/*------------------------------------------------------------------------- * * planner.c * The query optimizer external interface. * * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.181 2005/03/28 00:58:23 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include #include "catalog/pg_operator.h" #include "catalog/pg_type.h" #include "executor/executor.h" #include "executor/nodeAgg.h" #include "miscadmin.h" #include "nodes/makefuncs.h" #ifdef OPTIMIZER_DEBUG #include "nodes/print.h" #endif #include "optimizer/clauses.h" #include "optimizer/cost.h" #include "optimizer/pathnode.h" #include "optimizer/paths.h" #include "optimizer/planmain.h" #include "optimizer/planner.h" #include "optimizer/prep.h" #include "optimizer/subselect.h" #include "optimizer/tlist.h" #include "optimizer/var.h" #include "parser/parsetree.h" #include "parser/parse_expr.h" #include "parser/parse_oper.h" #include "utils/selfuncs.h" #include "utils/syscache.h" ParamListInfo PlannerBoundParamList = NULL; /* current boundParams */ /* Expression kind codes for preprocess_expression */ #define EXPRKIND_QUAL 0 #define EXPRKIND_TARGET 1 #define EXPRKIND_RTFUNC 2 #define EXPRKIND_LIMIT 3 #define EXPRKIND_ININFO 4 static Node *preprocess_expression(Query *parse, Node *expr, int kind); static void preprocess_qual_conditions(Query *parse, Node *jtnode); static Plan *inheritance_planner(Query *parse, List *inheritlist); static Plan *grouping_planner(Query *parse, double tuple_fraction); static bool hash_safe_grouping(Query *parse); static List *make_subplanTargetList(Query *parse, List *tlist, AttrNumber **groupColIdx, bool *need_tlist_eval); static void locate_grouping_columns(Query *parse, List *tlist, List *sub_tlist, AttrNumber *groupColIdx); static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist); /***************************************************************************** * * Query optimizer entry point * *****************************************************************************/ Plan * planner(Query *parse, bool isCursor, int cursorOptions, ParamListInfo boundParams) { double tuple_fraction; Plan *result_plan; Index save_PlannerQueryLevel; List *save_PlannerParamList; ParamListInfo save_PlannerBoundParamList; /* * The planner can be called recursively (an example is when * eval_const_expressions tries to pre-evaluate an SQL function). So, * these global state variables must be saved and restored. * * Query level and the param list cannot be moved into the Query * structure since their whole purpose is communication across * multiple sub-Queries. Also, boundParams is explicitly info from * outside the Query, and so is likewise better handled as a global * variable. * * Note we do NOT save and restore PlannerPlanId: it exists to assign * unique IDs to SubPlan nodes, and we want those IDs to be unique for * the life of a backend. Also, PlannerInitPlan is saved/restored in * subquery_planner, not here. */ save_PlannerQueryLevel = PlannerQueryLevel; save_PlannerParamList = PlannerParamList; save_PlannerBoundParamList = PlannerBoundParamList; /* Initialize state for handling outer-level references and params */ PlannerQueryLevel = 0; /* will be 1 in top-level subquery_planner */ PlannerParamList = NIL; PlannerBoundParamList = boundParams; /* Determine what fraction of the plan is likely to be scanned */ if (isCursor) { /* * We have no real idea how many tuples the user will ultimately * FETCH from a cursor, but it seems a good bet that he doesn't * want 'em all. Optimize for 10% retrieval (you gotta better * number? Should this be a SETtable parameter?) */ tuple_fraction = 0.10; } else { /* Default assumption is we need all the tuples */ tuple_fraction = 0.0; } /* primary planning entry point (may recurse for subqueries) */ result_plan = subquery_planner(parse, tuple_fraction); Assert(PlannerQueryLevel == 0); /* * If creating a plan for a scrollable cursor, make sure it can run * backwards on demand. Add a Material node at the top at need. */ if (isCursor && (cursorOptions & CURSOR_OPT_SCROLL)) { if (!ExecSupportsBackwardScan(result_plan)) result_plan = materialize_finished_plan(result_plan); } /* executor wants to know total number of Params used overall */ result_plan->nParamExec = list_length(PlannerParamList); /* final cleanup of the plan */ set_plan_references(result_plan, parse->rtable); /* restore state for outer planner, if any */ PlannerQueryLevel = save_PlannerQueryLevel; PlannerParamList = save_PlannerParamList; PlannerBoundParamList = save_PlannerBoundParamList; return result_plan; } /*-------------------- * subquery_planner * Invokes the planner on a subquery. We recurse to here for each * sub-SELECT found in the query tree. * * parse is the querytree produced by the parser & rewriter. * tuple_fraction is the fraction of tuples we expect will be retrieved. * tuple_fraction is interpreted as explained for grouping_planner, below. * * Basically, this routine does the stuff that should only be done once * per Query object. It then calls grouping_planner. At one time, * grouping_planner could be invoked recursively on the same Query object; * that's not currently true, but we keep the separation between the two * routines anyway, in case we need it again someday. * * subquery_planner will be called recursively to handle sub-Query nodes * found within the query's expressions and rangetable. * * Returns a query plan. *-------------------- */ Plan * subquery_planner(Query *parse, double tuple_fraction) { List *saved_initplan = PlannerInitPlan; int saved_planid = PlannerPlanId; bool hasOuterJoins; Plan *plan; List *newHaving; List *lst; ListCell *l; /* Set up for a new level of subquery */ PlannerQueryLevel++; PlannerInitPlan = NIL; /* * Look for IN clauses at the top level of WHERE, and transform them * into joins. Note that this step only handles IN clauses originally * at top level of WHERE; if we pull up any subqueries in the next * step, their INs are processed just before pulling them up. */ parse->in_info_list = NIL; if (parse->hasSubLinks) parse->jointree->quals = pull_up_IN_clauses(parse, parse->jointree->quals); /* * Check to see if any subqueries in the rangetable can be merged into * this query. */ parse->jointree = (FromExpr *) pull_up_subqueries(parse, (Node *) parse->jointree, false); /* * Detect whether any rangetable entries are RTE_JOIN kind; if not, we * can avoid the expense of doing flatten_join_alias_vars(). Also * check for outer joins --- if none, we can skip * reduce_outer_joins(). This must be done after we have done * pull_up_subqueries, of course. */ parse->hasJoinRTEs = false; hasOuterJoins = false; foreach(l, parse->rtable) { RangeTblEntry *rte = (RangeTblEntry *) lfirst(l); if (rte->rtekind == RTE_JOIN) { parse->hasJoinRTEs = true; if (IS_OUTER_JOIN(rte->jointype)) { hasOuterJoins = true; /* Can quit scanning once we find an outer join */ break; } } } /* * Set hasHavingQual to remember if HAVING clause is present. Needed * because preprocess_expression will reduce a constant-true condition * to an empty qual list ... but "HAVING TRUE" is not a semantic no-op. */ parse->hasHavingQual = (parse->havingQual != NULL); /* * Do expression preprocessing on targetlist and quals. */ parse->targetList = (List *) preprocess_expression(parse, (Node *) parse->targetList, EXPRKIND_TARGET); preprocess_qual_conditions(parse, (Node *) parse->jointree); parse->havingQual = preprocess_expression(parse, parse->havingQual, EXPRKIND_QUAL); parse->limitOffset = preprocess_expression(parse, parse->limitOffset, EXPRKIND_LIMIT); parse->limitCount = preprocess_expression(parse, parse->limitCount, EXPRKIND_LIMIT); parse->in_info_list = (List *) preprocess_expression(parse, (Node *) parse->in_info_list, EXPRKIND_ININFO); /* Also need to preprocess expressions for function RTEs */ foreach(l, parse->rtable) { RangeTblEntry *rte = (RangeTblEntry *) lfirst(l); if (rte->rtekind == RTE_FUNCTION) rte->funcexpr = preprocess_expression(parse, rte->funcexpr, EXPRKIND_RTFUNC); } /* * In some cases we may want to transfer a HAVING clause into WHERE. * We cannot do so if the HAVING clause contains aggregates (obviously) * or volatile functions (since a HAVING clause is supposed to be executed * only once per group). Also, it may be that the clause is so expensive * to execute that we're better off doing it only once per group, despite * the loss of selectivity. This is hard to estimate short of doing the * entire planning process twice, so we use a heuristic: clauses * containing subplans are left in HAVING. Otherwise, we move or copy * the HAVING clause into WHERE, in hopes of eliminating tuples before * aggregation instead of after. * * If the query has explicit grouping then we can simply move such a * clause into WHERE; any group that fails the clause will not be * in the output because none of its tuples will reach the grouping * or aggregation stage. Otherwise we must have a degenerate * (variable-free) HAVING clause, which we put in WHERE so that * query_planner() can use it in a gating Result node, but also keep * in HAVING to ensure that we don't emit a bogus aggregated row. * (This could be done better, but it seems not worth optimizing.) * * Note that both havingQual and parse->jointree->quals are in * implicitly-ANDed-list form at this point, even though they are * declared as Node *. */ newHaving = NIL; foreach(l, (List *) parse->havingQual) { Node *havingclause = (Node *) lfirst(l); if (contain_agg_clause(havingclause) || contain_volatile_functions(havingclause) || contain_subplans(havingclause)) { /* keep it in HAVING */ newHaving = lappend(newHaving, havingclause); } else if (parse->groupClause) { /* move it to WHERE */ parse->jointree->quals = (Node *) lappend((List *) parse->jointree->quals, havingclause); } else { /* put a copy in WHERE, keep it in HAVING */ parse->jointree->quals = (Node *) lappend((List *) parse->jointree->quals, copyObject(havingclause)); newHaving = lappend(newHaving, havingclause); } } parse->havingQual = (Node *) newHaving; /* * If we have any outer joins, try to reduce them to plain inner * joins. This step is most easily done after we've done expression * preprocessing. */ if (hasOuterJoins) reduce_outer_joins(parse); /* * See if we can simplify the jointree; opportunities for this may * come from having pulled up subqueries, or from flattening explicit * JOIN syntax. We must do this after flattening JOIN alias * variables, since eliminating explicit JOIN nodes from the jointree * will cause get_relids_for_join() to fail. But it should happen * after reduce_outer_joins, anyway. */ parse->jointree = (FromExpr *) simplify_jointree(parse, (Node *) parse->jointree); /* * Do the main planning. If we have an inherited target relation, * that needs special processing, else go straight to * grouping_planner. */ if (parse->resultRelation && (lst = expand_inherited_rtentry(parse, parse->resultRelation)) != NIL) plan = inheritance_planner(parse, lst); else plan = grouping_planner(parse, tuple_fraction); /* * If any subplans were generated, or if we're inside a subplan, build * initPlan list and extParam/allParam sets for plan nodes. */ if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1) { Cost initplan_cost = 0; /* Prepare extParam/allParam sets for all nodes in tree */ SS_finalize_plan(plan, parse->rtable); /* * SS_finalize_plan doesn't handle initPlans, so we have to * manually attach them to the topmost plan node, and add their * extParams to the topmost node's, too. * * We also add the total_cost of each initPlan to the startup cost of * the top node. This is a conservative overestimate, since in * fact each initPlan might be executed later than plan startup, * or even not at all. */ plan->initPlan = PlannerInitPlan; foreach(l, plan->initPlan) { SubPlan *initplan = (SubPlan *) lfirst(l); plan->extParam = bms_add_members(plan->extParam, initplan->plan->extParam); /* allParam must include all members of extParam */ plan->allParam = bms_add_members(plan->allParam, plan->extParam); initplan_cost += initplan->plan->total_cost; } plan->startup_cost += initplan_cost; plan->total_cost += initplan_cost; } /* Return to outer subquery context */ PlannerQueryLevel--; PlannerInitPlan = saved_initplan; /* we do NOT restore PlannerPlanId; that's not an oversight! */ return plan; } /* * preprocess_expression * Do subquery_planner's preprocessing work for an expression, * which can be a targetlist, a WHERE clause (including JOIN/ON * conditions), or a HAVING clause. */ static Node * preprocess_expression(Query *parse, Node *expr, int kind) { /* * If the query has any join RTEs, replace join alias variables with * base-relation variables. We must do this before sublink processing, * else sublinks expanded out from join aliases wouldn't get * processed. */ if (parse->hasJoinRTEs) expr = flatten_join_alias_vars(parse, expr); /* * Simplify constant expressions. * * Note: this also flattens nested AND and OR expressions into N-argument * form. All processing of a qual expression after this point must be * careful to maintain AND/OR flatness --- that is, do not generate a tree * with AND directly under AND, nor OR directly under OR. */ expr = eval_const_expressions(expr); /* * If it's a qual or havingQual, canonicalize it. */ if (kind == EXPRKIND_QUAL) { expr = (Node *) canonicalize_qual((Expr *) expr); #ifdef OPTIMIZER_DEBUG printf("After canonicalize_qual()\n"); pprint(expr); #endif } /* Expand SubLinks to SubPlans */ if (parse->hasSubLinks) expr = SS_process_sublinks(expr, (kind == EXPRKIND_QUAL)); /* * XXX do not insert anything here unless you have grokked the * comments in SS_replace_correlation_vars ... */ /* Replace uplevel vars with Param nodes */ if (PlannerQueryLevel > 1) expr = SS_replace_correlation_vars(expr); /* * If it's a qual or havingQual, convert it to implicit-AND format. * (We don't want to do this before eval_const_expressions, since the * latter would be unable to simplify a top-level AND correctly. Also, * SS_process_sublinks expects explicit-AND format.) */ if (kind == EXPRKIND_QUAL) expr = (Node *) make_ands_implicit((Expr *) expr); return expr; } /* * preprocess_qual_conditions * Recursively scan the query's jointree and do subquery_planner's * preprocessing work on each qual condition found therein. */ static void preprocess_qual_conditions(Query *parse, Node *jtnode) { if (jtnode == NULL) return; if (IsA(jtnode, RangeTblRef)) { /* nothing to do here */ } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; ListCell *l; foreach(l, f->fromlist) preprocess_qual_conditions(parse, lfirst(l)); f->quals = preprocess_expression(parse, f->quals, EXPRKIND_QUAL); } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; preprocess_qual_conditions(parse, j->larg); preprocess_qual_conditions(parse, j->rarg); j->quals = preprocess_expression(parse, j->quals, EXPRKIND_QUAL); } else elog(ERROR, "unrecognized node type: %d", (int) nodeTag(jtnode)); } /*-------------------- * inheritance_planner * Generate a plan in the case where the result relation is an * inheritance set. * * We have to handle this case differently from cases where a source * relation is an inheritance set. Source inheritance is expanded at * the bottom of the plan tree (see allpaths.c), but target inheritance * has to be expanded at the top. The reason is that for UPDATE, each * target relation needs a different targetlist matching its own column * set. (This is not so critical for DELETE, but for simplicity we treat * inherited DELETE the same way.) Fortunately, the UPDATE/DELETE target * can never be the nullable side of an outer join, so it's OK to generate * the plan this way. * * parse is the querytree produced by the parser & rewriter. * inheritlist is an integer list of RT indexes for the result relation set. * * Returns a query plan. *-------------------- */ static Plan * inheritance_planner(Query *parse, List *inheritlist) { int parentRTindex = parse->resultRelation; Oid parentOID = getrelid(parentRTindex, parse->rtable); int mainrtlength = list_length(parse->rtable); List *subplans = NIL; List *tlist = NIL; ListCell *l; foreach(l, inheritlist) { int childRTindex = lfirst_int(l); Oid childOID = getrelid(childRTindex, parse->rtable); Query *subquery; Plan *subplan; /* Generate modified query with this rel as target */ subquery = (Query *) adjust_inherited_attrs((Node *) parse, parentRTindex, parentOID, childRTindex, childOID); /* Generate plan */ subplan = grouping_planner(subquery, 0.0 /* retrieve all tuples */ ); subplans = lappend(subplans, subplan); /* * XXX my goodness this next bit is ugly. Really need to think about * ways to rein in planner's habit of scribbling on its input. * * Planning of the subquery might have modified the rangetable, * either by addition of RTEs due to expansion of inherited source * tables, or by changes of the Query structures inside subquery * RTEs. We have to ensure that this gets propagated back to the * master copy. However, if we aren't done planning yet, we also * need to ensure that subsequent calls to grouping_planner have * virgin sub-Queries to work from. So, if we are at the last * list entry, just copy the subquery rangetable back to the master * copy; if we are not, then extend the master copy by adding * whatever the subquery added. (We assume these added entries * will go untouched by the future grouping_planner calls. We are * also effectively assuming that sub-Queries will get planned * identically each time, or at least that the impacts on their * rangetables will be the same each time. Did I say this is ugly?) */ if (lnext(l) == NULL) parse->rtable = subquery->rtable; else { int subrtlength = list_length(subquery->rtable); if (subrtlength > mainrtlength) { List *subrt; subrt = list_copy_tail(subquery->rtable, mainrtlength); parse->rtable = list_concat(parse->rtable, subrt); mainrtlength = subrtlength; } } /* Save preprocessed tlist from first rel for use in Append */ if (tlist == NIL) tlist = subplan->targetlist; } /* Save the target-relations list for the executor, too */ parse->resultRelations = inheritlist; /* Mark result as unordered (probably unnecessary) */ parse->query_pathkeys = NIL; return (Plan *) make_append(subplans, true, tlist); } /*-------------------- * grouping_planner * Perform planning steps related to grouping, aggregation, etc. * This primarily means adding top-level processing to the basic * query plan produced by query_planner. * * parse is the querytree produced by the parser & rewriter. * tuple_fraction is the fraction of tuples we expect will be retrieved * * tuple_fraction is interpreted as follows: * 0: expect all tuples to be retrieved (normal case) * 0 < tuple_fraction < 1: expect the given fraction of tuples available * from the plan to be retrieved * tuple_fraction >= 1: tuple_fraction is the absolute number of tuples * expected to be retrieved (ie, a LIMIT specification) * * Returns a query plan. Also, parse->query_pathkeys is returned as the * actual output ordering of the plan (in pathkey format). *-------------------- */ static Plan * grouping_planner(Query *parse, double tuple_fraction) { List *tlist = parse->targetList; Plan *result_plan; List *current_pathkeys; List *sort_pathkeys; if (parse->setOperations) { List *set_sortclauses; /* * Construct the plan for set operations. The result will not * need any work except perhaps a top-level sort and/or LIMIT. */ result_plan = plan_set_operations(parse, &set_sortclauses); /* * Calculate pathkeys representing the sort order (if any) of the * set operation's result. We have to do this before overwriting * the sort key information... */ current_pathkeys = make_pathkeys_for_sortclauses(set_sortclauses, result_plan->targetlist); current_pathkeys = canonicalize_pathkeys(parse, current_pathkeys); /* * We should not need to call preprocess_targetlist, since we must * be in a SELECT query node. Instead, use the targetlist * returned by plan_set_operations (since this tells whether it * returned any resjunk columns!), and transfer any sort key * information from the original tlist. */ Assert(parse->commandType == CMD_SELECT); tlist = postprocess_setop_tlist(result_plan->targetlist, tlist); /* * Can't handle FOR UPDATE here (parser should have checked * already, but let's make sure). */ if (parse->rowMarks) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT"))); /* * Calculate pathkeys that represent result ordering requirements */ sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause, tlist); sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys); } else { /* No set operations, do regular planning */ List *sub_tlist; List *group_pathkeys; AttrNumber *groupColIdx = NULL; bool need_tlist_eval = true; QualCost tlist_cost; double sub_tuple_fraction; Path *cheapest_path; Path *sorted_path; double dNumGroups = 0; long numGroups = 0; AggClauseCounts agg_counts; int numGroupCols = list_length(parse->groupClause); bool use_hashed_grouping = false; MemSet(&agg_counts, 0, sizeof(AggClauseCounts)); /* Preprocess targetlist */ tlist = preprocess_targetlist(parse, tlist); /* * Generate appropriate target list for subplan; may be different * from tlist if grouping or aggregation is needed. */ sub_tlist = make_subplanTargetList(parse, tlist, &groupColIdx, &need_tlist_eval); /* * Calculate pathkeys that represent grouping/ordering * requirements */ group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause, tlist); sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause, tlist); /* * Will need actual number of aggregates for estimating costs. * * Note: we do not attempt to detect duplicate aggregates here; a * somewhat-overestimated count is okay for our present purposes. * * Note: think not that we can turn off hasAggs if we find no aggs. * It is possible for constant-expression simplification to remove * all explicit references to aggs, but we still have to follow * the aggregate semantics (eg, producing only one output row). */ if (parse->hasAggs) { count_agg_clauses((Node *) tlist, &agg_counts); count_agg_clauses(parse->havingQual, &agg_counts); } /* * Figure out whether we need a sorted result from query_planner. * * If we have a GROUP BY clause, then we want a result sorted * properly for grouping. Otherwise, if there is an ORDER BY * clause, we want to sort by the ORDER BY clause. (Note: if we * have both, and ORDER BY is a superset of GROUP BY, it would be * tempting to request sort by ORDER BY --- but that might just * leave us failing to exploit an available sort order at all. * Needs more thought...) */ if (parse->groupClause) parse->query_pathkeys = group_pathkeys; else if (parse->sortClause) parse->query_pathkeys = sort_pathkeys; else parse->query_pathkeys = NIL; /* * Adjust tuple_fraction if we see that we are going to apply * limiting/grouping/aggregation/etc. This is not overridable by * the caller, since it reflects plan actions that this routine * will certainly take, not assumptions about context. */ if (parse->limitCount != NULL) { /* * A LIMIT clause limits the absolute number of tuples * returned. However, if it's not a constant LIMIT then we * have to punt; for lack of a better idea, assume 10% of the * plan's result is wanted. */ double limit_fraction = 0.0; if (IsA(parse->limitCount, Const)) { Const *limitc = (Const *) parse->limitCount; int32 count = DatumGetInt32(limitc->constvalue); /* * A NULL-constant LIMIT represents "LIMIT ALL", which we * treat the same as no limit (ie, expect to retrieve all * the tuples). */ if (!limitc->constisnull && count > 0) { limit_fraction = (double) count; /* We must also consider the OFFSET, if present */ if (parse->limitOffset != NULL) { if (IsA(parse->limitOffset, Const)) { int32 offset; limitc = (Const *) parse->limitOffset; offset = DatumGetInt32(limitc->constvalue); if (!limitc->constisnull && offset > 0) limit_fraction += (double) offset; } else { /* OFFSET is an expression ... punt ... */ limit_fraction = 0.10; } } } } else { /* LIMIT is an expression ... punt ... */ limit_fraction = 0.10; } if (limit_fraction > 0.0) { /* * If we have absolute limits from both caller and LIMIT, * use the smaller value; if one is fractional and the * other absolute, treat the fraction as a fraction of the * absolute value; else we can multiply the two fractions * together. */ if (tuple_fraction >= 1.0) { if (limit_fraction >= 1.0) { /* both absolute */ tuple_fraction = Min(tuple_fraction, limit_fraction); } else { /* caller absolute, limit fractional */ tuple_fraction *= limit_fraction; if (tuple_fraction < 1.0) tuple_fraction = 1.0; } } else if (tuple_fraction > 0.0) { if (limit_fraction >= 1.0) { /* caller fractional, limit absolute */ tuple_fraction *= limit_fraction; if (tuple_fraction < 1.0) tuple_fraction = 1.0; } else { /* both fractional */ tuple_fraction *= limit_fraction; } } else { /* no info from caller, just use limit */ tuple_fraction = limit_fraction; } } } /* * With grouping or aggregation, the tuple fraction to pass to * query_planner() may be different from what it is at top level. */ sub_tuple_fraction = tuple_fraction; if (parse->groupClause) { /* * In GROUP BY mode, we have the little problem that we don't * really know how many input tuples will be needed to make a * group, so we can't translate an output LIMIT count into an * input count. For lack of a better idea, assume 25% of the * input data will be processed if there is any output limit. * However, if the caller gave us a fraction rather than an * absolute count, we can keep using that fraction (which * amounts to assuming that all the groups are about the same * size). */ if (sub_tuple_fraction >= 1.0) sub_tuple_fraction = 0.25; /* * If both GROUP BY and ORDER BY are specified, we will need * two levels of sort --- and, therefore, certainly need to * read all the input tuples --- unless ORDER BY is a subset * of GROUP BY. (We have not yet canonicalized the pathkeys, * so must use the slower noncanonical comparison method.) */ if (parse->groupClause && parse->sortClause && !noncanonical_pathkeys_contained_in(sort_pathkeys, group_pathkeys)) sub_tuple_fraction = 0.0; } else if (parse->hasAggs) { /* * Ungrouped aggregate will certainly want all the input * tuples. */ sub_tuple_fraction = 0.0; } else if (parse->distinctClause) { /* * SELECT DISTINCT, like GROUP, will absorb an unpredictable * number of input tuples per output tuple. Handle the same * way. */ if (sub_tuple_fraction >= 1.0) sub_tuple_fraction = 0.25; } /* * Generate the best unsorted and presorted paths for this Query * (but note there may not be any presorted path). */ query_planner(parse, sub_tlist, sub_tuple_fraction, &cheapest_path, &sorted_path); /* * We couldn't canonicalize group_pathkeys and sort_pathkeys * before running query_planner(), so do it now. */ group_pathkeys = canonicalize_pathkeys(parse, group_pathkeys); sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys); /* * Consider whether we might want to use hashed grouping. */ if (parse->groupClause) { List *groupExprs; double cheapest_path_rows; int cheapest_path_width; /* * Beware in this section of the possibility that * cheapest_path->parent is NULL. This could happen if user * does something silly like SELECT 'foo' GROUP BY 1; */ if (cheapest_path->parent) { cheapest_path_rows = cheapest_path->parent->rows; cheapest_path_width = cheapest_path->parent->width; } else { cheapest_path_rows = 1; /* assume non-set result */ cheapest_path_width = 100; /* arbitrary */ } /* * Always estimate the number of groups. We can't do this * until after running query_planner(), either. */ groupExprs = get_sortgrouplist_exprs(parse->groupClause, parse->targetList); dNumGroups = estimate_num_groups(parse, groupExprs, cheapest_path_rows); /* Also want it as a long int --- but 'ware overflow! */ numGroups = (long) Min(dNumGroups, (double) LONG_MAX); /* * Check can't-do-it conditions, including whether the * grouping operators are hashjoinable. * * Executor doesn't support hashed aggregation with DISTINCT * aggregates. (Doing so would imply storing *all* the input * values in the hash table, which seems like a certain * loser.) */ if (!enable_hashagg || !hash_safe_grouping(parse)) use_hashed_grouping = false; else if (agg_counts.numDistinctAggs != 0) use_hashed_grouping = false; else { /* * Use hashed grouping if (a) we think we can fit the * hashtable into work_mem, *and* (b) the estimated cost * is no more than doing it the other way. While avoiding * the need for sorted input is usually a win, the fact * that the output won't be sorted may be a loss; so we * need to do an actual cost comparison. */ Size hashentrysize; /* Estimate per-hash-entry space at tuple width... */ hashentrysize = cheapest_path_width; /* plus space for pass-by-ref transition values... */ hashentrysize += agg_counts.transitionSpace; /* plus the per-hash-entry overhead */ hashentrysize += hash_agg_entry_size(agg_counts.numAggs); if (hashentrysize * dNumGroups <= work_mem * 1024L) { /* * Okay, do the cost comparison. We need to consider * cheapest_path + hashagg [+ final sort] versus * either cheapest_path [+ sort] + group or agg [+ * final sort] or presorted_path + group or agg [+ * final sort] where brackets indicate a step that may * not be needed. We assume query_planner() will have * returned a presorted path only if it's a winner * compared to cheapest_path for this purpose. * * These path variables are dummies that just hold cost * fields; we don't make actual Paths for these steps. */ Path hashed_p; Path sorted_p; cost_agg(&hashed_p, parse, AGG_HASHED, agg_counts.numAggs, numGroupCols, dNumGroups, cheapest_path->startup_cost, cheapest_path->total_cost, cheapest_path_rows); /* Result of hashed agg is always unsorted */ if (sort_pathkeys) cost_sort(&hashed_p, parse, sort_pathkeys, hashed_p.total_cost, dNumGroups, cheapest_path_width); if (sorted_path) { sorted_p.startup_cost = sorted_path->startup_cost; sorted_p.total_cost = sorted_path->total_cost; current_pathkeys = sorted_path->pathkeys; } else { sorted_p.startup_cost = cheapest_path->startup_cost; sorted_p.total_cost = cheapest_path->total_cost; current_pathkeys = cheapest_path->pathkeys; } if (!pathkeys_contained_in(group_pathkeys, current_pathkeys)) { cost_sort(&sorted_p, parse, group_pathkeys, sorted_p.total_cost, cheapest_path_rows, cheapest_path_width); current_pathkeys = group_pathkeys; } if (parse->hasAggs) cost_agg(&sorted_p, parse, AGG_SORTED, agg_counts.numAggs, numGroupCols, dNumGroups, sorted_p.startup_cost, sorted_p.total_cost, cheapest_path_rows); else cost_group(&sorted_p, parse, numGroupCols, dNumGroups, sorted_p.startup_cost, sorted_p.total_cost, cheapest_path_rows); /* The Agg or Group node will preserve ordering */ if (sort_pathkeys && !pathkeys_contained_in(sort_pathkeys, current_pathkeys)) { cost_sort(&sorted_p, parse, sort_pathkeys, sorted_p.total_cost, dNumGroups, cheapest_path_width); } /* * Now make the decision using the top-level tuple * fraction. First we have to convert an absolute * count (LIMIT) into fractional form. */ if (tuple_fraction >= 1.0) tuple_fraction /= dNumGroups; if (compare_fractional_path_costs(&hashed_p, &sorted_p, tuple_fraction) < 0) { /* Hashed is cheaper, so use it */ use_hashed_grouping = true; } } } } /* * Select the best path and create a plan to execute it. * * If we are doing hashed grouping, we will always read all the input * tuples, so use the cheapest-total path. Otherwise, trust * query_planner's decision about which to use. */ if (sorted_path && !use_hashed_grouping) { result_plan = create_plan(parse, sorted_path); current_pathkeys = sorted_path->pathkeys; } else { result_plan = create_plan(parse, cheapest_path); current_pathkeys = cheapest_path->pathkeys; } /* * create_plan() returns a plan with just a "flat" tlist of * required Vars. Usually we need to insert the sub_tlist as the * tlist of the top plan node. However, we can skip that if we * determined that whatever query_planner chose to return will be * good enough. */ if (need_tlist_eval) { /* * If the top-level plan node is one that cannot do expression * evaluation, we must insert a Result node to project the * desired tlist. */ if (!is_projection_capable_plan(result_plan)) { result_plan = (Plan *) make_result(sub_tlist, NULL, result_plan); } else { /* * Otherwise, just replace the subplan's flat tlist with * the desired tlist. */ result_plan->targetlist = sub_tlist; } /* * Also, account for the cost of evaluation of the sub_tlist. * * Up to now, we have only been dealing with "flat" tlists, * containing just Vars. So their evaluation cost is zero * according to the model used by cost_qual_eval() (or if you * prefer, the cost is factored into cpu_tuple_cost). Thus we * can avoid accounting for tlist cost throughout * query_planner() and subroutines. But now we've inserted a * tlist that might contain actual operators, sub-selects, etc * --- so we'd better account for its cost. * * Below this point, any tlist eval cost for added-on nodes * should be accounted for as we create those nodes. * Presently, of the node types we can add on, only Agg and * Group project new tlists (the rest just copy their input * tuples) --- so make_agg() and make_group() are responsible * for computing the added cost. */ cost_qual_eval(&tlist_cost, sub_tlist); result_plan->startup_cost += tlist_cost.startup; result_plan->total_cost += tlist_cost.startup + tlist_cost.per_tuple * result_plan->plan_rows; } else { /* * Since we're using query_planner's tlist and not the one * make_subplanTargetList calculated, we have to refigure any * grouping-column indexes make_subplanTargetList computed. */ locate_grouping_columns(parse, tlist, result_plan->targetlist, groupColIdx); } /* * Insert AGG or GROUP node if needed, plus an explicit sort step * if necessary. * * HAVING clause, if any, becomes qual of the Agg or Group node. */ if (use_hashed_grouping) { /* Hashed aggregate plan --- no sort needed */ result_plan = (Plan *) make_agg(parse, tlist, (List *) parse->havingQual, AGG_HASHED, numGroupCols, groupColIdx, numGroups, agg_counts.numAggs, result_plan); /* Hashed aggregation produces randomly-ordered results */ current_pathkeys = NIL; } else if (parse->hasAggs) { /* Plain aggregate plan --- sort if needed */ AggStrategy aggstrategy; if (parse->groupClause) { if (!pathkeys_contained_in(group_pathkeys, current_pathkeys)) { result_plan = (Plan *) make_sort_from_groupcols(parse, parse->groupClause, groupColIdx, result_plan); current_pathkeys = group_pathkeys; } aggstrategy = AGG_SORTED; /* * The AGG node will not change the sort ordering of its * groups, so current_pathkeys describes the result too. */ } else { aggstrategy = AGG_PLAIN; /* Result will be only one row anyway; no sort order */ current_pathkeys = NIL; } result_plan = (Plan *) make_agg(parse, tlist, (List *) parse->havingQual, aggstrategy, numGroupCols, groupColIdx, numGroups, agg_counts.numAggs, result_plan); } else if (parse->groupClause) { /* * GROUP BY without aggregation, so insert a group node (plus the * appropriate sort node, if necessary). * * Add an explicit sort if we couldn't make the path come * out the way the GROUP node needs it. */ if (!pathkeys_contained_in(group_pathkeys, current_pathkeys)) { result_plan = (Plan *) make_sort_from_groupcols(parse, parse->groupClause, groupColIdx, result_plan); current_pathkeys = group_pathkeys; } result_plan = (Plan *) make_group(parse, tlist, (List *) parse->havingQual, numGroupCols, groupColIdx, dNumGroups, result_plan); /* The Group node won't change sort ordering */ } else if (parse->hasHavingQual) { /* * No aggregates, and no GROUP BY, but we have a HAVING qual. * This is a degenerate case in which we are supposed to emit * either 0 or 1 row depending on whether HAVING succeeds. * Furthermore, there cannot be any variables in either HAVING * or the targetlist, so we actually do not need the FROM table * at all! We can just throw away the plan-so-far and generate * a Result node. This is a sufficiently unusual corner case * that it's not worth contorting the structure of this routine * to avoid having to generate the plan in the first place. */ result_plan = (Plan *) make_result(tlist, parse->havingQual, NULL); } } /* end of if (setOperations) */ /* * If we were not able to make the plan come out in the right order, * add an explicit sort step. */ if (parse->sortClause) { if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys)) { result_plan = (Plan *) make_sort_from_sortclauses(parse, parse->sortClause, result_plan); current_pathkeys = sort_pathkeys; } } /* * If there is a DISTINCT clause, add the UNIQUE node. */ if (parse->distinctClause) { result_plan = (Plan *) make_unique(result_plan, parse->distinctClause); /* * If there was grouping or aggregation, leave plan_rows as-is * (ie, assume the result was already mostly unique). If not, * it's reasonable to assume the UNIQUE filter has effects * comparable to GROUP BY. */ if (!parse->groupClause && !parse->hasHavingQual && !parse->hasAggs) { List *distinctExprs; distinctExprs = get_sortgrouplist_exprs(parse->distinctClause, parse->targetList); result_plan->plan_rows = estimate_num_groups(parse, distinctExprs, result_plan->plan_rows); } } /* * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node. */ if (parse->limitOffset || parse->limitCount) { result_plan = (Plan *) make_limit(result_plan, parse->limitOffset, parse->limitCount); } /* * Return the actual output ordering in query_pathkeys for possible * use by an outer query level. */ parse->query_pathkeys = current_pathkeys; return result_plan; } /* * hash_safe_grouping - are grouping operators hashable? * * We assume hashed aggregation will work if the datatype's equality operator * is marked hashjoinable. */ static bool hash_safe_grouping(Query *parse) { ListCell *gl; foreach(gl, parse->groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(gl); TargetEntry *tle = get_sortgroupclause_tle(grpcl, parse->targetList); Operator optup; bool oprcanhash; optup = equality_oper(tle->resdom->restype, true); if (!optup) return false; oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash; ReleaseSysCache(optup); if (!oprcanhash) return false; } return true; } /*--------------- * make_subplanTargetList * Generate appropriate target list when grouping is required. * * When grouping_planner inserts Aggregate, Group, or Result plan nodes * above the result of query_planner, we typically want to pass a different * target list to query_planner than the outer plan nodes should have. * This routine generates the correct target list for the subplan. * * The initial target list passed from the parser already contains entries * for all ORDER BY and GROUP BY expressions, but it will not have entries * for variables used only in HAVING clauses; so we need to add those * variables to the subplan target list. Also, we flatten all expressions * except GROUP BY items into their component variables; the other expressions * will be computed by the inserted nodes rather than by the subplan. * For example, given a query like * SELECT a+b,SUM(c+d) FROM table GROUP BY a+b; * we want to pass this targetlist to the subplan: * a,b,c,d,a+b * where the a+b target will be used by the Sort/Group steps, and the * other targets will be used for computing the final results. (In the * above example we could theoretically suppress the a and b targets and * pass down only c,d,a+b, but it's not really worth the trouble to * eliminate simple var references from the subplan. We will avoid doing * the extra computation to recompute a+b at the outer level; see * replace_vars_with_subplan_refs() in setrefs.c.) * * If we are grouping or aggregating, *and* there are no non-Var grouping * expressions, then the returned tlist is effectively dummy; we do not * need to force it to be evaluated, because all the Vars it contains * should be present in the output of query_planner anyway. * * 'parse' is the query being processed. * 'tlist' is the query's target list. * 'groupColIdx' receives an array of column numbers for the GROUP BY * expressions (if there are any) in the subplan's target list. * 'need_tlist_eval' is set true if we really need to evaluate the * result tlist. * * The result is the targetlist to be passed to the subplan. *--------------- */ static List * make_subplanTargetList(Query *parse, List *tlist, AttrNumber **groupColIdx, bool *need_tlist_eval) { List *sub_tlist; List *extravars; int numCols; *groupColIdx = NULL; /* * If we're not grouping or aggregating, there's nothing to do here; * query_planner should receive the unmodified target list. */ if (!parse->hasAggs && !parse->groupClause && !parse->hasHavingQual) { *need_tlist_eval = true; return tlist; } /* * Otherwise, start with a "flattened" tlist (having just the vars * mentioned in the targetlist and HAVING qual --- but not upper- * level Vars; they will be replaced by Params later on). */ sub_tlist = flatten_tlist(tlist); extravars = pull_var_clause(parse->havingQual, false); sub_tlist = add_to_flat_tlist(sub_tlist, extravars); list_free(extravars); *need_tlist_eval = false; /* only eval if not flat tlist */ /* * If grouping, create sub_tlist entries for all GROUP BY expressions * (GROUP BY items that are simple Vars should be in the list * already), and make an array showing where the group columns are in * the sub_tlist. */ numCols = list_length(parse->groupClause); if (numCols > 0) { int keyno = 0; AttrNumber *grpColIdx; ListCell *gl; grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols); *groupColIdx = grpColIdx; foreach(gl, parse->groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(gl); Node *groupexpr = get_sortgroupclause_expr(grpcl, tlist); TargetEntry *te = NULL; ListCell *sl; /* Find or make a matching sub_tlist entry */ foreach(sl, sub_tlist) { te = (TargetEntry *) lfirst(sl); if (equal(groupexpr, te->expr)) break; } if (!sl) { te = makeTargetEntry(makeResdom(list_length(sub_tlist) + 1, exprType(groupexpr), exprTypmod(groupexpr), NULL, false), (Expr *) groupexpr); sub_tlist = lappend(sub_tlist, te); *need_tlist_eval = true; /* it's not flat anymore */ } /* and save its resno */ grpColIdx[keyno++] = te->resdom->resno; } } return sub_tlist; } /* * locate_grouping_columns * Locate grouping columns in the tlist chosen by query_planner. * * This is only needed if we don't use the sub_tlist chosen by * make_subplanTargetList. We have to forget the column indexes found * by that routine and re-locate the grouping vars in the real sub_tlist. */ static void locate_grouping_columns(Query *parse, List *tlist, List *sub_tlist, AttrNumber *groupColIdx) { int keyno = 0; ListCell *gl; /* * No work unless grouping. */ if (!parse->groupClause) { Assert(groupColIdx == NULL); return; } Assert(groupColIdx != NULL); foreach(gl, parse->groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(gl); Node *groupexpr = get_sortgroupclause_expr(grpcl, tlist); TargetEntry *te = NULL; ListCell *sl; foreach(sl, sub_tlist) { te = (TargetEntry *) lfirst(sl); if (equal(groupexpr, te->expr)) break; } if (!sl) elog(ERROR, "failed to locate grouping columns"); groupColIdx[keyno++] = te->resdom->resno; } } /* * postprocess_setop_tlist * Fix up targetlist returned by plan_set_operations(). * * We need to transpose sort key info from the orig_tlist into new_tlist. * NOTE: this would not be good enough if we supported resjunk sort keys * for results of set operations --- then, we'd need to project a whole * new tlist to evaluate the resjunk columns. For now, just ereport if we * find any resjunk columns in orig_tlist. */ static List * postprocess_setop_tlist(List *new_tlist, List *orig_tlist) { ListCell *l; ListCell *orig_tlist_item = list_head(orig_tlist); foreach(l, new_tlist) { TargetEntry *new_tle = (TargetEntry *) lfirst(l); TargetEntry *orig_tle; /* ignore resjunk columns in setop result */ if (new_tle->resdom->resjunk) continue; Assert(orig_tlist_item != NULL); orig_tle = (TargetEntry *) lfirst(orig_tlist_item); orig_tlist_item = lnext(orig_tlist_item); if (orig_tle->resdom->resjunk) /* should not happen */ elog(ERROR, "resjunk output columns are not implemented"); Assert(new_tle->resdom->resno == orig_tle->resdom->resno); Assert(new_tle->resdom->restype == orig_tle->resdom->restype); new_tle->resdom->ressortgroupref = orig_tle->resdom->ressortgroupref; } if (orig_tlist_item != NULL) elog(ERROR, "resjunk output columns are not implemented"); return new_tlist; }