/*------------------------------------------------------------------------- * * pathkeys.c * Utilities for matching and building path keys * * See src/backend/optimizer/README for a great deal of information about * the nature and use of path keys. * * * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.84 2007/04/15 20:09:28 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include "access/skey.h" #include "nodes/makefuncs.h" #include "nodes/plannodes.h" #include "optimizer/clauses.h" #include "optimizer/pathnode.h" #include "optimizer/paths.h" #include "optimizer/tlist.h" #include "parser/parsetree.h" #include "parser/parse_expr.h" #include "utils/lsyscache.h" /* * If an EC contains a const and isn't below-outer-join, any PathKey depending * on it must be redundant, since there's only one possible value of the key. */ #define MUST_BE_REDUNDANT(eclass) \ ((eclass)->ec_has_const && !(eclass)->ec_below_outer_join) static PathKey *makePathKey(EquivalenceClass *eclass, Oid opfamily, int strategy, bool nulls_first); static PathKey *make_canonical_pathkey(PlannerInfo *root, EquivalenceClass *eclass, Oid opfamily, int strategy, bool nulls_first); static bool pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys); static PathKey *make_pathkey_from_sortinfo(PlannerInfo *root, Expr *expr, Oid ordering_op, bool nulls_first, bool canonicalize); static Var *find_indexkey_var(PlannerInfo *root, RelOptInfo *rel, AttrNumber varattno); /**************************************************************************** * PATHKEY CONSTRUCTION AND REDUNDANCY TESTING ****************************************************************************/ /* * makePathKey * create a PathKey node * * This does not promise to create a canonical PathKey, it's merely a * convenience routine to build the specified node. */ static PathKey * makePathKey(EquivalenceClass *eclass, Oid opfamily, int strategy, bool nulls_first) { PathKey *pk = makeNode(PathKey); pk->pk_eclass = eclass; pk->pk_opfamily = opfamily; pk->pk_strategy = strategy; pk->pk_nulls_first = nulls_first; return pk; } /* * make_canonical_pathkey * Given the parameters for a PathKey, find any pre-existing matching * pathkey in the query's list of "canonical" pathkeys. Make a new * entry if there's not one already. * * Note that this function must not be used until after we have completed * merging EquivalenceClasses. */ static PathKey * make_canonical_pathkey(PlannerInfo *root, EquivalenceClass *eclass, Oid opfamily, int strategy, bool nulls_first) { PathKey *pk; ListCell *lc; MemoryContext oldcontext; /* The passed eclass might be non-canonical, so chase up to the top */ while (eclass->ec_merged) eclass = eclass->ec_merged; foreach(lc, root->canon_pathkeys) { pk = (PathKey *) lfirst(lc); if (eclass == pk->pk_eclass && opfamily == pk->pk_opfamily && strategy == pk->pk_strategy && nulls_first == pk->pk_nulls_first) return pk; } /* * Be sure canonical pathkeys are allocated in the main planning context. * Not an issue in normal planning, but it is for GEQO. */ oldcontext = MemoryContextSwitchTo(root->planner_cxt); pk = makePathKey(eclass, opfamily, strategy, nulls_first); root->canon_pathkeys = lappend(root->canon_pathkeys, pk); MemoryContextSwitchTo(oldcontext); return pk; } /* * pathkey_is_redundant * Is a pathkey redundant with one already in the given list? * * Both the given pathkey and the list members must be canonical for this * to work properly. We detect two cases: * * 1. If the new pathkey's equivalence class contains a constant, and isn't * below an outer join, then we can disregard it as a sort key. An example: * SELECT ... WHERE x = 42 ORDER BY x, y; * We may as well just sort by y. Note that because of opfamily matching, * this is semantically correct: we know that the equality constraint is one * that actually binds the variable to a single value in the terms of any * ordering operator that might go with the eclass. This rule not only lets * us simplify (or even skip) explicit sorts, but also allows matching index * sort orders to a query when there are don't-care index columns. * * 2. If the new pathkey's equivalence class is the same as that of any * existing member of the pathkey list, then it is redundant. Some examples: * SELECT ... ORDER BY x, x; * SELECT ... ORDER BY x, x DESC; * SELECT ... WHERE x = y ORDER BY x, y; * In all these cases the second sort key cannot distinguish values that are * considered equal by the first, and so there's no point in using it. * Note in particular that we need not compare opfamily (all the opfamilies * of the EC have the same notion of equality) nor sort direction. * * Because the equivclass.c machinery forms only one copy of any EC per query, * pointer comparison is enough to decide whether canonical ECs are the same. */ static bool pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys) { EquivalenceClass *new_ec = new_pathkey->pk_eclass; ListCell *lc; /* Assert we've been given canonical pathkeys */ Assert(!new_ec->ec_merged); /* Check for EC containing a constant --- unconditionally redundant */ if (MUST_BE_REDUNDANT(new_ec)) return true; /* If same EC already used in list, then redundant */ foreach(lc, pathkeys) { PathKey *old_pathkey = (PathKey *) lfirst(lc); /* Assert we've been given canonical pathkeys */ Assert(!old_pathkey->pk_eclass->ec_merged); if (new_ec == old_pathkey->pk_eclass) return true; } return false; } /* * canonicalize_pathkeys * Convert a not-necessarily-canonical pathkeys list to canonical form. * * Note that this function must not be used until after we have completed * merging EquivalenceClasses. */ List * canonicalize_pathkeys(PlannerInfo *root, List *pathkeys) { List *new_pathkeys = NIL; ListCell *l; foreach(l, pathkeys) { PathKey *pathkey = (PathKey *) lfirst(l); EquivalenceClass *eclass; PathKey *cpathkey; /* Find the canonical (merged) EquivalenceClass */ eclass = pathkey->pk_eclass; while (eclass->ec_merged) eclass = eclass->ec_merged; /* * If we can tell it's redundant just from the EC, skip. * pathkey_is_redundant would notice that, but we needn't even bother * constructing the node... */ if (MUST_BE_REDUNDANT(eclass)) continue; /* OK, build a canonicalized PathKey struct */ cpathkey = make_canonical_pathkey(root, eclass, pathkey->pk_opfamily, pathkey->pk_strategy, pathkey->pk_nulls_first); /* Add to list unless redundant */ if (!pathkey_is_redundant(cpathkey, new_pathkeys)) new_pathkeys = lappend(new_pathkeys, cpathkey); } return new_pathkeys; } /* * make_pathkey_from_sortinfo * Given an expression, a sortop, and a nulls-first flag, create * a PathKey. If canonicalize = true, the result is a "canonical" * PathKey, otherwise not. (But note it might be redundant anyway.) * * canonicalize should always be TRUE after EquivalenceClass merging has * been performed, but FALSE if we haven't done EquivalenceClass merging yet. */ static PathKey * make_pathkey_from_sortinfo(PlannerInfo *root, Expr *expr, Oid ordering_op, bool nulls_first, bool canonicalize) { Oid opfamily, opcintype; int16 strategy; Oid equality_op; List *opfamilies; EquivalenceClass *eclass; /* * An ordering operator fully determines the behavior of its opfamily, * so could only meaningfully appear in one family --- or perhaps two * if one builds a reverse-sort opfamily, but there's not much point in * that anymore. But EquivalenceClasses need to contain opfamily lists * based on the family membership of equality operators, which could * easily be bigger. So, look up the equality operator that goes with * the ordering operator (this should be unique) and get its membership. */ /* Find the operator in pg_amop --- failure shouldn't happen */ if (!get_ordering_op_properties(ordering_op, &opfamily, &opcintype, &strategy)) elog(ERROR, "operator %u is not a valid ordering operator", ordering_op); /* Get matching equality operator */ equality_op = get_opfamily_member(opfamily, opcintype, opcintype, BTEqualStrategyNumber); if (!OidIsValid(equality_op)) /* shouldn't happen */ elog(ERROR, "could not find equality operator for ordering operator %u", ordering_op); opfamilies = get_mergejoin_opfamilies(equality_op); if (!opfamilies) /* certainly should find some */ elog(ERROR, "could not find opfamilies for ordering operator %u", ordering_op); /* Now find or create a matching EquivalenceClass */ eclass = get_eclass_for_sort_expr(root, expr, opcintype, opfamilies); /* And finally we can find or create a PathKey node */ if (canonicalize) return make_canonical_pathkey(root, eclass, opfamily, strategy, nulls_first); else return makePathKey(eclass, opfamily, strategy, nulls_first); } /**************************************************************************** * PATHKEY COMPARISONS ****************************************************************************/ /* * compare_pathkeys * Compare two pathkeys to see if they are equivalent, and if not whether * one is "better" than the other. * * This function may only be applied to canonicalized pathkey lists. * In the canonical representation, pathkeys can be checked for equality * by simple pointer comparison. */ PathKeysComparison compare_pathkeys(List *keys1, List *keys2) { ListCell *key1, *key2; forboth(key1, keys1, key2, keys2) { PathKey *pathkey1 = (PathKey *) lfirst(key1); PathKey *pathkey2 = (PathKey *) lfirst(key2); /* * XXX would like to check that we've been given canonicalized input, * but PlannerInfo not accessible here... */ #ifdef NOT_USED Assert(list_member_ptr(root->canon_pathkeys, pathkey1)); Assert(list_member_ptr(root->canon_pathkeys, pathkey2)); #endif if (pathkey1 != pathkey2) return PATHKEYS_DIFFERENT; /* no need to keep looking */ } /* * If we reached the end of only one list, the other is longer and * therefore not a subset. */ if (key1 == NULL && key2 == NULL) return PATHKEYS_EQUAL; if (key1 != NULL) return PATHKEYS_BETTER1; /* key1 is longer */ return PATHKEYS_BETTER2; /* key2 is longer */ } /* * pathkeys_contained_in * Common special case of compare_pathkeys: we just want to know * if keys2 are at least as well sorted as keys1. */ bool pathkeys_contained_in(List *keys1, List *keys2) { switch (compare_pathkeys(keys1, keys2)) { case PATHKEYS_EQUAL: case PATHKEYS_BETTER2: return true; default: break; } return false; } /* * get_cheapest_path_for_pathkeys * Find the cheapest path (according to the specified criterion) that * satisfies the given pathkeys. Return NULL if no such path. * * 'paths' is a list of possible paths that all generate the same relation * 'pathkeys' represents a required ordering (already canonicalized!) * 'cost_criterion' is STARTUP_COST or TOTAL_COST */ Path * get_cheapest_path_for_pathkeys(List *paths, List *pathkeys, CostSelector cost_criterion) { Path *matched_path = NULL; ListCell *l; foreach(l, paths) { Path *path = (Path *) lfirst(l); /* * Since cost comparison is a lot cheaper than pathkey comparison, do * that first. (XXX is that still true?) */ if (matched_path != NULL && compare_path_costs(matched_path, path, cost_criterion) <= 0) continue; if (pathkeys_contained_in(pathkeys, path->pathkeys)) matched_path = path; } return matched_path; } /* * get_cheapest_fractional_path_for_pathkeys * Find the cheapest path (for retrieving a specified fraction of all * the tuples) that satisfies the given pathkeys. * Return NULL if no such path. * * See compare_fractional_path_costs() for the interpretation of the fraction * parameter. * * 'paths' is a list of possible paths that all generate the same relation * 'pathkeys' represents a required ordering (already canonicalized!) * 'fraction' is the fraction of the total tuples expected to be retrieved */ Path * get_cheapest_fractional_path_for_pathkeys(List *paths, List *pathkeys, double fraction) { Path *matched_path = NULL; ListCell *l; foreach(l, paths) { Path *path = (Path *) lfirst(l); /* * Since cost comparison is a lot cheaper than pathkey comparison, do * that first. */ if (matched_path != NULL && compare_fractional_path_costs(matched_path, path, fraction) <= 0) continue; if (pathkeys_contained_in(pathkeys, path->pathkeys)) matched_path = path; } return matched_path; } /**************************************************************************** * NEW PATHKEY FORMATION ****************************************************************************/ /* * build_index_pathkeys * Build a pathkeys list that describes the ordering induced by an index * scan using the given index. (Note that an unordered index doesn't * induce any ordering; such an index will have no sortop OIDS in * its sortops arrays, and we will return NIL.) * * If 'scandir' is BackwardScanDirection, attempt to build pathkeys * representing a backwards scan of the index. Return NIL if can't do it. * * The result is canonical, meaning that redundant pathkeys are removed; * it may therefore have fewer entries than there are index columns. * * We generate the full pathkeys list whether or not all are useful for the * current query. Caller should do truncate_useless_pathkeys(). */ List * build_index_pathkeys(PlannerInfo *root, IndexOptInfo *index, ScanDirection scandir) { List *retval = NIL; ListCell *indexprs_item = list_head(index->indexprs); int i; for (i = 0; i < index->ncolumns; i++) { Oid sortop; bool nulls_first; int ikey; Expr *indexkey; PathKey *cpathkey; if (ScanDirectionIsBackward(scandir)) { sortop = index->revsortop[i]; nulls_first = !index->nulls_first[i]; } else { sortop = index->fwdsortop[i]; nulls_first = index->nulls_first[i]; } if (!OidIsValid(sortop)) break; /* no more orderable columns */ ikey = index->indexkeys[i]; if (ikey != 0) { /* simple index column */ indexkey = (Expr *) find_indexkey_var(root, index->rel, ikey); } else { /* expression --- assume we need not copy it */ if (indexprs_item == NULL) elog(ERROR, "wrong number of index expressions"); indexkey = (Expr *) lfirst(indexprs_item); indexprs_item = lnext(indexprs_item); } /* OK, make a canonical pathkey for this sort key */ cpathkey = make_pathkey_from_sortinfo(root, indexkey, sortop, nulls_first, true); /* Add to list unless redundant */ if (!pathkey_is_redundant(cpathkey, retval)) retval = lappend(retval, cpathkey); } return retval; } /* * Find or make a Var node for the specified attribute of the rel. * * We first look for the var in the rel's target list, because that's * easy and fast. But the var might not be there (this should normally * only happen for vars that are used in WHERE restriction clauses, * but not in join clauses or in the SELECT target list). In that case, * gin up a Var node the hard way. */ static Var * find_indexkey_var(PlannerInfo *root, RelOptInfo *rel, AttrNumber varattno) { ListCell *temp; Index relid; Oid reloid, vartypeid; int32 type_mod; foreach(temp, rel->reltargetlist) { Var *var = (Var *) lfirst(temp); if (IsA(var, Var) && var->varattno == varattno) return var; } relid = rel->relid; reloid = getrelid(relid, root->parse->rtable); get_atttypetypmod(reloid, varattno, &vartypeid, &type_mod); return makeVar(relid, varattno, vartypeid, type_mod, 0); } /* * convert_subquery_pathkeys * Build a pathkeys list that describes the ordering of a subquery's * result, in the terms of the outer query. This is essentially a * task of conversion. * * 'rel': outer query's RelOptInfo for the subquery relation. * 'subquery_pathkeys': the subquery's output pathkeys, in its terms. * * It is not necessary for caller to do truncate_useless_pathkeys(), * because we select keys in a way that takes usefulness of the keys into * account. */ List * convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel, List *subquery_pathkeys) { List *retval = NIL; int retvallen = 0; int outer_query_keys = list_length(root->query_pathkeys); List *sub_tlist = rel->subplan->targetlist; ListCell *i; foreach(i, subquery_pathkeys) { PathKey *sub_pathkey = (PathKey *) lfirst(i); EquivalenceClass *sub_eclass = sub_pathkey->pk_eclass; PathKey *best_pathkey = NULL; int best_score = -1; ListCell *j; /* * The sub_pathkey's EquivalenceClass could contain multiple elements * (representing knowledge that multiple items are effectively equal). * Each element might match none, one, or more of the output columns * that are visible to the outer query. This means we may have * multiple possible representations of the sub_pathkey in the context * of the outer query. Ideally we would generate them all and put * them all into an EC of the outer query, thereby propagating * equality knowledge up to the outer query. Right now we cannot do * so, because the outer query's EquivalenceClasses are already frozen * when this is called. Instead we prefer the one that has the highest * "score" (number of EC peers, plus one if it matches the outer * query_pathkeys). This is the most likely to be useful in the outer * query. */ foreach(j, sub_eclass->ec_members) { EquivalenceMember *sub_member = (EquivalenceMember *) lfirst(j); Expr *sub_expr = sub_member->em_expr; Expr *rtarg; ListCell *k; /* * We handle two cases: the sub_pathkey key can be either an exact * match for a targetlist entry, or a RelabelType of a targetlist * entry. (The latter case is worth extra code because it arises * frequently in connection with varchar fields.) */ if (IsA(sub_expr, RelabelType)) rtarg = ((RelabelType *) sub_expr)->arg; else rtarg = NULL; foreach(k, sub_tlist) { TargetEntry *tle = (TargetEntry *) lfirst(k); Expr *outer_expr; EquivalenceClass *outer_ec; PathKey *outer_pk; int score; /* resjunk items aren't visible to outer query */ if (tle->resjunk) continue; if (equal(tle->expr, sub_expr)) { /* Exact match */ outer_expr = (Expr *) makeVar(rel->relid, tle->resno, exprType((Node *) tle->expr), exprTypmod((Node *) tle->expr), 0); } else if (rtarg && equal(tle->expr, rtarg)) { /* Match after discarding RelabelType */ outer_expr = (Expr *) makeVar(rel->relid, tle->resno, exprType((Node *) tle->expr), exprTypmod((Node *) tle->expr), 0); outer_expr = (Expr *) makeRelabelType((Expr *) outer_expr, ((RelabelType *) sub_expr)->resulttype, ((RelabelType *) sub_expr)->resulttypmod, ((RelabelType *) sub_expr)->relabelformat); } else continue; /* Found a representation for this sub_pathkey */ outer_ec = get_eclass_for_sort_expr(root, outer_expr, sub_member->em_datatype, sub_eclass->ec_opfamilies); outer_pk = make_canonical_pathkey(root, outer_ec, sub_pathkey->pk_opfamily, sub_pathkey->pk_strategy, sub_pathkey->pk_nulls_first); /* score = # of equivalence peers */ score = list_length(outer_ec->ec_members) - 1; /* +1 if it matches the proper query_pathkeys item */ if (retvallen < outer_query_keys && list_nth(root->query_pathkeys, retvallen) == outer_pk) score++; if (score > best_score) { best_pathkey = outer_pk; best_score = score; } } } /* * If we couldn't find a representation of this sub_pathkey, we're * done (we can't use the ones to its right, either). */ if (!best_pathkey) break; /* * Eliminate redundant ordering info; could happen if outer query * equivalences subquery keys... */ if (!pathkey_is_redundant(best_pathkey, retval)) { retval = lappend(retval, best_pathkey); retvallen++; } } return retval; } /* * build_join_pathkeys * Build the path keys for a join relation constructed by mergejoin or * nestloop join. This is normally the same as the outer path's keys. * * EXCEPTION: in a FULL or RIGHT join, we cannot treat the result as * having the outer path's path keys, because null lefthand rows may be * inserted at random points. It must be treated as unsorted. * * We truncate away any pathkeys that are uninteresting for higher joins. * * 'joinrel' is the join relation that paths are being formed for * 'jointype' is the join type (inner, left, full, etc) * 'outer_pathkeys' is the list of the current outer path's path keys * * Returns the list of new path keys. */ List * build_join_pathkeys(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, List *outer_pathkeys) { if (jointype == JOIN_FULL || jointype == JOIN_RIGHT) return NIL; /* * This used to be quite a complex bit of code, but now that all pathkey * sublists start out life canonicalized, we don't have to do a darn thing * here! * * We do, however, need to truncate the pathkeys list, since it may * contain pathkeys that were useful for forming this joinrel but are * uninteresting to higher levels. */ return truncate_useless_pathkeys(root, joinrel, outer_pathkeys); } /**************************************************************************** * PATHKEYS AND SORT CLAUSES ****************************************************************************/ /* * make_pathkeys_for_sortclauses * Generate a pathkeys list that represents the sort order specified * by a list of SortClauses (GroupClauses will work too!) * * If canonicalize is TRUE, the resulting PathKeys are all in canonical form; * otherwise not. canonicalize should always be TRUE after EquivalenceClass * merging has been performed, but FALSE if we haven't done EquivalenceClass * merging yet. (We provide this option because grouping_planner() needs to * be able to represent requested pathkeys before the equivalence classes have * been created for the query.) * * 'sortclauses' is a list of SortClause or GroupClause nodes * 'tlist' is the targetlist to find the referenced tlist entries in */ List * make_pathkeys_for_sortclauses(PlannerInfo *root, List *sortclauses, List *tlist, bool canonicalize) { List *pathkeys = NIL; ListCell *l; foreach(l, sortclauses) { SortClause *sortcl = (SortClause *) lfirst(l); Expr *sortkey; PathKey *pathkey; sortkey = (Expr *) get_sortgroupclause_expr(sortcl, tlist); pathkey = make_pathkey_from_sortinfo(root, sortkey, sortcl->sortop, sortcl->nulls_first, canonicalize); /* Canonical form eliminates redundant ordering keys */ if (canonicalize) { if (!pathkey_is_redundant(pathkey, pathkeys)) pathkeys = lappend(pathkeys, pathkey); } else pathkeys = lappend(pathkeys, pathkey); } return pathkeys; } /**************************************************************************** * PATHKEYS AND MERGECLAUSES ****************************************************************************/ /* * cache_mergeclause_eclasses * Make the cached EquivalenceClass links valid in a mergeclause * restrictinfo. * * RestrictInfo contains fields in which we may cache pointers to * EquivalenceClasses for the left and right inputs of the mergeclause. * (If the mergeclause is a true equivalence clause these will be the * same EquivalenceClass, otherwise not.) */ void cache_mergeclause_eclasses(PlannerInfo *root, RestrictInfo *restrictinfo) { Assert(restrictinfo->mergeopfamilies != NIL); /* the cached values should be either both set or both not */ if (restrictinfo->left_ec == NULL) { Expr *clause = restrictinfo->clause; Oid lefttype, righttype; /* Need the declared input types of the operator */ op_input_types(((OpExpr *) clause)->opno, &lefttype, &righttype); /* Find or create a matching EquivalenceClass for each side */ restrictinfo->left_ec = get_eclass_for_sort_expr(root, (Expr *) get_leftop(clause), lefttype, restrictinfo->mergeopfamilies); restrictinfo->right_ec = get_eclass_for_sort_expr(root, (Expr *) get_rightop(clause), righttype, restrictinfo->mergeopfamilies); } else Assert(restrictinfo->right_ec != NULL); } /* * find_mergeclauses_for_pathkeys * This routine attempts to find a set of mergeclauses that can be * used with a specified ordering for one of the input relations. * If successful, it returns a list of mergeclauses. * * 'pathkeys' is a pathkeys list showing the ordering of an input path. * 'outer_keys' is TRUE if these keys are for the outer input path, * FALSE if for inner. * 'restrictinfos' is a list of mergejoinable restriction clauses for the * join relation being formed. * * The restrictinfos must be marked (via outer_is_left) to show which side * of each clause is associated with the current outer path. (See * select_mergejoin_clauses()) * * The result is NIL if no merge can be done, else a maximal list of * usable mergeclauses (represented as a list of their restrictinfo nodes). */ List * find_mergeclauses_for_pathkeys(PlannerInfo *root, List *pathkeys, bool outer_keys, List *restrictinfos) { List *mergeclauses = NIL; ListCell *i; /* make sure we have eclasses cached in the clauses */ foreach(i, restrictinfos) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(i); cache_mergeclause_eclasses(root, rinfo); } foreach(i, pathkeys) { PathKey *pathkey = (PathKey *) lfirst(i); EquivalenceClass *pathkey_ec = pathkey->pk_eclass; List *matched_restrictinfos = NIL; ListCell *j; /*---------- * A mergejoin clause matches a pathkey if it has the same EC. * If there are multiple matching clauses, take them all. In plain * inner-join scenarios we expect only one match, because * equivalence-class processing will have removed any redundant * mergeclauses. However, in outer-join scenarios there might be * multiple matches. An example is * * select * from a full join b * on a.v1 = b.v1 and a.v2 = b.v2 and a.v1 = b.v2; * * Given the pathkeys ({a.v1}, {a.v2}) it is okay to return all three * clauses (in the order a.v1=b.v1, a.v1=b.v2, a.v2=b.v2) and indeed * we *must* do so or we will be unable to form a valid plan. * * We expect that the given pathkeys list is canonical, which means * no two members have the same EC, so it's not possible for this * code to enter the same mergeclause into the result list twice. * * XXX it's possible that multiple matching clauses might have * different ECs on the other side, in which case the order we put * them into our result makes a difference in the pathkeys required * for the other input path. However this routine hasn't got any info * about which order would be best, so for now we disregard that case * (which is probably a corner case anyway). *---------- */ foreach(j, restrictinfos) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(j); EquivalenceClass *clause_ec; if (outer_keys) clause_ec = rinfo->outer_is_left ? rinfo->left_ec : rinfo->right_ec; else clause_ec = rinfo->outer_is_left ? rinfo->right_ec : rinfo->left_ec; if (clause_ec == pathkey_ec) matched_restrictinfos = lappend(matched_restrictinfos, rinfo); } /* * If we didn't find a mergeclause, we're done --- any additional * sort-key positions in the pathkeys are useless. (But we can still * mergejoin if we found at least one mergeclause.) */ if (matched_restrictinfos == NIL) break; /* * If we did find usable mergeclause(s) for this sort-key position, * add them to result list. */ mergeclauses = list_concat(mergeclauses, matched_restrictinfos); } return mergeclauses; } /* * select_outer_pathkeys_for_merge * Builds a pathkey list representing a possible sort ordering * that can be used with the given mergeclauses. * * 'mergeclauses' is a list of RestrictInfos for mergejoin clauses * that will be used in a merge join. * 'joinrel' is the join relation we are trying to construct. * * The restrictinfos must be marked (via outer_is_left) to show which side * of each clause is associated with the current outer path. (See * select_mergejoin_clauses()) * * Returns a pathkeys list that can be applied to the outer relation. * * Since we assume here that a sort is required, there is no particular use * in matching any available ordering of the outerrel. (joinpath.c has an * entirely separate code path for considering sort-free mergejoins.) Rather, * it's interesting to try to match the requested query_pathkeys so that a * second output sort may be avoided; and failing that, we try to list "more * popular" keys (those with the most unmatched EquivalenceClass peers) * earlier, in hopes of making the resulting ordering useful for as many * higher-level mergejoins as possible. */ List * select_outer_pathkeys_for_merge(PlannerInfo *root, List *mergeclauses, RelOptInfo *joinrel) { List *pathkeys = NIL; int nClauses = list_length(mergeclauses); EquivalenceClass **ecs; int *scores; int necs; ListCell *lc; int j; /* Might have no mergeclauses */ if (nClauses == 0) return NIL; /* * Make arrays of the ECs used by the mergeclauses (dropping any * duplicates) and their "popularity" scores. */ ecs = (EquivalenceClass **) palloc(nClauses * sizeof(EquivalenceClass *)); scores = (int *) palloc(nClauses * sizeof(int)); necs = 0; foreach(lc, mergeclauses) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc); EquivalenceClass *oeclass; int score; ListCell *lc2; /* get the outer eclass */ cache_mergeclause_eclasses(root, rinfo); if (rinfo->outer_is_left) oeclass = rinfo->left_ec; else oeclass = rinfo->right_ec; /* reject duplicates */ for (j = 0; j < necs; j++) { if (ecs[j] == oeclass) break; } if (j < necs) continue; /* compute score */ score = 0; foreach(lc2, oeclass->ec_members) { EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2); /* Potential future join partner? */ if (!em->em_is_const && !em->em_is_child && !bms_overlap(em->em_relids, joinrel->relids)) score++; } ecs[necs] = oeclass; scores[necs] = score; necs++; } /* * Find out if we have all the ECs mentioned in query_pathkeys; if so * we can generate a sort order that's also useful for final output. * There is no percentage in a partial match, though, so we have to * have 'em all. */ if (root->query_pathkeys) { foreach(lc, root->query_pathkeys) { PathKey *query_pathkey = (PathKey *) lfirst(lc); EquivalenceClass *query_ec = query_pathkey->pk_eclass; for (j = 0; j < necs; j++) { if (ecs[j] == query_ec) break; /* found match */ } if (j >= necs) break; /* didn't find match */ } /* if we got to the end of the list, we have them all */ if (lc == NULL) { /* copy query_pathkeys as starting point for our output */ pathkeys = list_copy(root->query_pathkeys); /* mark their ECs as already-emitted */ foreach(lc, root->query_pathkeys) { PathKey *query_pathkey = (PathKey *) lfirst(lc); EquivalenceClass *query_ec = query_pathkey->pk_eclass; for (j = 0; j < necs; j++) { if (ecs[j] == query_ec) { scores[j] = -1; break; } } } } } /* * Add remaining ECs to the list in popularity order, using a default * sort ordering. (We could use qsort() here, but the list length is * usually so small it's not worth it.) */ for (;;) { int best_j; int best_score; EquivalenceClass *ec; PathKey *pathkey; best_j = 0; best_score = scores[0]; for (j = 1; j < necs; j++) { if (scores[j] > best_score) { best_j = j; best_score = scores[j]; } } if (best_score < 0) break; /* all done */ ec = ecs[best_j]; scores[best_j] = -1; pathkey = make_canonical_pathkey(root, ec, linitial_oid(ec->ec_opfamilies), BTLessStrategyNumber, false); /* can't be redundant because no duplicate ECs */ Assert(!pathkey_is_redundant(pathkey, pathkeys)); pathkeys = lappend(pathkeys, pathkey); } pfree(ecs); pfree(scores); return pathkeys; } /* * make_inner_pathkeys_for_merge * Builds a pathkey list representing the explicit sort order that * must be applied to an inner path to make it usable with the * given mergeclauses. * * 'mergeclauses' is a list of RestrictInfos for mergejoin clauses * that will be used in a merge join. * 'outer_pathkeys' are the already-known canonical pathkeys for the outer * side of the join. * * The restrictinfos must be marked (via outer_is_left) to show which side * of each clause is associated with the current outer path. (See * select_mergejoin_clauses()) * * Returns a pathkeys list that can be applied to the inner relation. * * Note that it is not this routine's job to decide whether sorting is * actually needed for a particular input path. Assume a sort is necessary; * just make the keys, eh? */ List * make_inner_pathkeys_for_merge(PlannerInfo *root, List *mergeclauses, List *outer_pathkeys) { List *pathkeys = NIL; EquivalenceClass *lastoeclass; PathKey *opathkey; ListCell *lc; ListCell *lop; lastoeclass = NULL; opathkey = NULL; lop = list_head(outer_pathkeys); foreach(lc, mergeclauses) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc); EquivalenceClass *oeclass; EquivalenceClass *ieclass; PathKey *pathkey; cache_mergeclause_eclasses(root, rinfo); if (rinfo->outer_is_left) { oeclass = rinfo->left_ec; ieclass = rinfo->right_ec; } else { oeclass = rinfo->right_ec; ieclass = rinfo->left_ec; } /* outer eclass should match current or next pathkeys */ /* we check this carefully for debugging reasons */ if (oeclass != lastoeclass) { if (!lop) elog(ERROR, "too few pathkeys for mergeclauses"); opathkey = (PathKey *) lfirst(lop); lop = lnext(lop); lastoeclass = opathkey->pk_eclass; if (oeclass != lastoeclass) elog(ERROR, "outer pathkeys do not match mergeclause"); } /* * Often, we'll have same EC on both sides, in which case the outer * pathkey is also canonical for the inner side, and we can skip a * useless search. */ if (ieclass == oeclass) pathkey = opathkey; else pathkey = make_canonical_pathkey(root, ieclass, opathkey->pk_opfamily, opathkey->pk_strategy, opathkey->pk_nulls_first); /* * Don't generate redundant pathkeys (can happen if multiple * mergeclauses refer to same EC). */ if (!pathkey_is_redundant(pathkey, pathkeys)) pathkeys = lappend(pathkeys, pathkey); } return pathkeys; } /**************************************************************************** * PATHKEY USEFULNESS CHECKS * * We only want to remember as many of the pathkeys of a path as have some * potential use, either for subsequent mergejoins or for meeting the query's * requested output ordering. This ensures that add_path() won't consider * a path to have a usefully different ordering unless it really is useful. * These routines check for usefulness of given pathkeys. ****************************************************************************/ /* * pathkeys_useful_for_merging * Count the number of pathkeys that may be useful for mergejoins * above the given relation. * * We consider a pathkey potentially useful if it corresponds to the merge * ordering of either side of any joinclause for the rel. This might be * overoptimistic, since joinclauses that require different other relations * might never be usable at the same time, but trying to be exact is likely * to be more trouble than it's worth. */ int pathkeys_useful_for_merging(PlannerInfo *root, RelOptInfo *rel, List *pathkeys) { int useful = 0; ListCell *i; foreach(i, pathkeys) { PathKey *pathkey = (PathKey *) lfirst(i); bool matched = false; ListCell *j; /* * First look into the EquivalenceClass of the pathkey, to see if * there are any members not yet joined to the rel. If so, it's * surely possible to generate a mergejoin clause using them. */ if (rel->has_eclass_joins && eclass_useful_for_merging(pathkey->pk_eclass, rel)) matched = true; else { /* * Otherwise search the rel's joininfo list, which contains * non-EquivalenceClass-derivable join clauses that might * nonetheless be mergejoinable. */ foreach(j, rel->joininfo) { RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(j); if (restrictinfo->mergeopfamilies == NIL) continue; cache_mergeclause_eclasses(root, restrictinfo); if (pathkey->pk_eclass == restrictinfo->left_ec || pathkey->pk_eclass == restrictinfo->right_ec) { matched = true; break; } } } /* * If we didn't find a mergeclause, we're done --- any additional * sort-key positions in the pathkeys are useless. (But we can still * mergejoin if we found at least one mergeclause.) */ if (matched) useful++; else break; } return useful; } /* * pathkeys_useful_for_ordering * Count the number of pathkeys that are useful for meeting the * query's requested output ordering. * * Unlike merge pathkeys, this is an all-or-nothing affair: it does us * no good to order by just the first key(s) of the requested ordering. * So the result is always either 0 or list_length(root->query_pathkeys). */ int pathkeys_useful_for_ordering(PlannerInfo *root, List *pathkeys) { if (root->query_pathkeys == NIL) return 0; /* no special ordering requested */ if (pathkeys == NIL) return 0; /* unordered path */ if (pathkeys_contained_in(root->query_pathkeys, pathkeys)) { /* It's useful ... or at least the first N keys are */ return list_length(root->query_pathkeys); } return 0; /* path ordering not useful */ } /* * truncate_useless_pathkeys * Shorten the given pathkey list to just the useful pathkeys. */ List * truncate_useless_pathkeys(PlannerInfo *root, RelOptInfo *rel, List *pathkeys) { int nuseful; int nuseful2; nuseful = pathkeys_useful_for_merging(root, rel, pathkeys); nuseful2 = pathkeys_useful_for_ordering(root, pathkeys); if (nuseful2 > nuseful) nuseful = nuseful2; /* * Note: not safe to modify input list destructively, but we can avoid * copying the list if we're not actually going to change it */ if (nuseful == 0) return NIL; else if (nuseful == list_length(pathkeys)) return pathkeys; else return list_truncate(list_copy(pathkeys), nuseful); } /* * has_useful_pathkeys * Detect whether the specified rel could have any pathkeys that are * useful according to truncate_useless_pathkeys(). * * This is a cheap test that lets us skip building pathkeys at all in very * simple queries. It's OK to err in the direction of returning "true" when * there really aren't any usable pathkeys, but erring in the other direction * is bad --- so keep this in sync with the routines above! * * We could make the test more complex, for example checking to see if any of * the joinclauses are really mergejoinable, but that likely wouldn't win * often enough to repay the extra cycles. Queries with neither a join nor * a sort are reasonably common, though, so this much work seems worthwhile. */ bool has_useful_pathkeys(PlannerInfo *root, RelOptInfo *rel) { if (rel->joininfo != NIL || rel->has_eclass_joins) return true; /* might be able to use pathkeys for merging */ if (root->query_pathkeys != NIL) return true; /* might be able to use them for ordering */ return false; /* definitely useless */ }