  *     get_cheapest_parameterized_child_path()
  21  *     accumulate_append_subpath()
  22  *
  23  *  public functions:
  24  *     standard_join_search(): This funcion is not static. The reason for
  25  *        including this function is make_rels_by_clause_joins. In order to
  26  *        avoid generating apparently unwanted join combination, we decided to
  27  *        change the behavior of make_join_rel, which is called under this
  28  *        function.
  29  *
  30  * src/backend/optimizer/path/joinrels.c
  31  *
  32  *      public functions:
  33  *     join_search_one_level(): We have to modify this to call my definition of
  34  *                  make_rels_by_clause_joins.
  35  *
  36  *      static functions:
  37  *     make_rels_by_clause_joins()
  38  *     make_rels_by_clauseless_joins()
  39  *     join_is_legal()
  40  *     has_join_restriction()
  41  *     is_dummy_rel()
  42  *     mark_dummy_rel()
  43  *     restriction_is_constant_false()
  44  *
  45  *
  46  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
  47  * Portions Copyright (c) 1994, Regents of the University of California
  48  *
  49  *-------------------------------------------------------------------------
  50  */
  51
  52
  53 /*
  54  * set_plain_rel_pathlist
  55  *        Build access paths for a plain relation (no subquery, no inheritance)
  56  */
  57 static void
  58 set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
  59 {
  60         Relids          required_outer;
  61
  62         /*
  63          * We don't support pushing join clauses into the quals of a seqscan, but
  64          * it could still have required parameterization due to LATERAL refs in
  65          * its tlist.
  66          */
  67         required_outer = rel->lateral_relids;
  68
  69         /* Consider sequential scan */
  70         add_path(rel, create_seqscan_path(root, rel, required_outer, 0));
  71
  72         /* If appropriate, consider parallel sequential scan */
  73         if (rel->consider_parallel && required_outer == NULL)
  74                 create_plain_partial_paths(root, rel);
  75
  76         /* Consider index scans */
  77         create_index_paths(root, rel);
  78
  79         /* Consider TID scans */
  80         create_tidscan_paths(root, rel);
  81 }
  82
  83 /*
  84  * set_append_rel_pathlist
  85  *        Build access paths for an "append relation"
  86  */
  87 static void
  88 set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
  89                                                 Index rti, RangeTblEntry *rte)
  90 {
  91         int                     parentRTindex = rti;
  92         List       *live_childrels = NIL;
  93         List       *subpaths = NIL;
  94         bool            subpaths_valid = true;
  95         List       *partial_subpaths = NIL;
  96         bool            partial_subpaths_valid = true;
  97         List       *all_child_pathkeys = NIL;
  98         List       *all_child_outers = NIL;
  99         ListCell   *l;
 100
 101         /*
 102          * Generate access paths for each member relation, and remember the
 103          * cheapest path for each one.  Also, identify all pathkeys (orderings)
 104          * and parameterizations (required_outer sets) available for the member
 105          * relations.
 106          */
 107         foreach(l, root->append_rel_list)
 108         {
 109                 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
 110                 int                     childRTindex;
 111                 RangeTblEntry *childRTE;
 112                 RelOptInfo *childrel;
 113                 ListCell   *lcp;
 114
 115                 /* append_rel_list contains all append rels; ignore others */
 116                 if (appinfo->parent_relid != parentRTindex)
 117                         continue;
 118
 119                 /* Re-locate the child RTE and RelOptInfo */
 120                 childRTindex = appinfo->child_relid;
 121                 childRTE = root->simple_rte_array[childRTindex];
 122                 childrel = root->simple_rel_array[childRTindex];
 123
 124                 /*
 125                  * If set_append_rel_size() decided the parent appendrel was
 126                  * parallel-unsafe at some point after visiting this child rel, we
 127                  * need to propagate the unsafety marking down to the child, so that
 128                  * we don't generate useless partial paths for it.
 129                  */
 130                 if (!rel->consider_parallel)
 131                         childrel->consider_parallel = false;
 132
 133                 /*
 134                  * Compute the child's access paths.
 135                  */
 136                 set_rel_pathlist(root, childrel, childRTindex, childRTE);
 137
 138                 /*
 139                  * If child is dummy, ignore it.
 140                  */
 141                 if (IS_DUMMY_REL(childrel))
 142                         continue;
 143
 144                 /*
 145                  * Child is live, so add it to the live_childrels list for use below.
 146                  */
 147                 live_childrels = lappend(live_childrels, childrel);
 148
 149                 /*
 150                  * If child has an unparameterized cheapest-total path, add that to
 151                  * the unparameterized Append path we are constructing for the parent.
 152                  * If not, there's no workable unparameterized path.
 153                  */
 154                 if (childrel->cheapest_total_path->param_info == NULL)
 155                         subpaths = accumulate_append_subpath(subpaths,
 156                                                                                           childrel->cheapest_total_path);
 157                 else
 158                         subpaths_valid = false;
 159
 160                 /* Same idea, but for a partial plan. */
 161                 if (childrel->partial_pathlist != NIL)
 162                         partial_subpaths = accumulate_append_subpath(partial_subpaths,
 163                                                                            linitial(childrel->partial_pathlist));
 164                 else
 165                         partial_subpaths_valid = false;
 166
 167                 /*
 168                  * Collect lists of all the available path orderings and
 169                  * parameterizations for all the children.  We use these as a
 170                  * heuristic to indicate which sort orderings and parameterizations we
 171                  * should build Append and MergeAppend paths for.
 172                  */
 173                 foreach(lcp, childrel->pathlist)
 174                 {
 175                         Path       *childpath = (Path *) lfirst(lcp);
 176                         List       *childkeys = childpath->pathkeys;
 177                         Relids          childouter = PATH_REQ_OUTER(childpath);
 178
 179                         /* Unsorted paths don't contribute to pathkey list */
 180                         if (childkeys != NIL)
 181                         {
 182                                 ListCell   *lpk;
 183                                 bool            found = false;
 184
 185                                 /* Have we already seen this ordering? */
 186                                 foreach(lpk, all_child_pathkeys)
 187                                 {
 188                                         List       *existing_pathkeys = (List *) lfirst(lpk);
 189
 190                                         if (compare_pathkeys(existing_pathkeys,
 191                                                                                  childkeys) == PATHKEYS_EQUAL)
 192                                         {
 193                                                 found = true;
 194                                                 break;
 195                                         }
 196                                 }
 197                                 if (!found)
 198                                 {
 199                                         /* No, so add it to all_child_pathkeys */
 200                                         all_child_pathkeys = lappend(all_child_pathkeys,
 201                                                                                                  childkeys);
 202                                 }
 203                         }
 204
 205                         /* Unparameterized paths don't contribute to param-set list */
 206                         if (childouter)
 207                         {
 208                                 ListCell   *lco;
 209                                 bool            found = false;
 210
 211                                 /* Have we already seen this param set? */
 212                                 foreach(lco, all_child_outers)
 213                                 {
 214                                         Relids          existing_outers = (Relids) lfirst(lco);
 215
 216                                         if (bms_equal(existing_outers, childouter))
 217                                         {
 218                                                 found = true;
 219                                                 break;
 220                                         }
 221                                 }
 222                                 if (!found)
 223                                 {
 224                                         /* No, so add it to all_child_outers */
 225                                         all_child_outers = lappend(all_child_outers,
 226                                                                                            childouter);
 227                                 }
 228                         }
 229                 }
 230         }
 231
 232         /*
 233          * If we found unparameterized paths for all children, build an unordered,
 234          * unparameterized Append path for the rel.  (Note: this is correct even
 235          * if we have zero or one live subpath due to constraint exclusion.)
 236          */
 237         if (subpaths_valid)
 238                 add_path(rel, (Path *) create_append_path(rel, subpaths, NULL, 0));
 239
 240         /*
 241          * Consider an append of partial unordered, unparameterized partial paths.
 242          */
 243         if (partial_subpaths_valid)
 244         {
 245                 AppendPath *appendpath;
 246                 ListCell   *lc;
 247                 int                     parallel_workers = 0;
 248
 249                 /*
 250                  * Decide on the number of workers to request for this append path.
 251                  * For now, we just use the maximum value from among the members.  It
 252                  * might be useful to use a higher number if the Append node were
 253                  * smart enough to spread out the workers, but it currently isn't.
 254                  */
 255                 foreach(lc, partial_subpaths)
 256                 {
 257                         Path       *path = lfirst(lc);
 258
 259                         parallel_workers = Max(parallel_workers, path->parallel_workers);
 260                 }
 261                 Assert(parallel_workers > 0);
 262
 263                 /* Generate a partial append path. */
 264                 appendpath = create_append_path(rel, partial_subpaths, NULL,
 265                                                                                 parallel_workers);
 266                 add_partial_path(rel, (Path *) appendpath);
 267         }
 268
 269         /*
 270          * Also build unparameterized MergeAppend paths based on the collected
 271          * list of child pathkeys.
 272          */
 273         if (subpaths_valid)
 274                 generate_mergeappend_paths(root, rel, live_childrels,
 275                                                                    all_child_pathkeys);
 276
 277         /*
 278          * Build Append paths for each parameterization seen among the child rels.
 279          * (This may look pretty expensive, but in most cases of practical
 280          * interest, the child rels will expose mostly the same parameterizations,
 281          * so that not that many cases actually get considered here.)
 282          *
 283          * The Append node itself cannot enforce quals, so all qual checking must
 284          * be done in the child paths.  This means that to have a parameterized
 285          * Append path, we must have the exact same parameterization for each
 286          * child path; otherwise some children might be failing to check the
 287          * moved-down quals.  To make them match up, we can try to increase the
 288          * parameterization of lesser-parameterized paths.
 289          */
 290         foreach(l, all_child_outers)
 291         {
 292                 Relids          required_outer = (Relids) lfirst(l);
 293                 ListCell   *lcr;
 294
 295                 /* Select the child paths for an Append with this parameterization */
 296                 subpaths = NIL;
 297                 subpaths_valid = true;
 298                 foreach(lcr, live_childrels)
 299                 {
 300                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 301                         Path       *subpath;
 302
 303                         subpath = get_cheapest_parameterized_child_path(root,
 304                                                                                                                         childrel,
 305                                                                                                                         required_outer);
 306                         if (subpath == NULL)
 307                         {
 308                                 /* failed to make a suitable path for this child */
 309                                 subpaths_valid = false;
 310                                 break;
 311                         }
 312                         subpaths = accumulate_append_subpath(subpaths, subpath);
 313                 }
 314
 315                 if (subpaths_valid)
 316                         add_path(rel, (Path *)
 317                                          create_append_path(rel, subpaths, required_outer, 0));
 318         }
 319 }
 320
 321 /*
 322  * generate_mergeappend_paths
 323  *              Generate MergeAppend paths for an append relation
 324  *
 325  * Generate a path for each ordering (pathkey list) appearing in
 326  * all_child_pathkeys.
 327  *
 328  * We consider both cheapest-startup and cheapest-total cases, ie, for each
 329  * interesting ordering, collect all the cheapest startup subpaths and all the
 330  * cheapest total paths, and build a MergeAppend path for each case.
 331  *
 332  * We don't currently generate any parameterized MergeAppend paths.  While
 333  * it would not take much more code here to do so, it's very unclear that it
 334  * is worth the planning cycles to investigate such paths: there's little
 335  * use for an ordered path on the inside of a nestloop.  In fact, it's likely
 336  * that the current coding of add_path would reject such paths out of hand,
 337  * because add_path gives no credit for sort ordering of parameterized paths,
 338  * and a parameterized MergeAppend is going to be more expensive than the
 339  * corresponding parameterized Append path.  If we ever try harder to support
 340  * parameterized mergejoin plans, it might be worth adding support for
 341  * parameterized MergeAppends to feed such joins.  (See notes in
 342  * optimizer/README for why that might not ever happen, though.)
 343  */
 344 static void
 345 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
 346                                                    List *live_childrels,
 347                                                    List *all_child_pathkeys)
 348 {
 349         ListCell   *lcp;
 350
 351         foreach(lcp, all_child_pathkeys)
 352         {
 353                 List       *pathkeys = (List *) lfirst(lcp);
 354                 List       *startup_subpaths = NIL;
 355                 List       *total_subpaths = NIL;
 356                 bool            startup_neq_total = false;
 357                 ListCell   *lcr;
 358
 359                 /* Select the child paths for this ordering... */
 360                 foreach(lcr, live_childrels)
 361                 {
 362                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 363                         Path       *cheapest_startup,
 364                                            *cheapest_total;
 365
 366                         /* Locate the right paths, if they are available. */
 367                         cheapest_startup =
 368                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 369                                                                                            pathkeys,
 370                                                                                            NULL,
 371                                                                                            STARTUP_COST);
 372                         cheapest_total =
 373                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 374                                                                                            pathkeys,
 375                                                                                            NULL,
 376                                                                                            TOTAL_COST);
 377
 378                         /*
 379                          * If we can't find any paths with the right order just use the
 380                          * cheapest-total path; we'll have to sort it later.
 381                          */
 382                         if (cheapest_startup == NULL || cheapest_total == NULL)
 383                         {
 384                                 cheapest_startup = cheapest_total =
 385                                         childrel->cheapest_total_path;
 386                                 /* Assert we do have an unparameterized path for this child */
 387                                 Assert(cheapest_total->param_info == NULL);
 388                         }
 389
 390                         /*
 391                          * Notice whether we actually have different paths for the
 392                          * "cheapest" and "total" cases; frequently there will be no point
 393                          * in two create_merge_append_path() calls.
 394                          */
 395                         if (cheapest_startup != cheapest_total)
 396                                 startup_neq_total = true;
 397
 398                         startup_subpaths =
 399                                 accumulate_append_subpath(startup_subpaths, cheapest_startup);
 400                         total_subpaths =
 401                                 accumulate_append_subpath(total_subpaths, cheapest_total);
 402                 }
 403
 404                 /* ... and build the MergeAppend paths */
 405                 add_path(rel, (Path *) create_merge_append_path(root,
 406                                                                                                                 rel,
 407                                                                                                                 startup_subpaths,
 408                                                                                                                 pathkeys,
 409                                                                                                                 NULL));
 410                 if (startup_neq_total)
 411                         add_path(rel, (Path *) create_merge_append_path(root,
 412                                                                                                                         rel,
 413                                                                                                                         total_subpaths,
 414                                                                                                                         pathkeys,
 415                                                                                                                         NULL));
 416         }
 417 }
 418
 419 /*
 420  * get_cheapest_parameterized_child_path
 421  *              Get cheapest path for this relation that has exactly the requested
 422  *              parameterization.
 423  *
 424  * Returns NULL if unable to create such a path.
 425  */
 426 static Path *
 427 get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
 428                                                                           Relids required_outer)
 429 {
 430         Path       *cheapest;
 431         ListCell   *lc;
 432
 433         /*
 434          * Look up the cheapest existing path with no more than the needed
 435          * parameterization.  If it has exactly the needed parameterization, we're
 436          * done.
 437          */
 438         cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
 439                                                                                           NIL,
 440                                                                                           required_outer,
 441                                                                                           TOTAL_COST);
 442         Assert(cheapest != NULL);
 443         if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
 444                 return cheapest;
 445
 446         /*
 447          * Otherwise, we can "reparameterize" an existing path to match the given
 448          * parameterization, which effectively means pushing down additional
 449          * joinquals to be checked within the path's scan.  However, some existing
 450          * paths might check the available joinquals already while others don't;
 451          * therefore, it's not clear which existing path will be cheapest after
 452          * reparameterization.  We have to go through them all and find out.
 453          */
 454         cheapest = NULL;
 455         foreach(lc, rel->pathlist)
 456         {
 457                 Path       *path = (Path *) lfirst(lc);
 458
 459                 /* Can't use it if it needs more than requested parameterization */
 460                 if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
 461                         continue;
 462
 463                 /*
 464                  * Reparameterization can only increase the path's cost, so if it's
 465                  * already more expensive than the current cheapest, forget it.
 466                  */
 467                 if (cheapest != NULL &&
 468                         compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
 469                         continue;
 470
 471                 /* Reparameterize if needed, then recheck cost */
 472                 if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
 473                 {
 474                         path = reparameterize_path(root, path, required_outer, 1.0);
 475                         if (path == NULL)
 476                                 continue;               /* failed to reparameterize this one */
 477                         Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));
 478
 479                         if (cheapest != NULL &&
 480                                 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
 481                                 continue;
 482                 }
 483
 484                 /* We have a new best path */
 485                 cheapest = path;
 486         }
 487
 488         /* Return the best path, or NULL if we found no suitable candidate */
 489         return cheapest;
 490 }
 491
 492 /*
 493  * accumulate_append_subpath
 494  *              Add a subpath to the list being built for an Append or MergeAppend
 495  *
 496  * It's possible that the child is itself an Append or MergeAppend path, in
 497  * which case we can "cut out the middleman" and just add its child paths to
 498  * our own list.  (We don't try to do this earlier because we need to apply
 499  * both levels of transformation to the quals.)
 500  *
 501  * Note that if we omit a child MergeAppend in this way, we are effectively
 502  * omitting a sort step, which seems fine: if the parent is to be an Append,
 503  * its result would be unsorted anyway, while if the parent is to be a
 504  * MergeAppend, there's no point in a separate sort on a child.
 505  */
 506 static List *
 507 accumulate_append_subpath(List *subpaths, Path *path)
 508 {
 509         if (IsA(path, AppendPath))
 510         {
 511                 AppendPath *apath = (AppendPath *) path;
 512
 513                 /* list_copy is important here to avoid sharing list substructure */
 514                 return list_concat(subpaths, list_copy(apath->subpaths));
 515         }
 516         else if (IsA(path, MergeAppendPath))
 517         {
 518                 MergeAppendPath *mpath = (MergeAppendPath *) path;
 519
 520                 /* list_copy is important here to avoid sharing list substructure */
 521                 return list_concat(subpaths, list_copy(mpath->subpaths));
 522         }
 523         else
 524                 return lappend(subpaths, path);
 525 }
 526
 527 /*
 528  * standard_join_search
 529  *        Find possible joinpaths for a query by successively finding ways
 530  *        to join component relations into join relations.
 531  *
 532  * 'levels_needed' is the number of iterations needed, ie, the number of
 533  *              independent jointree items in the query.  This is > 1.
 534  *
 535  * 'initial_rels' is a list of RelOptInfo nodes for each independent
 536  *              jointree item.  These are the components to be joined together.
 537  *              Note that levels_needed == list_length(initial_rels).
 538  *
 539  * Returns the final level of join relations, i.e., the relation that is
 540  * the result of joining all the original relations together.
 541  * At least one implementation path must be provided for this relation and
 542  * all required sub-relations.
 543  *
 544  * To support loadable plugins that modify planner behavior by changing the
 545  * join searching algorithm, we provide a hook variable that lets a plugin
 546  * replace or supplement this function.  Any such hook must return the same
 547  * final join relation as the standard code would, but it might have a
 548  * different set of implementation paths attached, and only the sub-joinrels
 549  * needed for these paths need have been instantiated.
 550  *
 551  * Note to plugin authors: the functions invoked during standard_join_search()
 552  * modify root->join_rel_list and root->join_rel_hash.  If you want to do more
 553  * than one join-order search, you'll probably need to save and restore the
 554  * original states of those data structures.  See geqo_eval() for an example.
 555  */
 556 RelOptInfo *
 557 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
 558 {
 559         int                     lev;
 560         RelOptInfo *rel;
 561
 562         /*
 563          * This function cannot be invoked recursively within any one planning
 564          * problem, so join_rel_level[] can't be in use already.
 565          */
 566         Assert(root->join_rel_level == NULL);
 567
 568         /*
 569          * We employ a simple "dynamic programming" algorithm: we first find all
 570          * ways to build joins of two jointree items, then all ways to build joins
 571          * of three items (from two-item joins and single items), then four-item
 572          * joins, and so on until we have considered all ways to join all the
 573          * items into one rel.
 574          *
 575          * root->join_rel_level[j] is a list of all the j-item rels.  Initially we
 576          * set root->join_rel_level[1] to represent all the single-jointree-item
 577          * relations.
 578          */
 579         root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
 580
 581         root->join_rel_level[1] = initial_rels;
 582
 583         for (lev = 2; lev <= levels_needed; lev++)
 584         {
 585                 ListCell   *lc;
 586
 587                 /*
 588                  * Determine all possible pairs of relations to be joined at this
 589                  * level, and build paths for making each one from every available
 590                  * pair of lower-level relations.
 591                  */
 592                 join_search_one_level(root, lev);
 593
 594                 /*
 595                  * Run generate_gather_paths() for each just-processed joinrel.  We
 596                  * could not do this earlier because both regular and partial paths
 597                  * can get added to a particular joinrel at multiple times within
 598                  * join_search_one_level.  After that, we're done creating paths for
 599                  * the joinrel, so run set_cheapest().
 600                  */
 601                 foreach(lc, root->join_rel_level[lev])
 602                 {
 603                         rel = (RelOptInfo *) lfirst(lc);
 604
 605                         /* Create GatherPaths for any useful partial paths for rel */
 606                         generate_gather_paths(root, rel);
 607
 608                         /* Find and save the cheapest paths for this rel */
 609                         set_cheapest(rel);
 610
 611 #ifdef OPTIMIZER_DEBUG
 612                         debug_print_rel(root, rel);
 613 #endif
 614                 }
 615         }
 616
 617         /*
 618          * We should have a single rel at the final level.
 619          */
 620         if (root->join_rel_level[levels_needed] == NIL)
 621                 elog(ERROR, "failed to build any %d-way joins", levels_needed);
 622         Assert(list_length(root->join_rel_level[levels_needed]) == 1);
 623
 624         rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
 625
 626         root->join_rel_level = NULL;
 627
 628         return rel;
 629 }
 630
 631 /*
 632  * create_plain_partial_paths
 633  *        Build partial access paths for parallel scan of a plain relation
 634  */
 635 static void
 636 create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
 637 {
 638         int                     parallel_workers;
 639
 640         parallel_workers = compute_parallel_worker(rel, rel->pages);
 641
 642         /* If any limit was set to zero, the user doesn't want a parallel scan. */
 643         if (parallel_workers <= 0)
 644                 return;
 645
 646         /* Add an unordered partial path based on a parallel sequential scan. */
 647         add_partial_path(rel, create_seqscan_path(root, rel, NULL, parallel_workers));
 648 }
 649
 650 /*
 651  * Compute the number of parallel workers that should be used to scan a
 652  * relation.  "pages" is the number of pages from the relation that we
 653  * expect to scan.
 654  */
 655 static int
 656 compute_parallel_worker(RelOptInfo *rel, BlockNumber pages)
 657 {
 658         int                     parallel_workers;
 659
 660         /*
 661          * If the user has set the parallel_workers reloption, use that; otherwise
 662          * select a default number of workers.
 663          */
 664         if (rel->rel_parallel_workers != -1)
 665                 parallel_workers = rel->rel_parallel_workers;
 666         else
 667         {
 668                 int                     parallel_threshold;
 669
 670                 /*
 671                  * If this relation is too small to be worth a parallel scan, just
 672                  * return without doing anything ... unless it's an inheritance child.
 673                  * In that case, we want to generate a parallel path here anyway.  It
 674                  * might not be worthwhile just for this relation, but when combined
 675                  * with all of its inheritance siblings it may well pay off.
 676                  */
 677                 if (pages < (BlockNumber) min_parallel_relation_size &&
 678                         rel->reloptkind == RELOPT_BASEREL)
 679                         return 0;
 680
 681                 /*
 682                  * Select the number of workers based on the log of the size of the
 683                  * relation.  This probably needs to be a good deal more
 684                  * sophisticated, but we need something here for now.  Note that the
 685                  * upper limit of the min_parallel_relation_size GUC is chosen to
 686                  * prevent overflow here.
 687                  */
 688                 parallel_workers = 1;
 689                 parallel_threshold = Max(min_parallel_relation_size, 1);
 690                 while (pages >= (BlockNumber) (parallel_threshold * 3))
 691                 {
 692                         parallel_workers++;
 693                         parallel_threshold *= 3;
 694                         if (parallel_threshold > INT_MAX / 3)
 695                                 break;                  /* avoid overflow */
 696                 }
 697         }
 698
 699         /*
 700          * In no case use more than max_parallel_workers_per_gather workers.
 701          */
 702         parallel_workers = Min(parallel_workers, max_parallel_workers_per_gather);
 703
 704         return parallel_workers;
 705 }
 706
 707
 708 /*
 709  * join_search_one_level
 710  *        Consider ways to produce join relations containing exactly 'level'
 711  *        jointree items.  (This is one step of the dynamic-programming method
 712  *        embodied in standard_join_search.)  Join rel nodes for each feasible
 713  *        combination of lower-level rels are created and returned in a list.
 714  *        Implementation paths are created for each such joinrel, too.
 715  *
 716  * level: level of rels we want to make this time
 717  * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
 718  *
 719  * The result is returned in root->join_rel_level[level].
 720  */
 721 void
 722 join_search_one_level(PlannerInfo *root, int level)
 723 {
 724         List      **joinrels = root->join_rel_level;
 725         ListCell   *r;
 726         int                     k;
 727
 728         Assert(joinrels[level] == NIL);
 729
 730         /* Set join_cur_level so that new joinrels are added to proper list */
 731         root->join_cur_level = level;
 732
 733         /*
 734          * First, consider left-sided and right-sided plans, in which rels of
 735          * exactly level-1 member relations are joined against initial relations.
 736          * We prefer to join using join clauses, but if we find a rel of level-1
 737          * members that has no join clauses, we will generate Cartesian-product
 738          * joins against all initial rels not already contained in it.
 739          */
 740         foreach(r, joinrels[level - 1])
 741         {
 742                 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 743
 744                 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
 745                         has_join_restriction(root, old_rel))
 746                 {
 747                         /*
 748                          * There are join clauses or join order restrictions relevant to
 749                          * this rel, so consider joins between this rel and (only) those
 750                          * initial rels it is linked to by a clause or restriction.
 751                          *
 752                          * At level 2 this condition is symmetric, so there is no need to
 753                          * look at initial rels before this one in the list; we already
 754                          * considered such joins when we were at the earlier rel.  (The
 755                          * mirror-image joins are handled automatically by make_join_rel.)
 756                          * In later passes (level > 2), we join rels of the previous level
 757                          * to each initial rel they don't already include but have a join
 758                          * clause or restriction with.
 759                          */
 760                         ListCell   *other_rels;
 761
 762                         if (level == 2)         /* consider remaining initial rels */
 763                                 other_rels = lnext(r);
 764                         else    /* consider all initial rels */
 765                                 other_rels = list_head(joinrels[1]);
 766
 767                         make_rels_by_clause_joins(root,
 768                                                                           old_rel,
 769                                                                           other_rels);
 770                 }
 771                 else
 772                 {
 773                         /*
 774                          * Oops, we have a relation that is not joined to any other
 775                          * relation, either directly or by join-order restrictions.
 776                          * Cartesian product time.
 777                          *
 778                          * We consider a cartesian product with each not-already-included
 779                          * initial rel, whether it has other join clauses or not.  At
 780                          * level 2, if there are two or more clauseless initial rels, we
 781                          * will redundantly consider joining them in both directions; but
 782                          * such cases aren't common enough to justify adding complexity to
 783                          * avoid the duplicated effort.
 784                          */
 785                         make_rels_by_clauseless_joins(root,
 786                                                                                   old_rel,
 787                                                                                   list_head(joinrels[1]));
 788                 }
 789         }
 790
 791         /*
 792          * Now, consider "bushy plans" in which relations of k initial rels are
 793          * joined to relations of level-k initial rels, for 2 <= k <= level-2.
 794          *
 795          * We only consider bushy-plan joins for pairs of rels where there is a
 796          * suitable join clause (or join order restriction), in order to avoid
 797          * unreasonable growth of planning time.
 798          */
 799         for (k = 2;; k++)
 800         {
 801                 int                     other_level = level - k;
 802
 803                 /*
 804                  * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
 805                  * need to go as far as the halfway point.
 806                  */
 807                 if (k > other_level)
 808                         break;
 809
 810                 foreach(r, joinrels[k])
 811                 {
 812                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 813                         ListCell   *other_rels;
 814                         ListCell   *r2;
 815
 816                         /*
 817                          * We can ignore relations without join clauses here, unless they
 818                          * participate in join-order restrictions --- then we might have
 819                          * to force a bushy join plan.
 820                          */
 821                         if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
 822                                 !has_join_restriction(root, old_rel))
 823                                 continue;
 824
 825                         if (k == other_level)
 826                                 other_rels = lnext(r);  /* only consider remaining rels */
 827                         else
 828                                 other_rels = list_head(joinrels[other_level]);
 829
 830                         for_each_cell(r2, other_rels)
 831                         {
 832                                 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
 833
 834                                 if (!bms_overlap(old_rel->relids, new_rel->relids))
 835                                 {
 836                                         /*
 837                                          * OK, we can build a rel of the right level from this
 838                                          * pair of rels.  Do so if there is at least one relevant
 839                                          * join clause or join order restriction.
 840                                          */
 841                                         if (have_relevant_joinclause(root, old_rel, new_rel) ||
 842                                                 have_join_order_restriction(root, old_rel, new_rel))
 843                                         {
 844                                                 (void) make_join_rel(root, old_rel, new_rel);
 845                                         }
 846                                 }
 847                         }
 848                 }
 849         }
 850
 851         /*----------
 852          * Last-ditch effort: if we failed to find any usable joins so far, force
 853          * a set of cartesian-product joins to be generated.  This handles the
 854          * special case where all the available rels have join clauses but we
 855          * cannot use any of those clauses yet.  This can only happen when we are
 856          * considering a join sub-problem (a sub-joinlist) and all the rels in the
 857          * sub-problem have only join clauses with rels outside the sub-problem.
 858          * An example is
 859          *
 860          *              SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
 861          *              WHERE a.w = c.x and b.y = d.z;
 862          *
 863          * If the "a INNER JOIN b" sub-problem does not get flattened into the
 864          * upper level, we must be willing to make a cartesian join of a and b;
 865          * but the code above will not have done so, because it thought that both
 866          * a and b have joinclauses.  We consider only left-sided and right-sided
 867          * cartesian joins in this case (no bushy).
 868          *----------
 869          */
 870         if (joinrels[level] == NIL)
 871         {
 872                 /*
 873                  * This loop is just like the first one, except we always call
 874                  * make_rels_by_clauseless_joins().
 875                  */
 876                 foreach(r, joinrels[level - 1])
 877                 {
 878                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 879
 880                         make_rels_by_clauseless_joins(root,
 881                                                                                   old_rel,
 882                                                                                   list_head(joinrels[1]));
 883                 }
 884
 885                 /*----------
 886                  * When special joins are involved, there may be no legal way
 887                  * to make an N-way join for some values of N.  For example consider
 888                  *
 889                  * SELECT ... FROM t1 WHERE
 890                  *       x IN (SELECT ... FROM t2,t3 WHERE ...) AND
 891                  *       y IN (SELECT ... FROM t4,t5 WHERE ...)
 892                  *
 893                  * We will flatten this query to a 5-way join problem, but there are
 894                  * no 4-way joins that join_is_legal() will consider legal.  We have
 895                  * to accept failure at level 4 and go on to discover a workable
 896                  * bushy plan at level 5.
 897                  *
 898                  * However, if there are no special joins and no lateral references
 899                  * then join_is_legal() should never fail, and so the following sanity
 900                  * check is useful.
 901                  *----------
 902                  */
 903                 if (joinrels[level] == NIL &&
 904                         root->join_info_list == NIL &&
 905                         !root->hasLateralRTEs)
 906                         elog(ERROR, "failed to build any %d-way joins", level);
 907         }
 908 }
 909
 910 /*
 911  * make_rels_by_clause_joins
 912  *        Build joins between the given relation 'old_rel' and other relations
 913  *        that participate in join clauses that 'old_rel' also participates in
 914  *        (or participate in join-order restrictions with it).
 915  *        The join rels are returned in root->join_rel_level[join_cur_level].
 916  *
 917  * Note: at levels above 2 we will generate the same joined relation in
 918  * multiple ways --- for example (a join b) join c is the same RelOptInfo as
 919  * (b join c) join a, though the second case will add a different set of Paths
 920  * to it.  This is the reason for using the join_rel_level mechanism, which
 921  * automatically ensures that each new joinrel is only added to the list once.
 922  *
 923  * 'old_rel' is the relation entry for the relation to be joined
 924  * 'other_rels': the first cell in a linked list containing the other
 925  * rels to be considered for joining
 926  *
 927  * Currently, this is only used with initial rels in other_rels, but it
 928  * will work for joining to joinrels too.
 929  */
 930 static void
 931 make_rels_by_clause_joins(PlannerInfo *root,
 932                                                   RelOptInfo *old_rel,
 933                                                   ListCell *other_rels)
 934 {
 935         ListCell   *l;
 936
 937         for_each_cell(l, other_rels)
 938         {
 939                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 940
 941                 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
 942                         (have_relevant_joinclause(root, old_rel, other_rel) ||
 943                          have_join_order_restriction(root, old_rel, other_rel)))
 944                 {
 945                         (void) make_join_rel(root, old_rel, other_rel);
 946                 }
 947         }
 948 }
 949
 950 /*
 951  * make_rels_by_clauseless_joins
 952  *        Given a relation 'old_rel' and a list of other relations
 953  *        'other_rels', create a join relation between 'old_rel' and each
 954  *        member of 'other_rels' that isn't already included in 'old_rel'.
 955  *        The join rels are returned in root->join_rel_level[join_cur_level].
 956  *
 957  * 'old_rel' is the relation entry for the relation to be joined
 958  * 'other_rels': the first cell of a linked list containing the
 959  * other rels to be considered for joining
 960  *
 961  * Currently, this is only used with initial rels in other_rels, but it would
 962  * work for joining to joinrels too.
 963  */
 964 static void
 965 make_rels_by_clauseless_joins(PlannerInfo *root,
 966                                                           RelOptInfo *old_rel,
 967                                                           ListCell *other_rels)
 968 {
 969         ListCell   *l;
 970
 971         for_each_cell(l, other_rels)
 972         {
 973                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 974
 975                 if (!bms_overlap(other_rel->relids, old_rel->relids))
 976                 {
 977                         (void) make_join_rel(root, old_rel, other_rel);
 978                 }
 979         }
 980 }
 981
 982 /*
 983  * join_is_legal
 984  *         Determine whether a proposed join is legal given the query's
 985  *         join order constraints; and if it is, determine the join type.
 986  *
 987  * Caller must supply not only the two rels, but the union of their relids.
 988  * (We could simplify the API by computing joinrelids locally, but this
 989  * would be redundant work in the normal path through make_join_rel.)
 990  *
 991  * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
 992  * else it's set to point to the associated SpecialJoinInfo node.  Also,
 993  * *reversed_p is set TRUE if the given relations need to be swapped to
 994  * match the SpecialJoinInfo node.
 995  */
 996 static bool
 997 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 998                           Relids joinrelids,
 999                           SpecialJoinInfo **sjinfo_p, bool *reversed_p)
1000 {
1001         SpecialJoinInfo *match_sjinfo;
1002         bool            reversed;
1003         bool            unique_ified;
1004         bool            must_be_leftjoin;
1005         ListCell   *l;
1006
1007         /*
1008          * Ensure output params are set on failure return.  This is just to
1009          * suppress uninitialized-variable warnings from overly anal compilers.
1010          */
1011         *sjinfo_p = NULL;
1012         *reversed_p = false;
1013
1014         /*
1015          * If we have any special joins, the proposed join might be illegal; and
1016          * in any case we have to determine its join type.  Scan the join info
1017          * list for matches and conflicts.
1018          */
1019         match_sjinfo = NULL;
1020         reversed = false;
1021         unique_ified = false;
1022         must_be_leftjoin = false;
1023
1024         foreach(l, root->join_info_list)
1025         {
1026                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1027
1028                 /*
1029                  * This special join is not relevant unless its RHS overlaps the
1030                  * proposed join.  (Check this first as a fast path for dismissing
1031                  * most irrelevant SJs quickly.)
1032                  */
1033                 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
1034                         continue;
1035
1036                 /*
1037                  * Also, not relevant if proposed join is fully contained within RHS
1038                  * (ie, we're still building up the RHS).
1039                  */
1040                 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
1041                         continue;
1042
1043                 /*
1044                  * Also, not relevant if SJ is already done within either input.
1045                  */
1046                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
1047                         bms_is_subset(sjinfo->min_righthand, rel1->relids))
1048                         continue;
1049                 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
1050                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
1051                         continue;
1052
1053                 /*
1054                  * If it's a semijoin and we already joined the RHS to any other rels
1055                  * within either input, then we must have unique-ified the RHS at that
1056                  * point (see below).  Therefore the semijoin is no longer relevant in
1057                  * this join path.
1058                  */
1059                 if (sjinfo->jointype == JOIN_SEMI)
1060                 {
1061                         if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
1062                                 !bms_equal(sjinfo->syn_righthand, rel1->relids))
1063                                 continue;
1064                         if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
1065                                 !bms_equal(sjinfo->syn_righthand, rel2->relids))
1066                                 continue;
1067                 }
1068
1069                 /*
1070                  * If one input contains min_lefthand and the other contains
1071                  * min_righthand, then we can perform the SJ at this join.
1072                  *
1073                  * Reject if we get matches to more than one SJ; that implies we're
1074                  * considering something that's not really valid.
1075                  */
1076                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
1077                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
1078                 {
1079                         if (match_sjinfo)
1080                                 return false;   /* invalid join path */
1081                         match_sjinfo = sjinfo;
1082                         reversed = false;
1083                 }
1084                 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
1085                                  bms_is_subset(sjinfo->min_righthand, rel1->relids))
1086                 {
1087                         if (match_sjinfo)
1088                                 return false;   /* invalid join path */
1089                         match_sjinfo = sjinfo;
1090                         reversed = true;
1091                 }
1092                 else if (sjinfo->jointype == JOIN_SEMI &&
1093                                  bms_equal(sjinfo->syn_righthand, rel2->relids) &&
1094                                  create_unique_path(root, rel2, rel2->cheapest_total_path,
1095                                                                         sjinfo) != NULL)
1096                 {
1097                         /*----------
1098                          * For a semijoin, we can join the RHS to anything else by
1099                          * unique-ifying the RHS (if the RHS can be unique-ified).
1100                          * We will only get here if we have the full RHS but less
1101                          * than min_lefthand on the LHS.
1102                          *
1103                          * The reason to consider such a join path is exemplified by
1104                          *      SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
1105                          * If we insist on doing this as a semijoin we will first have
1106                          * to form the cartesian product of A*B.  But if we unique-ify
1107                          * C then the semijoin becomes a plain innerjoin and we can join
1108                          * in any order, eg C to A and then to B.  When C is much smaller
1109                          * than A and B this can be a huge win.  So we allow C to be
1110                          * joined to just A or just B here, and then make_join_rel has
1111                          * to handle the case properly.
1112                          *
1113                          * Note that actually we'll allow unique-ified C to be joined to
1114                          * some other relation D here, too.  That is legal, if usually not
1115                          * very sane, and this routine is only concerned with legality not
1116                          * with whether the join is good strategy.
1117                          *----------
1118                          */
1119                         if (match_sjinfo)
1120                                 return false;   /* invalid join path */
1121                         match_sjinfo = sjinfo;
1122                         reversed = false;
1123                         unique_ified = true;
1124                 }
1125                 else if (sjinfo->jointype == JOIN_SEMI &&
1126                                  bms_equal(sjinfo->syn_righthand, rel1->relids) &&
1127                                  create_unique_path(root, rel1, rel1->cheapest_total_path,
1128                                                                         sjinfo) != NULL)
1129                 {
1130                         /* Reversed semijoin case */
1131                         if (match_sjinfo)
1132                                 return false;   /* invalid join path */
1133                         match_sjinfo = sjinfo;
1134                         reversed = true;
1135                         unique_ified = true;
1136                 }
1137                 else
1138                 {
1139                         /*
1140                          * Otherwise, the proposed join overlaps the RHS but isn't a valid
1141                          * implementation of this SJ.  But don't panic quite yet: the RHS
1142                          * violation might have occurred previously, in one or both input
1143                          * relations, in which case we must have previously decided that
1144                          * it was OK to commute some other SJ with this one.  If we need
1145                          * to perform this join to finish building up the RHS, rejecting
1146                          * it could lead to not finding any plan at all.  (This can occur
1147                          * because of the heuristics elsewhere in this file that postpone
1148                          * clauseless joins: we might not consider doing a clauseless join
1149                          * within the RHS until after we've performed other, validly
1150                          * commutable SJs with one or both sides of the clauseless join.)
1151                          * This consideration boils down to the rule that if both inputs
1152                          * overlap the RHS, we can allow the join --- they are either
1153                          * fully within the RHS, or represent previously-allowed joins to
1154                          * rels outside it.
1155                          */
1156                         if (bms_overlap(rel1->relids, sjinfo->min_righthand) &&
1157                                 bms_overlap(rel2->relids, sjinfo->min_righthand))
1158                                 continue;               /* assume valid previous violation of RHS */
1159
1160                         /*
1161                          * The proposed join could still be legal, but only if we're
1162                          * allowed to associate it into the RHS of this SJ.  That means
1163                          * this SJ must be a LEFT join (not SEMI or ANTI, and certainly
1164                          * not FULL) and the proposed join must not overlap the LHS.
1165                          */
1166                         if (sjinfo->jointype != JOIN_LEFT ||
1167                                 bms_overlap(joinrelids, sjinfo->min_lefthand))
1168                                 return false;   /* invalid join path */
1169
1170                         /*
1171                          * To be valid, the proposed join must be a LEFT join; otherwise
1172                          * it can't associate into this SJ's RHS.  But we may not yet have
1173                          * found the SpecialJoinInfo matching the proposed join, so we
1174                          * can't test that yet.  Remember the requirement for later.
1175                          */
1176                         must_be_leftjoin = true;
1177                 }
1178         }
1179
1180         /*
1181          * Fail if violated any SJ's RHS and didn't match to a LEFT SJ: the
1182          * proposed join can't associate into an SJ's RHS.
1183          *
1184          * Also, fail if the proposed join's predicate isn't strict; we're
1185          * essentially checking to see if we can apply outer-join identity 3, and
1186          * that's a requirement.  (This check may be redundant with checks in
1187          * make_outerjoininfo, but I'm not quite sure, and it's cheap to test.)
1188          */
1189         if (must_be_leftjoin &&
1190                 (match_sjinfo == NULL ||
1191                  match_sjinfo->jointype != JOIN_LEFT ||
1192                  !match_sjinfo->lhs_strict))
1193                 return false;                   /* invalid join path */
1194
1195         /*
1196          * We also have to check for constraints imposed by LATERAL references.
1197          */
1198         if (root->hasLateralRTEs)
1199         {
1200                 bool            lateral_fwd;
1201                 bool            lateral_rev;
1202                 Relids          join_lateral_rels;
1203
1204                 /*
1205                  * The proposed rels could each contain lateral references to the
1206                  * other, in which case the join is impossible.  If there are lateral
1207                  * references in just one direction, then the join has to be done with
1208                  * a nestloop with the lateral referencer on the inside.  If the join
1209                  * matches an SJ that cannot be implemented by such a nestloop, the
1210                  * join is impossible.
1211                  *
1212                  * Also, if the lateral reference is only indirect, we should reject
1213                  * the join; whatever rel(s) the reference chain goes through must be
1214                  * joined to first.
1215                  *
1216                  * Another case that might keep us from building a valid plan is the
1217                  * implementation restriction described by have_dangerous_phv().
1218                  */
1219                 lateral_fwd = bms_overlap(rel1->relids, rel2->lateral_relids);
1220                 lateral_rev = bms_overlap(rel2->relids, rel1->lateral_relids);
1221                 if (lateral_fwd && lateral_rev)
1222                         return false;           /* have lateral refs in both directions */
1223                 if (lateral_fwd)
1224                 {
1225                         /* has to be implemented as nestloop with rel1 on left */
1226                         if (match_sjinfo &&
1227                                 (reversed ||
1228                                  unique_ified ||
1229                                  match_sjinfo->jointype == JOIN_FULL))
1230                                 return false;   /* not implementable as nestloop */
1231                         /* check there is a direct reference from rel2 to rel1 */
1232                         if (!bms_overlap(rel1->relids, rel2->direct_lateral_relids))
1233                                 return false;   /* only indirect refs, so reject */
1234                         /* check we won't have a dangerous PHV */
1235                         if (have_dangerous_phv(root, rel1->relids, rel2->lateral_relids))
1236                                 return false;   /* might be unable to handle required PHV */
1237                 }
1238                 else if (lateral_rev)
1239                 {
1240                         /* has to be implemented as nestloop with rel2 on left */
1241                         if (match_sjinfo &&
1242                                 (!reversed ||
1243                                  unique_ified ||
1244                                  match_sjinfo->jointype == JOIN_FULL))
1245                                 return false;   /* not implementable as nestloop */
1246                         /* check there is a direct reference from rel1 to rel2 */
1247                         if (!bms_overlap(rel2->relids, rel1->direct_lateral_relids))
1248                                 return false;   /* only indirect refs, so reject */
1249                         /* check we won't have a dangerous PHV */
1250                         if (have_dangerous_phv(root, rel2->relids, rel1->lateral_relids))
1251                                 return false;   /* might be unable to handle required PHV */
1252                 }
1253
1254                 /*
1255                  * LATERAL references could also cause problems later on if we accept
1256                  * this join: if the join's minimum parameterization includes any rels
1257                  * that would have to be on the inside of an outer join with this join
1258                  * rel, then it's never going to be possible to build the complete
1259                  * query using this join.  We should reject this join not only because
1260                  * it'll save work, but because if we don't, the clauseless-join
1261                  * heuristics might think that legality of this join means that some
1262                  * other join rel need not be formed, and that could lead to failure
1263                  * to find any plan at all.  We have to consider not only rels that
1264                  * are directly on the inner side of an OJ with the joinrel, but also
1265                  * ones that are indirectly so, so search to find all such rels.
1266                  */
1267                 join_lateral_rels = min_join_parameterization(root, joinrelids,
1268                                                                                                           rel1, rel2);
1269                 if (join_lateral_rels)
1270                 {
1271                         Relids          join_plus_rhs = bms_copy(joinrelids);
1272                         bool            more;
1273
1274                         do
1275                         {
1276                                 more = false;
1277                                 foreach(l, root->join_info_list)
1278                                 {
1279                                         SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1280
1281                                         if (bms_overlap(sjinfo->min_lefthand, join_plus_rhs) &&
1282                                                 !bms_is_subset(sjinfo->min_righthand, join_plus_rhs))
1283                                         {
1284                                                 join_plus_rhs = bms_add_members(join_plus_rhs,
1285                                                                                                           sjinfo->min_righthand);
1286                                                 more = true;
1287                                         }
1288                                         /* full joins constrain both sides symmetrically */
1289                                         if (sjinfo->jointype == JOIN_FULL &&
1290                                                 bms_overlap(sjinfo->min_righthand, join_plus_rhs) &&
1291                                                 !bms_is_subset(sjinfo->min_lefthand, join_plus_rhs))
1292                                         {
1293                                                 join_plus_rhs = bms_add_members(join_plus_rhs,
1294                                                                                                                 sjinfo->min_lefthand);
1295                                                 more = true;
1296                                         }
1297                                 }
1298                         } while (more);
1299                         if (bms_overlap(join_plus_rhs, join_lateral_rels))
1300                                 return false;   /* will not be able to join to some RHS rel */
1301                 }
1302         }
1303
1304         /* Otherwise, it's a valid join */
1305         *sjinfo_p = match_sjinfo;
1306         *reversed_p = reversed;
1307         return true;
1308 }
1309
1310 /*
1311  * has_join_restriction
1312  *              Detect whether the specified relation has join-order restrictions,
1313  *              due to being inside an outer join or an IN (sub-SELECT),
1314  *              or participating in any LATERAL references or multi-rel PHVs.
1315  *
1316  * Essentially, this tests whether have_join_order_restriction() could
1317  * succeed with this rel and some other one.  It's OK if we sometimes
1318  * say "true" incorrectly.  (Therefore, we don't bother with the relatively
1319  * expensive has_legal_joinclause test.)
1320  */
1321 static bool
1322 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
1323 {
1324         ListCell   *l;
1325
1326         if (rel->lateral_relids != NULL || rel->lateral_referencers != NULL)
1327                 return true;
1328
1329         foreach(l, root->placeholder_list)
1330         {
1331                 PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
1332
1333                 if (bms_is_subset(rel->relids, phinfo->ph_eval_at) &&
1334                         !bms_equal(rel->relids, phinfo->ph_eval_at))
1335                         return true;
1336         }
1337
1338         foreach(l, root->join_info_list)
1339         {
1340                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1341
1342                 /* ignore full joins --- other mechanisms preserve their ordering */
1343                 if (sjinfo->jointype == JOIN_FULL)
1344                         continue;
1345
1346                 /* ignore if SJ is already contained in rel */
1347                 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
1348                         bms_is_subset(sjinfo->min_righthand, rel->relids))
1349                         continue;
1350
1351                 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
1352                 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
1353                         bms_overlap(sjinfo->min_righthand, rel->relids))
1354                         return true;
1355         }
1356
1357         return false;
1358 }
1359
1360 /*
1361  * is_dummy_rel --- has relation been proven empty?
1362  */
1363 static bool
1364 is_dummy_rel(RelOptInfo *rel)
1365 {
1366         return IS_DUMMY_REL(rel);
1367 }
1368
1369 /*
1370  * Mark a relation as proven empty.
1371  *
1372  * During GEQO planning, this can get invoked more than once on the same
1373  * baserel struct, so it's worth checking to see if the rel is already marked
1374  * dummy.
1375  *
1376  * Also, when called during GEQO join planning, we are in a short-lived
1377  * memory context.  We must make sure that the dummy path attached to a
1378  * baserel survives the GEQO cycle, else the baserel is trashed for future
1379  * GEQO cycles.  On the other hand, when we are marking a joinrel during GEQO,
1380  * we don't want the dummy path to clutter the main planning context.  Upshot
1381  * is that the best solution is to explicitly make the dummy path in the same
1382  * context the given RelOptInfo is in.
1383  */
1384 static void
1385 mark_dummy_rel(RelOptInfo *rel)
1386 {
1387         MemoryContext oldcontext;
1388
1389         /* Already marked? */
1390         if (is_dummy_rel(rel))
1391                 return;
1392
1393         /* No, so choose correct context to make the dummy path in */
1394         oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
1395
1396         /* Set dummy size estimate */
1397         rel->rows = 0;
1398
1399         /* Evict any previously chosen paths */
1400         rel->pathlist = NIL;
1401         rel->partial_pathlist = NIL;
1402
1403         /* Set up the dummy path */
1404         add_path(rel, (Path *) create_append_path(rel, NIL, NULL, 0));
1405
1406         /* Set or update cheapest_total_path and related fields */
1407         set_cheapest(rel);
1408
1409         MemoryContextSwitchTo(oldcontext);
1410 }
1411
1412 /*
1413  * restriction_is_constant_false --- is a restrictlist just FALSE?
1414  *
1415  * In cases where a qual is provably constant FALSE, eval_const_expressions
1416  * will generally have thrown away anything that's ANDed with it.  In outer
1417  * join situations this will leave us computing cartesian products only to
1418  * decide there's no match for an outer row, which is pretty stupid.  So,
1419  * we need to detect the case.
1420  *
1421  * If only_pushed_down is TRUE, then consider only pushed-down quals.
1422  */
1423 static bool
1424 restriction_is_constant_false(List *restrictlist, bool only_pushed_down)
1425 {
1426         ListCell   *lc;
1427
1428         /*
1429          * Despite the above comment, the restriction list we see here might
1430          * possibly have other members besides the FALSE constant, since other
1431          * quals could get "pushed down" to the outer join level.  So we check
1432          * each member of the list.
1433          */
1434         foreach(lc, restrictlist)
1435         {
1436                 RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
1437
1438                 Assert(IsA(rinfo, RestrictInfo));
1439                 if (only_pushed_down && !rinfo->is_pushed_down)
1440                         continue;
1441
1442                 if (rinfo->clause && IsA(rinfo->clause, Const))
1443                 {
1444                         Const      *con = (Const *) rinfo->clause;
1445
1446                         /* constant NULL is as good as constant FALSE for our purposes */
1447                         if (con->constisnull)
1448                                 return true;
1449                         if (!DatumGetBool(con->constvalue))
1450                                 return true;
1451                 }
1452         }
1453         return false;
1454 }