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  *     accumulate_append_subpath()
  10  *     standard_join_search()
  11  *
  12  * src/backend/optimizer/path/joinrels.c
  13  *     join_search_one_level()
  14  *     make_rels_by_clause_joins()
  15  *     make_rels_by_clauseless_joins()
  16  *     join_is_legal()
  17  *     has_join_restriction()
  18  *     is_dummy_rel()
  19  *     mark_dummy_rel()
  20  *     restriction_is_constant_false()
  21  *
  22  * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
  23  * Portions Copyright (c) 1994, Regents of the University of California
  24  *
  25  *-------------------------------------------------------------------------
  26  */
  27
  28 /*
  29  * set_append_rel_pathlist
  30  *        Build access paths for an "append relation"
  31  */
  32 static void
  33 set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
  34                                                 Index rti, RangeTblEntry *rte)
  35 {
  36         int                     parentRTindex = rti;
  37         List       *live_childrels = NIL;
  38         List       *subpaths = NIL;
  39         List       *all_child_pathkeys = NIL;
  40         List       *all_child_outers = NIL;
  41         ListCell   *l;
  42
  43         /*
  44          * Generate access paths for each member relation, and remember the
  45          * cheapest path for each one.  Also, identify all pathkeys (orderings)
  46          * and parameterizations (required_outer sets) available for the member
  47          * relations.
  48          */
  49         foreach(l, root->append_rel_list)
  50         {
  51                 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
  52                 int                     childRTindex;
  53                 RangeTblEntry *childRTE;
  54                 RelOptInfo *childrel;
  55                 ListCell   *lcp;
  56
  57                 /* append_rel_list contains all append rels; ignore others */
  58                 if (appinfo->parent_relid != parentRTindex)
  59                         continue;
  60
  61                 /* Re-locate the child RTE and RelOptInfo */
  62                 childRTindex = appinfo->child_relid;
  63                 childRTE = root->simple_rte_array[childRTindex];
  64                 childrel = root->simple_rel_array[childRTindex];
  65
  66                 /*
  67                  * Compute the child's access paths.
  68                  */
  69                 set_rel_pathlist(root, childrel, childRTindex, childRTE);
  70
  71                 /*
  72                  * If child is dummy, ignore it.
  73                  */
  74                 if (IS_DUMMY_REL(childrel))
  75                         continue;
  76
  77                 /*
  78                  * Child is live, so add its cheapest access path to the Append path
  79                  * we are constructing for the parent.
  80                  */
  81                 subpaths = accumulate_append_subpath(subpaths,
  82                                                                                          childrel->cheapest_total_path);
  83
  84                 /* Remember which childrels are live, for logic below */
  85                 live_childrels = lappend(live_childrels, childrel);
  86
  87                 /*
  88                  * Collect lists of all the available path orderings and
  89                  * parameterizations for all the children.      We use these as a
  90                  * heuristic to indicate which sort orderings and parameterizations we
  91                  * should build Append and MergeAppend paths for.
  92                  */
  93                 foreach(lcp, childrel->pathlist)
  94                 {
  95                         Path       *childpath = (Path *) lfirst(lcp);
  96                         List       *childkeys = childpath->pathkeys;
  97                         Relids          childouter = PATH_REQ_OUTER(childpath);
  98
  99                         /* Unsorted paths don't contribute to pathkey list */
 100                         if (childkeys != NIL)
 101                         {
 102                                 ListCell   *lpk;
 103                                 bool            found = false;
 104
 105                                 /* Have we already seen this ordering? */
 106                                 foreach(lpk, all_child_pathkeys)
 107                                 {
 108                                         List       *existing_pathkeys = (List *) lfirst(lpk);
 109
 110                                         if (compare_pathkeys(existing_pathkeys,
 111                                                                                  childkeys) == PATHKEYS_EQUAL)
 112                                         {
 113                                                 found = true;
 114                                                 break;
 115                                         }
 116                                 }
 117                                 if (!found)
 118                                 {
 119                                         /* No, so add it to all_child_pathkeys */
 120                                         all_child_pathkeys = lappend(all_child_pathkeys,
 121                                                                                                  childkeys);
 122                                 }
 123                         }
 124
 125                         /* Unparameterized paths don't contribute to param-set list */
 126                         if (childouter)
 127                         {
 128                                 ListCell   *lco;
 129                                 bool            found = false;
 130
 131                                 /* Have we already seen this param set? */
 132                                 foreach(lco, all_child_outers)
 133                                 {
 134                                         Relids          existing_outers = (Relids) lfirst(lco);
 135
 136                                         if (bms_equal(existing_outers, childouter))
 137                                         {
 138                                                 found = true;
 139                                                 break;
 140                                         }
 141                                 }
 142                                 if (!found)
 143                                 {
 144                                         /* No, so add it to all_child_outers */
 145                                         all_child_outers = lappend(all_child_outers,
 146                                                                                            childouter);
 147                                 }
 148                         }
 149                 }
 150         }
 151
 152         /*
 153          * Next, build an unordered, unparameterized Append path for the rel.
 154          * (Note: this is correct even if we have zero or one live subpath due to
 155          * constraint exclusion.)
 156          */
 157         add_path(rel, (Path *) create_append_path(rel, subpaths, NULL));
 158
 159         /*
 160          * Build unparameterized MergeAppend paths based on the collected list of
 161          * child pathkeys.
 162          */
 163         generate_mergeappend_paths(root, rel, live_childrels, all_child_pathkeys);
 164
 165         /*
 166          * Build Append paths for each parameterization seen among the child rels.
 167          * (This may look pretty expensive, but in most cases of practical
 168          * interest, the child rels will expose mostly the same parameterizations,
 169          * so that not that many cases actually get considered here.)
 170          *
 171          * The Append node itself cannot enforce quals, so all qual checking must
 172          * be done in the child paths.  This means that to have a parameterized
 173          * Append path, we must have the exact same parameterization for each
 174          * child path; otherwise some children might be failing to check the
 175          * moved-down quals.  To make them match up, we can try to increase the
 176          * parameterization of lesser-parameterized paths.
 177          */
 178         foreach(l, all_child_outers)
 179         {
 180                 Relids          required_outer = (Relids) lfirst(l);
 181                 bool            ok = true;
 182                 ListCell   *lcr;
 183
 184                 /* Select the child paths for an Append with this parameterization */
 185                 subpaths = NIL;
 186                 foreach(lcr, live_childrels)
 187                 {
 188                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 189                         Path       *cheapest_total;
 190
 191                         cheapest_total =
 192                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 193                                                                                            NIL,
 194                                                                                            required_outer,
 195                                                                                            TOTAL_COST);
 196                         Assert(cheapest_total != NULL);
 197
 198                         /* Children must have exactly the desired parameterization */
 199                         if (!bms_equal(PATH_REQ_OUTER(cheapest_total), required_outer))
 200                         {
 201                                 cheapest_total = reparameterize_path(root, cheapest_total,
 202                                                                                                          required_outer, 1.0);
 203                                 if (cheapest_total == NULL)
 204                                 {
 205                                         ok = false;
 206                                         break;
 207                                 }
 208                         }
 209
 210                         subpaths = accumulate_append_subpath(subpaths, cheapest_total);
 211                 }
 212
 213                 if (ok)
 214                         add_path(rel, (Path *)
 215                                          create_append_path(rel, subpaths, required_outer));
 216         }
 217
 218         /* Select cheapest paths */
 219         set_cheapest(rel);
 220 }
 221
 222 /*
 223  * generate_mergeappend_paths
 224  *              Generate MergeAppend paths for an append relation
 225  *
 226  * Generate a path for each ordering (pathkey list) appearing in
 227  * all_child_pathkeys.
 228  *
 229  * We consider both cheapest-startup and cheapest-total cases, ie, for each
 230  * interesting ordering, collect all the cheapest startup subpaths and all the
 231  * cheapest total paths, and build a MergeAppend path for each case.
 232  *
 233  * We don't currently generate any parameterized MergeAppend paths.  While
 234  * it would not take much more code here to do so, it's very unclear that it
 235  * is worth the planning cycles to investigate such paths: there's little
 236  * use for an ordered path on the inside of a nestloop.  In fact, it's likely
 237  * that the current coding of add_path would reject such paths out of hand,
 238  * because add_path gives no credit for sort ordering of parameterized paths,
 239  * and a parameterized MergeAppend is going to be more expensive than the
 240  * corresponding parameterized Append path.  If we ever try harder to support
 241  * parameterized mergejoin plans, it might be worth adding support for
 242  * parameterized MergeAppends to feed such joins.  (See notes in
 243  * optimizer/README for why that might not ever happen, though.)
 244  */
 245 static void
 246 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
 247                                                    List *live_childrels,
 248                                                    List *all_child_pathkeys)
 249 {
 250         ListCell   *lcp;
 251
 252         foreach(lcp, all_child_pathkeys)
 253         {
 254                 List       *pathkeys = (List *) lfirst(lcp);
 255                 List       *startup_subpaths = NIL;
 256                 List       *total_subpaths = NIL;
 257                 bool            startup_neq_total = false;
 258                 ListCell   *lcr;
 259
 260                 /* Select the child paths for this ordering... */
 261                 foreach(lcr, live_childrels)
 262                 {
 263                         RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
 264                         Path       *cheapest_startup,
 265                                            *cheapest_total;
 266
 267                         /* Locate the right paths, if they are available. */
 268                         cheapest_startup =
 269                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 270                                                                                            pathkeys,
 271                                                                                            NULL,
 272                                                                                            STARTUP_COST);
 273                         cheapest_total =
 274                                 get_cheapest_path_for_pathkeys(childrel->pathlist,
 275                                                                                            pathkeys,
 276                                                                                            NULL,
 277                                                                                            TOTAL_COST);
 278
 279                         /*
 280                          * If we can't find any paths with the right order just use the
 281                          * cheapest-total path; we'll have to sort it later.
 282                          */
 283                         if (cheapest_startup == NULL || cheapest_total == NULL)
 284                         {
 285                                 cheapest_startup = cheapest_total =
 286                                         childrel->cheapest_total_path;
 287                                 /* Assert we do have an unparameterized path for this child */
 288                                 Assert(cheapest_total->param_info == NULL);
 289                         }
 290
 291                         /*
 292                          * Notice whether we actually have different paths for the
 293                          * "cheapest" and "total" cases; frequently there will be no point
 294                          * in two create_merge_append_path() calls.
 295                          */
 296                         if (cheapest_startup != cheapest_total)
 297                                 startup_neq_total = true;
 298
 299                         startup_subpaths =
 300                                 accumulate_append_subpath(startup_subpaths, cheapest_startup);
 301                         total_subpaths =
 302                                 accumulate_append_subpath(total_subpaths, cheapest_total);
 303                 }
 304
 305                 /* ... and build the MergeAppend paths */
 306                 add_path(rel, (Path *) create_merge_append_path(root,
 307                                                                                                                 rel,
 308                                                                                                                 startup_subpaths,
 309                                                                                                                 pathkeys,
 310                                                                                                                 NULL));
 311                 if (startup_neq_total)
 312                         add_path(rel, (Path *) create_merge_append_path(root,
 313                                                                                                                         rel,
 314                                                                                                                         total_subpaths,
 315                                                                                                                         pathkeys,
 316                                                                                                                         NULL));
 317         }
 318 }
 319
 320 /*
 321  * accumulate_append_subpath
 322  *              Add a subpath to the list being built for an Append or MergeAppend
 323  *
 324  * It's possible that the child is itself an Append path, in which case
 325  * we can "cut out the middleman" and just add its child paths to our
 326  * own list.  (We don't try to do this earlier because we need to
 327  * apply both levels of transformation to the quals.)
 328  */
 329 static List *
 330 accumulate_append_subpath(List *subpaths, Path *path)
 331 {
 332         if (IsA(path, AppendPath))
 333         {
 334                 AppendPath *apath = (AppendPath *) path;
 335
 336                 /* list_copy is important here to avoid sharing list substructure */
 337                 return list_concat(subpaths, list_copy(apath->subpaths));
 338         }
 339         else
 340                 return lappend(subpaths, path);
 341 }
 342
 343 /*
 344  * standard_join_search
 345  *        Find possible joinpaths for a query by successively finding ways
 346  *        to join component relations into join relations.
 347  *
 348  * 'levels_needed' is the number of iterations needed, ie, the number of
 349  *              independent jointree items in the query.  This is > 1.
 350  *
 351  * 'initial_rels' is a list of RelOptInfo nodes for each independent
 352  *              jointree item.  These are the components to be joined together.
 353  *              Note that levels_needed == list_length(initial_rels).
 354  *
 355  * Returns the final level of join relations, i.e., the relation that is
 356  * the result of joining all the original relations together.
 357  * At least one implementation path must be provided for this relation and
 358  * all required sub-relations.
 359  *
 360  * To support loadable plugins that modify planner behavior by changing the
 361  * join searching algorithm, we provide a hook variable that lets a plugin
 362  * replace or supplement this function.  Any such hook must return the same
 363  * final join relation as the standard code would, but it might have a
 364  * different set of implementation paths attached, and only the sub-joinrels
 365  * needed for these paths need have been instantiated.
 366  *
 367  * Note to plugin authors: the functions invoked during standard_join_search()
 368  * modify root->join_rel_list and root->join_rel_hash.  If you want to do more
 369  * than one join-order search, you'll probably need to save and restore the
 370  * original states of those data structures.  See geqo_eval() for an example.
 371  */
 372 RelOptInfo *
 373 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
 374 {
 375         int                     lev;
 376         RelOptInfo *rel;
 377
 378         /*
 379          * This function cannot be invoked recursively within any one planning
 380          * problem, so join_rel_level[] can't be in use already.
 381          */
 382         Assert(root->join_rel_level == NULL);
 383
 384         /*
 385          * We employ a simple "dynamic programming" algorithm: we first find all
 386          * ways to build joins of two jointree items, then all ways to build joins
 387          * of three items (from two-item joins and single items), then four-item
 388          * joins, and so on until we have considered all ways to join all the
 389          * items into one rel.
 390          *
 391          * root->join_rel_level[j] is a list of all the j-item rels.  Initially we
 392          * set root->join_rel_level[1] to represent all the single-jointree-item
 393          * relations.
 394          */
 395         root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
 396
 397         root->join_rel_level[1] = initial_rels;
 398
 399         for (lev = 2; lev <= levels_needed; lev++)
 400         {
 401                 ListCell   *lc;
 402
 403                 /*
 404                  * Determine all possible pairs of relations to be joined at this
 405                  * level, and build paths for making each one from every available
 406                  * pair of lower-level relations.
 407                  */
 408                 join_search_one_level(root, lev);
 409
 410                 /*
 411                  * Do cleanup work on each just-processed rel.
 412                  */
 413                 foreach(lc, root->join_rel_level[lev])
 414                 {
 415                         rel = (RelOptInfo *) lfirst(lc);
 416
 417                         /* Find and save the cheapest paths for this rel */
 418                         set_cheapest(rel);
 419
 420 #ifdef OPTIMIZER_DEBUG
 421                         debug_print_rel(root, rel);
 422 #endif
 423                 }
 424         }
 425
 426         /*
 427          * We should have a single rel at the final level.
 428          */
 429         if (root->join_rel_level[levels_needed] == NIL)
 430                 elog(ERROR, "failed to build any %d-way joins", levels_needed);
 431         Assert(list_length(root->join_rel_level[levels_needed]) == 1);
 432
 433         rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
 434
 435         root->join_rel_level = NULL;
 436
 437         return rel;
 438 }
 439
 440 /*
 441  * join_search_one_level
 442  *        Consider ways to produce join relations containing exactly 'level'
 443  *        jointree items.  (This is one step of the dynamic-programming method
 444  *        embodied in standard_join_search.)  Join rel nodes for each feasible
 445  *        combination of lower-level rels are created and returned in a list.
 446  *        Implementation paths are created for each such joinrel, too.
 447  *
 448  * level: level of rels we want to make this time
 449  * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
 450  *
 451  * The result is returned in root->join_rel_level[level].
 452  */
 453 void
 454 join_search_one_level(PlannerInfo *root, int level)
 455 {
 456         List      **joinrels = root->join_rel_level;
 457         ListCell   *r;
 458         int                     k;
 459
 460         Assert(joinrels[level] == NIL);
 461
 462         /* Set join_cur_level so that new joinrels are added to proper list */
 463         root->join_cur_level = level;
 464
 465         /*
 466          * First, consider left-sided and right-sided plans, in which rels of
 467          * exactly level-1 member relations are joined against initial relations.
 468          * We prefer to join using join clauses, but if we find a rel of level-1
 469          * members that has no join clauses, we will generate Cartesian-product
 470          * joins against all initial rels not already contained in it.
 471          */
 472         foreach(r, joinrels[level - 1])
 473         {
 474                 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 475
 476                 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
 477                         has_join_restriction(root, old_rel))
 478                 {
 479                         /*
 480                          * There are join clauses or join order restrictions relevant to
 481                          * this rel, so consider joins between this rel and (only) those
 482                          * initial rels it is linked to by a clause or restriction.
 483                          *
 484                          * At level 2 this condition is symmetric, so there is no need to
 485                          * look at initial rels before this one in the list; we already
 486                          * considered such joins when we were at the earlier rel.  (The
 487                          * mirror-image joins are handled automatically by make_join_rel.)
 488                          * In later passes (level > 2), we join rels of the previous level
 489                          * to each initial rel they don't already include but have a join
 490                          * clause or restriction with.
 491                          */
 492                         ListCell   *other_rels;
 493
 494                         if (level == 2)         /* consider remaining initial rels */
 495                                 other_rels = lnext(r);
 496                         else    /* consider all initial rels */
 497                                 other_rels = list_head(joinrels[1]);
 498
 499                         make_rels_by_clause_joins(root,
 500                                                                           old_rel,
 501                                                                           other_rels);
 502                 }
 503                 else
 504                 {
 505                         /*
 506                          * Oops, we have a relation that is not joined to any other
 507                          * relation, either directly or by join-order restrictions.
 508                          * Cartesian product time.
 509                          *
 510                          * We consider a cartesian product with each not-already-included
 511                          * initial rel, whether it has other join clauses or not.  At
 512                          * level 2, if there are two or more clauseless initial rels, we
 513                          * will redundantly consider joining them in both directions; but
 514                          * such cases aren't common enough to justify adding complexity to
 515                          * avoid the duplicated effort.
 516                          */
 517                         make_rels_by_clauseless_joins(root,
 518                                                                                   old_rel,
 519                                                                                   list_head(joinrels[1]));
 520                 }
 521         }
 522
 523         /*
 524          * Now, consider "bushy plans" in which relations of k initial rels are
 525          * joined to relations of level-k initial rels, for 2 <= k <= level-2.
 526          *
 527          * We only consider bushy-plan joins for pairs of rels where there is a
 528          * suitable join clause (or join order restriction), in order to avoid
 529          * unreasonable growth of planning time.
 530          */
 531         for (k = 2;; k++)
 532         {
 533                 int                     other_level = level - k;
 534
 535                 /*
 536                  * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
 537                  * need to go as far as the halfway point.
 538                  */
 539                 if (k > other_level)
 540                         break;
 541
 542                 foreach(r, joinrels[k])
 543                 {
 544                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 545                         ListCell   *other_rels;
 546                         ListCell   *r2;
 547
 548                         /*
 549                          * We can ignore relations without join clauses here, unless they
 550                          * participate in join-order restrictions --- then we might have
 551                          * to force a bushy join plan.
 552                          */
 553                         if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
 554                                 !has_join_restriction(root, old_rel))
 555                                 continue;
 556
 557                         if (k == other_level)
 558                                 other_rels = lnext(r);  /* only consider remaining rels */
 559                         else
 560                                 other_rels = list_head(joinrels[other_level]);
 561
 562                         for_each_cell(r2, other_rels)
 563                         {
 564                                 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
 565
 566                                 if (!bms_overlap(old_rel->relids, new_rel->relids))
 567                                 {
 568                                         /*
 569                                          * OK, we can build a rel of the right level from this
 570                                          * pair of rels.  Do so if there is at least one relevant
 571                                          * join clause or join order restriction.
 572                                          */
 573                                         if (have_relevant_joinclause(root, old_rel, new_rel) ||
 574                                                 have_join_order_restriction(root, old_rel, new_rel))
 575                                         {
 576                                                 (void) make_join_rel(root, old_rel, new_rel);
 577                                         }
 578                                 }
 579                         }
 580                 }
 581         }
 582
 583         /*----------
 584          * Last-ditch effort: if we failed to find any usable joins so far, force
 585          * a set of cartesian-product joins to be generated.  This handles the
 586          * special case where all the available rels have join clauses but we
 587          * cannot use any of those clauses yet.  This can only happen when we are
 588          * considering a join sub-problem (a sub-joinlist) and all the rels in the
 589          * sub-problem have only join clauses with rels outside the sub-problem.
 590          * An example is
 591          *
 592          *              SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
 593          *              WHERE a.w = c.x and b.y = d.z;
 594          *
 595          * If the "a INNER JOIN b" sub-problem does not get flattened into the
 596          * upper level, we must be willing to make a cartesian join of a and b;
 597          * but the code above will not have done so, because it thought that both
 598          * a and b have joinclauses.  We consider only left-sided and right-sided
 599          * cartesian joins in this case (no bushy).
 600          *----------
 601          */
 602         if (joinrels[level] == NIL)
 603         {
 604                 /*
 605                  * This loop is just like the first one, except we always call
 606                  * make_rels_by_clauseless_joins().
 607                  */
 608                 foreach(r, joinrels[level - 1])
 609                 {
 610                         RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
 611
 612                         make_rels_by_clauseless_joins(root,
 613                                                                                   old_rel,
 614                                                                                   list_head(joinrels[1]));
 615                 }
 616
 617                 /*----------
 618                  * When special joins are involved, there may be no legal way
 619                  * to make an N-way join for some values of N.  For example consider
 620                  *
 621                  * SELECT ... FROM t1 WHERE
 622                  *       x IN (SELECT ... FROM t2,t3 WHERE ...) AND
 623                  *       y IN (SELECT ... FROM t4,t5 WHERE ...)
 624                  *
 625                  * We will flatten this query to a 5-way join problem, but there are
 626                  * no 4-way joins that join_is_legal() will consider legal.  We have
 627                  * to accept failure at level 4 and go on to discover a workable
 628                  * bushy plan at level 5.
 629                  *
 630                  * However, if there are no special joins and no lateral references
 631                  * then join_is_legal() should never fail, and so the following sanity
 632                  * check is useful.
 633                  *----------
 634                  */
 635                 if (joinrels[level] == NIL &&
 636                         root->join_info_list == NIL &&
 637                         root->lateral_info_list == NIL)
 638                         elog(ERROR, "failed to build any %d-way joins", level);
 639         }
 640 }
 641
 642 /*
 643  * make_rels_by_clause_joins
 644  *        Build joins between the given relation 'old_rel' and other relations
 645  *        that participate in join clauses that 'old_rel' also participates in
 646  *        (or participate in join-order restrictions with it).
 647  *        The join rels are returned in root->join_rel_level[join_cur_level].
 648  *
 649  * Note: at levels above 2 we will generate the same joined relation in
 650  * multiple ways --- for example (a join b) join c is the same RelOptInfo as
 651  * (b join c) join a, though the second case will add a different set of Paths
 652  * to it.  This is the reason for using the join_rel_level mechanism, which
 653  * automatically ensures that each new joinrel is only added to the list once.
 654  *
 655  * 'old_rel' is the relation entry for the relation to be joined
 656  * 'other_rels': the first cell in a linked list containing the other
 657  * rels to be considered for joining
 658  *
 659  * Currently, this is only used with initial rels in other_rels, but it
 660  * will work for joining to joinrels too.
 661  */
 662 static void
 663 make_rels_by_clause_joins(PlannerInfo *root,
 664                                                   RelOptInfo *old_rel,
 665                                                   ListCell *other_rels)
 666 {
 667         ListCell   *l;
 668
 669         for_each_cell(l, other_rels)
 670         {
 671                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 672
 673                 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
 674                         (have_relevant_joinclause(root, old_rel, other_rel) ||
 675                          have_join_order_restriction(root, old_rel, other_rel)))
 676                 {
 677                         (void) make_join_rel(root, old_rel, other_rel);
 678                 }
 679         }
 680 }
 681
 682 /*
 683  * make_rels_by_clauseless_joins
 684  *        Given a relation 'old_rel' and a list of other relations
 685  *        'other_rels', create a join relation between 'old_rel' and each
 686  *        member of 'other_rels' that isn't already included in 'old_rel'.
 687  *        The join rels are returned in root->join_rel_level[join_cur_level].
 688  *
 689  * 'old_rel' is the relation entry for the relation to be joined
 690  * 'other_rels': the first cell of a linked list containing the
 691  * other rels to be considered for joining
 692  *
 693  * Currently, this is only used with initial rels in other_rels, but it would
 694  * work for joining to joinrels too.
 695  */
 696 static void
 697 make_rels_by_clauseless_joins(PlannerInfo *root,
 698                                                           RelOptInfo *old_rel,
 699                                                           ListCell *other_rels)
 700 {
 701         ListCell   *l;
 702
 703         for_each_cell(l, other_rels)
 704         {
 705                 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 706
 707                 if (!bms_overlap(other_rel->relids, old_rel->relids))
 708                 {
 709                         (void) make_join_rel(root, old_rel, other_rel);
 710                 }
 711         }
 712 }
 713
 714 /*
 715  * join_is_legal
 716  *         Determine whether a proposed join is legal given the query's
 717  *         join order constraints; and if it is, determine the join type.
 718  *
 719  * Caller must supply not only the two rels, but the union of their relids.
 720  * (We could simplify the API by computing joinrelids locally, but this
 721  * would be redundant work in the normal path through make_join_rel.)
 722  *
 723  * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
 724  * else it's set to point to the associated SpecialJoinInfo node.  Also,
 725  * *reversed_p is set TRUE if the given relations need to be swapped to
 726  * match the SpecialJoinInfo node.
 727  */
 728 static bool
 729 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 730                           Relids joinrelids,
 731                           SpecialJoinInfo **sjinfo_p, bool *reversed_p)
 732 {
 733         SpecialJoinInfo *match_sjinfo;
 734         bool            reversed;
 735         bool            unique_ified;
 736         bool            is_valid_inner;
 737         bool            lateral_fwd;
 738         bool            lateral_rev;
 739         ListCell   *l;
 740
 741         /*
 742          * Ensure output params are set on failure return.      This is just to
 743          * suppress uninitialized-variable warnings from overly anal compilers.
 744          */
 745         *sjinfo_p = NULL;
 746         *reversed_p = false;
 747
 748         /*
 749          * If we have any special joins, the proposed join might be illegal; and
 750          * in any case we have to determine its join type.      Scan the join info
 751          * list for conflicts.
 752          */
 753         match_sjinfo = NULL;
 754         reversed = false;
 755         unique_ified = false;
 756         is_valid_inner = true;
 757
 758         foreach(l, root->join_info_list)
 759         {
 760                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
 761
 762                 /*
 763                  * This special join is not relevant unless its RHS overlaps the
 764                  * proposed join.  (Check this first as a fast path for dismissing
 765                  * most irrelevant SJs quickly.)
 766                  */
 767                 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
 768                         continue;
 769
 770                 /*
 771                  * Also, not relevant if proposed join is fully contained within RHS
 772                  * (ie, we're still building up the RHS).
 773                  */
 774                 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
 775                         continue;
 776
 777                 /*
 778                  * Also, not relevant if SJ is already done within either input.
 779                  */
 780                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 781                         bms_is_subset(sjinfo->min_righthand, rel1->relids))
 782                         continue;
 783                 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
 784                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
 785                         continue;
 786
 787                 /*
 788                  * If it's a semijoin and we already joined the RHS to any other rels
 789                  * within either input, then we must have unique-ified the RHS at that
 790                  * point (see below).  Therefore the semijoin is no longer relevant in
 791                  * this join path.
 792                  */
 793                 if (sjinfo->jointype == JOIN_SEMI)
 794                 {
 795                         if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
 796                                 !bms_equal(sjinfo->syn_righthand, rel1->relids))
 797                                 continue;
 798                         if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
 799                                 !bms_equal(sjinfo->syn_righthand, rel2->relids))
 800                                 continue;
 801                 }
 802
 803                 /*
 804                  * If one input contains min_lefthand and the other contains
 805                  * min_righthand, then we can perform the SJ at this join.
 806                  *
 807                  * Barf if we get matches to more than one SJ (is that possible?)
 808                  */
 809                 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
 810                         bms_is_subset(sjinfo->min_righthand, rel2->relids))
 811                 {
 812                         if (match_sjinfo)
 813                                 return false;   /* invalid join path */
 814                         match_sjinfo = sjinfo;
 815                         reversed = false;
 816                 }
 817                 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
 818                                  bms_is_subset(sjinfo->min_righthand, rel1->relids))
 819                 {
 820                         if (match_sjinfo)
 821                                 return false;   /* invalid join path */
 822                         match_sjinfo = sjinfo;
 823                         reversed = true;
 824                 }
 825                 else if (sjinfo->jointype == JOIN_SEMI &&
 826                                  bms_equal(sjinfo->syn_righthand, rel2->relids) &&
 827                                  create_unique_path(root, rel2, rel2->cheapest_total_path,
 828                                                                         sjinfo) != NULL)
 829                 {
 830                         /*----------
 831                          * For a semijoin, we can join the RHS to anything else by
 832                          * unique-ifying the RHS (if the RHS can be unique-ified).
 833                          * We will only get here if we have the full RHS but less
 834                          * than min_lefthand on the LHS.
 835                          *
 836                          * The reason to consider such a join path is exemplified by
 837                          *      SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
 838                          * If we insist on doing this as a semijoin we will first have
 839                          * to form the cartesian product of A*B.  But if we unique-ify
 840                          * C then the semijoin becomes a plain innerjoin and we can join
 841                          * in any order, eg C to A and then to B.  When C is much smaller
 842                          * than A and B this can be a huge win.  So we allow C to be
 843                          * joined to just A or just B here, and then make_join_rel has
 844                          * to handle the case properly.
 845                          *
 846                          * Note that actually we'll allow unique-ified C to be joined to
 847                          * some other relation D here, too.  That is legal, if usually not
 848                          * very sane, and this routine is only concerned with legality not
 849                          * with whether the join is good strategy.
 850                          *----------
 851                          */
 852                         if (match_sjinfo)
 853                                 return false;   /* invalid join path */
 854                         match_sjinfo = sjinfo;
 855                         reversed = false;
 856                         unique_ified = true;
 857                 }
 858                 else if (sjinfo->jointype == JOIN_SEMI &&
 859                                  bms_equal(sjinfo->syn_righthand, rel1->relids) &&
 860                                  create_unique_path(root, rel1, rel1->cheapest_total_path,
 861                                                                         sjinfo) != NULL)
 862                 {
 863                         /* Reversed semijoin case */
 864                         if (match_sjinfo)
 865                                 return false;   /* invalid join path */
 866                         match_sjinfo = sjinfo;
 867                         reversed = true;
 868                         unique_ified = true;
 869                 }
 870                 else
 871                 {
 872                         /*----------
 873                          * Otherwise, the proposed join overlaps the RHS but isn't
 874                          * a valid implementation of this SJ.  It might still be
 875                          * a legal join, however.  If both inputs overlap the RHS,
 876                          * assume that it's OK.  Since the inputs presumably got past
 877                          * this function's checks previously, they can't overlap the
 878                          * LHS and their violations of the RHS boundary must represent
 879                          * SJs that have been determined to commute with this one.
 880                          * We have to allow this to work correctly in cases like
 881                          *              (a LEFT JOIN (b JOIN (c LEFT JOIN d)))
 882                          * when the c/d join has been determined to commute with the join
 883                          * to a, and hence d is not part of min_righthand for the upper
 884                          * join.  It should be legal to join b to c/d but this will appear
 885                          * as a violation of the upper join's RHS.
 886                          * Furthermore, if one input overlaps the RHS and the other does
 887                          * not, we should still allow the join if it is a valid
 888                          * implementation of some other SJ.  We have to allow this to
 889                          * support the associative identity
 890                          *              (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab
 891                          * since joining B directly to C violates the lower SJ's RHS.
 892                          * We assume that make_outerjoininfo() set things up correctly
 893                          * so that we'll only match to some SJ if the join is valid.
 894                          * Set flag here to check at bottom of loop.
 895                          *----------
 896                          */
 897                         if (sjinfo->jointype != JOIN_SEMI &&
 898                                 bms_overlap(rel1->relids, sjinfo->min_righthand) &&
 899                                 bms_overlap(rel2->relids, sjinfo->min_righthand))
 900                         {
 901                                 /* seems OK */
 902                                 Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand));
 903                         }
 904                         else
 905                                 is_valid_inner = false;
 906                 }
 907         }
 908
 909         /*
 910          * Fail if violated some SJ's RHS and didn't match to another SJ. However,
 911          * "matching" to a semijoin we are implementing by unique-ification
 912          * doesn't count (think: it's really an inner join).
 913          */
 914         if (!is_valid_inner &&
 915                 (match_sjinfo == NULL || unique_ified))
 916                 return false;                   /* invalid join path */
 917
 918         /*
 919          * We also have to check for constraints imposed by LATERAL references.
 920          * The proposed rels could each contain lateral references to the other,
 921          * in which case the join is impossible.  If there are lateral references
 922          * in just one direction, then the join has to be done with a nestloop
 923          * with the lateral referencer on the inside.  If the join matches an SJ
 924          * that cannot be implemented by such a nestloop, the join is impossible.
 925          */
 926         lateral_fwd = lateral_rev = false;
 927         foreach(l, root->lateral_info_list)
 928         {
 929                 LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
 930
 931                 if (bms_is_subset(ljinfo->lateral_rhs, rel2->relids) &&
 932                         bms_overlap(ljinfo->lateral_lhs, rel1->relids))
 933                 {
 934                         /* has to be implemented as nestloop with rel1 on left */
 935                         if (lateral_rev)
 936                                 return false;   /* have lateral refs in both directions */
 937                         lateral_fwd = true;
 938                         if (!bms_is_subset(ljinfo->lateral_lhs, rel1->relids))
 939                                 return false;   /* rel1 can't compute the required parameter */
 940                         if (match_sjinfo &&
 941                                 (reversed || match_sjinfo->jointype == JOIN_FULL))
 942                                 return false;   /* not implementable as nestloop */
 943                 }
 944                 if (bms_is_subset(ljinfo->lateral_rhs, rel1->relids) &&
 945                         bms_overlap(ljinfo->lateral_lhs, rel2->relids))
 946                 {
 947                         /* has to be implemented as nestloop with rel2 on left */
 948                         if (lateral_fwd)
 949                                 return false;   /* have lateral refs in both directions */
 950                         lateral_rev = true;
 951                         if (!bms_is_subset(ljinfo->lateral_lhs, rel2->relids))
 952                                 return false;   /* rel2 can't compute the required parameter */
 953                         if (match_sjinfo &&
 954                                 (!reversed || match_sjinfo->jointype == JOIN_FULL))
 955                                 return false;   /* not implementable as nestloop */
 956                 }
 957         }
 958
 959         /* Otherwise, it's a valid join */
 960         *sjinfo_p = match_sjinfo;
 961         *reversed_p = reversed;
 962         return true;
 963 }
 964
 965 /*
 966  * has_join_restriction
 967  *              Detect whether the specified relation has join-order restrictions,
 968  *              due to being inside an outer join or an IN (sub-SELECT),
 969  *              or participating in any LATERAL references.
 970  *
 971  * Essentially, this tests whether have_join_order_restriction() could
 972  * succeed with this rel and some other one.  It's OK if we sometimes
 973  * say "true" incorrectly.      (Therefore, we don't bother with the relatively
 974  * expensive has_legal_joinclause test.)
 975  */
 976 static bool
 977 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
 978 {
 979         ListCell   *l;
 980
 981         foreach(l, root->lateral_info_list)
 982         {
 983                 LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
 984
 985                 if (bms_is_subset(ljinfo->lateral_rhs, rel->relids) ||
 986                         bms_overlap(ljinfo->lateral_lhs, rel->relids))
 987                         return true;
 988         }
 989
 990         foreach(l, root->join_info_list)
 991         {
 992                 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
 993
 994                 /* ignore full joins --- other mechanisms preserve their ordering */
 995                 if (sjinfo->jointype == JOIN_FULL)
 996                         continue;
 997
 998                 /* ignore if SJ is already contained in rel */
 999                 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
1000                         bms_is_subset(sjinfo->min_righthand, rel->relids))
1001                         continue;
1002
1003                 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
1004                 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
1005                         bms_overlap(sjinfo->min_righthand, rel->relids))
1006                         return true;
1007         }
1008
1009         return false;
1010 }
1011
1012 /*
1013  * is_dummy_rel --- has relation been proven empty?
1014  */
1015 static bool
1016 is_dummy_rel(RelOptInfo *rel)
1017 {
1018         return IS_DUMMY_REL(rel);
1019 }
1020
1021 /*
1022  * Mark a relation as proven empty.
1023  *
1024  * During GEQO planning, this can get invoked more than once on the same
1025  * baserel struct, so it's worth checking to see if the rel is already marked
1026  * dummy.
1027  *
1028  * Also, when called during GEQO join planning, we are in a short-lived
1029  * memory context.      We must make sure that the dummy path attached to a
1030  * baserel survives the GEQO cycle, else the baserel is trashed for future
1031  * GEQO cycles.  On the other hand, when we are marking a joinrel during GEQO,
1032  * we don't want the dummy path to clutter the main planning context.  Upshot
1033  * is that the best solution is to explicitly make the dummy path in the same
1034  * context the given RelOptInfo is in.
1035  */
1036 static void
1037 mark_dummy_rel(RelOptInfo *rel)
1038 {
1039         MemoryContext oldcontext;
1040
1041         /* Already marked? */
1042         if (is_dummy_rel(rel))
1043                 return;
1044
1045         /* No, so choose correct context to make the dummy path in */
1046         oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
1047
1048         /* Set dummy size estimate */
1049         rel->rows = 0;
1050
1051         /* Evict any previously chosen paths */
1052         rel->pathlist = NIL;
1053
1054         /* Set up the dummy path */
1055         add_path(rel, (Path *) create_append_path(rel, NIL, NULL));
1056
1057         /* Set or update cheapest_total_path and related fields */
1058         set_cheapest(rel);
1059
1060         MemoryContextSwitchTo(oldcontext);
1061 }
1062
1063 /*
1064  * restriction_is_constant_false --- is a restrictlist just FALSE?
1065  *
1066  * In cases where a qual is provably constant FALSE, eval_const_expressions
1067  * will generally have thrown away anything that's ANDed with it.  In outer
1068  * join situations this will leave us computing cartesian products only to
1069  * decide there's no match for an outer row, which is pretty stupid.  So,
1070  * we need to detect the case.
1071  *
1072  * If only_pushed_down is TRUE, then consider only pushed-down quals.
1073  */
1074 static bool
1075 restriction_is_constant_false(List *restrictlist, bool only_pushed_down)
1076 {
1077         ListCell   *lc;
1078
1079         /*
1080          * Despite the above comment, the restriction list we see here might
1081          * possibly have other members besides the FALSE constant, since other
1082          * quals could get "pushed down" to the outer join level.  So we check
1083          * each member of the list.
1084          */
1085         foreach(lc, restrictlist)
1086         {
1087                 RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
1088
1089                 Assert(IsA(rinfo, RestrictInfo));
1090                 if (only_pushed_down && !rinfo->is_pushed_down)
1091                         continue;
1092
1093                 if (rinfo->clause && IsA(rinfo->clause, Const))
1094                 {
1095                         Const      *con = (Const *) rinfo->clause;
1096
1097                         /* constant NULL is as good as constant FALSE for our purposes */
1098                         if (con->constisnull)
1099                                 return true;
1100                         if (!DatumGetBool(con->constvalue))
1101                                 return true;
1102                 }
1103         }
1104         return false;
1105 }