/*------------------------------------------------------------------------- * * pathnode.c * Routines to manipulate pathlists and create path nodes * * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.128 2006/06/06 17:59:57 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include #include "catalog/pg_operator.h" #include "executor/executor.h" #include "miscadmin.h" #include "nodes/plannodes.h" #include "optimizer/clauses.h" #include "optimizer/cost.h" #include "optimizer/pathnode.h" #include "optimizer/paths.h" #include "optimizer/restrictinfo.h" #include "optimizer/tlist.h" #include "parser/parse_expr.h" #include "parser/parse_oper.h" #include "parser/parsetree.h" #include "utils/memutils.h" #include "utils/selfuncs.h" #include "utils/syscache.h" static List *translate_sub_tlist(List *tlist, int relid); static bool query_is_distinct_for(Query *query, List *colnos); static bool hash_safe_tlist(List *tlist); /***************************************************************************** * MISC. PATH UTILITIES *****************************************************************************/ /* * compare_path_costs * Return -1, 0, or +1 according as path1 is cheaper, the same cost, * or more expensive than path2 for the specified criterion. */ int compare_path_costs(Path *path1, Path *path2, CostSelector criterion) { if (criterion == STARTUP_COST) { if (path1->startup_cost < path2->startup_cost) return -1; if (path1->startup_cost > path2->startup_cost) return +1; /* * If paths have the same startup cost (not at all unlikely), order * them by total cost. */ if (path1->total_cost < path2->total_cost) return -1; if (path1->total_cost > path2->total_cost) return +1; } else { if (path1->total_cost < path2->total_cost) return -1; if (path1->total_cost > path2->total_cost) return +1; /* * If paths have the same total cost, order them by startup cost. */ if (path1->startup_cost < path2->startup_cost) return -1; if (path1->startup_cost > path2->startup_cost) return +1; } return 0; } /* * compare_fuzzy_path_costs * Return -1, 0, or +1 according as path1 is cheaper, the same cost, * or more expensive than path2 for the specified criterion. * * This differs from compare_path_costs in that we consider the costs the * same if they agree to within a "fuzz factor". This is used by add_path * to avoid keeping both of a pair of paths that really have insignificantly * different cost. */ static int compare_fuzzy_path_costs(Path *path1, Path *path2, CostSelector criterion) { /* * We use a fuzz factor of 1% of the smaller cost. * * XXX does this percentage need to be user-configurable? */ if (criterion == STARTUP_COST) { if (path1->startup_cost > path2->startup_cost * 1.01) return +1; if (path2->startup_cost > path1->startup_cost * 1.01) return -1; /* * If paths have the same startup cost (not at all unlikely), order * them by total cost. */ if (path1->total_cost > path2->total_cost * 1.01) return +1; if (path2->total_cost > path1->total_cost * 1.01) return -1; } else { if (path1->total_cost > path2->total_cost * 1.01) return +1; if (path2->total_cost > path1->total_cost * 1.01) return -1; /* * If paths have the same total cost, order them by startup cost. */ if (path1->startup_cost > path2->startup_cost * 1.01) return +1; if (path2->startup_cost > path1->startup_cost * 1.01) return -1; } return 0; } /* * compare_path_fractional_costs * Return -1, 0, or +1 according as path1 is cheaper, the same cost, * or more expensive than path2 for fetching the specified fraction * of the total tuples. * * If fraction is <= 0 or > 1, we interpret it as 1, ie, we select the * path with the cheaper total_cost. */ int compare_fractional_path_costs(Path *path1, Path *path2, double fraction) { Cost cost1, cost2; if (fraction <= 0.0 || fraction >= 1.0) return compare_path_costs(path1, path2, TOTAL_COST); cost1 = path1->startup_cost + fraction * (path1->total_cost - path1->startup_cost); cost2 = path2->startup_cost + fraction * (path2->total_cost - path2->startup_cost); if (cost1 < cost2) return -1; if (cost1 > cost2) return +1; return 0; } /* * set_cheapest * Find the minimum-cost paths from among a relation's paths, * and save them in the rel's cheapest-path fields. * * This is normally called only after we've finished constructing the path * list for the rel node. * * If we find two paths of identical costs, try to keep the better-sorted one. * The paths might have unrelated sort orderings, in which case we can only * guess which might be better to keep, but if one is superior then we * definitely should keep it. */ void set_cheapest(RelOptInfo *parent_rel) { List *pathlist = parent_rel->pathlist; ListCell *p; Path *cheapest_startup_path; Path *cheapest_total_path; Assert(IsA(parent_rel, RelOptInfo)); if (pathlist == NIL) elog(ERROR, "could not devise a query plan for the given query"); cheapest_startup_path = cheapest_total_path = (Path *) linitial(pathlist); for_each_cell(p, lnext(list_head(pathlist))) { Path *path = (Path *) lfirst(p); int cmp; cmp = compare_path_costs(cheapest_startup_path, path, STARTUP_COST); if (cmp > 0 || (cmp == 0 && compare_pathkeys(cheapest_startup_path->pathkeys, path->pathkeys) == PATHKEYS_BETTER2)) cheapest_startup_path = path; cmp = compare_path_costs(cheapest_total_path, path, TOTAL_COST); if (cmp > 0 || (cmp == 0 && compare_pathkeys(cheapest_total_path->pathkeys, path->pathkeys) == PATHKEYS_BETTER2)) cheapest_total_path = path; } parent_rel->cheapest_startup_path = cheapest_startup_path; parent_rel->cheapest_total_path = cheapest_total_path; parent_rel->cheapest_unique_path = NULL; /* computed only if needed */ } /* * add_path * Consider a potential implementation path for the specified parent rel, * and add it to the rel's pathlist if it is worthy of consideration. * A path is worthy if it has either a better sort order (better pathkeys) * or cheaper cost (on either dimension) than any of the existing old paths. * * We also remove from the rel's pathlist any old paths that are dominated * by new_path --- that is, new_path is both cheaper and at least as well * ordered. * * The pathlist is kept sorted by TOTAL_COST metric, with cheaper paths * at the front. No code depends on that for correctness; it's simply * a speed hack within this routine. Doing it that way makes it more * likely that we will reject an inferior path after a few comparisons, * rather than many comparisons. * * NOTE: discarded Path objects are immediately pfree'd to reduce planner * memory consumption. We dare not try to free the substructure of a Path, * since much of it may be shared with other Paths or the query tree itself; * but just recycling discarded Path nodes is a very useful savings in * a large join tree. We can recycle the List nodes of pathlist, too. * * BUT: we do not pfree IndexPath objects, since they may be referenced as * children of BitmapHeapPaths as well as being paths in their own right. * * 'parent_rel' is the relation entry to which the path corresponds. * 'new_path' is a potential path for parent_rel. * * Returns nothing, but modifies parent_rel->pathlist. */ void add_path(RelOptInfo *parent_rel, Path *new_path) { bool accept_new = true; /* unless we find a superior old path */ ListCell *insert_after = NULL; /* where to insert new item */ ListCell *p1_prev = NULL; ListCell *p1; /* * This is a convenient place to check for query cancel --- no part of the * planner goes very long without calling add_path(). */ CHECK_FOR_INTERRUPTS(); /* * Loop to check proposed new path against old paths. Note it is possible * for more than one old path to be tossed out because new_path dominates * it. */ p1 = list_head(parent_rel->pathlist); /* cannot use foreach here */ while (p1 != NULL) { Path *old_path = (Path *) lfirst(p1); bool remove_old = false; /* unless new proves superior */ int costcmp; /* * As of Postgres 8.0, we use fuzzy cost comparison to avoid wasting * cycles keeping paths that are really not significantly different in * cost. */ costcmp = compare_fuzzy_path_costs(new_path, old_path, TOTAL_COST); /* * If the two paths compare differently for startup and total cost, * then we want to keep both, and we can skip the (much slower) * comparison of pathkeys. If they compare the same, proceed with the * pathkeys comparison. Note: this test relies on the fact that * compare_fuzzy_path_costs will only return 0 if both costs are * effectively equal (and, therefore, there's no need to call it twice * in that case). */ if (costcmp == 0 || costcmp == compare_fuzzy_path_costs(new_path, old_path, STARTUP_COST)) { switch (compare_pathkeys(new_path->pathkeys, old_path->pathkeys)) { case PATHKEYS_EQUAL: if (costcmp < 0) remove_old = true; /* new dominates old */ else if (costcmp > 0) accept_new = false; /* old dominates new */ else { /* * Same pathkeys, and fuzzily the same cost, so keep * just one --- but we'll do an exact cost comparison * to decide which. */ if (compare_path_costs(new_path, old_path, TOTAL_COST) < 0) remove_old = true; /* new dominates old */ else accept_new = false; /* old equals or dominates new */ } break; case PATHKEYS_BETTER1: if (costcmp <= 0) remove_old = true; /* new dominates old */ break; case PATHKEYS_BETTER2: if (costcmp >= 0) accept_new = false; /* old dominates new */ break; case PATHKEYS_DIFFERENT: /* keep both paths, since they have different ordering */ break; } } /* * Remove current element from pathlist if dominated by new. */ if (remove_old) { parent_rel->pathlist = list_delete_cell(parent_rel->pathlist, p1, p1_prev); /* * Delete the data pointed-to by the deleted cell, if possible */ if (!IsA(old_path, IndexPath)) pfree(old_path); /* Advance list pointer */ if (p1_prev) p1 = lnext(p1_prev); else p1 = list_head(parent_rel->pathlist); } else { /* new belongs after this old path if it has cost >= old's */ if (costcmp >= 0) insert_after = p1; /* Advance list pointers */ p1_prev = p1; p1 = lnext(p1); } /* * If we found an old path that dominates new_path, we can quit * scanning the pathlist; we will not add new_path, and we assume * new_path cannot dominate any other elements of the pathlist. */ if (!accept_new) break; } if (accept_new) { /* Accept the new path: insert it at proper place in pathlist */ if (insert_after) lappend_cell(parent_rel->pathlist, insert_after, new_path); else parent_rel->pathlist = lcons(new_path, parent_rel->pathlist); } else { /* Reject and recycle the new path */ if (!IsA(new_path, IndexPath)) pfree(new_path); } } /***************************************************************************** * PATH NODE CREATION ROUTINES *****************************************************************************/ /* * create_seqscan_path * Creates a path corresponding to a sequential scan, returning the * pathnode. */ Path * create_seqscan_path(PlannerInfo *root, RelOptInfo *rel) { Path *pathnode = makeNode(Path); pathnode->pathtype = T_SeqScan; pathnode->parent = rel; pathnode->pathkeys = NIL; /* seqscan has unordered result */ cost_seqscan(pathnode, root, rel); return pathnode; } /* * create_index_path * Creates a path node for an index scan. * * 'index' is a usable index. * 'clause_groups' is a list of lists of RestrictInfo nodes * to be used as index qual conditions in the scan. * 'pathkeys' describes the ordering of the path. * 'indexscandir' is ForwardScanDirection or BackwardScanDirection * for an ordered index, or NoMovementScanDirection for * an unordered index. * 'outer_rel' is the outer relation if this is a join inner indexscan path. * (pathkeys and indexscandir are ignored if so.) NULL if not. * * Returns the new path node. */ IndexPath * create_index_path(PlannerInfo *root, IndexOptInfo *index, List *clause_groups, List *pathkeys, ScanDirection indexscandir, RelOptInfo *outer_rel) { IndexPath *pathnode = makeNode(IndexPath); RelOptInfo *rel = index->rel; List *indexquals, *allclauses; /* * For a join inner scan, there's no point in marking the path with any * pathkeys, since it will only ever be used as the inner path of a * nestloop, and so its ordering does not matter. For the same reason we * don't really care what order it's scanned in. (We could expect the * caller to supply the correct values, but it's easier to force it here.) */ if (outer_rel != NULL) { pathkeys = NIL; indexscandir = NoMovementScanDirection; } pathnode->path.pathtype = T_IndexScan; pathnode->path.parent = rel; pathnode->path.pathkeys = pathkeys; /* Convert clauses to indexquals the executor can handle */ indexquals = expand_indexqual_conditions(index, clause_groups); /* Flatten the clause-groups list to produce indexclauses list */ allclauses = flatten_clausegroups_list(clause_groups); /* Fill in the pathnode */ pathnode->indexinfo = index; pathnode->indexclauses = allclauses; pathnode->indexquals = indexquals; pathnode->isjoininner = (outer_rel != NULL); pathnode->indexscandir = indexscandir; if (outer_rel != NULL) { /* * We must compute the estimated number of output rows for the * indexscan. This is less than rel->rows because of the additional * selectivity of the join clauses. Since clause_groups may contain * both restriction and join clauses, we have to do a set union to get * the full set of clauses that must be considered to compute the * correct selectivity. (Without the union operation, we might have * some restriction clauses appearing twice, which'd mislead * clauselist_selectivity into double-counting their selectivity. * However, since RestrictInfo nodes aren't copied when linking them * into different lists, it should be sufficient to use pointer * comparison to remove duplicates.) * * Always assume the join type is JOIN_INNER; even if some of the join * clauses come from other contexts, that's not our problem. */ allclauses = list_union_ptr(rel->baserestrictinfo, allclauses); pathnode->rows = rel->tuples * clauselist_selectivity(root, allclauses, rel->relid, /* do not use 0! */ JOIN_INNER); /* Like costsize.c, force estimate to be at least one row */ pathnode->rows = clamp_row_est(pathnode->rows); } else { /* * The number of rows is the same as the parent rel's estimate, since * this isn't a join inner indexscan. */ pathnode->rows = rel->rows; } cost_index(pathnode, root, index, indexquals, outer_rel); return pathnode; } /* * create_bitmap_heap_path * Creates a path node for a bitmap scan. * * 'bitmapqual' is a tree of IndexPath, BitmapAndPath, and BitmapOrPath nodes. * * If this is a join inner indexscan path, the component IndexPaths should * have been costed accordingly, and TRUE should be passed for isjoininner. */ BitmapHeapPath * create_bitmap_heap_path(PlannerInfo *root, RelOptInfo *rel, Path *bitmapqual, bool isjoininner) { BitmapHeapPath *pathnode = makeNode(BitmapHeapPath); pathnode->path.pathtype = T_BitmapHeapScan; pathnode->path.parent = rel; pathnode->path.pathkeys = NIL; /* always unordered */ pathnode->bitmapqual = bitmapqual; pathnode->isjoininner = isjoininner; if (isjoininner) { /* * We must compute the estimated number of output rows for the * indexscan. This is less than rel->rows because of the additional * selectivity of the join clauses. We make use of the selectivity * estimated for the bitmap to do this; this isn't really quite right * since there may be restriction conditions not included in the * bitmap ... */ Cost indexTotalCost; Selectivity indexSelectivity; cost_bitmap_tree_node(bitmapqual, &indexTotalCost, &indexSelectivity); pathnode->rows = rel->tuples * indexSelectivity; if (pathnode->rows > rel->rows) pathnode->rows = rel->rows; /* Like costsize.c, force estimate to be at least one row */ pathnode->rows = clamp_row_est(pathnode->rows); } else { /* * The number of rows is the same as the parent rel's estimate, since * this isn't a join inner indexscan. */ pathnode->rows = rel->rows; } cost_bitmap_heap_scan(&pathnode->path, root, rel, bitmapqual); return pathnode; } /* * create_bitmap_and_path * Creates a path node representing a BitmapAnd. */ BitmapAndPath * create_bitmap_and_path(PlannerInfo *root, RelOptInfo *rel, List *bitmapquals) { BitmapAndPath *pathnode = makeNode(BitmapAndPath); pathnode->path.pathtype = T_BitmapAnd; pathnode->path.parent = rel; pathnode->path.pathkeys = NIL; /* always unordered */ pathnode->bitmapquals = bitmapquals; /* this sets bitmapselectivity as well as the regular cost fields: */ cost_bitmap_and_node(pathnode, root); return pathnode; } /* * create_bitmap_or_path * Creates a path node representing a BitmapOr. */ BitmapOrPath * create_bitmap_or_path(PlannerInfo *root, RelOptInfo *rel, List *bitmapquals) { BitmapOrPath *pathnode = makeNode(BitmapOrPath); pathnode->path.pathtype = T_BitmapOr; pathnode->path.parent = rel; pathnode->path.pathkeys = NIL; /* always unordered */ pathnode->bitmapquals = bitmapquals; /* this sets bitmapselectivity as well as the regular cost fields: */ cost_bitmap_or_node(pathnode, root); return pathnode; } /* * create_tidscan_path * Creates a path corresponding to a scan by TID, returning the pathnode. */ TidPath * create_tidscan_path(PlannerInfo *root, RelOptInfo *rel, List *tidquals) { TidPath *pathnode = makeNode(TidPath); pathnode->path.pathtype = T_TidScan; pathnode->path.parent = rel; pathnode->path.pathkeys = NIL; pathnode->tidquals = tidquals; cost_tidscan(&pathnode->path, root, rel, tidquals); return pathnode; } /* * create_append_path * Creates a path corresponding to an Append plan, returning the * pathnode. */ AppendPath * create_append_path(RelOptInfo *rel, List *subpaths) { AppendPath *pathnode = makeNode(AppendPath); ListCell *l; pathnode->path.pathtype = T_Append; pathnode->path.parent = rel; pathnode->path.pathkeys = NIL; /* result is always considered * unsorted */ pathnode->subpaths = subpaths; pathnode->path.startup_cost = 0; pathnode->path.total_cost = 0; foreach(l, subpaths) { Path *subpath = (Path *) lfirst(l); if (l == list_head(subpaths)) /* first node? */ pathnode->path.startup_cost = subpath->startup_cost; pathnode->path.total_cost += subpath->total_cost; } return pathnode; } /* * create_result_path * Creates a path corresponding to a Result plan, returning the * pathnode. */ ResultPath * create_result_path(RelOptInfo *rel, Path *subpath, List *constantqual) { ResultPath *pathnode = makeNode(ResultPath); pathnode->path.pathtype = T_Result; pathnode->path.parent = rel; /* may be NULL */ if (subpath) pathnode->path.pathkeys = subpath->pathkeys; else pathnode->path.pathkeys = NIL; pathnode->subpath = subpath; pathnode->constantqual = constantqual; /* Ideally should define cost_result(), but I'm too lazy */ if (subpath) { pathnode->path.startup_cost = subpath->startup_cost; pathnode->path.total_cost = subpath->total_cost; } else { pathnode->path.startup_cost = 0; pathnode->path.total_cost = cpu_tuple_cost; } return pathnode; } /* * create_material_path * Creates a path corresponding to a Material plan, returning the * pathnode. */ MaterialPath * create_material_path(RelOptInfo *rel, Path *subpath) { MaterialPath *pathnode = makeNode(MaterialPath); pathnode->path.pathtype = T_Material; pathnode->path.parent = rel; pathnode->path.pathkeys = subpath->pathkeys; pathnode->subpath = subpath; cost_material(&pathnode->path, subpath->total_cost, rel->rows, rel->width); return pathnode; } /* * create_unique_path * Creates a path representing elimination of distinct rows from the * input data. * * If used at all, this is likely to be called repeatedly on the same rel; * and the input subpath should always be the same (the cheapest_total path * for the rel). So we cache the result. */ UniquePath * create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath) { UniquePath *pathnode; Path sort_path; /* dummy for result of cost_sort */ Path agg_path; /* dummy for result of cost_agg */ MemoryContext oldcontext; List *sub_targetlist; ListCell *l; int numCols; /* Caller made a mistake if subpath isn't cheapest_total */ Assert(subpath == rel->cheapest_total_path); /* If result already cached, return it */ if (rel->cheapest_unique_path) return (UniquePath *) rel->cheapest_unique_path; /* * We must ensure path struct is allocated in same context as parent rel; * otherwise GEQO memory management causes trouble. (Compare * best_inner_indexscan().) */ oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel)); pathnode = makeNode(UniquePath); /* There is no substructure to allocate, so can switch back right away */ MemoryContextSwitchTo(oldcontext); pathnode->path.pathtype = T_Unique; pathnode->path.parent = rel; /* * Treat the output as always unsorted, since we don't necessarily have * pathkeys to represent it. */ pathnode->path.pathkeys = NIL; pathnode->subpath = subpath; /* * Try to identify the targetlist that will actually be unique-ified. In * current usage, this routine is only used for sub-selects of IN clauses, * so we should be able to find the tlist in in_info_list. */ sub_targetlist = NIL; foreach(l, root->in_info_list) { InClauseInfo *ininfo = (InClauseInfo *) lfirst(l); if (bms_equal(ininfo->righthand, rel->relids)) { sub_targetlist = ininfo->sub_targetlist; break; } } /* * If the input is a subquery whose output must be unique already, then we * don't need to do anything. The test for uniqueness has to consider * exactly which columns we are extracting; for example "SELECT DISTINCT * x,y" doesn't guarantee that x alone is distinct. So we cannot check for * this optimization unless we found our own targetlist above, and it * consists only of simple Vars referencing subquery outputs. (Possibly * we could do something with expressions in the subquery outputs, too, * but for now keep it simple.) */ if (sub_targetlist && rel->rtekind == RTE_SUBQUERY) { RangeTblEntry *rte = rt_fetch(rel->relid, root->parse->rtable); List *sub_tlist_colnos; sub_tlist_colnos = translate_sub_tlist(sub_targetlist, rel->relid); if (sub_tlist_colnos && query_is_distinct_for(rte->subquery, sub_tlist_colnos)) { pathnode->umethod = UNIQUE_PATH_NOOP; pathnode->rows = rel->rows; pathnode->path.startup_cost = subpath->startup_cost; pathnode->path.total_cost = subpath->total_cost; pathnode->path.pathkeys = subpath->pathkeys; rel->cheapest_unique_path = (Path *) pathnode; return pathnode; } } /* * If we know the targetlist, try to estimate number of result rows; * otherwise punt. */ if (sub_targetlist) { pathnode->rows = estimate_num_groups(root, sub_targetlist, rel->rows); numCols = list_length(sub_targetlist); } else { pathnode->rows = rel->rows; numCols = list_length(rel->reltargetlist); } /* * Estimate cost for sort+unique implementation */ cost_sort(&sort_path, root, NIL, subpath->total_cost, rel->rows, rel->width); /* * Charge one cpu_operator_cost per comparison per input tuple. We assume * all columns get compared at most of the tuples. (XXX probably this is * an overestimate.) This should agree with make_unique. */ sort_path.total_cost += cpu_operator_cost * rel->rows * numCols; /* * Is it safe to use a hashed implementation? If so, estimate and compare * costs. We only try this if we know the targetlist for sure (else we * can't be sure about the datatypes involved). */ pathnode->umethod = UNIQUE_PATH_SORT; if (enable_hashagg && sub_targetlist && hash_safe_tlist(sub_targetlist)) { /* * Estimate the overhead per hashtable entry at 64 bytes (same as in * planner.c). */ int hashentrysize = rel->width + 64; if (hashentrysize * pathnode->rows <= work_mem * 1024L) { cost_agg(&agg_path, root, AGG_HASHED, 0, numCols, pathnode->rows, subpath->startup_cost, subpath->total_cost, rel->rows); if (agg_path.total_cost < sort_path.total_cost) pathnode->umethod = UNIQUE_PATH_HASH; } } if (pathnode->umethod == UNIQUE_PATH_HASH) { pathnode->path.startup_cost = agg_path.startup_cost; pathnode->path.total_cost = agg_path.total_cost; } else { pathnode->path.startup_cost = sort_path.startup_cost; pathnode->path.total_cost = sort_path.total_cost; } rel->cheapest_unique_path = (Path *) pathnode; return pathnode; } /* * translate_sub_tlist - get subquery column numbers represented by tlist * * The given targetlist should contain only Vars referencing the given relid. * Extract their varattnos (ie, the column numbers of the subquery) and return * as an integer List. * * If any of the tlist items is not a simple Var, we cannot determine whether * the subquery's uniqueness condition (if any) matches ours, so punt and * return NIL. */ static List * translate_sub_tlist(List *tlist, int relid) { List *result = NIL; ListCell *l; foreach(l, tlist) { Var *var = (Var *) lfirst(l); if (!var || !IsA(var, Var) || var->varno != relid) return NIL; /* punt */ result = lappend_int(result, var->varattno); } return result; } /* * query_is_distinct_for - does query never return duplicates of the * specified columns? * * colnos is an integer list of output column numbers (resno's). We are * interested in whether rows consisting of just these columns are certain * to be distinct. */ static bool query_is_distinct_for(Query *query, List *colnos) { ListCell *l; /* * DISTINCT (including DISTINCT ON) guarantees uniqueness if all the * columns in the DISTINCT clause appear in colnos. */ if (query->distinctClause) { foreach(l, query->distinctClause) { SortClause *scl = (SortClause *) lfirst(l); TargetEntry *tle = get_sortgroupclause_tle(scl, query->targetList); if (!list_member_int(colnos, tle->resno)) break; /* exit early if no match */ } if (l == NULL) /* had matches for all? */ return true; } /* * Similarly, GROUP BY guarantees uniqueness if all the grouped columns * appear in colnos. */ if (query->groupClause) { foreach(l, query->groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(l); TargetEntry *tle = get_sortgroupclause_tle(grpcl, query->targetList); if (!list_member_int(colnos, tle->resno)) break; /* exit early if no match */ } if (l == NULL) /* had matches for all? */ return true; } else { /* * If we have no GROUP BY, but do have aggregates or HAVING, then the * result is at most one row so it's surely unique. */ if (query->hasAggs || query->havingQual) return true; } /* * UNION, INTERSECT, EXCEPT guarantee uniqueness of the whole output row, * except with ALL */ if (query->setOperations) { SetOperationStmt *topop = (SetOperationStmt *) query->setOperations; Assert(IsA(topop, SetOperationStmt)); Assert(topop->op != SETOP_NONE); if (!topop->all) { /* We're good if all the nonjunk output columns are in colnos */ foreach(l, query->targetList) { TargetEntry *tle = (TargetEntry *) lfirst(l); if (!tle->resjunk && !list_member_int(colnos, tle->resno)) break; /* exit early if no match */ } if (l == NULL) /* had matches for all? */ return true; } } /* * XXX Are there any other cases in which we can easily see the result * must be distinct? */ return false; } /* * hash_safe_tlist - can datatypes of given tlist be hashed? * * We assume hashed aggregation will work if the datatype's equality operator * is marked hashjoinable. * * XXX this probably should be somewhere else. See also hash_safe_grouping * in plan/planner.c. */ static bool hash_safe_tlist(List *tlist) { ListCell *tl; foreach(tl, tlist) { Node *expr = (Node *) lfirst(tl); Operator optup; bool oprcanhash; optup = equality_oper(exprType(expr), true); if (!optup) return false; oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash; ReleaseSysCache(optup); if (!oprcanhash) return false; } return true; } /* * create_subqueryscan_path * Creates a path corresponding to a sequential scan of a subquery, * returning the pathnode. */ Path * create_subqueryscan_path(RelOptInfo *rel, List *pathkeys) { Path *pathnode = makeNode(Path); pathnode->pathtype = T_SubqueryScan; pathnode->parent = rel; pathnode->pathkeys = pathkeys; cost_subqueryscan(pathnode, rel); return pathnode; } /* * create_functionscan_path * Creates a path corresponding to a sequential scan of a function, * returning the pathnode. */ Path * create_functionscan_path(PlannerInfo *root, RelOptInfo *rel) { Path *pathnode = makeNode(Path); pathnode->pathtype = T_FunctionScan; pathnode->parent = rel; pathnode->pathkeys = NIL; /* for now, assume unordered result */ cost_functionscan(pathnode, root, rel); return pathnode; } /* * create_nestloop_path * Creates a pathnode corresponding to a nestloop join between two * relations. * * 'joinrel' is the join relation. * 'jointype' is the type of join required * 'outer_path' is the outer path * 'inner_path' is the inner path * 'restrict_clauses' are the RestrictInfo nodes to apply at the join * 'pathkeys' are the path keys of the new join path * * Returns the resulting path node. */ NestPath * create_nestloop_path(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, Path *outer_path, Path *inner_path, List *restrict_clauses, List *pathkeys) { NestPath *pathnode = makeNode(NestPath); pathnode->path.pathtype = T_NestLoop; pathnode->path.parent = joinrel; pathnode->jointype = jointype; pathnode->outerjoinpath = outer_path; pathnode->innerjoinpath = inner_path; pathnode->joinrestrictinfo = restrict_clauses; pathnode->path.pathkeys = pathkeys; cost_nestloop(pathnode, root); return pathnode; } /* * create_mergejoin_path * Creates a pathnode corresponding to a mergejoin join between * two relations * * 'joinrel' is the join relation * 'jointype' is the type of join required * 'outer_path' is the outer path * 'inner_path' is the inner path * 'restrict_clauses' are the RestrictInfo nodes to apply at the join * 'pathkeys' are the path keys of the new join path * 'mergeclauses' are the RestrictInfo nodes to use as merge clauses * (this should be a subset of the restrict_clauses list) * 'outersortkeys' are the sort varkeys for the outer relation * 'innersortkeys' are the sort varkeys for the inner relation */ MergePath * create_mergejoin_path(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, Path *outer_path, Path *inner_path, List *restrict_clauses, List *pathkeys, List *mergeclauses, List *outersortkeys, List *innersortkeys) { MergePath *pathnode = makeNode(MergePath); /* * If the given paths are already well enough ordered, we can skip doing * an explicit sort. */ if (outersortkeys && pathkeys_contained_in(outersortkeys, outer_path->pathkeys)) outersortkeys = NIL; if (innersortkeys && pathkeys_contained_in(innersortkeys, inner_path->pathkeys)) innersortkeys = NIL; /* * If we are not sorting the inner path, we may need a materialize node to * ensure it can be marked/restored. (Sort does support mark/restore, so * no materialize is needed in that case.) * * Since the inner side must be ordered, and only Sorts and IndexScans can * create order to begin with, you might think there's no problem --- but * you'd be wrong. Nestloop and merge joins can *preserve* the order of * their inputs, so they can be selected as the input of a mergejoin, and * they don't support mark/restore at present. */ if (innersortkeys == NIL && !ExecSupportsMarkRestore(inner_path->pathtype)) inner_path = (Path *) create_material_path(inner_path->parent, inner_path); pathnode->jpath.path.pathtype = T_MergeJoin; pathnode->jpath.path.parent = joinrel; pathnode->jpath.jointype = jointype; pathnode->jpath.outerjoinpath = outer_path; pathnode->jpath.innerjoinpath = inner_path; pathnode->jpath.joinrestrictinfo = restrict_clauses; pathnode->jpath.path.pathkeys = pathkeys; pathnode->path_mergeclauses = mergeclauses; pathnode->outersortkeys = outersortkeys; pathnode->innersortkeys = innersortkeys; cost_mergejoin(pathnode, root); return pathnode; } /* * create_hashjoin_path * Creates a pathnode corresponding to a hash join between two relations. * * 'joinrel' is the join relation * 'jointype' is the type of join required * 'outer_path' is the cheapest outer path * 'inner_path' is the cheapest inner path * 'restrict_clauses' are the RestrictInfo nodes to apply at the join * 'hashclauses' are the RestrictInfo nodes to use as hash clauses * (this should be a subset of the restrict_clauses list) */ HashPath * create_hashjoin_path(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, Path *outer_path, Path *inner_path, List *restrict_clauses, List *hashclauses) { HashPath *pathnode = makeNode(HashPath); pathnode->jpath.path.pathtype = T_HashJoin; pathnode->jpath.path.parent = joinrel; pathnode->jpath.jointype = jointype; pathnode->jpath.outerjoinpath = outer_path; pathnode->jpath.innerjoinpath = inner_path; pathnode->jpath.joinrestrictinfo = restrict_clauses; /* A hashjoin never has pathkeys, since its ordering is unpredictable */ pathnode->jpath.path.pathkeys = NIL; pathnode->path_hashclauses = hashclauses; cost_hashjoin(pathnode, root); return pathnode; }