granicus.if.org Git - postgresql/blob - src/backend/optimizer/plan/planner.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * planner.c
   4  *        The query optimizer external interface.
   5  *
   6  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.186 2005/05/22 22:30:19 tgl Exp $
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15
  16 #include "postgres.h"
  17
  18 #include <limits.h>
  19
  20 #include "catalog/pg_operator.h"
  21 #include "catalog/pg_type.h"
  22 #include "executor/executor.h"
  23 #include "executor/nodeAgg.h"
  24 #include "miscadmin.h"
  25 #include "nodes/makefuncs.h"
  26 #ifdef OPTIMIZER_DEBUG
  27 #include "nodes/print.h"
  28 #endif
  29 #include "optimizer/clauses.h"
  30 #include "optimizer/cost.h"
  31 #include "optimizer/pathnode.h"
  32 #include "optimizer/paths.h"
  33 #include "optimizer/planmain.h"
  34 #include "optimizer/planner.h"
  35 #include "optimizer/prep.h"
  36 #include "optimizer/subselect.h"
  37 #include "optimizer/tlist.h"
  38 #include "optimizer/var.h"
  39 #include "parser/parsetree.h"
  40 #include "parser/parse_expr.h"
  41 #include "parser/parse_oper.h"
  42 #include "utils/selfuncs.h"
  43 #include "utils/syscache.h"
  44
  45
  46 ParamListInfo PlannerBoundParamList = NULL;             /* current boundParams */
  47
  48
  49 /* Expression kind codes for preprocess_expression */
  50 #define EXPRKIND_QUAL   0
  51 #define EXPRKIND_TARGET 1
  52 #define EXPRKIND_RTFUNC 2
  53 #define EXPRKIND_LIMIT  3
  54 #define EXPRKIND_ININFO 4
  55
  56
  57 static Node *preprocess_expression(Query *parse, Node *expr, int kind);
  58 static void preprocess_qual_conditions(Query *parse, Node *jtnode);
  59 static Plan *inheritance_planner(Query *parse, List *inheritlist);
  60 static Plan *grouping_planner(Query *parse, double tuple_fraction);
  61 static bool choose_hashed_grouping(Query *parse, double tuple_fraction,
  62                                            Path *cheapest_path, Path *sorted_path,
  63                                            List *sort_pathkeys, List *group_pathkeys,
  64                                            double dNumGroups, AggClauseCounts *agg_counts);
  65 static bool hash_safe_grouping(Query *parse);
  66 static List *make_subplanTargetList(Query *parse, List *tlist,
  67                                            AttrNumber **groupColIdx, bool *need_tlist_eval);
  68 static void locate_grouping_columns(Query *parse,
  69                                                 List *tlist,
  70                                                 List *sub_tlist,
  71                                                 AttrNumber *groupColIdx);
  72 static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
  73
  74
  75 /*****************************************************************************
  76  *
  77  *         Query optimizer entry point
  78  *
  79  *****************************************************************************/
  80 Plan *
  81 planner(Query *parse, bool isCursor, int cursorOptions,
  82                 ParamListInfo boundParams)
  83 {
  84         double          tuple_fraction;
  85         Plan       *result_plan;
  86         Index           save_PlannerQueryLevel;
  87         List       *save_PlannerParamList;
  88         ParamListInfo save_PlannerBoundParamList;
  89
  90         /*
  91          * The planner can be called recursively (an example is when
  92          * eval_const_expressions tries to pre-evaluate an SQL function). So,
  93          * these global state variables must be saved and restored.
  94          *
  95          * Query level and the param list cannot be moved into the Query
  96          * structure since their whole purpose is communication across
  97          * multiple sub-Queries. Also, boundParams is explicitly info from
  98          * outside the Query, and so is likewise better handled as a global
  99          * variable.
 100          *
 101          * Note we do NOT save and restore PlannerPlanId: it exists to assign
 102          * unique IDs to SubPlan nodes, and we want those IDs to be unique for
 103          * the life of a backend.  Also, PlannerInitPlan is saved/restored in
 104          * subquery_planner, not here.
 105          */
 106         save_PlannerQueryLevel = PlannerQueryLevel;
 107         save_PlannerParamList = PlannerParamList;
 108         save_PlannerBoundParamList = PlannerBoundParamList;
 109
 110         /* Initialize state for handling outer-level references and params */
 111         PlannerQueryLevel = 0;          /* will be 1 in top-level subquery_planner */
 112         PlannerParamList = NIL;
 113         PlannerBoundParamList = boundParams;
 114
 115         /* Determine what fraction of the plan is likely to be scanned */
 116         if (isCursor)
 117         {
 118                 /*
 119                  * We have no real idea how many tuples the user will ultimately
 120                  * FETCH from a cursor, but it seems a good bet that he doesn't
 121                  * want 'em all.  Optimize for 10% retrieval (you gotta better
 122                  * number?      Should this be a SETtable parameter?)
 123                  */
 124                 tuple_fraction = 0.10;
 125         }
 126         else
 127         {
 128                 /* Default assumption is we need all the tuples */
 129                 tuple_fraction = 0.0;
 130         }
 131
 132         /* primary planning entry point (may recurse for subqueries) */
 133         result_plan = subquery_planner(parse, tuple_fraction);
 134
 135         Assert(PlannerQueryLevel == 0);
 136
 137         /*
 138          * If creating a plan for a scrollable cursor, make sure it can run
 139          * backwards on demand.  Add a Material node at the top at need.
 140          */
 141         if (isCursor && (cursorOptions & CURSOR_OPT_SCROLL))
 142         {
 143                 if (!ExecSupportsBackwardScan(result_plan))
 144                         result_plan = materialize_finished_plan(result_plan);
 145         }
 146
 147         /* final cleanup of the plan */
 148         result_plan = set_plan_references(result_plan, parse->rtable);
 149
 150         /* executor wants to know total number of Params used overall */
 151         result_plan->nParamExec = list_length(PlannerParamList);
 152
 153         /* restore state for outer planner, if any */
 154         PlannerQueryLevel = save_PlannerQueryLevel;
 155         PlannerParamList = save_PlannerParamList;
 156         PlannerBoundParamList = save_PlannerBoundParamList;
 157
 158         return result_plan;
 159 }
 160
 161
 162 /*--------------------
 163  * subquery_planner
 164  *        Invokes the planner on a subquery.  We recurse to here for each
 165  *        sub-SELECT found in the query tree.
 166  *
 167  * parse is the querytree produced by the parser & rewriter.
 168  * tuple_fraction is the fraction of tuples we expect will be retrieved.
 169  * tuple_fraction is interpreted as explained for grouping_planner, below.
 170  *
 171  * Basically, this routine does the stuff that should only be done once
 172  * per Query object.  It then calls grouping_planner.  At one time,
 173  * grouping_planner could be invoked recursively on the same Query object;
 174  * that's not currently true, but we keep the separation between the two
 175  * routines anyway, in case we need it again someday.
 176  *
 177  * subquery_planner will be called recursively to handle sub-Query nodes
 178  * found within the query's expressions and rangetable.
 179  *
 180  * Returns a query plan.
 181  *--------------------
 182  */
 183 Plan *
 184 subquery_planner(Query *parse, double tuple_fraction)
 185 {
 186         List       *saved_initplan = PlannerInitPlan;
 187         int                     saved_planid = PlannerPlanId;
 188         bool            hasOuterJoins;
 189         Plan       *plan;
 190         List       *newHaving;
 191         List       *lst;
 192         ListCell   *l;
 193
 194         /* Set up for a new level of subquery */
 195         PlannerQueryLevel++;
 196         PlannerInitPlan = NIL;
 197
 198         /*
 199          * Look for IN clauses at the top level of WHERE, and transform them
 200          * into joins.  Note that this step only handles IN clauses originally
 201          * at top level of WHERE; if we pull up any subqueries in the next
 202          * step, their INs are processed just before pulling them up.
 203          */
 204         parse->in_info_list = NIL;
 205         if (parse->hasSubLinks)
 206                 parse->jointree->quals = pull_up_IN_clauses(parse,
 207                                                                                                  parse->jointree->quals);
 208
 209         /*
 210          * Check to see if any subqueries in the rangetable can be merged into
 211          * this query.
 212          */
 213         parse->jointree = (FromExpr *)
 214                 pull_up_subqueries(parse, (Node *) parse->jointree, false);
 215
 216         /*
 217          * Detect whether any rangetable entries are RTE_JOIN kind; if not, we
 218          * can avoid the expense of doing flatten_join_alias_vars().  Also
 219          * check for outer joins --- if none, we can skip
 220          * reduce_outer_joins(). This must be done after we have done
 221          * pull_up_subqueries, of course.
 222          */
 223         parse->hasJoinRTEs = false;
 224         hasOuterJoins = false;
 225         foreach(l, parse->rtable)
 226         {
 227                 RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 228
 229                 if (rte->rtekind == RTE_JOIN)
 230                 {
 231                         parse->hasJoinRTEs = true;
 232                         if (IS_OUTER_JOIN(rte->jointype))
 233                         {
 234                                 hasOuterJoins = true;
 235                                 /* Can quit scanning once we find an outer join */
 236                                 break;
 237                         }
 238                 }
 239         }
 240
 241         /*
 242          * Set hasHavingQual to remember if HAVING clause is present.  Needed
 243          * because preprocess_expression will reduce a constant-true condition
 244          * to an empty qual list ... but "HAVING TRUE" is not a semantic no-op.
 245          */
 246         parse->hasHavingQual = (parse->havingQual != NULL);
 247
 248         /*
 249          * Do expression preprocessing on targetlist and quals.
 250          */
 251         parse->targetList = (List *)
 252                 preprocess_expression(parse, (Node *) parse->targetList,
 253                                                           EXPRKIND_TARGET);
 254
 255         preprocess_qual_conditions(parse, (Node *) parse->jointree);
 256
 257         parse->havingQual = preprocess_expression(parse, parse->havingQual,
 258                                                                                           EXPRKIND_QUAL);
 259
 260         parse->limitOffset = preprocess_expression(parse, parse->limitOffset,
 261                                                                                            EXPRKIND_LIMIT);
 262         parse->limitCount = preprocess_expression(parse, parse->limitCount,
 263                                                                                           EXPRKIND_LIMIT);
 264
 265         parse->in_info_list = (List *)
 266                 preprocess_expression(parse, (Node *) parse->in_info_list,
 267                                                           EXPRKIND_ININFO);
 268
 269         /* Also need to preprocess expressions for function RTEs */
 270         foreach(l, parse->rtable)
 271         {
 272                 RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 273
 274                 if (rte->rtekind == RTE_FUNCTION)
 275                         rte->funcexpr = preprocess_expression(parse, rte->funcexpr,
 276                                                                                                   EXPRKIND_RTFUNC);
 277         }
 278
 279         /*
 280          * In some cases we may want to transfer a HAVING clause into WHERE.
 281          * We cannot do so if the HAVING clause contains aggregates (obviously)
 282          * or volatile functions (since a HAVING clause is supposed to be executed
 283          * only once per group).  Also, it may be that the clause is so expensive
 284          * to execute that we're better off doing it only once per group, despite
 285          * the loss of selectivity.  This is hard to estimate short of doing the
 286          * entire planning process twice, so we use a heuristic: clauses
 287          * containing subplans are left in HAVING.  Otherwise, we move or copy
 288          * the HAVING clause into WHERE, in hopes of eliminating tuples before
 289          * aggregation instead of after.
 290          *
 291          * If the query has explicit grouping then we can simply move such a
 292          * clause into WHERE; any group that fails the clause will not be
 293          * in the output because none of its tuples will reach the grouping
 294          * or aggregation stage.  Otherwise we must have a degenerate
 295          * (variable-free) HAVING clause, which we put in WHERE so that
 296          * query_planner() can use it in a gating Result node, but also keep
 297          * in HAVING to ensure that we don't emit a bogus aggregated row.
 298          * (This could be done better, but it seems not worth optimizing.)
 299          *
 300          * Note that both havingQual and parse->jointree->quals are in
 301          * implicitly-ANDed-list form at this point, even though they are
 302          * declared as Node *.
 303          */
 304         newHaving = NIL;
 305         foreach(l, (List *) parse->havingQual)
 306         {
 307                 Node       *havingclause = (Node *) lfirst(l);
 308
 309                 if (contain_agg_clause(havingclause) ||
 310                         contain_volatile_functions(havingclause) ||
 311                         contain_subplans(havingclause))
 312                 {
 313                         /* keep it in HAVING */
 314                         newHaving = lappend(newHaving, havingclause);
 315                 }
 316                 else if (parse->groupClause)
 317                 {
 318                         /* move it to WHERE */
 319                         parse->jointree->quals = (Node *)
 320                                 lappend((List *) parse->jointree->quals, havingclause);
 321                 }
 322                 else
 323                 {
 324                         /* put a copy in WHERE, keep it in HAVING */
 325                         parse->jointree->quals = (Node *)
 326                                 lappend((List *) parse->jointree->quals,
 327                                                 copyObject(havingclause));
 328                         newHaving = lappend(newHaving, havingclause);
 329                 }
 330         }
 331         parse->havingQual = (Node *) newHaving;
 332
 333         /*
 334          * If we have any outer joins, try to reduce them to plain inner
 335          * joins. This step is most easily done after we've done expression
 336          * preprocessing.
 337          */
 338         if (hasOuterJoins)
 339                 reduce_outer_joins(parse);
 340
 341         /*
 342          * See if we can simplify the jointree; opportunities for this may
 343          * come from having pulled up subqueries, or from flattening explicit
 344          * JOIN syntax.  We must do this after flattening JOIN alias
 345          * variables, since eliminating explicit JOIN nodes from the jointree
 346          * will cause get_relids_for_join() to fail.  But it should happen
 347          * after reduce_outer_joins, anyway.
 348          */
 349         parse->jointree = (FromExpr *)
 350                 simplify_jointree(parse, (Node *) parse->jointree);
 351
 352         /*
 353          * Do the main planning.  If we have an inherited target relation,
 354          * that needs special processing, else go straight to
 355          * grouping_planner.
 356          */
 357         if (parse->resultRelation &&
 358                 (lst = expand_inherited_rtentry(parse, parse->resultRelation)) != NIL)
 359                 plan = inheritance_planner(parse, lst);
 360         else
 361                 plan = grouping_planner(parse, tuple_fraction);
 362
 363         /*
 364          * If any subplans were generated, or if we're inside a subplan, build
 365          * initPlan list and extParam/allParam sets for plan nodes, and attach
 366          * the initPlans to the top plan node.
 367          */
 368         if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1)
 369                 SS_finalize_plan(plan, parse->rtable);
 370
 371         /* Return to outer subquery context */
 372         PlannerQueryLevel--;
 373         PlannerInitPlan = saved_initplan;
 374         /* we do NOT restore PlannerPlanId; that's not an oversight! */
 375
 376         return plan;
 377 }
 378
 379 /*
 380  * preprocess_expression
 381  *              Do subquery_planner's preprocessing work for an expression,
 382  *              which can be a targetlist, a WHERE clause (including JOIN/ON
 383  *              conditions), or a HAVING clause.
 384  */
 385 static Node *
 386 preprocess_expression(Query *parse, Node *expr, int kind)
 387 {
 388         /*
 389          * If the query has any join RTEs, replace join alias variables with
 390          * base-relation variables. We must do this before sublink processing,
 391          * else sublinks expanded out from join aliases wouldn't get
 392          * processed.
 393          */
 394         if (parse->hasJoinRTEs)
 395                 expr = flatten_join_alias_vars(parse, expr);
 396
 397         /*
 398          * Simplify constant expressions.
 399          *
 400          * Note: this also flattens nested AND and OR expressions into N-argument
 401          * form.  All processing of a qual expression after this point must be
 402          * careful to maintain AND/OR flatness --- that is, do not generate a tree
 403          * with AND directly under AND, nor OR directly under OR.
 404          */
 405         expr = eval_const_expressions(expr);
 406
 407         /*
 408          * If it's a qual or havingQual, canonicalize it.
 409          */
 410         if (kind == EXPRKIND_QUAL)
 411         {
 412                 expr = (Node *) canonicalize_qual((Expr *) expr);
 413
 414 #ifdef OPTIMIZER_DEBUG
 415                 printf("After canonicalize_qual()\n");
 416                 pprint(expr);
 417 #endif
 418         }
 419
 420         /* Expand SubLinks to SubPlans */
 421         if (parse->hasSubLinks)
 422                 expr = SS_process_sublinks(expr, (kind == EXPRKIND_QUAL));
 423
 424         /*
 425          * XXX do not insert anything here unless you have grokked the
 426          * comments in SS_replace_correlation_vars ...
 427          */
 428
 429         /* Replace uplevel vars with Param nodes */
 430         if (PlannerQueryLevel > 1)
 431                 expr = SS_replace_correlation_vars(expr);
 432
 433         /*
 434          * If it's a qual or havingQual, convert it to implicit-AND format.
 435          * (We don't want to do this before eval_const_expressions, since the
 436          * latter would be unable to simplify a top-level AND correctly. Also,
 437          * SS_process_sublinks expects explicit-AND format.)
 438          */
 439         if (kind == EXPRKIND_QUAL)
 440                 expr = (Node *) make_ands_implicit((Expr *) expr);
 441
 442         return expr;
 443 }
 444
 445 /*
 446  * preprocess_qual_conditions
 447  *              Recursively scan the query's jointree and do subquery_planner's
 448  *              preprocessing work on each qual condition found therein.
 449  */
 450 static void
 451 preprocess_qual_conditions(Query *parse, Node *jtnode)
 452 {
 453         if (jtnode == NULL)
 454                 return;
 455         if (IsA(jtnode, RangeTblRef))
 456         {
 457                 /* nothing to do here */
 458         }
 459         else if (IsA(jtnode, FromExpr))
 460         {
 461                 FromExpr   *f = (FromExpr *) jtnode;
 462                 ListCell   *l;
 463
 464                 foreach(l, f->fromlist)
 465                         preprocess_qual_conditions(parse, lfirst(l));
 466
 467                 f->quals = preprocess_expression(parse, f->quals, EXPRKIND_QUAL);
 468         }
 469         else if (IsA(jtnode, JoinExpr))
 470         {
 471                 JoinExpr   *j = (JoinExpr *) jtnode;
 472
 473                 preprocess_qual_conditions(parse, j->larg);
 474                 preprocess_qual_conditions(parse, j->rarg);
 475
 476                 j->quals = preprocess_expression(parse, j->quals, EXPRKIND_QUAL);
 477         }
 478         else
 479                 elog(ERROR, "unrecognized node type: %d",
 480                          (int) nodeTag(jtnode));
 481 }
 482
 483 /*--------------------
 484  * inheritance_planner
 485  *        Generate a plan in the case where the result relation is an
 486  *        inheritance set.
 487  *
 488  * We have to handle this case differently from cases where a source
 489  * relation is an inheritance set.      Source inheritance is expanded at
 490  * the bottom of the plan tree (see allpaths.c), but target inheritance
 491  * has to be expanded at the top.  The reason is that for UPDATE, each
 492  * target relation needs a different targetlist matching its own column
 493  * set.  (This is not so critical for DELETE, but for simplicity we treat
 494  * inherited DELETE the same way.)      Fortunately, the UPDATE/DELETE target
 495  * can never be the nullable side of an outer join, so it's OK to generate
 496  * the plan this way.
 497  *
 498  * parse is the querytree produced by the parser & rewriter.
 499  * inheritlist is an integer list of RT indexes for the result relation set.
 500  *
 501  * Returns a query plan.
 502  *--------------------
 503  */
 504 static Plan *
 505 inheritance_planner(Query *parse, List *inheritlist)
 506 {
 507         int                     parentRTindex = parse->resultRelation;
 508         Oid                     parentOID = getrelid(parentRTindex, parse->rtable);
 509         int                     mainrtlength = list_length(parse->rtable);
 510         List       *subplans = NIL;
 511         List       *tlist = NIL;
 512         ListCell   *l;
 513
 514         foreach(l, inheritlist)
 515         {
 516                 int                     childRTindex = lfirst_int(l);
 517                 Oid                     childOID = getrelid(childRTindex, parse->rtable);
 518                 Query      *subquery;
 519                 Plan       *subplan;
 520
 521                 /* Generate modified query with this rel as target */
 522                 subquery = (Query *) adjust_inherited_attrs((Node *) parse,
 523                                                                                                 parentRTindex, parentOID,
 524                                                                                                  childRTindex, childOID);
 525                 /* Generate plan */
 526                 subplan = grouping_planner(subquery, 0.0 /* retrieve all tuples */ );
 527                 subplans = lappend(subplans, subplan);
 528
 529                 /*
 530                  * XXX my goodness this next bit is ugly.  Really need to think about
 531                  * ways to rein in planner's habit of scribbling on its input.
 532                  *
 533                  * Planning of the subquery might have modified the rangetable,
 534                  * either by addition of RTEs due to expansion of inherited source
 535                  * tables, or by changes of the Query structures inside subquery
 536                  * RTEs.  We have to ensure that this gets propagated back to the
 537                  * master copy.  However, if we aren't done planning yet, we also
 538                  * need to ensure that subsequent calls to grouping_planner have
 539                  * virgin sub-Queries to work from.  So, if we are at the last
 540                  * list entry, just copy the subquery rangetable back to the master
 541                  * copy; if we are not, then extend the master copy by adding
 542                  * whatever the subquery added.  (We assume these added entries
 543                  * will go untouched by the future grouping_planner calls.  We are
 544                  * also effectively assuming that sub-Queries will get planned
 545                  * identically each time, or at least that the impacts on their
 546                  * rangetables will be the same each time.  Did I say this is ugly?)
 547                  */
 548                 if (lnext(l) == NULL)
 549                         parse->rtable = subquery->rtable;
 550                 else
 551                 {
 552                         int             subrtlength = list_length(subquery->rtable);
 553
 554                         if (subrtlength > mainrtlength)
 555                         {
 556                                 List       *subrt;
 557
 558                                 subrt = list_copy_tail(subquery->rtable, mainrtlength);
 559                                 parse->rtable = list_concat(parse->rtable, subrt);
 560                                 mainrtlength = subrtlength;
 561                         }
 562                 }
 563
 564                 /* Save preprocessed tlist from first rel for use in Append */
 565                 if (tlist == NIL)
 566                         tlist = subplan->targetlist;
 567         }
 568
 569         /* Save the target-relations list for the executor, too */
 570         parse->resultRelations = inheritlist;
 571
 572         /* Mark result as unordered (probably unnecessary) */
 573         parse->query_pathkeys = NIL;
 574
 575         return (Plan *) make_append(subplans, true, tlist);
 576 }
 577
 578 /*--------------------
 579  * grouping_planner
 580  *        Perform planning steps related to grouping, aggregation, etc.
 581  *        This primarily means adding top-level processing to the basic
 582  *        query plan produced by query_planner.
 583  *
 584  * parse is the querytree produced by the parser & rewriter.
 585  * tuple_fraction is the fraction of tuples we expect will be retrieved
 586  *
 587  * tuple_fraction is interpreted as follows:
 588  *        0: expect all tuples to be retrieved (normal case)
 589  *        0 < tuple_fraction < 1: expect the given fraction of tuples available
 590  *              from the plan to be retrieved
 591  *        tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
 592  *              expected to be retrieved (ie, a LIMIT specification)
 593  *
 594  * Returns a query plan.  Also, parse->query_pathkeys is returned as the
 595  * actual output ordering of the plan (in pathkey format).
 596  *--------------------
 597  */
 598 static Plan *
 599 grouping_planner(Query *parse, double tuple_fraction)
 600 {
 601         List       *tlist = parse->targetList;
 602         Plan       *result_plan;
 603         List       *current_pathkeys;
 604         List       *sort_pathkeys;
 605
 606         if (parse->setOperations)
 607         {
 608                 List       *set_sortclauses;
 609
 610                 /*
 611                  * Construct the plan for set operations.  The result will not
 612                  * need any work except perhaps a top-level sort and/or LIMIT.
 613                  */
 614                 result_plan = plan_set_operations(parse,
 615                                                                                   &set_sortclauses);
 616
 617                 /*
 618                  * Calculate pathkeys representing the sort order (if any) of the
 619                  * set operation's result.  We have to do this before overwriting
 620                  * the sort key information...
 621                  */
 622                 current_pathkeys = make_pathkeys_for_sortclauses(set_sortclauses,
 623                                                                                                 result_plan->targetlist);
 624                 current_pathkeys = canonicalize_pathkeys(parse, current_pathkeys);
 625
 626                 /*
 627                  * We should not need to call preprocess_targetlist, since we must
 628                  * be in a SELECT query node.  Instead, use the targetlist
 629                  * returned by plan_set_operations (since this tells whether it
 630                  * returned any resjunk columns!), and transfer any sort key
 631                  * information from the original tlist.
 632                  */
 633                 Assert(parse->commandType == CMD_SELECT);
 634
 635                 tlist = postprocess_setop_tlist(result_plan->targetlist, tlist);
 636
 637                 /*
 638                  * Can't handle FOR UPDATE/SHARE here (parser should have checked
 639                  * already, but let's make sure).
 640                  */
 641                 if (parse->rowMarks)
 642                         ereport(ERROR,
 643                                         (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 644                                          errmsg("SELECT FOR UPDATE/SHARE is not allowed with UNION/INTERSECT/EXCEPT")));
 645
 646                 /*
 647                  * Calculate pathkeys that represent result ordering requirements
 648                  */
 649                 sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
 650                                                                                                           tlist);
 651                 sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
 652         }
 653         else
 654         {
 655                 /* No set operations, do regular planning */
 656                 List       *sub_tlist;
 657                 List       *group_pathkeys;
 658                 AttrNumber *groupColIdx = NULL;
 659                 bool            need_tlist_eval = true;
 660                 QualCost        tlist_cost;
 661                 double          sub_tuple_fraction;
 662                 Path       *cheapest_path;
 663                 Path       *sorted_path;
 664                 Path       *best_path;
 665                 double          dNumGroups = 0;
 666                 long            numGroups = 0;
 667                 AggClauseCounts agg_counts;
 668                 int                     numGroupCols = list_length(parse->groupClause);
 669                 bool            use_hashed_grouping = false;
 670
 671                 MemSet(&agg_counts, 0, sizeof(AggClauseCounts));
 672
 673                 /* Preprocess targetlist */
 674                 tlist = preprocess_targetlist(parse, tlist);
 675
 676                 /*
 677                  * Generate appropriate target list for subplan; may be different
 678                  * from tlist if grouping or aggregation is needed.
 679                  */
 680                 sub_tlist = make_subplanTargetList(parse, tlist,
 681                                                                                  &groupColIdx, &need_tlist_eval);
 682
 683                 /*
 684                  * Calculate pathkeys that represent grouping/ordering
 685                  * requirements
 686                  */
 687                 group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause,
 688                                                                                                            tlist);
 689                 sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
 690                                                                                                           tlist);
 691
 692                 /*
 693                  * Will need actual number of aggregates for estimating costs.
 694                  *
 695                  * Note: we do not attempt to detect duplicate aggregates here; a
 696                  * somewhat-overestimated count is okay for our present purposes.
 697                  *
 698                  * Note: think not that we can turn off hasAggs if we find no aggs.
 699                  * It is possible for constant-expression simplification to remove
 700                  * all explicit references to aggs, but we still have to follow
 701                  * the aggregate semantics (eg, producing only one output row).
 702                  */
 703                 if (parse->hasAggs)
 704                 {
 705                         count_agg_clauses((Node *) tlist, &agg_counts);
 706                         count_agg_clauses(parse->havingQual, &agg_counts);
 707                 }
 708
 709                 /*
 710                  * Figure out whether we need a sorted result from query_planner.
 711                  *
 712                  * If we have a GROUP BY clause, then we want a result sorted
 713                  * properly for grouping.  Otherwise, if there is an ORDER BY
 714                  * clause, we want to sort by the ORDER BY clause.      (Note: if we
 715                  * have both, and ORDER BY is a superset of GROUP BY, it would be
 716                  * tempting to request sort by ORDER BY --- but that might just
 717                  * leave us failing to exploit an available sort order at all.
 718                  * Needs more thought...)
 719                  */
 720                 if (parse->groupClause)
 721                         parse->query_pathkeys = group_pathkeys;
 722                 else if (parse->sortClause)
 723                         parse->query_pathkeys = sort_pathkeys;
 724                 else
 725                         parse->query_pathkeys = NIL;
 726
 727                 /*
 728                  * Adjust tuple_fraction if we see that we are going to apply
 729                  * limiting/grouping/aggregation/etc.  This is not overridable by
 730                  * the caller, since it reflects plan actions that this routine
 731                  * will certainly take, not assumptions about context.
 732                  */
 733                 if (parse->limitCount != NULL)
 734                 {
 735                         /*
 736                          * A LIMIT clause limits the absolute number of tuples
 737                          * returned. However, if it's not a constant LIMIT then we
 738                          * have to punt; for lack of a better idea, assume 10% of the
 739                          * plan's result is wanted.
 740                          */
 741                         double          limit_fraction = 0.0;
 742
 743                         if (IsA(parse->limitCount, Const))
 744                         {
 745                                 Const      *limitc = (Const *) parse->limitCount;
 746                                 int32           count = DatumGetInt32(limitc->constvalue);
 747
 748                                 /*
 749                                  * A NULL-constant LIMIT represents "LIMIT ALL", which we
 750                                  * treat the same as no limit (ie, expect to retrieve all
 751                                  * the tuples).
 752                                  */
 753                                 if (!limitc->constisnull && count > 0)
 754                                 {
 755                                         limit_fraction = (double) count;
 756                                         /* We must also consider the OFFSET, if present */
 757                                         if (parse->limitOffset != NULL)
 758                                         {
 759                                                 if (IsA(parse->limitOffset, Const))
 760                                                 {
 761                                                         int32           offset;
 762
 763                                                         limitc = (Const *) parse->limitOffset;
 764                                                         offset = DatumGetInt32(limitc->constvalue);
 765                                                         if (!limitc->constisnull && offset > 0)
 766                                                                 limit_fraction += (double) offset;
 767                                                 }
 768                                                 else
 769                                                 {
 770                                                         /* OFFSET is an expression ... punt ... */
 771                                                         limit_fraction = 0.10;
 772                                                 }
 773                                         }
 774                                 }
 775                         }
 776                         else
 777                         {
 778                                 /* LIMIT is an expression ... punt ... */
 779                                 limit_fraction = 0.10;
 780                         }
 781
 782                         if (limit_fraction > 0.0)
 783                         {
 784                                 /*
 785                                  * If we have absolute limits from both caller and LIMIT,
 786                                  * use the smaller value; if one is fractional and the
 787                                  * other absolute, treat the fraction as a fraction of the
 788                                  * absolute value; else we can multiply the two fractions
 789                                  * together.
 790                                  */
 791                                 if (tuple_fraction >= 1.0)
 792                                 {
 793                                         if (limit_fraction >= 1.0)
 794                                         {
 795                                                 /* both absolute */
 796                                                 tuple_fraction = Min(tuple_fraction, limit_fraction);
 797                                         }
 798                                         else
 799                                         {
 800                                                 /* caller absolute, limit fractional */
 801                                                 tuple_fraction *= limit_fraction;
 802                                                 if (tuple_fraction < 1.0)
 803                                                         tuple_fraction = 1.0;
 804                                         }
 805                                 }
 806                                 else if (tuple_fraction > 0.0)
 807                                 {
 808                                         if (limit_fraction >= 1.0)
 809                                         {
 810                                                 /* caller fractional, limit absolute */
 811                                                 tuple_fraction *= limit_fraction;
 812                                                 if (tuple_fraction < 1.0)
 813                                                         tuple_fraction = 1.0;
 814                                         }
 815                                         else
 816                                         {
 817                                                 /* both fractional */
 818                                                 tuple_fraction *= limit_fraction;
 819                                         }
 820                                 }
 821                                 else
 822                                 {
 823                                         /* no info from caller, just use limit */
 824                                         tuple_fraction = limit_fraction;
 825                                 }
 826                         }
 827                 }
 828
 829                 /*
 830                  * With grouping or aggregation, the tuple fraction to pass to
 831                  * query_planner() may be different from what it is at top level.
 832                  */
 833                 sub_tuple_fraction = tuple_fraction;
 834
 835                 if (parse->groupClause)
 836                 {
 837                         /*
 838                          * In GROUP BY mode, we have the little problem that we don't
 839                          * really know how many input tuples will be needed to make a
 840                          * group, so we can't translate an output LIMIT count into an
 841                          * input count.  For lack of a better idea, assume 25% of the
 842                          * input data will be processed if there is any output limit.
 843                          * However, if the caller gave us a fraction rather than an
 844                          * absolute count, we can keep using that fraction (which
 845                          * amounts to assuming that all the groups are about the same
 846                          * size).
 847                          */
 848                         if (sub_tuple_fraction >= 1.0)
 849                                 sub_tuple_fraction = 0.25;
 850
 851                         /*
 852                          * If both GROUP BY and ORDER BY are specified, we will need
 853                          * two levels of sort --- and, therefore, certainly need to
 854                          * read all the input tuples --- unless ORDER BY is a subset
 855                          * of GROUP BY.  (We have not yet canonicalized the pathkeys,
 856                          * so must use the slower noncanonical comparison method.)
 857                          */
 858                         if (parse->groupClause && parse->sortClause &&
 859                                 !noncanonical_pathkeys_contained_in(sort_pathkeys,
 860                                                                                                         group_pathkeys))
 861                                 sub_tuple_fraction = 0.0;
 862                 }
 863                 else if (parse->hasAggs)
 864                 {
 865                         /*
 866                          * Ungrouped aggregate will certainly want all the input
 867                          * tuples.
 868                          */
 869                         sub_tuple_fraction = 0.0;
 870                 }
 871                 else if (parse->distinctClause)
 872                 {
 873                         /*
 874                          * SELECT DISTINCT, like GROUP, will absorb an unpredictable
 875                          * number of input tuples per output tuple.  Handle the same
 876                          * way.
 877                          */
 878                         if (sub_tuple_fraction >= 1.0)
 879                                 sub_tuple_fraction = 0.25;
 880                 }
 881
 882                 /*
 883                  * Generate the best unsorted and presorted paths for this Query
 884                  * (but note there may not be any presorted path).
 885                  */
 886                 query_planner(parse, sub_tlist, sub_tuple_fraction,
 887                                           &cheapest_path, &sorted_path);
 888
 889                 /*
 890                  * We couldn't canonicalize group_pathkeys and sort_pathkeys
 891                  * before running query_planner(), so do it now.
 892                  */
 893                 group_pathkeys = canonicalize_pathkeys(parse, group_pathkeys);
 894                 sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
 895
 896                 /*
 897                  * If grouping, estimate the number of groups.  (We can't do this
 898                  * until after running query_planner(), either.)  Then decide
 899                  * whether we want to use hashed grouping.
 900                  */
 901                 if (parse->groupClause)
 902                 {
 903                         List       *groupExprs;
 904                         double          cheapest_path_rows;
 905
 906                         /*
 907                          * Beware of the possibility that cheapest_path->parent is NULL.
 908                          * This could happen if user does something silly like
 909                          *              SELECT 'foo' GROUP BY 1;
 910                          */
 911                         if (cheapest_path->parent)
 912                                 cheapest_path_rows = cheapest_path->parent->rows;
 913                         else
 914                                 cheapest_path_rows = 1; /* assume non-set result */
 915
 916                         groupExprs = get_sortgrouplist_exprs(parse->groupClause,
 917                                                                                                  parse->targetList);
 918                         dNumGroups = estimate_num_groups(parse,
 919                                                                                          groupExprs,
 920                                                                                          cheapest_path_rows);
 921                         /* Also want it as a long int --- but 'ware overflow! */
 922                         numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
 923
 924                         use_hashed_grouping =
 925                                 choose_hashed_grouping(parse, tuple_fraction,
 926                                                                            cheapest_path, sorted_path,
 927                                                                            sort_pathkeys, group_pathkeys,
 928                                                                            dNumGroups, &agg_counts);
 929                 }
 930
 931                 /*
 932                  * Select the best path.  If we are doing hashed grouping, we will
 933                  * always read all the input tuples, so use the cheapest-total
 934                  * path. Otherwise, trust query_planner's decision about which to use.
 935                  */
 936                 if (use_hashed_grouping || !sorted_path)
 937                         best_path = cheapest_path;
 938                 else
 939                         best_path = sorted_path;
 940
 941                 /*
 942                  * Check to see if it's possible to optimize MIN/MAX aggregates.
 943                  * If so, we will forget all the work we did so far to choose a
 944                  * "regular" path ... but we had to do it anyway to be able to
 945                  * tell which way is cheaper.
 946                  */
 947                 result_plan = optimize_minmax_aggregates(parse,
 948                                                                                                  tlist,
 949                                                                                                  best_path);
 950                 if (result_plan != NULL)
 951                 {
 952                         /*
 953                          * optimize_minmax_aggregates generated the full plan, with
 954                          * the right tlist, and it has no sort order.
 955                          */
 956                         current_pathkeys = NIL;
 957                 }
 958                 else
 959                 {
 960                         /*
 961                          * Normal case --- create a plan according to query_planner's
 962                          * results.
 963                          */
 964                         result_plan = create_plan(parse, best_path);
 965                         current_pathkeys = best_path->pathkeys;
 966
 967                         /*
 968                          * create_plan() returns a plan with just a "flat" tlist of
 969                          * required Vars.  Usually we need to insert the sub_tlist as the
 970                          * tlist of the top plan node.  However, we can skip that if we
 971                          * determined that whatever query_planner chose to return will be
 972                          * good enough.
 973                          */
 974                         if (need_tlist_eval)
 975                         {
 976                                 /*
 977                                  * If the top-level plan node is one that cannot do expression
 978                                  * evaluation, we must insert a Result node to project the
 979                                  * desired tlist.
 980                                  */
 981                                 if (!is_projection_capable_plan(result_plan))
 982                                 {
 983                                         result_plan = (Plan *) make_result(sub_tlist, NULL,
 984                                                                                                            result_plan);
 985                                 }
 986                                 else
 987                                 {
 988                                         /*
 989                                          * Otherwise, just replace the subplan's flat tlist with
 990                                          * the desired tlist.
 991                                          */
 992                                         result_plan->targetlist = sub_tlist;
 993                                 }
 994
 995                                 /*
 996                                  * Also, account for the cost of evaluation of the sub_tlist.
 997                                  *
 998                                  * Up to now, we have only been dealing with "flat" tlists,
 999                                  * containing just Vars.  So their evaluation cost is zero
1000                                  * according to the model used by cost_qual_eval() (or if you
1001                                  * prefer, the cost is factored into cpu_tuple_cost).  Thus we
1002                                  * can avoid accounting for tlist cost throughout
1003                                  * query_planner() and subroutines.  But now we've inserted a
1004                                  * tlist that might contain actual operators, sub-selects, etc
1005                                  * --- so we'd better account for its cost.
1006                                  *
1007                                  * Below this point, any tlist eval cost for added-on nodes
1008                                  * should be accounted for as we create those nodes.
1009                                  * Presently, of the node types we can add on, only Agg and
1010                                  * Group project new tlists (the rest just copy their input
1011                                  * tuples) --- so make_agg() and make_group() are responsible
1012                                  * for computing the added cost.
1013                                  */
1014                                 cost_qual_eval(&tlist_cost, sub_tlist);
1015                                 result_plan->startup_cost += tlist_cost.startup;
1016                                 result_plan->total_cost += tlist_cost.startup +
1017                                         tlist_cost.per_tuple * result_plan->plan_rows;
1018                         }
1019                         else
1020                         {
1021                                 /*
1022                                  * Since we're using query_planner's tlist and not the one
1023                                  * make_subplanTargetList calculated, we have to refigure any
1024                                  * grouping-column indexes make_subplanTargetList computed.
1025                                  */
1026                                 locate_grouping_columns(parse, tlist, result_plan->targetlist,
1027                                                                                 groupColIdx);
1028                         }
1029
1030                         /*
1031                          * Insert AGG or GROUP node if needed, plus an explicit sort step
1032                          * if necessary.
1033                          *
1034                          * HAVING clause, if any, becomes qual of the Agg or Group node.
1035                          */
1036                         if (use_hashed_grouping)
1037                         {
1038                                 /* Hashed aggregate plan --- no sort needed */
1039                                 result_plan = (Plan *) make_agg(parse,
1040                                                                                                 tlist,
1041                                                                                                 (List *) parse->havingQual,
1042                                                                                                 AGG_HASHED,
1043                                                                                                 numGroupCols,
1044                                                                                                 groupColIdx,
1045                                                                                                 numGroups,
1046                                                                                                 agg_counts.numAggs,
1047                                                                                                 result_plan);
1048                                 /* Hashed aggregation produces randomly-ordered results */
1049                                 current_pathkeys = NIL;
1050                         }
1051                         else if (parse->hasAggs)
1052                         {
1053                                 /* Plain aggregate plan --- sort if needed */
1054                                 AggStrategy aggstrategy;
1055
1056                                 if (parse->groupClause)
1057                                 {
1058                                         if (!pathkeys_contained_in(group_pathkeys,
1059                                                                                            current_pathkeys))
1060                                         {
1061                                                 result_plan = (Plan *)
1062                                                         make_sort_from_groupcols(parse,
1063                                                                                                          parse->groupClause,
1064                                                                                                          groupColIdx,
1065                                                                                                          result_plan);
1066                                                 current_pathkeys = group_pathkeys;
1067                                         }
1068                                         aggstrategy = AGG_SORTED;
1069
1070                                         /*
1071                                          * The AGG node will not change the sort ordering of its
1072                                          * groups, so current_pathkeys describes the result too.
1073                                          */
1074                                 }
1075                                 else
1076                                 {
1077                                         aggstrategy = AGG_PLAIN;
1078                                         /* Result will be only one row anyway; no sort order */
1079                                         current_pathkeys = NIL;
1080                                 }
1081
1082                                 result_plan = (Plan *) make_agg(parse,
1083                                                                                                 tlist,
1084                                                                                                 (List *) parse->havingQual,
1085                                                                                                 aggstrategy,
1086                                                                                                 numGroupCols,
1087                                                                                                 groupColIdx,
1088                                                                                                 numGroups,
1089                                                                                                 agg_counts.numAggs,
1090                                                                                                 result_plan);
1091                         }
1092                         else if (parse->groupClause)
1093                         {
1094                                 /*
1095                                  * GROUP BY without aggregation, so insert a group node (plus
1096                                  * the appropriate sort node, if necessary).
1097                                  *
1098                                  * Add an explicit sort if we couldn't make the path come
1099                                  * out the way the GROUP node needs it.
1100                                  */
1101                                 if (!pathkeys_contained_in(group_pathkeys, current_pathkeys))
1102                                 {
1103                                         result_plan = (Plan *)
1104                                                 make_sort_from_groupcols(parse,
1105                                                                                                  parse->groupClause,
1106                                                                                                  groupColIdx,
1107                                                                                                  result_plan);
1108                                         current_pathkeys = group_pathkeys;
1109                                 }
1110
1111                                 result_plan = (Plan *) make_group(parse,
1112                                                                                                   tlist,
1113                                                                                                   (List *) parse->havingQual,
1114                                                                                                   numGroupCols,
1115                                                                                                   groupColIdx,
1116                                                                                                   dNumGroups,
1117                                                                                                   result_plan);
1118                                 /* The Group node won't change sort ordering */
1119                         }
1120                         else if (parse->hasHavingQual)
1121                         {
1122                                 /*
1123                                  * No aggregates, and no GROUP BY, but we have a HAVING qual.
1124                                  * This is a degenerate case in which we are supposed to emit
1125                                  * either 0 or 1 row depending on whether HAVING succeeds.
1126                                  * Furthermore, there cannot be any variables in either HAVING
1127                                  * or the targetlist, so we actually do not need the FROM table
1128                                  * at all!  We can just throw away the plan-so-far and generate
1129                                  * a Result node.  This is a sufficiently unusual corner case
1130                                  * that it's not worth contorting the structure of this routine
1131                                  * to avoid having to generate the plan in the first place.
1132                                  */
1133                                 result_plan = (Plan *) make_result(tlist,
1134                                                                                                    parse->havingQual,
1135                                                                                                    NULL);
1136                         }
1137                 }                                               /* end of non-minmax-aggregate case */
1138         }                                                       /* end of if (setOperations) */
1139
1140         /*
1141          * If we were not able to make the plan come out in the right order,
1142          * add an explicit sort step.
1143          */
1144         if (parse->sortClause)
1145         {
1146                 if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys))
1147                 {
1148                         result_plan = (Plan *)
1149                                 make_sort_from_sortclauses(parse,
1150                                                                                    parse->sortClause,
1151                                                                                    result_plan);
1152                         current_pathkeys = sort_pathkeys;
1153                 }
1154         }
1155
1156         /*
1157          * If there is a DISTINCT clause, add the UNIQUE node.
1158          */
1159         if (parse->distinctClause)
1160         {
1161                 result_plan = (Plan *) make_unique(result_plan, parse->distinctClause);
1162
1163                 /*
1164                  * If there was grouping or aggregation, leave plan_rows as-is
1165                  * (ie, assume the result was already mostly unique).  If not,
1166                  * it's reasonable to assume the UNIQUE filter has effects
1167                  * comparable to GROUP BY.
1168                  */
1169                 if (!parse->groupClause && !parse->hasHavingQual && !parse->hasAggs)
1170                 {
1171                         List       *distinctExprs;
1172
1173                         distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
1174                                                                                                         parse->targetList);
1175                         result_plan->plan_rows = estimate_num_groups(parse,
1176                                                                                                                  distinctExprs,
1177                                                                                                  result_plan->plan_rows);
1178                 }
1179         }
1180
1181         /*
1182          * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
1183          */
1184         if (parse->limitOffset || parse->limitCount)
1185         {
1186                 result_plan = (Plan *) make_limit(result_plan,
1187                                                                                   parse->limitOffset,
1188                                                                                   parse->limitCount);
1189         }
1190
1191         /*
1192          * Return the actual output ordering in query_pathkeys for possible
1193          * use by an outer query level.
1194          */
1195         parse->query_pathkeys = current_pathkeys;
1196
1197         return result_plan;
1198 }
1199
1200 /*
1201  * choose_hashed_grouping - should we use hashed grouping?
1202  */
1203 static bool
1204 choose_hashed_grouping(Query *parse, double tuple_fraction,
1205                                            Path *cheapest_path, Path *sorted_path,
1206                                            List *sort_pathkeys, List *group_pathkeys,
1207                                            double dNumGroups, AggClauseCounts *agg_counts)
1208 {
1209         int                     numGroupCols = list_length(parse->groupClause);
1210         double          cheapest_path_rows;
1211         int                     cheapest_path_width;
1212         Size            hashentrysize;
1213         List       *current_pathkeys;
1214         Path            hashed_p;
1215         Path            sorted_p;
1216
1217         /*
1218          * Check can't-do-it conditions, including whether the grouping operators
1219          * are hashjoinable.
1220          *
1221          * Executor doesn't support hashed aggregation with DISTINCT aggregates.
1222          * (Doing so would imply storing *all* the input values in the hash table,
1223          * which seems like a certain loser.)
1224          */
1225         if (!enable_hashagg)
1226                 return false;
1227         if (agg_counts->numDistinctAggs != 0)
1228                 return false;
1229         if (!hash_safe_grouping(parse))
1230                 return false;
1231
1232         /*
1233          * Don't do it if it doesn't look like the hashtable will fit into
1234          * work_mem.
1235          *
1236          * Beware here of the possibility that cheapest_path->parent is NULL.
1237          * This could happen if user does something silly like
1238          *              SELECT 'foo' GROUP BY 1;
1239          */
1240         if (cheapest_path->parent)
1241         {
1242                 cheapest_path_rows = cheapest_path->parent->rows;
1243                 cheapest_path_width = cheapest_path->parent->width;
1244         }
1245         else
1246         {
1247                 cheapest_path_rows = 1;                         /* assume non-set result */
1248                 cheapest_path_width = 100;                      /* arbitrary */
1249         }
1250
1251         /* Estimate per-hash-entry space at tuple width... */
1252         hashentrysize = cheapest_path_width;
1253         /* plus space for pass-by-ref transition values... */
1254         hashentrysize += agg_counts->transitionSpace;
1255         /* plus the per-hash-entry overhead */
1256         hashentrysize += hash_agg_entry_size(agg_counts->numAggs);
1257
1258         if (hashentrysize * dNumGroups > work_mem * 1024L)
1259                 return false;
1260
1261         /*
1262          * See if the estimated cost is no more than doing it the other way.
1263          * While avoiding the need for sorted input is usually a win, the fact
1264          * that the output won't be sorted may be a loss; so we need to do an
1265          * actual cost comparison.
1266          *
1267          * We need to consider
1268          *              cheapest_path + hashagg [+ final sort]
1269          * versus either
1270          *              cheapest_path [+ sort] + group or agg [+ final sort]
1271          * or
1272          *              presorted_path + group or agg [+ final sort]
1273          * where brackets indicate a step that may not be needed. We assume
1274          * query_planner() will have returned a presorted path only if it's a
1275          * winner compared to cheapest_path for this purpose.
1276          *
1277          * These path variables are dummies that just hold cost fields; we don't
1278          * make actual Paths for these steps.
1279          */
1280         cost_agg(&hashed_p, parse, AGG_HASHED, agg_counts->numAggs,
1281                          numGroupCols, dNumGroups,
1282                          cheapest_path->startup_cost, cheapest_path->total_cost,
1283                          cheapest_path_rows);
1284         /* Result of hashed agg is always unsorted */
1285         if (sort_pathkeys)
1286                 cost_sort(&hashed_p, parse, sort_pathkeys, hashed_p.total_cost,
1287                                   dNumGroups, cheapest_path_width);
1288
1289         if (sorted_path)
1290         {
1291                 sorted_p.startup_cost = sorted_path->startup_cost;
1292                 sorted_p.total_cost = sorted_path->total_cost;
1293                 current_pathkeys = sorted_path->pathkeys;
1294         }
1295         else
1296         {
1297                 sorted_p.startup_cost = cheapest_path->startup_cost;
1298                 sorted_p.total_cost = cheapest_path->total_cost;
1299                 current_pathkeys = cheapest_path->pathkeys;
1300         }
1301         if (!pathkeys_contained_in(group_pathkeys,
1302                                                            current_pathkeys))
1303         {
1304                 cost_sort(&sorted_p, parse, group_pathkeys, sorted_p.total_cost,
1305                                   cheapest_path_rows, cheapest_path_width);
1306                 current_pathkeys = group_pathkeys;
1307         }
1308
1309         if (parse->hasAggs)
1310                 cost_agg(&sorted_p, parse, AGG_SORTED, agg_counts->numAggs,
1311                                  numGroupCols, dNumGroups,
1312                                  sorted_p.startup_cost, sorted_p.total_cost,
1313                                  cheapest_path_rows);
1314         else
1315                 cost_group(&sorted_p, parse, numGroupCols, dNumGroups,
1316                                    sorted_p.startup_cost, sorted_p.total_cost,
1317                                    cheapest_path_rows);
1318         /* The Agg or Group node will preserve ordering */
1319         if (sort_pathkeys &&
1320                 !pathkeys_contained_in(sort_pathkeys, current_pathkeys))
1321                 cost_sort(&sorted_p, parse, sort_pathkeys, sorted_p.total_cost,
1322                                   dNumGroups, cheapest_path_width);
1323
1324         /*
1325          * Now make the decision using the top-level tuple fraction.  First we
1326          * have to convert an absolute count (LIMIT) into fractional form.
1327          */
1328         if (tuple_fraction >= 1.0)
1329                 tuple_fraction /= dNumGroups;
1330
1331         if (compare_fractional_path_costs(&hashed_p, &sorted_p,
1332                                                                           tuple_fraction) < 0)
1333         {
1334                 /* Hashed is cheaper, so use it */
1335                 return true;
1336         }
1337         return false;
1338 }
1339
1340 /*
1341  * hash_safe_grouping - are grouping operators hashable?
1342  *
1343  * We assume hashed aggregation will work if the datatype's equality operator
1344  * is marked hashjoinable.
1345  */
1346 static bool
1347 hash_safe_grouping(Query *parse)
1348 {
1349         ListCell   *gl;
1350
1351         foreach(gl, parse->groupClause)
1352         {
1353                 GroupClause *grpcl = (GroupClause *) lfirst(gl);
1354                 TargetEntry *tle = get_sortgroupclause_tle(grpcl, parse->targetList);
1355                 Operator        optup;
1356                 bool            oprcanhash;
1357
1358                 optup = equality_oper(exprType((Node *) tle->expr), true);
1359                 if (!optup)
1360                         return false;
1361                 oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash;
1362                 ReleaseSysCache(optup);
1363                 if (!oprcanhash)
1364                         return false;
1365         }
1366         return true;
1367 }
1368
1369 /*---------------
1370  * make_subplanTargetList
1371  *        Generate appropriate target list when grouping is required.
1372  *
1373  * When grouping_planner inserts Aggregate, Group, or Result plan nodes
1374  * above the result of query_planner, we typically want to pass a different
1375  * target list to query_planner than the outer plan nodes should have.
1376  * This routine generates the correct target list for the subplan.
1377  *
1378  * The initial target list passed from the parser already contains entries
1379  * for all ORDER BY and GROUP BY expressions, but it will not have entries
1380  * for variables used only in HAVING clauses; so we need to add those
1381  * variables to the subplan target list.  Also, we flatten all expressions
1382  * except GROUP BY items into their component variables; the other expressions
1383  * will be computed by the inserted nodes rather than by the subplan.
1384  * For example, given a query like
1385  *              SELECT a+b,SUM(c+d) FROM table GROUP BY a+b;
1386  * we want to pass this targetlist to the subplan:
1387  *              a,b,c,d,a+b
1388  * where the a+b target will be used by the Sort/Group steps, and the
1389  * other targets will be used for computing the final results.  (In the
1390  * above example we could theoretically suppress the a and b targets and
1391  * pass down only c,d,a+b, but it's not really worth the trouble to
1392  * eliminate simple var references from the subplan.  We will avoid doing
1393  * the extra computation to recompute a+b at the outer level; see
1394  * replace_vars_with_subplan_refs() in setrefs.c.)
1395  *
1396  * If we are grouping or aggregating, *and* there are no non-Var grouping
1397  * expressions, then the returned tlist is effectively dummy; we do not
1398  * need to force it to be evaluated, because all the Vars it contains
1399  * should be present in the output of query_planner anyway.
1400  *
1401  * 'parse' is the query being processed.
1402  * 'tlist' is the query's target list.
1403  * 'groupColIdx' receives an array of column numbers for the GROUP BY
1404  *                      expressions (if there are any) in the subplan's target list.
1405  * 'need_tlist_eval' is set true if we really need to evaluate the
1406  *                      result tlist.
1407  *
1408  * The result is the targetlist to be passed to the subplan.
1409  *---------------
1410  */
1411 static List *
1412 make_subplanTargetList(Query *parse,
1413                                            List *tlist,
1414                                            AttrNumber **groupColIdx,
1415                                            bool *need_tlist_eval)
1416 {
1417         List       *sub_tlist;
1418         List       *extravars;
1419         int                     numCols;
1420
1421         *groupColIdx = NULL;
1422
1423         /*
1424          * If we're not grouping or aggregating, there's nothing to do here;
1425          * query_planner should receive the unmodified target list.
1426          */
1427         if (!parse->hasAggs && !parse->groupClause && !parse->hasHavingQual)
1428         {
1429                 *need_tlist_eval = true;
1430                 return tlist;
1431         }
1432
1433         /*
1434          * Otherwise, start with a "flattened" tlist (having just the vars
1435          * mentioned in the targetlist and HAVING qual --- but not upper-
1436          * level Vars; they will be replaced by Params later on).
1437          */
1438         sub_tlist = flatten_tlist(tlist);
1439         extravars = pull_var_clause(parse->havingQual, false);
1440         sub_tlist = add_to_flat_tlist(sub_tlist, extravars);
1441         list_free(extravars);
1442         *need_tlist_eval = false;       /* only eval if not flat tlist */
1443
1444         /*
1445          * If grouping, create sub_tlist entries for all GROUP BY expressions
1446          * (GROUP BY items that are simple Vars should be in the list
1447          * already), and make an array showing where the group columns are in
1448          * the sub_tlist.
1449          */
1450         numCols = list_length(parse->groupClause);
1451         if (numCols > 0)
1452         {
1453                 int                     keyno = 0;
1454                 AttrNumber *grpColIdx;
1455                 ListCell   *gl;
1456
1457                 grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);
1458                 *groupColIdx = grpColIdx;
1459
1460                 foreach(gl, parse->groupClause)
1461                 {
1462                         GroupClause *grpcl = (GroupClause *) lfirst(gl);
1463                         Node       *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
1464                         TargetEntry *te = NULL;
1465                         ListCell   *sl;
1466
1467                         /* Find or make a matching sub_tlist entry */
1468                         foreach(sl, sub_tlist)
1469                         {
1470                                 te = (TargetEntry *) lfirst(sl);
1471                                 if (equal(groupexpr, te->expr))
1472                                         break;
1473                         }
1474                         if (!sl)
1475                         {
1476                                 te = makeTargetEntry((Expr *) groupexpr,
1477                                                                          list_length(sub_tlist) + 1,
1478                                                                          NULL,
1479                                                                          false);
1480                                 sub_tlist = lappend(sub_tlist, te);
1481                                 *need_tlist_eval = true;                /* it's not flat anymore */
1482                         }
1483
1484                         /* and save its resno */
1485                         grpColIdx[keyno++] = te->resno;
1486                 }
1487         }
1488
1489         return sub_tlist;
1490 }
1491
1492 /*
1493  * locate_grouping_columns
1494  *              Locate grouping columns in the tlist chosen by query_planner.
1495  *
1496  * This is only needed if we don't use the sub_tlist chosen by
1497  * make_subplanTargetList.      We have to forget the column indexes found
1498  * by that routine and re-locate the grouping vars in the real sub_tlist.
1499  */
1500 static void
1501 locate_grouping_columns(Query *parse,
1502                                                 List *tlist,
1503                                                 List *sub_tlist,
1504                                                 AttrNumber *groupColIdx)
1505 {
1506         int                     keyno = 0;
1507         ListCell   *gl;
1508
1509         /*
1510          * No work unless grouping.
1511          */
1512         if (!parse->groupClause)
1513         {
1514                 Assert(groupColIdx == NULL);
1515                 return;
1516         }
1517         Assert(groupColIdx != NULL);
1518
1519         foreach(gl, parse->groupClause)
1520         {
1521                 GroupClause *grpcl = (GroupClause *) lfirst(gl);
1522                 Node       *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
1523                 TargetEntry *te = NULL;
1524                 ListCell   *sl;
1525
1526                 foreach(sl, sub_tlist)
1527                 {
1528                         te = (TargetEntry *) lfirst(sl);
1529                         if (equal(groupexpr, te->expr))
1530                                 break;
1531                 }
1532                 if (!sl)
1533                         elog(ERROR, "failed to locate grouping columns");
1534
1535                 groupColIdx[keyno++] = te->resno;
1536         }
1537 }
1538
1539 /*
1540  * postprocess_setop_tlist
1541  *        Fix up targetlist returned by plan_set_operations().
1542  *
1543  * We need to transpose sort key info from the orig_tlist into new_tlist.
1544  * NOTE: this would not be good enough if we supported resjunk sort keys
1545  * for results of set operations --- then, we'd need to project a whole
1546  * new tlist to evaluate the resjunk columns.  For now, just ereport if we
1547  * find any resjunk columns in orig_tlist.
1548  */
1549 static List *
1550 postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
1551 {
1552         ListCell   *l;
1553         ListCell   *orig_tlist_item = list_head(orig_tlist);
1554
1555         foreach(l, new_tlist)
1556         {
1557                 TargetEntry *new_tle = (TargetEntry *) lfirst(l);
1558                 TargetEntry *orig_tle;
1559
1560                 /* ignore resjunk columns in setop result */
1561                 if (new_tle->resjunk)
1562                         continue;
1563
1564                 Assert(orig_tlist_item != NULL);
1565                 orig_tle = (TargetEntry *) lfirst(orig_tlist_item);
1566                 orig_tlist_item = lnext(orig_tlist_item);
1567                 if (orig_tle->resjunk)                  /* should not happen */
1568                         elog(ERROR, "resjunk output columns are not implemented");
1569                 Assert(new_tle->resno == orig_tle->resno);
1570                 new_tle->ressortgroupref = orig_tle->ressortgroupref;
1571         }
1572         if (orig_tlist_item != NULL)
1573                 elog(ERROR, "resjunk output columns are not implemented");
1574         return new_tlist;
1575 }