/*------------------------------------------------------------------------- * * planner.c * The query optimizer external interface. * * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.127 2002/11/06 22:31:24 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include "catalog/pg_type.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/analyze.h" #include "parser/parsetree.h" #include "parser/parse_expr.h" #include "rewrite/rewriteManip.h" #include "utils/lsyscache.h" /* Expression kind codes for preprocess_expression */ #define EXPRKIND_TARGET 0 #define EXPRKIND_WHERE 1 #define EXPRKIND_HAVING 2 static Node *pull_up_subqueries(Query *parse, Node *jtnode, bool below_outer_join); static bool is_simple_subquery(Query *subquery); static bool has_nullable_targetlist(Query *subquery); static void resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist); static Node *preprocess_jointree(Query *parse, Node *jtnode); 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 List *make_subplanTargetList(Query *parse, List *tlist, AttrNumber **groupColIdx); static Plan *make_groupsortplan(Query *parse, List *groupClause, AttrNumber *grpColIdx, Plan *subplan); static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist); /***************************************************************************** * * Query optimizer entry point * *****************************************************************************/ Plan * planner(Query *parse) { Plan *result_plan; Index save_PlannerQueryLevel; List *save_PlannerParamVar; /* * 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. * * These vars cannot be moved into the Query structure since their whole * purpose is communication across multiple sub-Queries. * * 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_PlannerParamVar = PlannerParamVar; /* Initialize state for handling outer-level references and params */ PlannerQueryLevel = 0; /* will be 1 in top-level subquery_planner */ PlannerParamVar = NIL; /* primary planning entry point (may recurse for subqueries) */ result_plan = subquery_planner(parse, -1.0 /* default case */ ); Assert(PlannerQueryLevel == 0); /* executor wants to know total number of Params used overall */ result_plan->nParamExec = length(PlannerParamVar); /* final cleanup of the plan */ set_plan_references(result_plan, parse->rtable); /* restore state for outer planner, if any */ PlannerQueryLevel = save_PlannerQueryLevel; PlannerParamVar = save_PlannerParamVar; 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; Plan *plan; List *newHaving; List *lst; /* Set up for a new level of subquery */ PlannerQueryLevel++; PlannerInitPlan = NIL; /* * 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); /* * If so, we may have created opportunities to simplify the jointree. */ parse->jointree = (FromExpr *) preprocess_jointree(parse, (Node *) parse->jointree); /* * 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_HAVING); /* Also need to preprocess expressions for function RTEs */ foreach(lst, parse->rtable) { RangeTblEntry *rte = (RangeTblEntry *) lfirst(lst); if (rte->rtekind == RTE_FUNCTION) rte->funcexpr = preprocess_expression(parse, rte->funcexpr, EXPRKIND_TARGET); /* These are not targetlist items, but close enough... */ } /* * Check for ungrouped variables passed to subplans in targetlist and * HAVING clause (but not in WHERE or JOIN/ON clauses, since those are * evaluated before grouping). We can't do this any earlier because * we must use the preprocessed targetlist for comparisons of grouped * expressions. */ if (parse->hasSubLinks && (parse->groupClause != NIL || parse->hasAggs)) check_subplans_for_ungrouped_vars(parse); /* * A HAVING clause without aggregates is equivalent to a WHERE clause * (except it can only refer to grouped fields). Transfer any * agg-free clauses of the HAVING qual into WHERE. This may seem like * wasting cycles to cater to stupidly-written queries, but there are * other reasons for doing it. Firstly, if the query contains no aggs * at all, then we aren't going to generate an Agg plan node, and so * there'll be no place to execute HAVING conditions; without this * transfer, we'd lose the HAVING condition entirely, which is wrong. * Secondly, when we push down a qual condition into a sub-query, it's * easiest to push the qual into HAVING always, in case it contains * aggs, and then let this code sort it out. * * Note that both havingQual and parse->jointree->quals are in * implicitly-ANDed-list form at this point, even though they are * declared as Node *. Also note that contain_agg_clause does not * recurse into sub-selects, which is exactly what we need here. */ newHaving = NIL; foreach(lst, (List *) parse->havingQual) { Node *havingclause = (Node *) lfirst(lst); if (contain_agg_clause(havingclause)) newHaving = lappend(newHaving, havingclause); else parse->jointree->quals = (Node *) lappend((List *) parse->jointree->quals, havingclause); } parse->havingQual = (Node *) newHaving; /* * 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_inherted_rtentry(parse, parse->resultRelation, false)) != 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 * subPlan, extParam and locParam lists for plan nodes. */ if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1) { (void) SS_finalize_plan(plan, parse->rtable); /* * At the moment, SS_finalize_plan doesn't handle initPlans and so * we assign them to the topmost plan node. */ plan->initPlan = PlannerInitPlan; /* Must add the initPlans' extParams to the topmost node's, too */ foreach(lst, plan->initPlan) { SubPlan *subplan = (SubPlan *) lfirst(lst); plan->extParam = set_unioni(plan->extParam, subplan->plan->extParam); } } /* Return to outer subquery context */ PlannerQueryLevel--; PlannerInitPlan = saved_initplan; /* we do NOT restore PlannerPlanId; that's not an oversight! */ return plan; } /* * pull_up_subqueries * Look for subqueries in the rangetable that can be pulled up into * the parent query. If the subquery has no special features like * grouping/aggregation then we can merge it into the parent's jointree. * * below_outer_join is true if this jointree node is within the nullable * side of an outer join. This restricts what we can do. * * A tricky aspect of this code is that if we pull up a subquery we have * to replace Vars that reference the subquery's outputs throughout the * parent query, including quals attached to jointree nodes above the one * we are currently processing! We handle this by being careful not to * change the jointree structure while recursing: no nodes other than * subquery RangeTblRef entries will be replaced. Also, we can't turn * ResolveNew loose on the whole jointree, because it'll return a mutated * copy of the tree; we have to invoke it just on the quals, instead. */ static Node * pull_up_subqueries(Query *parse, Node *jtnode, bool below_outer_join) { if (jtnode == NULL) return NULL; if (IsA(jtnode, RangeTblRef)) { int varno = ((RangeTblRef *) jtnode)->rtindex; RangeTblEntry *rte = rt_fetch(varno, parse->rtable); Query *subquery = rte->subquery; /* * Is this a subquery RTE, and if so, is the subquery simple * enough to pull up? (If not, do nothing at this node.) * * If we are inside an outer join, only pull up subqueries whose * targetlists are nullable --- otherwise substituting their tlist * entries for upper Var references would do the wrong thing (the * results wouldn't become NULL when they're supposed to). XXX * This could be improved by generating pseudo-variables for such * expressions; we'd have to figure out how to get the pseudo- * variables evaluated at the right place in the modified plan * tree. Fix it someday. * * Note: even if the subquery itself is simple enough, we can't pull * it up if there is a reference to its whole tuple result. * Perhaps a pseudo-variable is the answer here too. */ if (rte->rtekind == RTE_SUBQUERY && is_simple_subquery(subquery) && (!below_outer_join || has_nullable_targetlist(subquery)) && !contain_whole_tuple_var((Node *) parse, varno, 0)) { int rtoffset; List *subtlist; List *rt; /* * First, recursively pull up the subquery's subqueries, so * that this routine's processing is complete for its jointree * and rangetable. NB: if the same subquery is referenced * from multiple jointree items (which can't happen normally, * but might after rule rewriting), then we will invoke this * processing multiple times on that subquery. OK because * nothing will happen after the first time. We do have to be * careful to copy everything we pull up, however, or risk * having chunks of structure multiply linked. */ subquery->jointree = (FromExpr *) pull_up_subqueries(subquery, (Node *) subquery->jointree, below_outer_join); /* * Now make a modifiable copy of the subquery that we can run * OffsetVarNodes and IncrementVarSublevelsUp on. */ subquery = copyObject(subquery); /* * Adjust level-0 varnos in subquery so that we can append its * rangetable to upper query's. */ rtoffset = length(parse->rtable); OffsetVarNodes((Node *) subquery, rtoffset, 0); /* * Upper-level vars in subquery are now one level closer to their * parent than before. */ IncrementVarSublevelsUp((Node *) subquery, -1, 1); /* * Replace all of the top query's references to the subquery's * outputs with copies of the adjusted subtlist items, being * careful not to replace any of the jointree structure. * (This'd be a lot cleaner if we could use * query_tree_mutator.) */ subtlist = subquery->targetList; parse->targetList = (List *) ResolveNew((Node *) parse->targetList, varno, 0, subtlist, CMD_SELECT, 0); resolvenew_in_jointree((Node *) parse->jointree, varno, subtlist); Assert(parse->setOperations == NULL); parse->havingQual = ResolveNew(parse->havingQual, varno, 0, subtlist, CMD_SELECT, 0); foreach(rt, parse->rtable) { RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt); if (rte->rtekind == RTE_JOIN) rte->joinaliasvars = (List *) ResolveNew((Node *) rte->joinaliasvars, varno, 0, subtlist, CMD_SELECT, 0); } /* * Now append the adjusted rtable entries to upper query. (We * hold off until after fixing the upper rtable entries; no * point in running that code on the subquery ones too.) */ parse->rtable = nconc(parse->rtable, subquery->rtable); /* * Pull up any FOR UPDATE markers, too. (OffsetVarNodes * already adjusted the marker values, so just nconc the * list.) */ parse->rowMarks = nconc(parse->rowMarks, subquery->rowMarks); /* * Miscellaneous housekeeping. */ parse->hasSubLinks |= subquery->hasSubLinks; /* subquery won't be pulled up if it hasAggs, so no work there */ /* * Return the adjusted subquery jointree to replace the * RangeTblRef entry in my jointree. */ return (Node *) subquery->jointree; } } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *l; foreach(l, f->fromlist) lfirst(l) = pull_up_subqueries(parse, lfirst(l), below_outer_join); } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; /* Recurse, being careful to tell myself when inside outer join */ switch (j->jointype) { case JOIN_INNER: j->larg = pull_up_subqueries(parse, j->larg, below_outer_join); j->rarg = pull_up_subqueries(parse, j->rarg, below_outer_join); break; case JOIN_LEFT: j->larg = pull_up_subqueries(parse, j->larg, below_outer_join); j->rarg = pull_up_subqueries(parse, j->rarg, true); break; case JOIN_FULL: j->larg = pull_up_subqueries(parse, j->larg, true); j->rarg = pull_up_subqueries(parse, j->rarg, true); break; case JOIN_RIGHT: j->larg = pull_up_subqueries(parse, j->larg, true); j->rarg = pull_up_subqueries(parse, j->rarg, below_outer_join); break; case JOIN_UNION: /* * This is where we fail if upper levels of planner * haven't rewritten UNION JOIN as an Append ... */ elog(ERROR, "UNION JOIN is not implemented yet"); break; default: elog(ERROR, "pull_up_subqueries: unexpected join type %d", j->jointype); break; } } else elog(ERROR, "pull_up_subqueries: unexpected node type %d", nodeTag(jtnode)); return jtnode; } /* * is_simple_subquery * Check a subquery in the range table to see if it's simple enough * to pull up into the parent query. */ static bool is_simple_subquery(Query *subquery) { /* * Let's just make sure it's a valid subselect ... */ if (!IsA(subquery, Query) || subquery->commandType != CMD_SELECT || subquery->resultRelation != 0 || subquery->into != NULL || subquery->isPortal) elog(ERROR, "is_simple_subquery: subquery is bogus"); /* * Can't currently pull up a query with setops. Maybe after querytree * redesign... */ if (subquery->setOperations) return false; /* * Can't pull up a subquery involving grouping, aggregation, sorting, * or limiting. */ if (subquery->hasAggs || subquery->groupClause || subquery->havingQual || subquery->sortClause || subquery->distinctClause || subquery->limitOffset || subquery->limitCount) return false; /* * Don't pull up a subquery that has any set-returning functions in * its targetlist. Otherwise we might well wind up inserting * set-returning functions into places where they mustn't go, such as * quals of higher queries. */ if (expression_returns_set((Node *) subquery->targetList)) return false; /* * Hack: don't try to pull up a subquery with an empty jointree. * query_planner() will correctly generate a Result plan for a * jointree that's totally empty, but I don't think the right things * happen if an empty FromExpr appears lower down in a jointree. Not * worth working hard on this, just to collapse SubqueryScan/Result * into Result... */ if (subquery->jointree->fromlist == NIL) return false; return true; } /* * has_nullable_targetlist * Check a subquery in the range table to see if all the non-junk * targetlist items are simple variables (and, hence, will correctly * go to NULL when examined above the point of an outer join). * * A possible future extension is to accept strict functions of simple * variables, eg, "x + 1". */ static bool has_nullable_targetlist(Query *subquery) { List *l; foreach(l, subquery->targetList) { TargetEntry *tle = (TargetEntry *) lfirst(l); /* ignore resjunk columns */ if (tle->resdom->resjunk) continue; /* Okay if tlist item is a simple Var */ if (tle->expr && IsA(tle->expr, Var)) continue; return false; } return true; } /* * Helper routine for pull_up_subqueries: do ResolveNew on every expression * in the jointree, without changing the jointree structure itself. Ugly, * but there's no other way... */ static void resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist) { if (jtnode == NULL) return; if (IsA(jtnode, RangeTblRef)) { /* nothing to do here */ } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *l; foreach(l, f->fromlist) resolvenew_in_jointree(lfirst(l), varno, subtlist); f->quals = ResolveNew(f->quals, varno, 0, subtlist, CMD_SELECT, 0); } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; resolvenew_in_jointree(j->larg, varno, subtlist); resolvenew_in_jointree(j->rarg, varno, subtlist); j->quals = ResolveNew(j->quals, varno, 0, subtlist, CMD_SELECT, 0); /* * We don't bother to update the colvars list, since it won't be * used again ... */ } else elog(ERROR, "resolvenew_in_jointree: unexpected node type %d", nodeTag(jtnode)); } /* * preprocess_jointree * Attempt to simplify a query's jointree. * * If we succeed in pulling up a subquery then we might form a jointree * in which a FromExpr is a direct child of another FromExpr. In that * case we can consider collapsing the two FromExprs into one. This is * an optional conversion, since the planner will work correctly either * way. But we may find a better plan (at the cost of more planning time) * if we merge the two nodes. * * NOTE: don't try to do this in the same jointree scan that does subquery * pullup! Since we're changing the jointree structure here, that wouldn't * work reliably --- see comments for pull_up_subqueries(). */ static Node * preprocess_jointree(Query *parse, Node *jtnode) { if (jtnode == NULL) return NULL; if (IsA(jtnode, RangeTblRef)) { /* nothing to do here... */ } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *newlist = NIL; List *l; foreach(l, f->fromlist) { Node *child = (Node *) lfirst(l); /* Recursively simplify the child... */ child = preprocess_jointree(parse, child); /* Now, is it a FromExpr? */ if (child && IsA(child, FromExpr)) { /* * Yes, so do we want to merge it into parent? Always do * so if child has just one element (since that doesn't * make the parent's list any longer). Otherwise we have * to be careful about the increase in planning time * caused by combining the two join search spaces into * one. Our heuristic is to merge if the merge will * produce a join list no longer than GEQO_RELS/2. * (Perhaps need an additional user parameter?) */ FromExpr *subf = (FromExpr *) child; int childlen = length(subf->fromlist); int myothers = length(newlist) + length(lnext(l)); if (childlen <= 1 || (childlen + myothers) <= geqo_rels / 2) { newlist = nconc(newlist, subf->fromlist); f->quals = make_and_qual(subf->quals, f->quals); } else newlist = lappend(newlist, child); } else newlist = lappend(newlist, child); } f->fromlist = newlist; } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; /* Can't usefully change the JoinExpr, but recurse on children */ j->larg = preprocess_jointree(parse, j->larg); j->rarg = preprocess_jointree(parse, j->rarg); } else elog(ERROR, "preprocess_jointree: unexpected node type %d", nodeTag(jtnode)); return jtnode; } /* * 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) { bool has_join_rtes; List *rt; /* * Simplify constant expressions. * * Note that at this point quals have not yet been converted to * implicit-AND form, so we can apply eval_const_expressions directly. * Also note that we need to do this before SS_process_sublinks, * because that routine inserts bogus "Const" nodes. */ expr = eval_const_expressions(expr); /* * If it's a qual or havingQual, canonicalize it, and convert it to * implicit-AND format. * * XXX Is there any value in re-applying eval_const_expressions after * canonicalize_qual? */ if (kind != EXPRKIND_TARGET) { expr = (Node *) canonicalize_qual((Expr *) expr, true); #ifdef OPTIMIZER_DEBUG printf("After canonicalize_qual()\n"); pprint(expr); #endif } /* Expand SubLinks to SubPlans */ if (parse->hasSubLinks) expr = SS_process_sublinks(expr); /* Replace uplevel vars with Param nodes */ if (PlannerQueryLevel > 1) expr = SS_replace_correlation_vars(expr); /* * If the query has any join RTEs, try to replace join alias variables * with base-relation variables, to allow quals to be pushed down. We * must do this after sublink processing, since it does not recurse * into sublinks. * * The flattening pass is expensive enough that it seems worthwhile to * scan the rangetable to see if we can avoid it. */ has_join_rtes = false; foreach(rt, parse->rtable) { RangeTblEntry *rte = lfirst(rt); if (rte->rtekind == RTE_JOIN) { has_join_rtes = true; break; } } if (has_join_rtes) expr = flatten_join_alias_vars(expr, parse->rtable, false); 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; List *l; foreach(l, f->fromlist) preprocess_qual_conditions(parse, lfirst(l)); f->quals = preprocess_expression(parse, f->quals, EXPRKIND_WHERE); } 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_WHERE); } else elog(ERROR, "preprocess_qual_conditions: unexpected node type %d", 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); List *subplans = NIL; List *tlist = NIL; List *l; foreach(l, inheritlist) { int childRTindex = lfirsti(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); /* 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; 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: determine fraction by inspection of query (normal case) * 0: expect all tuples to be retrieved * 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) * The normal case is to pass -1, but some callers pass values >= 0 to * override this routine's determination of the appropriate fraction. * * Returns a query plan. *-------------------- */ 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) { /* * 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); /* * 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) elog(ERROR, "SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT"); /* * We set current_pathkeys NIL indicating we do not know sort * order. This is correct when the top set operation is UNION * ALL, since the appended-together results are unsorted even if * the subplans were sorted. For other set operations we could be * smarter --- room for future improvement! */ current_pathkeys = NIL; /* * Calculate pathkeys that represent 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; Path *cheapest_path; Path *sorted_path; bool use_hashed_grouping = false; /* Preprocess targetlist in case we are inside an INSERT/UPDATE. */ tlist = preprocess_targetlist(tlist, parse->commandType, parse->resultRelation, parse->rtable); /* * Add TID targets for rels selected FOR UPDATE (should this be * done in preprocess_targetlist?). The executor uses the TID to * know which rows to lock, much as for UPDATE or DELETE. */ if (parse->rowMarks) { List *l; /* * We've got trouble if the FOR UPDATE appears inside * grouping, since grouping renders a reference to individual * tuple CTIDs invalid. This is also checked at parse time, * but that's insufficient because of rule substitution, query * pullup, etc. */ CheckSelectForUpdate(parse); /* * Currently the executor only supports FOR UPDATE at top * level */ if (PlannerQueryLevel > 1) elog(ERROR, "SELECT FOR UPDATE is not allowed in subselects"); foreach(l, parse->rowMarks) { Index rti = lfirsti(l); char *resname; Resdom *resdom; Var *var; TargetEntry *ctid; resname = (char *) palloc(32); snprintf(resname, 32, "ctid%u", rti); resdom = makeResdom(length(tlist) + 1, TIDOID, -1, resname, true); var = makeVar(rti, SelfItemPointerAttributeNumber, TIDOID, -1, 0); ctid = makeTargetEntry(resdom, (Node *) var); tlist = lappend(tlist, ctid); } } /* * Generate appropriate target list for subplan; may be different * from tlist if grouping or aggregation is needed. */ sub_tlist = make_subplanTargetList(parse, tlist, &groupColIdx); /* * 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); /* * 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; /* * Figure out whether we expect to retrieve all the tuples that * the plan can generate, or to stop early due to outside factors * such as a cursor. If the caller passed a value >= 0, believe * that value, else do our own examination of the query context. */ if (tuple_fraction < 0.0) { /* Initial assumption is we need all the tuples */ tuple_fraction = 0.0; /* * Check for retrieve-into-portal, ie DECLARE CURSOR. * * 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?) */ if (parse->isPortal) tuple_fraction = 0.10; } /* * 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; } } } 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 (tuple_fraction >= 1.0) 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)) tuple_fraction = 0.0; } else if (parse->hasAggs) { /* * Ungrouped aggregate will certainly want all the input * tuples. */ 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 (tuple_fraction >= 1.0) 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, 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) { /* * 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 (parse->hasAggs && (contain_distinct_agg_clause((Node *) tlist) || contain_distinct_agg_clause(parse->havingQual))) use_hashed_grouping = false; else { #if 0 /* much more to do here */ /* TEMPORARY HOTWIRE FOR TESTING */ use_hashed_grouping = true; #endif } } /* * Select the best path and create a plan to execute it. * * If no special sort order is wanted, or if the cheapest path is * already appropriately ordered, use the cheapest path. * Otherwise, look to see if we have an already-ordered path that is * cheaper than doing an explicit sort on the cheapest-total-cost * path. */ if (parse->query_pathkeys == NIL || pathkeys_contained_in(parse->query_pathkeys, cheapest_path->pathkeys)) { result_plan = create_plan(parse, cheapest_path); current_pathkeys = cheapest_path->pathkeys; } else if (sorted_path) { Path sort_path; /* dummy for result of cost_sort */ cost_sort(&sort_path, parse, parse->query_pathkeys, sorted_path->parent->rows, sorted_path->parent->width); sort_path.startup_cost += cheapest_path->total_cost; sort_path.total_cost += cheapest_path->total_cost; if (compare_fractional_path_costs(sorted_path, &sort_path, tuple_fraction) <= 0) { /* Presorted path is cheaper, use it */ result_plan = create_plan(parse, sorted_path); current_pathkeys = sorted_path->pathkeys; } else { /* otherwise, doing it the hard way is still cheaper */ result_plan = create_plan(parse, cheapest_path); current_pathkeys = cheapest_path->pathkeys; } } else { /* * No sorted path, so we must use the cheapest-total path. * The actual sort step will be generated below. */ 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. We want to insert the sub_tlist as the tlist of the top * plan node. If the top-level plan node is one that cannot do * expression evaluation, we must insert a Result node to project the * desired tlist. * Currently, the only plan node we might see here that falls into * that category is Append. */ if (IsA(result_plan, Append)) { result_plan = (Plan *) make_result(sub_tlist, NULL, result_plan); } else { /* * Otherwise, just replace the flat tlist with the desired tlist. */ result_plan->targetlist = sub_tlist; } /* * Insert AGG or GROUP node if needed, plus an explicit sort step * if necessary. * * HAVING clause, if any, becomes qual of the Agg node */ if (use_hashed_grouping) { /* Hashed aggregate plan --- no sort needed */ result_plan = (Plan *) make_agg(tlist, (List *) parse->havingQual, AGG_HASHED, length(parse->groupClause), groupColIdx, 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 = make_groupsortplan(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(tlist, (List *) parse->havingQual, aggstrategy, length(parse->groupClause), groupColIdx, result_plan); } else { /* * If there are no Aggs, we shouldn't have any HAVING qual anymore */ Assert(parse->havingQual == NULL); /* * If we have a GROUP BY clause, insert a group node (plus the * appropriate sort node, if necessary). */ if (parse->groupClause) { /* * 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 = make_groupsortplan(parse, parse->groupClause, groupColIdx, result_plan); current_pathkeys = group_pathkeys; } result_plan = (Plan *) make_group(tlist, length(parse->groupClause), groupColIdx, result_plan); } } } /* 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 = make_sortplan(parse, tlist, result_plan, parse->sortClause); } /* * If there is a DISTINCT clause, add the UNIQUE node. */ if (parse->distinctClause) { result_plan = (Plan *) make_unique(tlist, result_plan, parse->distinctClause); } /* * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node. */ if (parse->limitOffset || parse->limitCount) { result_plan = (Plan *) make_limit(tlist, result_plan, parse->limitOffset, parse->limitCount); } return result_plan; } /*--------------- * make_subplanTargetList * Generate appropriate target list when grouping is required. * * When grouping_planner inserts Aggregate or Group 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, if we are doing either * grouping or aggregation, 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.) * * '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. * * The result is the targetlist to be passed to the subplan. *--------------- */ static List * make_subplanTargetList(Query *parse, List *tlist, AttrNumber **groupColIdx) { List *sub_tlist; List *extravars; int numCols; *groupColIdx = NULL; /* * If we're not grouping or aggregating, nothing to do here; * query_planner should receive the unmodified target list. */ if (!parse->hasAggs && !parse->groupClause && !parse->havingQual) 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); freeList(extravars); /* * 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 = length(parse->groupClause); if (numCols > 0) { int keyno = 0; AttrNumber *grpColIdx; List *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; List *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(length(sub_tlist) + 1, exprType(groupexpr), exprTypmod(groupexpr), NULL, false), groupexpr); sub_tlist = lappend(sub_tlist, te); } /* and save its resno */ grpColIdx[keyno++] = te->resdom->resno; } } return sub_tlist; } /* * make_groupsortplan * Add a Sort node to explicitly sort according to the GROUP BY clause. * * Note: the Sort node always just takes a copy of the subplan's tlist * plus ordering information. (This might seem inefficient if the * subplan contains complex GROUP BY expressions, but in fact Sort * does not evaluate its targetlist --- it only outputs the same * tuples in a new order. So the expressions we might be copying * are just dummies with no extra execution cost.) */ static Plan * make_groupsortplan(Query *parse, List *groupClause, AttrNumber *grpColIdx, Plan *subplan) { List *sort_tlist = new_unsorted_tlist(subplan->targetlist); int keyno = 0; List *gl; foreach(gl, groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(gl); TargetEntry *te = nth(grpColIdx[keyno] - 1, sort_tlist); Resdom *resdom = te->resdom; /* * Check for the possibility of duplicate group-by clauses --- * the parser should have removed 'em, but the Sort executor * will get terribly confused if any get through! */ if (resdom->reskey == 0) { /* OK, insert the ordering info needed by the executor. */ resdom->reskey = ++keyno; resdom->reskeyop = grpcl->sortop; } } Assert(keyno > 0); return (Plan *) make_sort(parse, sort_tlist, subplan, keyno); } /* * make_sortplan * Add a Sort node to implement an explicit ORDER BY clause. */ Plan * make_sortplan(Query *parse, List *tlist, Plan *plannode, List *sortcls) { List *sort_tlist; List *i; int keyno = 0; /* * First make a copy of the tlist so that we don't corrupt the * original. */ sort_tlist = new_unsorted_tlist(tlist); foreach(i, sortcls) { SortClause *sortcl = (SortClause *) lfirst(i); TargetEntry *tle = get_sortgroupclause_tle(sortcl, sort_tlist); Resdom *resdom = tle->resdom; /* * Check for the possibility of duplicate order-by clauses --- the * parser should have removed 'em, but the executor will get * terribly confused if any get through! */ if (resdom->reskey == 0) { /* OK, insert the ordering info needed by the executor. */ resdom->reskey = ++keyno; resdom->reskeyop = sortcl->sortop; } } Assert(keyno > 0); return (Plan *) make_sort(parse, sort_tlist, plannode, keyno); } /* * 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 elog if we * find any resjunk columns in orig_tlist. */ static List * postprocess_setop_tlist(List *new_tlist, List *orig_tlist) { List *l; 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 != NIL); orig_tle = (TargetEntry *) lfirst(orig_tlist); orig_tlist = lnext(orig_tlist); if (orig_tle->resdom->resjunk) elog(ERROR, "postprocess_setop_tlist: resjunk output columns 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 != NIL) elog(ERROR, "postprocess_setop_tlist: resjunk output columns not implemented"); return new_tlist; }