/*------------------------------------------------------------------------- * * allpaths.c * Routines to find possible search paths for processing a query * * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/optimizer/path/allpaths.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include #include #include "access/sysattr.h" #include "access/tsmapi.h" #include "catalog/pg_class.h" #include "catalog/pg_operator.h" #include "catalog/pg_proc.h" #include "foreign/fdwapi.h" #include "miscadmin.h" #include "nodes/makefuncs.h" #include "nodes/nodeFuncs.h" #include "nodes/supportnodes.h" #ifdef OPTIMIZER_DEBUG #include "nodes/print.h" #endif #include "optimizer/appendinfo.h" #include "optimizer/clauses.h" #include "optimizer/cost.h" #include "optimizer/geqo.h" #include "optimizer/optimizer.h" #include "optimizer/pathnode.h" #include "optimizer/paths.h" #include "optimizer/plancat.h" #include "optimizer/planner.h" #include "optimizer/tlist.h" #include "parser/parse_clause.h" #include "parser/parsetree.h" #include "partitioning/partbounds.h" #include "port/pg_bitutils.h" #include "rewrite/rewriteManip.h" #include "utils/lsyscache.h" /* Bitmask flags for pushdown_safety_info.unsafeFlags */ #define UNSAFE_HAS_VOLATILE_FUNC (1 << 0) #define UNSAFE_HAS_SET_FUNC (1 << 1) #define UNSAFE_NOTIN_DISTINCTON_CLAUSE (1 << 2) #define UNSAFE_NOTIN_PARTITIONBY_CLAUSE (1 << 3) #define UNSAFE_TYPE_MISMATCH (1 << 4) /* results of subquery_is_pushdown_safe */ typedef struct pushdown_safety_info { unsigned char *unsafeFlags; /* bitmask of reasons why this target list * column is unsafe for qual pushdown, or 0 if * no reason. */ bool unsafeVolatile; /* don't push down volatile quals */ bool unsafeLeaky; /* don't push down leaky quals */ } pushdown_safety_info; /* Return type for qual_is_pushdown_safe */ typedef enum pushdown_safe_type { PUSHDOWN_UNSAFE, /* unsafe to push qual into subquery */ PUSHDOWN_SAFE, /* safe to push qual into subquery */ PUSHDOWN_WINDOWCLAUSE_RUNCOND, /* unsafe, but may work as WindowClause * run condition */ } pushdown_safe_type; /* These parameters are set by GUC */ bool enable_geqo = false; /* just in case GUC doesn't set it */ int geqo_threshold; int min_parallel_table_scan_size; int min_parallel_index_scan_size; /* Hook for plugins to get control in set_rel_pathlist() */ set_rel_pathlist_hook_type set_rel_pathlist_hook = NULL; /* Hook for plugins to replace standard_join_search() */ join_search_hook_type join_search_hook = NULL; static void set_base_rel_consider_startup(PlannerInfo *root); static void set_base_rel_sizes(PlannerInfo *root); static void set_base_rel_pathlists(PlannerInfo *root); static void set_rel_size(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte); static void set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte); static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel); static void set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte); static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte); static void generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, List *live_childrels, List *all_child_pathkeys); static Path *get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer); static void accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths); static Path *get_singleton_append_subpath(Path *path); static void set_dummy_rel_pathlist(RelOptInfo *rel); static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte); static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_values_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_result_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte); static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist); static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery, pushdown_safety_info *safetyInfo); static bool recurse_pushdown_safe(Node *setOp, Query *topquery, pushdown_safety_info *safetyInfo); static void check_output_expressions(Query *subquery, pushdown_safety_info *safetyInfo); static void compare_tlist_datatypes(List *tlist, List *colTypes, pushdown_safety_info *safetyInfo); static bool targetIsInAllPartitionLists(TargetEntry *tle, Query *query); static pushdown_safe_type qual_is_pushdown_safe(Query *subquery, Index rti, RestrictInfo *rinfo, pushdown_safety_info *safetyInfo); static void subquery_push_qual(Query *subquery, RangeTblEntry *rte, Index rti, Node *qual); static void recurse_push_qual(Node *setOp, Query *topquery, RangeTblEntry *rte, Index rti, Node *qual); static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel, Bitmapset *extra_used_attrs); /* * make_one_rel * Finds all possible access paths for executing a query, returning a * single rel that represents the join of all base rels in the query. */ RelOptInfo * make_one_rel(PlannerInfo *root, List *joinlist) { RelOptInfo *rel; Index rti; double total_pages; /* Mark base rels as to whether we care about fast-start plans */ set_base_rel_consider_startup(root); /* * Compute size estimates and consider_parallel flags for each base rel. */ set_base_rel_sizes(root); /* * We should now have size estimates for every actual table involved in * the query, and we also know which if any have been deleted from the * query by join removal, pruned by partition pruning, or eliminated by * constraint exclusion. So we can now compute total_table_pages. * * Note that appendrels are not double-counted here, even though we don't * bother to distinguish RelOptInfos for appendrel parents, because the * parents will have pages = 0. * * XXX if a table is self-joined, we will count it once per appearance, * which perhaps is the wrong thing ... but that's not completely clear, * and detecting self-joins here is difficult, so ignore it for now. */ total_pages = 0; for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *brel = root->simple_rel_array[rti]; /* there may be empty slots corresponding to non-baserel RTEs */ if (brel == NULL) continue; Assert(brel->relid == rti); /* sanity check on array */ if (IS_DUMMY_REL(brel)) continue; if (IS_SIMPLE_REL(brel)) total_pages += (double) brel->pages; } root->total_table_pages = total_pages; /* * Generate access paths for each base rel. */ set_base_rel_pathlists(root); /* * Generate access paths for the entire join tree. */ rel = make_rel_from_joinlist(root, joinlist); /* * The result should join all and only the query's base + outer-join rels. */ Assert(bms_equal(rel->relids, root->all_query_rels)); return rel; } /* * set_base_rel_consider_startup * Set the consider_[param_]startup flags for each base-relation entry. * * For the moment, we only deal with consider_param_startup here; because the * logic for consider_startup is pretty trivial and is the same for every base * relation, we just let build_simple_rel() initialize that flag correctly to * start with. If that logic ever gets more complicated it would probably * be better to move it here. */ static void set_base_rel_consider_startup(PlannerInfo *root) { /* * Since parameterized paths can only be used on the inside of a nestloop * join plan, there is usually little value in considering fast-start * plans for them. However, for relations that are on the RHS of a SEMI * or ANTI join, a fast-start plan can be useful because we're only going * to care about fetching one tuple anyway. * * To minimize growth of planning time, we currently restrict this to * cases where the RHS is a single base relation, not a join; there is no * provision for consider_param_startup to get set at all on joinrels. * Also we don't worry about appendrels. costsize.c's costing rules for * nestloop semi/antijoins don't consider such cases either. */ ListCell *lc; foreach(lc, root->join_info_list) { SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc); int varno; if ((sjinfo->jointype == JOIN_SEMI || sjinfo->jointype == JOIN_ANTI) && bms_get_singleton_member(sjinfo->syn_righthand, &varno)) { RelOptInfo *rel = find_base_rel(root, varno); rel->consider_param_startup = true; } } } /* * set_base_rel_sizes * Set the size estimates (rows and widths) for each base-relation entry. * Also determine whether to consider parallel paths for base relations. * * We do this in a separate pass over the base rels so that rowcount * estimates are available for parameterized path generation, and also so * that each rel's consider_parallel flag is set correctly before we begin to * generate paths. */ static void set_base_rel_sizes(PlannerInfo *root) { Index rti; for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *rel = root->simple_rel_array[rti]; RangeTblEntry *rte; /* there may be empty slots corresponding to non-baserel RTEs */ if (rel == NULL) continue; Assert(rel->relid == rti); /* sanity check on array */ /* ignore RTEs that are "other rels" */ if (rel->reloptkind != RELOPT_BASEREL) continue; rte = root->simple_rte_array[rti]; /* * If parallelism is allowable for this query in general, see whether * it's allowable for this rel in particular. We have to do this * before set_rel_size(), because (a) if this rel is an inheritance * parent, set_append_rel_size() will use and perhaps change the rel's * consider_parallel flag, and (b) for some RTE types, set_rel_size() * goes ahead and makes paths immediately. */ if (root->glob->parallelModeOK) set_rel_consider_parallel(root, rel, rte); set_rel_size(root, rel, rti, rte); } } /* * set_base_rel_pathlists * Finds all paths available for scanning each base-relation entry. * Sequential scan and any available indices are considered. * Each useful path is attached to its relation's 'pathlist' field. */ static void set_base_rel_pathlists(PlannerInfo *root) { Index rti; for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *rel = root->simple_rel_array[rti]; /* there may be empty slots corresponding to non-baserel RTEs */ if (rel == NULL) continue; Assert(rel->relid == rti); /* sanity check on array */ /* ignore RTEs that are "other rels" */ if (rel->reloptkind != RELOPT_BASEREL) continue; set_rel_pathlist(root, rel, rti, root->simple_rte_array[rti]); } } /* * set_rel_size * Set size estimates for a base relation */ static void set_rel_size(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte) { if (rel->reloptkind == RELOPT_BASEREL && relation_excluded_by_constraints(root, rel, rte)) { /* * We proved we don't need to scan the rel via constraint exclusion, * so set up a single dummy path for it. Here we only check this for * regular baserels; if it's an otherrel, CE was already checked in * set_append_rel_size(). * * In this case, we go ahead and set up the relation's path right away * instead of leaving it for set_rel_pathlist to do. This is because * we don't have a convention for marking a rel as dummy except by * assigning a dummy path to it. */ set_dummy_rel_pathlist(rel); } else if (rte->inh) { /* It's an "append relation", process accordingly */ set_append_rel_size(root, rel, rti, rte); } else { switch (rel->rtekind) { case RTE_RELATION: if (rte->relkind == RELKIND_FOREIGN_TABLE) { /* Foreign table */ set_foreign_size(root, rel, rte); } else if (rte->relkind == RELKIND_PARTITIONED_TABLE) { /* * We could get here if asked to scan a partitioned table * with ONLY. In that case we shouldn't scan any of the * partitions, so mark it as a dummy rel. */ set_dummy_rel_pathlist(rel); } else if (rte->tablesample != NULL) { /* Sampled relation */ set_tablesample_rel_size(root, rel, rte); } else { /* Plain relation */ set_plain_rel_size(root, rel, rte); } break; case RTE_SUBQUERY: /* * Subqueries don't support making a choice between * parameterized and unparameterized paths, so just go ahead * and build their paths immediately. */ set_subquery_pathlist(root, rel, rti, rte); break; case RTE_FUNCTION: set_function_size_estimates(root, rel); break; case RTE_TABLEFUNC: set_tablefunc_size_estimates(root, rel); break; case RTE_VALUES: set_values_size_estimates(root, rel); break; case RTE_CTE: /* * CTEs don't support making a choice between parameterized * and unparameterized paths, so just go ahead and build their * paths immediately. */ if (rte->self_reference) set_worktable_pathlist(root, rel, rte); else set_cte_pathlist(root, rel, rte); break; case RTE_NAMEDTUPLESTORE: /* Might as well just build the path immediately */ set_namedtuplestore_pathlist(root, rel, rte); break; case RTE_RESULT: /* Might as well just build the path immediately */ set_result_pathlist(root, rel, rte); break; default: elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind); break; } } /* * We insist that all non-dummy rels have a nonzero rowcount estimate. */ Assert(rel->rows > 0 || IS_DUMMY_REL(rel)); } /* * set_rel_pathlist * Build access paths for a base relation */ static void set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte) { if (IS_DUMMY_REL(rel)) { /* We already proved the relation empty, so nothing more to do */ } else if (rte->inh) { /* It's an "append relation", process accordingly */ set_append_rel_pathlist(root, rel, rti, rte); } else { switch (rel->rtekind) { case RTE_RELATION: if (rte->relkind == RELKIND_FOREIGN_TABLE) { /* Foreign table */ set_foreign_pathlist(root, rel, rte); } else if (rte->tablesample != NULL) { /* Sampled relation */ set_tablesample_rel_pathlist(root, rel, rte); } else { /* Plain relation */ set_plain_rel_pathlist(root, rel, rte); } break; case RTE_SUBQUERY: /* Subquery --- fully handled during set_rel_size */ break; case RTE_FUNCTION: /* RangeFunction */ set_function_pathlist(root, rel, rte); break; case RTE_TABLEFUNC: /* Table Function */ set_tablefunc_pathlist(root, rel, rte); break; case RTE_VALUES: /* Values list */ set_values_pathlist(root, rel, rte); break; case RTE_CTE: /* CTE reference --- fully handled during set_rel_size */ break; case RTE_NAMEDTUPLESTORE: /* tuplestore reference --- fully handled during set_rel_size */ break; case RTE_RESULT: /* simple Result --- fully handled during set_rel_size */ break; default: elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind); break; } } /* * Allow a plugin to editorialize on the set of Paths for this base * relation. It could add new paths (such as CustomPaths) by calling * add_path(), or add_partial_path() if parallel aware. It could also * delete or modify paths added by the core code. */ if (set_rel_pathlist_hook) (*set_rel_pathlist_hook) (root, rel, rti, rte); /* * If this is a baserel, we should normally consider gathering any partial * paths we may have created for it. We have to do this after calling the * set_rel_pathlist_hook, else it cannot add partial paths to be included * here. * * However, if this is an inheritance child, skip it. Otherwise, we could * end up with a very large number of gather nodes, each trying to grab * its own pool of workers. Instead, we'll consider gathering partial * paths for the parent appendrel. * * Also, if this is the topmost scan/join rel, we postpone gathering until * the final scan/join targetlist is available (see grouping_planner). */ if (rel->reloptkind == RELOPT_BASEREL && !bms_equal(rel->relids, root->all_query_rels)) generate_useful_gather_paths(root, rel, false); /* Now find the cheapest of the paths for this rel */ set_cheapest(rel); #ifdef OPTIMIZER_DEBUG pprint(rel); #endif } /* * set_plain_rel_size * Set size estimates for a plain relation (no subquery, no inheritance) */ static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { /* * Test any partial indexes of rel for applicability. We must do this * first since partial unique indexes can affect size estimates. */ check_index_predicates(root, rel); /* Mark rel with estimated output rows, width, etc */ set_baserel_size_estimates(root, rel); } /* * If this relation could possibly be scanned from within a worker, then set * its consider_parallel flag. */ static void set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { /* * The flag has previously been initialized to false, so we can just * return if it becomes clear that we can't safely set it. */ Assert(!rel->consider_parallel); /* Don't call this if parallelism is disallowed for the entire query. */ Assert(root->glob->parallelModeOK); /* This should only be called for baserels and appendrel children. */ Assert(IS_SIMPLE_REL(rel)); /* Assorted checks based on rtekind. */ switch (rte->rtekind) { case RTE_RELATION: /* * Currently, parallel workers can't access the leader's temporary * tables. We could possibly relax this if we wrote all of its * local buffers at the start of the query and made no changes * thereafter (maybe we could allow hint bit changes), and if we * taught the workers to read them. Writing a large number of * temporary buffers could be expensive, though, and we don't have * the rest of the necessary infrastructure right now anyway. So * for now, bail out if we see a temporary table. */ if (get_rel_persistence(rte->relid) == RELPERSISTENCE_TEMP) return; /* * Table sampling can be pushed down to workers if the sample * function and its arguments are safe. */ if (rte->tablesample != NULL) { char proparallel = func_parallel(rte->tablesample->tsmhandler); if (proparallel != PROPARALLEL_SAFE) return; if (!is_parallel_safe(root, (Node *) rte->tablesample->args)) return; } /* * Ask FDWs whether they can support performing a ForeignScan * within a worker. Most often, the answer will be no. For * example, if the nature of the FDW is such that it opens a TCP * connection with a remote server, each parallel worker would end * up with a separate connection, and these connections might not * be appropriately coordinated between workers and the leader. */ if (rte->relkind == RELKIND_FOREIGN_TABLE) { Assert(rel->fdwroutine); if (!rel->fdwroutine->IsForeignScanParallelSafe) return; if (!rel->fdwroutine->IsForeignScanParallelSafe(root, rel, rte)) return; } /* * There are additional considerations for appendrels, which we'll * deal with in set_append_rel_size and set_append_rel_pathlist. * For now, just set consider_parallel based on the rel's own * quals and targetlist. */ break; case RTE_SUBQUERY: /* * There's no intrinsic problem with scanning a subquery-in-FROM * (as distinct from a SubPlan or InitPlan) in a parallel worker. * If the subquery doesn't happen to have any parallel-safe paths, * then flagging it as consider_parallel won't change anything, * but that's true for plain tables, too. We must set * consider_parallel based on the rel's own quals and targetlist, * so that if a subquery path is parallel-safe but the quals and * projection we're sticking onto it are not, we correctly mark * the SubqueryScanPath as not parallel-safe. (Note that * set_subquery_pathlist() might push some of these quals down * into the subquery itself, but that doesn't change anything.) * * We can't push sub-select containing LIMIT/OFFSET to workers as * there is no guarantee that the row order will be fully * deterministic, and applying LIMIT/OFFSET will lead to * inconsistent results at the top-level. (In some cases, where * the result is ordered, we could relax this restriction. But it * doesn't currently seem worth expending extra effort to do so.) */ { Query *subquery = castNode(Query, rte->subquery); if (limit_needed(subquery)) return; } break; case RTE_JOIN: /* Shouldn't happen; we're only considering baserels here. */ Assert(false); return; case RTE_FUNCTION: /* Check for parallel-restricted functions. */ if (!is_parallel_safe(root, (Node *) rte->functions)) return; break; case RTE_TABLEFUNC: /* not parallel safe */ return; case RTE_VALUES: /* Check for parallel-restricted functions. */ if (!is_parallel_safe(root, (Node *) rte->values_lists)) return; break; case RTE_CTE: /* * CTE tuplestores aren't shared among parallel workers, so we * force all CTE scans to happen in the leader. Also, populating * the CTE would require executing a subplan that's not available * in the worker, might be parallel-restricted, and must get * executed only once. */ return; case RTE_NAMEDTUPLESTORE: /* * tuplestore cannot be shared, at least without more * infrastructure to support that. */ return; case RTE_RESULT: /* RESULT RTEs, in themselves, are no problem. */ break; case RTE_GROUP: /* Shouldn't happen; we're only considering baserels here. */ Assert(false); return; } /* * If there's anything in baserestrictinfo that's parallel-restricted, we * give up on parallelizing access to this relation. We could consider * instead postponing application of the restricted quals until we're * above all the parallelism in the plan tree, but it's not clear that * that would be a win in very many cases, and it might be tricky to make * outer join clauses work correctly. It would likely break equivalence * classes, too. */ if (!is_parallel_safe(root, (Node *) rel->baserestrictinfo)) return; /* * Likewise, if the relation's outputs are not parallel-safe, give up. * (Usually, they're just Vars, but sometimes they're not.) */ if (!is_parallel_safe(root, (Node *) rel->reltarget->exprs)) return; /* We have a winner. */ rel->consider_parallel = true; } /* * set_plain_rel_pathlist * Build access paths for a plain relation (no subquery, no inheritance) */ static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; /* * We don't support pushing join clauses into the quals of a seqscan, but * it could still have required parameterization due to LATERAL refs in * its tlist. */ required_outer = rel->lateral_relids; /* * Consider TID scans. * * If create_tidscan_paths returns true, then a TID scan path is forced. * This happens when rel->baserestrictinfo contains CurrentOfExpr, because * the executor can't handle any other type of path for such queries. * Hence, we return without adding any other paths. */ if (create_tidscan_paths(root, rel)) return; /* Consider sequential scan */ add_path(rel, create_seqscan_path(root, rel, required_outer, 0)); /* If appropriate, consider parallel sequential scan */ if (rel->consider_parallel && required_outer == NULL) create_plain_partial_paths(root, rel); /* Consider index scans */ create_index_paths(root, rel); } /* * create_plain_partial_paths * Build partial access paths for parallel scan of a plain relation */ static void create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel) { int parallel_workers; parallel_workers = compute_parallel_worker(rel, rel->pages, -1, max_parallel_workers_per_gather); /* If any limit was set to zero, the user doesn't want a parallel scan. */ if (parallel_workers <= 0) return; /* Add an unordered partial path based on a parallel sequential scan. */ add_partial_path(rel, create_seqscan_path(root, rel, NULL, parallel_workers)); } /* * set_tablesample_rel_size * Set size estimates for a sampled relation */ static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { TableSampleClause *tsc = rte->tablesample; TsmRoutine *tsm; BlockNumber pages; double tuples; /* * Test any partial indexes of rel for applicability. We must do this * first since partial unique indexes can affect size estimates. */ check_index_predicates(root, rel); /* * Call the sampling method's estimation function to estimate the number * of pages it will read and the number of tuples it will return. (Note: * we assume the function returns sane values.) */ tsm = GetTsmRoutine(tsc->tsmhandler); tsm->SampleScanGetSampleSize(root, rel, tsc->args, &pages, &tuples); /* * For the moment, because we will only consider a SampleScan path for the * rel, it's okay to just overwrite the pages and tuples estimates for the * whole relation. If we ever consider multiple path types for sampled * rels, we'll need more complication. */ rel->pages = pages; rel->tuples = tuples; /* Mark rel with estimated output rows, width, etc */ set_baserel_size_estimates(root, rel); } /* * set_tablesample_rel_pathlist * Build access paths for a sampled relation */ static void set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; Path *path; /* * We don't support pushing join clauses into the quals of a samplescan, * but it could still have required parameterization due to LATERAL refs * in its tlist or TABLESAMPLE arguments. */ required_outer = rel->lateral_relids; /* Consider sampled scan */ path = create_samplescan_path(root, rel, required_outer); /* * If the sampling method does not support repeatable scans, we must avoid * plans that would scan the rel multiple times. Ideally, we'd simply * avoid putting the rel on the inside of a nestloop join; but adding such * a consideration to the planner seems like a great deal of complication * to support an uncommon usage of second-rate sampling methods. Instead, * if there is a risk that the query might perform an unsafe join, just * wrap the SampleScan in a Materialize node. We can check for joins by * counting the membership of all_query_rels (note that this correctly * counts inheritance trees as single rels). If we're inside a subquery, * we can't easily check whether a join might occur in the outer query, so * just assume one is possible. * * GetTsmRoutine is relatively expensive compared to the other tests here, * so check repeatable_across_scans last, even though that's a bit odd. */ if ((root->query_level > 1 || bms_membership(root->all_query_rels) != BMS_SINGLETON) && !(GetTsmRoutine(rte->tablesample->tsmhandler)->repeatable_across_scans)) { path = (Path *) create_material_path(rel, path); } add_path(rel, path); /* For the moment, at least, there are no other paths to consider */ } /* * set_foreign_size * Set size estimates for a foreign table RTE */ static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { /* Mark rel with estimated output rows, width, etc */ set_foreign_size_estimates(root, rel); /* Let FDW adjust the size estimates, if it can */ rel->fdwroutine->GetForeignRelSize(root, rel, rte->relid); /* ... but do not let it set the rows estimate to zero */ rel->rows = clamp_row_est(rel->rows); /* * Also, make sure rel->tuples is not insane relative to rel->rows. * Notably, this ensures sanity if pg_class.reltuples contains -1 and the * FDW doesn't do anything to replace that. */ rel->tuples = Max(rel->tuples, rel->rows); } /* * set_foreign_pathlist * Build access paths for a foreign table RTE */ static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { /* Call the FDW's GetForeignPaths function to generate path(s) */ rel->fdwroutine->GetForeignPaths(root, rel, rte->relid); } /* * set_append_rel_size * Set size estimates for a simple "append relation" * * The passed-in rel and RTE represent the entire append relation. The * relation's contents are computed by appending together the output of the * individual member relations. Note that in the non-partitioned inheritance * case, the first member relation is actually the same table as is mentioned * in the parent RTE ... but it has a different RTE and RelOptInfo. This is * a good thing because their outputs are not the same size. */ static void set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte) { int parentRTindex = rti; bool has_live_children; double parent_tuples; double parent_rows; double parent_size; double *parent_attrsizes; int nattrs; ListCell *l; /* Guard against stack overflow due to overly deep inheritance tree. */ check_stack_depth(); Assert(IS_SIMPLE_REL(rel)); /* * If this is a partitioned baserel, set the consider_partitionwise_join * flag; currently, we only consider partitionwise joins with the baserel * if its targetlist doesn't contain a whole-row Var. */ if (enable_partitionwise_join && rel->reloptkind == RELOPT_BASEREL && rte->relkind == RELKIND_PARTITIONED_TABLE && bms_is_empty(rel->attr_needed[InvalidAttrNumber - rel->min_attr])) rel->consider_partitionwise_join = true; /* * Initialize to compute size estimates for whole append relation. * * We handle tuples estimates by setting "tuples" to the total number of * tuples accumulated from each live child, rather than using "rows". * Although an appendrel itself doesn't directly enforce any quals, its * child relations may. Therefore, setting "tuples" equal to "rows" for * an appendrel isn't always appropriate, and can lead to inaccurate cost * estimates. For example, when estimating the number of distinct values * from an appendrel, we would be unable to adjust the estimate based on * the restriction selectivity (see estimate_num_groups). * * We handle width estimates by weighting the widths of different child * rels proportionally to their number of rows. This is sensible because * the use of width estimates is mainly to compute the total relation * "footprint" if we have to sort or hash it. To do this, we sum the * total equivalent size (in "double" arithmetic) and then divide by the * total rowcount estimate. This is done separately for the total rel * width and each attribute. * * Note: if you consider changing this logic, beware that child rels could * have zero rows and/or width, if they were excluded by constraints. */ has_live_children = false; parent_tuples = 0; parent_rows = 0; parent_size = 0; nattrs = rel->max_attr - rel->min_attr + 1; parent_attrsizes = (double *) palloc0(nattrs * sizeof(double)); foreach(l, root->append_rel_list) { AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l); int childRTindex; RangeTblEntry *childRTE; RelOptInfo *childrel; List *childrinfos; ListCell *parentvars; ListCell *childvars; ListCell *lc; /* append_rel_list contains all append rels; ignore others */ if (appinfo->parent_relid != parentRTindex) continue; childRTindex = appinfo->child_relid; childRTE = root->simple_rte_array[childRTindex]; /* * The child rel's RelOptInfo was already created during * add_other_rels_to_query. */ childrel = find_base_rel(root, childRTindex); Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL); /* We may have already proven the child to be dummy. */ if (IS_DUMMY_REL(childrel)) continue; /* * We have to copy the parent's targetlist and quals to the child, * with appropriate substitution of variables. However, the * baserestrictinfo quals were already copied/substituted when the * child RelOptInfo was built. So we don't need any additional setup * before applying constraint exclusion. */ if (relation_excluded_by_constraints(root, childrel, childRTE)) { /* * This child need not be scanned, so we can omit it from the * appendrel. */ set_dummy_rel_pathlist(childrel); continue; } /* * Constraint exclusion failed, so copy the parent's join quals and * targetlist to the child, with appropriate variable substitutions. * * We skip join quals that came from above outer joins that can null * this rel, since they would be of no value while generating paths * for the child. This saves some effort while processing the child * rel, and it also avoids an implementation restriction in * adjust_appendrel_attrs (it can't apply nullingrels to a non-Var). */ childrinfos = NIL; foreach(lc, rel->joininfo) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc); if (!bms_overlap(rinfo->clause_relids, rel->nulling_relids)) childrinfos = lappend(childrinfos, adjust_appendrel_attrs(root, (Node *) rinfo, 1, &appinfo)); } childrel->joininfo = childrinfos; /* * Now for the child's targetlist. * * NB: the resulting childrel->reltarget->exprs may contain arbitrary * expressions, which otherwise would not occur in a rel's targetlist. * Code that might be looking at an appendrel child must cope with * such. (Normally, a rel's targetlist would only include Vars and * PlaceHolderVars.) XXX we do not bother to update the cost or width * fields of childrel->reltarget; not clear if that would be useful. */ childrel->reltarget->exprs = (List *) adjust_appendrel_attrs(root, (Node *) rel->reltarget->exprs, 1, &appinfo); /* * We have to make child entries in the EquivalenceClass data * structures as well. This is needed either if the parent * participates in some eclass joins (because we will want to consider * inner-indexscan joins on the individual children) or if the parent * has useful pathkeys (because we should try to build MergeAppend * paths that produce those sort orderings). */ if (rel->has_eclass_joins || has_useful_pathkeys(root, rel)) add_child_rel_equivalences(root, appinfo, rel, childrel); childrel->has_eclass_joins = rel->has_eclass_joins; /* * Note: we could compute appropriate attr_needed data for the child's * variables, by transforming the parent's attr_needed through the * translated_vars mapping. However, currently there's no need * because attr_needed is only examined for base relations not * otherrels. So we just leave the child's attr_needed empty. */ /* * If we consider partitionwise joins with the parent rel, do the same * for partitioned child rels. * * Note: here we abuse the consider_partitionwise_join flag by setting * it for child rels that are not themselves partitioned. We do so to * tell try_partitionwise_join() that the child rel is sufficiently * valid to be used as a per-partition input, even if it later gets * proven to be dummy. (It's not usable until we've set up the * reltarget and EC entries, which we just did.) */ if (rel->consider_partitionwise_join) childrel->consider_partitionwise_join = true; /* * If parallelism is allowable for this query in general, see whether * it's allowable for this childrel in particular. But if we've * already decided the appendrel is not parallel-safe as a whole, * there's no point in considering parallelism for this child. For * consistency, do this before calling set_rel_size() for the child. */ if (root->glob->parallelModeOK && rel->consider_parallel) set_rel_consider_parallel(root, childrel, childRTE); /* * Compute the child's size. */ set_rel_size(root, childrel, childRTindex, childRTE); /* * It is possible that constraint exclusion detected a contradiction * within a child subquery, even though we didn't prove one above. If * so, we can skip this child. */ if (IS_DUMMY_REL(childrel)) continue; /* We have at least one live child. */ has_live_children = true; /* * If any live child is not parallel-safe, treat the whole appendrel * as not parallel-safe. In future we might be able to generate plans * in which some children are farmed out to workers while others are * not; but we don't have that today, so it's a waste to consider * partial paths anywhere in the appendrel unless it's all safe. * (Child rels visited before this one will be unmarked in * set_append_rel_pathlist().) */ if (!childrel->consider_parallel) rel->consider_parallel = false; /* * Accumulate size information from each live child. */ Assert(childrel->rows > 0); parent_tuples += childrel->tuples; parent_rows += childrel->rows; parent_size += childrel->reltarget->width * childrel->rows; /* * Accumulate per-column estimates too. We need not do anything for * PlaceHolderVars in the parent list. If child expression isn't a * Var, or we didn't record a width estimate for it, we have to fall * back on a datatype-based estimate. * * By construction, child's targetlist is 1-to-1 with parent's. */ forboth(parentvars, rel->reltarget->exprs, childvars, childrel->reltarget->exprs) { Var *parentvar = (Var *) lfirst(parentvars); Node *childvar = (Node *) lfirst(childvars); if (IsA(parentvar, Var) && parentvar->varno == parentRTindex) { int pndx = parentvar->varattno - rel->min_attr; int32 child_width = 0; if (IsA(childvar, Var) && ((Var *) childvar)->varno == childrel->relid) { int cndx = ((Var *) childvar)->varattno - childrel->min_attr; child_width = childrel->attr_widths[cndx]; } if (child_width <= 0) child_width = get_typavgwidth(exprType(childvar), exprTypmod(childvar)); Assert(child_width > 0); parent_attrsizes[pndx] += child_width * childrel->rows; } } } if (has_live_children) { /* * Save the finished size estimates. */ int i; Assert(parent_rows > 0); rel->tuples = parent_tuples; rel->rows = parent_rows; rel->reltarget->width = rint(parent_size / parent_rows); for (i = 0; i < nattrs; i++) rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows); /* * Note that we leave rel->pages as zero; this is important to avoid * double-counting the appendrel tree in total_table_pages. */ } else { /* * All children were excluded by constraints, so mark the whole * appendrel dummy. We must do this in this phase so that the rel's * dummy-ness is visible when we generate paths for other rels. */ set_dummy_rel_pathlist(rel); } pfree(parent_attrsizes); } /* * set_append_rel_pathlist * Build access paths for an "append relation" */ static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte) { int parentRTindex = rti; List *live_childrels = NIL; ListCell *l; /* * Generate access paths for each member relation, and remember the * non-dummy children. */ foreach(l, root->append_rel_list) { AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l); int childRTindex; RangeTblEntry *childRTE; RelOptInfo *childrel; /* append_rel_list contains all append rels; ignore others */ if (appinfo->parent_relid != parentRTindex) continue; /* Re-locate the child RTE and RelOptInfo */ childRTindex = appinfo->child_relid; childRTE = root->simple_rte_array[childRTindex]; childrel = root->simple_rel_array[childRTindex]; /* * If set_append_rel_size() decided the parent appendrel was * parallel-unsafe at some point after visiting this child rel, we * need to propagate the unsafety marking down to the child, so that * we don't generate useless partial paths for it. */ if (!rel->consider_parallel) childrel->consider_parallel = false; /* * Compute the child's access paths. */ set_rel_pathlist(root, childrel, childRTindex, childRTE); /* * If child is dummy, ignore it. */ if (IS_DUMMY_REL(childrel)) continue; /* * Child is live, so add it to the live_childrels list for use below. */ live_childrels = lappend(live_childrels, childrel); } /* Add paths to the append relation. */ add_paths_to_append_rel(root, rel, live_childrels); } /* * add_paths_to_append_rel * Generate paths for the given append relation given the set of non-dummy * child rels. * * The function collects all parameterizations and orderings supported by the * non-dummy children. For every such parameterization or ordering, it creates * an append path collecting one path from each non-dummy child with given * parameterization or ordering. Similarly it collects partial paths from * non-dummy children to create partial append paths. */ void add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel, List *live_childrels) { List *subpaths = NIL; bool subpaths_valid = true; List *startup_subpaths = NIL; bool startup_subpaths_valid = true; List *partial_subpaths = NIL; List *pa_partial_subpaths = NIL; List *pa_nonpartial_subpaths = NIL; bool partial_subpaths_valid = true; bool pa_subpaths_valid; List *all_child_pathkeys = NIL; List *all_child_outers = NIL; ListCell *l; double partial_rows = -1; /* If appropriate, consider parallel append */ pa_subpaths_valid = enable_parallel_append && rel->consider_parallel; /* * For every non-dummy child, remember the cheapest path. Also, identify * all pathkeys (orderings) and parameterizations (required_outer sets) * available for the non-dummy member relations. */ foreach(l, live_childrels) { RelOptInfo *childrel = lfirst(l); ListCell *lcp; Path *cheapest_partial_path = NULL; /* * If child has an unparameterized cheapest-total path, add that to * the unparameterized Append path we are constructing for the parent. * If not, there's no workable unparameterized path. * * With partitionwise aggregates, the child rel's pathlist may be * empty, so don't assume that a path exists here. */ if (childrel->pathlist != NIL && childrel->cheapest_total_path->param_info == NULL) accumulate_append_subpath(childrel->cheapest_total_path, &subpaths, NULL); else subpaths_valid = false; /* * When the planner is considering cheap startup plans, we'll also * collect all the cheapest_startup_paths (if set) and build an * AppendPath containing those as subpaths. */ if (rel->consider_startup && childrel->cheapest_startup_path != NULL) { Path *cheapest_path; /* * With an indication of how many tuples the query should provide, * the optimizer tries to choose the path optimal for that * specific number of tuples. */ if (root->tuple_fraction > 0.0) cheapest_path = get_cheapest_fractional_path(childrel, root->tuple_fraction); else cheapest_path = childrel->cheapest_startup_path; /* cheapest_startup_path must not be a parameterized path. */ Assert(cheapest_path->param_info == NULL); accumulate_append_subpath(cheapest_path, &startup_subpaths, NULL); } else startup_subpaths_valid = false; /* Same idea, but for a partial plan. */ if (childrel->partial_pathlist != NIL) { cheapest_partial_path = linitial(childrel->partial_pathlist); accumulate_append_subpath(cheapest_partial_path, &partial_subpaths, NULL); } else partial_subpaths_valid = false; /* * Same idea, but for a parallel append mixing partial and non-partial * paths. */ if (pa_subpaths_valid) { Path *nppath = NULL; nppath = get_cheapest_parallel_safe_total_inner(childrel->pathlist); if (cheapest_partial_path == NULL && nppath == NULL) { /* Neither a partial nor a parallel-safe path? Forget it. */ pa_subpaths_valid = false; } else if (nppath == NULL || (cheapest_partial_path != NULL && cheapest_partial_path->total_cost < nppath->total_cost)) { /* Partial path is cheaper or the only option. */ Assert(cheapest_partial_path != NULL); accumulate_append_subpath(cheapest_partial_path, &pa_partial_subpaths, &pa_nonpartial_subpaths); } else { /* * Either we've got only a non-partial path, or we think that * a single backend can execute the best non-partial path * faster than all the parallel backends working together can * execute the best partial path. * * It might make sense to be more aggressive here. Even if * the best non-partial path is more expensive than the best * partial path, it could still be better to choose the * non-partial path if there are several such paths that can * be given to different workers. For now, we don't try to * figure that out. */ accumulate_append_subpath(nppath, &pa_nonpartial_subpaths, NULL); } } /* * Collect lists of all the available path orderings and * parameterizations for all the children. We use these as a * heuristic to indicate which sort orderings and parameterizations we * should build Append and MergeAppend paths for. */ foreach(lcp, childrel->pathlist) { Path *childpath = (Path *) lfirst(lcp); List *childkeys = childpath->pathkeys; Relids childouter = PATH_REQ_OUTER(childpath); /* Unsorted paths don't contribute to pathkey list */ if (childkeys != NIL) { ListCell *lpk; bool found = false; /* Have we already seen this ordering? */ foreach(lpk, all_child_pathkeys) { List *existing_pathkeys = (List *) lfirst(lpk); if (compare_pathkeys(existing_pathkeys, childkeys) == PATHKEYS_EQUAL) { found = true; break; } } if (!found) { /* No, so add it to all_child_pathkeys */ all_child_pathkeys = lappend(all_child_pathkeys, childkeys); } } /* Unparameterized paths don't contribute to param-set list */ if (childouter) { ListCell *lco; bool found = false; /* Have we already seen this param set? */ foreach(lco, all_child_outers) { Relids existing_outers = (Relids) lfirst(lco); if (bms_equal(existing_outers, childouter)) { found = true; break; } } if (!found) { /* No, so add it to all_child_outers */ all_child_outers = lappend(all_child_outers, childouter); } } } } /* * If we found unparameterized paths for all children, build an unordered, * unparameterized Append path for the rel. (Note: this is correct even * if we have zero or one live subpath due to constraint exclusion.) */ if (subpaths_valid) add_path(rel, (Path *) create_append_path(root, rel, subpaths, NIL, NIL, NULL, 0, false, -1)); /* build an AppendPath for the cheap startup paths, if valid */ if (startup_subpaths_valid) add_path(rel, (Path *) create_append_path(root, rel, startup_subpaths, NIL, NIL, NULL, 0, false, -1)); /* * Consider an append of unordered, unparameterized partial paths. Make * it parallel-aware if possible. */ if (partial_subpaths_valid && partial_subpaths != NIL) { AppendPath *appendpath; ListCell *lc; int parallel_workers = 0; /* Find the highest number of workers requested for any subpath. */ foreach(lc, partial_subpaths) { Path *path = lfirst(lc); parallel_workers = Max(parallel_workers, path->parallel_workers); } Assert(parallel_workers > 0); /* * If the use of parallel append is permitted, always request at least * log2(# of children) workers. We assume it can be useful to have * extra workers in this case because they will be spread out across * the children. The precise formula is just a guess, but we don't * want to end up with a radically different answer for a table with N * partitions vs. an unpartitioned table with the same data, so the * use of some kind of log-scaling here seems to make some sense. */ if (enable_parallel_append) { parallel_workers = Max(parallel_workers, pg_leftmost_one_pos32(list_length(live_childrels)) + 1); parallel_workers = Min(parallel_workers, max_parallel_workers_per_gather); } Assert(parallel_workers > 0); /* Generate a partial append path. */ appendpath = create_append_path(root, rel, NIL, partial_subpaths, NIL, NULL, parallel_workers, enable_parallel_append, -1); /* * Make sure any subsequent partial paths use the same row count * estimate. */ partial_rows = appendpath->path.rows; /* Add the path. */ add_partial_path(rel, (Path *) appendpath); } /* * Consider a parallel-aware append using a mix of partial and non-partial * paths. (This only makes sense if there's at least one child which has * a non-partial path that is substantially cheaper than any partial path; * otherwise, we should use the append path added in the previous step.) */ if (pa_subpaths_valid && pa_nonpartial_subpaths != NIL) { AppendPath *appendpath; ListCell *lc; int parallel_workers = 0; /* * Find the highest number of workers requested for any partial * subpath. */ foreach(lc, pa_partial_subpaths) { Path *path = lfirst(lc); parallel_workers = Max(parallel_workers, path->parallel_workers); } /* * Same formula here as above. It's even more important in this * instance because the non-partial paths won't contribute anything to * the planned number of parallel workers. */ parallel_workers = Max(parallel_workers, pg_leftmost_one_pos32(list_length(live_childrels)) + 1); parallel_workers = Min(parallel_workers, max_parallel_workers_per_gather); Assert(parallel_workers > 0); appendpath = create_append_path(root, rel, pa_nonpartial_subpaths, pa_partial_subpaths, NIL, NULL, parallel_workers, true, partial_rows); add_partial_path(rel, (Path *) appendpath); } /* * Also build unparameterized ordered append paths based on the collected * list of child pathkeys. */ if (subpaths_valid) generate_orderedappend_paths(root, rel, live_childrels, all_child_pathkeys); /* * Build Append paths for each parameterization seen among the child rels. * (This may look pretty expensive, but in most cases of practical * interest, the child rels will expose mostly the same parameterizations, * so that not that many cases actually get considered here.) * * The Append node itself cannot enforce quals, so all qual checking must * be done in the child paths. This means that to have a parameterized * Append path, we must have the exact same parameterization for each * child path; otherwise some children might be failing to check the * moved-down quals. To make them match up, we can try to increase the * parameterization of lesser-parameterized paths. */ foreach(l, all_child_outers) { Relids required_outer = (Relids) lfirst(l); ListCell *lcr; /* Select the child paths for an Append with this parameterization */ subpaths = NIL; subpaths_valid = true; foreach(lcr, live_childrels) { RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr); Path *subpath; if (childrel->pathlist == NIL) { /* failed to make a suitable path for this child */ subpaths_valid = false; break; } subpath = get_cheapest_parameterized_child_path(root, childrel, required_outer); if (subpath == NULL) { /* failed to make a suitable path for this child */ subpaths_valid = false; break; } accumulate_append_subpath(subpath, &subpaths, NULL); } if (subpaths_valid) add_path(rel, (Path *) create_append_path(root, rel, subpaths, NIL, NIL, required_outer, 0, false, -1)); } /* * When there is only a single child relation, the Append path can inherit * any ordering available for the child rel's path, so that it's useful to * consider ordered partial paths. Above we only considered the cheapest * partial path for each child, but let's also make paths using any * partial paths that have pathkeys. */ if (list_length(live_childrels) == 1) { RelOptInfo *childrel = (RelOptInfo *) linitial(live_childrels); /* skip the cheapest partial path, since we already used that above */ for_each_from(l, childrel->partial_pathlist, 1) { Path *path = (Path *) lfirst(l); AppendPath *appendpath; /* skip paths with no pathkeys. */ if (path->pathkeys == NIL) continue; appendpath = create_append_path(root, rel, NIL, list_make1(path), NIL, NULL, path->parallel_workers, true, partial_rows); add_partial_path(rel, (Path *) appendpath); } } } /* * generate_orderedappend_paths * Generate ordered append paths for an append relation * * Usually we generate MergeAppend paths here, but there are some special * cases where we can generate simple Append paths, because the subpaths * can provide tuples in the required order already. * * We generate a path for each ordering (pathkey list) appearing in * all_child_pathkeys. * * We consider both cheapest-startup and cheapest-total cases, ie, for each * interesting ordering, collect all the cheapest startup subpaths and all the * cheapest total paths, and build a suitable path for each case. * * We don't currently generate any parameterized ordered paths here. While * it would not take much more code here to do so, it's very unclear that it * is worth the planning cycles to investigate such paths: there's little * use for an ordered path on the inside of a nestloop. In fact, it's likely * that the current coding of add_path would reject such paths out of hand, * because add_path gives no credit for sort ordering of parameterized paths, * and a parameterized MergeAppend is going to be more expensive than the * corresponding parameterized Append path. If we ever try harder to support * parameterized mergejoin plans, it might be worth adding support for * parameterized paths here to feed such joins. (See notes in * optimizer/README for why that might not ever happen, though.) */ static void generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, List *live_childrels, List *all_child_pathkeys) { ListCell *lcp; List *partition_pathkeys = NIL; List *partition_pathkeys_desc = NIL; bool partition_pathkeys_partial = true; bool partition_pathkeys_desc_partial = true; /* * Some partitioned table setups may allow us to use an Append node * instead of a MergeAppend. This is possible in cases such as RANGE * partitioned tables where it's guaranteed that an earlier partition must * contain rows which come earlier in the sort order. To detect whether * this is relevant, build pathkey descriptions of the partition ordering, * for both forward and reverse scans. */ if (rel->part_scheme != NULL && IS_SIMPLE_REL(rel) && partitions_are_ordered(rel->boundinfo, rel->live_parts)) { partition_pathkeys = build_partition_pathkeys(root, rel, ForwardScanDirection, &partition_pathkeys_partial); partition_pathkeys_desc = build_partition_pathkeys(root, rel, BackwardScanDirection, &partition_pathkeys_desc_partial); /* * You might think we should truncate_useless_pathkeys here, but * allowing partition keys which are a subset of the query's pathkeys * can often be useful. For example, consider a table partitioned by * RANGE (a, b), and a query with ORDER BY a, b, c. If we have child * paths that can produce the a, b, c ordering (perhaps via indexes on * (a, b, c)) then it works to consider the appendrel output as * ordered by a, b, c. */ } /* Now consider each interesting sort ordering */ foreach(lcp, all_child_pathkeys) { List *pathkeys = (List *) lfirst(lcp); List *startup_subpaths = NIL; List *total_subpaths = NIL; List *fractional_subpaths = NIL; bool startup_neq_total = false; bool match_partition_order; bool match_partition_order_desc; int end_index; int first_index; int direction; /* * Determine if this sort ordering matches any partition pathkeys we * have, for both ascending and descending partition order. If the * partition pathkeys happen to be contained in pathkeys then it still * works, as described above, providing that the partition pathkeys * are complete and not just a prefix of the partition keys. (In such * cases we'll be relying on the child paths to have sorted the * lower-order columns of the required pathkeys.) */ match_partition_order = pathkeys_contained_in(pathkeys, partition_pathkeys) || (!partition_pathkeys_partial && pathkeys_contained_in(partition_pathkeys, pathkeys)); match_partition_order_desc = !match_partition_order && (pathkeys_contained_in(pathkeys, partition_pathkeys_desc) || (!partition_pathkeys_desc_partial && pathkeys_contained_in(partition_pathkeys_desc, pathkeys))); /* * When the required pathkeys match the reverse of the partition * order, we must build the list of paths in reverse starting with the * last matching partition first. We can get away without making any * special cases for this in the loop below by just looping backward * over the child relations in this case. */ if (match_partition_order_desc) { /* loop backward */ first_index = list_length(live_childrels) - 1; end_index = -1; direction = -1; /* * Set this to true to save us having to check for * match_partition_order_desc in the loop below. */ match_partition_order = true; } else { /* for all other case, loop forward */ first_index = 0; end_index = list_length(live_childrels); direction = 1; } /* Select the child paths for this ordering... */ for (int i = first_index; i != end_index; i += direction) { RelOptInfo *childrel = list_nth_node(RelOptInfo, live_childrels, i); Path *cheapest_startup, *cheapest_total, *cheapest_fractional = NULL; /* Locate the right paths, if they are available. */ cheapest_startup = get_cheapest_path_for_pathkeys(childrel->pathlist, pathkeys, NULL, STARTUP_COST, false); cheapest_total = get_cheapest_path_for_pathkeys(childrel->pathlist, pathkeys, NULL, TOTAL_COST, false); /* * If we can't find any paths with the right order just use the * cheapest-total path; we'll have to sort it later. */ if (cheapest_startup == NULL || cheapest_total == NULL) { cheapest_startup = cheapest_total = childrel->cheapest_total_path; /* Assert we do have an unparameterized path for this child */ Assert(cheapest_total->param_info == NULL); } /* * When building a fractional path, determine a cheapest * fractional path for each child relation too. Looking at startup * and total costs is not enough, because the cheapest fractional * path may be dominated by two separate paths (one for startup, * one for total). * * When needed (building fractional path), determine the cheapest * fractional path too. */ if (root->tuple_fraction > 0) { double path_fraction = root->tuple_fraction; /* * Merge Append considers only live children relations. Dummy * relations must be filtered out before. */ Assert(childrel->rows > 0); /* Convert absolute limit to a path fraction */ if (path_fraction >= 1.0) path_fraction /= childrel->rows; cheapest_fractional = get_cheapest_fractional_path_for_pathkeys(childrel->pathlist, pathkeys, NULL, path_fraction); /* * If we found no path with matching pathkeys, use the * cheapest total path instead. * * XXX We might consider partially sorted paths too (with an * incremental sort on top). But we'd have to build all the * incremental paths, do the costing etc. */ if (!cheapest_fractional) cheapest_fractional = cheapest_total; } /* * Notice whether we actually have different paths for the * "cheapest" and "total" cases; frequently there will be no point * in two create_merge_append_path() calls. */ if (cheapest_startup != cheapest_total) startup_neq_total = true; /* * Collect the appropriate child paths. The required logic varies * for the Append and MergeAppend cases. */ if (match_partition_order) { /* * We're going to make a plain Append path. We don't need * most of what accumulate_append_subpath would do, but we do * want to cut out child Appends or MergeAppends if they have * just a single subpath (and hence aren't doing anything * useful). */ cheapest_startup = get_singleton_append_subpath(cheapest_startup); cheapest_total = get_singleton_append_subpath(cheapest_total); startup_subpaths = lappend(startup_subpaths, cheapest_startup); total_subpaths = lappend(total_subpaths, cheapest_total); if (cheapest_fractional) { cheapest_fractional = get_singleton_append_subpath(cheapest_fractional); fractional_subpaths = lappend(fractional_subpaths, cheapest_fractional); } } else { /* * Otherwise, rely on accumulate_append_subpath to collect the * child paths for the MergeAppend. */ accumulate_append_subpath(cheapest_startup, &startup_subpaths, NULL); accumulate_append_subpath(cheapest_total, &total_subpaths, NULL); if (cheapest_fractional) accumulate_append_subpath(cheapest_fractional, &fractional_subpaths, NULL); } } /* ... and build the Append or MergeAppend paths */ if (match_partition_order) { /* We only need Append */ add_path(rel, (Path *) create_append_path(root, rel, startup_subpaths, NIL, pathkeys, NULL, 0, false, -1)); if (startup_neq_total) add_path(rel, (Path *) create_append_path(root, rel, total_subpaths, NIL, pathkeys, NULL, 0, false, -1)); if (fractional_subpaths) add_path(rel, (Path *) create_append_path(root, rel, fractional_subpaths, NIL, pathkeys, NULL, 0, false, -1)); } else { /* We need MergeAppend */ add_path(rel, (Path *) create_merge_append_path(root, rel, startup_subpaths, pathkeys, NULL)); if (startup_neq_total) add_path(rel, (Path *) create_merge_append_path(root, rel, total_subpaths, pathkeys, NULL)); if (fractional_subpaths) add_path(rel, (Path *) create_merge_append_path(root, rel, fractional_subpaths, pathkeys, NULL)); } } } /* * get_cheapest_parameterized_child_path * Get cheapest path for this relation that has exactly the requested * parameterization. * * Returns NULL if unable to create such a path. */ static Path * get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer) { Path *cheapest; ListCell *lc; /* * Look up the cheapest existing path with no more than the needed * parameterization. If it has exactly the needed parameterization, we're * done. */ cheapest = get_cheapest_path_for_pathkeys(rel->pathlist, NIL, required_outer, TOTAL_COST, false); Assert(cheapest != NULL); if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer)) return cheapest; /* * Otherwise, we can "reparameterize" an existing path to match the given * parameterization, which effectively means pushing down additional * joinquals to be checked within the path's scan. However, some existing * paths might check the available joinquals already while others don't; * therefore, it's not clear which existing path will be cheapest after * reparameterization. We have to go through them all and find out. */ cheapest = NULL; foreach(lc, rel->pathlist) { Path *path = (Path *) lfirst(lc); /* Can't use it if it needs more than requested parameterization */ if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer)) continue; /* * Reparameterization can only increase the path's cost, so if it's * already more expensive than the current cheapest, forget it. */ if (cheapest != NULL && compare_path_costs(cheapest, path, TOTAL_COST) <= 0) continue; /* Reparameterize if needed, then recheck cost */ if (!bms_equal(PATH_REQ_OUTER(path), required_outer)) { path = reparameterize_path(root, path, required_outer, 1.0); if (path == NULL) continue; /* failed to reparameterize this one */ Assert(bms_equal(PATH_REQ_OUTER(path), required_outer)); if (cheapest != NULL && compare_path_costs(cheapest, path, TOTAL_COST) <= 0) continue; } /* We have a new best path */ cheapest = path; } /* Return the best path, or NULL if we found no suitable candidate */ return cheapest; } /* * accumulate_append_subpath * Add a subpath to the list being built for an Append or MergeAppend. * * It's possible that the child is itself an Append or MergeAppend path, in * which case we can "cut out the middleman" and just add its child paths to * our own list. (We don't try to do this earlier because we need to apply * both levels of transformation to the quals.) * * Note that if we omit a child MergeAppend in this way, we are effectively * omitting a sort step, which seems fine: if the parent is to be an Append, * its result would be unsorted anyway, while if the parent is to be a * MergeAppend, there's no point in a separate sort on a child. * * Normally, either path is a partial path and subpaths is a list of partial * paths, or else path is a non-partial plan and subpaths is a list of those. * However, if path is a parallel-aware Append, then we add its partial path * children to subpaths and the rest to special_subpaths. If the latter is * NULL, we don't flatten the path at all (unless it contains only partial * paths). */ static void accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths) { if (IsA(path, AppendPath)) { AppendPath *apath = (AppendPath *) path; if (!apath->path.parallel_aware || apath->first_partial_path == 0) { *subpaths = list_concat(*subpaths, apath->subpaths); return; } else if (special_subpaths != NULL) { List *new_special_subpaths; /* Split Parallel Append into partial and non-partial subpaths */ *subpaths = list_concat(*subpaths, list_copy_tail(apath->subpaths, apath->first_partial_path)); new_special_subpaths = list_copy_head(apath->subpaths, apath->first_partial_path); *special_subpaths = list_concat(*special_subpaths, new_special_subpaths); return; } } else if (IsA(path, MergeAppendPath)) { MergeAppendPath *mpath = (MergeAppendPath *) path; *subpaths = list_concat(*subpaths, mpath->subpaths); return; } *subpaths = lappend(*subpaths, path); } /* * get_singleton_append_subpath * Returns the single subpath of an Append/MergeAppend, or just * return 'path' if it's not a single sub-path Append/MergeAppend. * * Note: 'path' must not be a parallel-aware path. */ static Path * get_singleton_append_subpath(Path *path) { Assert(!path->parallel_aware); if (IsA(path, AppendPath)) { AppendPath *apath = (AppendPath *) path; if (list_length(apath->subpaths) == 1) return (Path *) linitial(apath->subpaths); } else if (IsA(path, MergeAppendPath)) { MergeAppendPath *mpath = (MergeAppendPath *) path; if (list_length(mpath->subpaths) == 1) return (Path *) linitial(mpath->subpaths); } return path; } /* * set_dummy_rel_pathlist * Build a dummy path for a relation that's been excluded by constraints * * Rather than inventing a special "dummy" path type, we represent this as an * AppendPath with no members (see also IS_DUMMY_APPEND/IS_DUMMY_REL macros). * * (See also mark_dummy_rel, which does basically the same thing, but is * typically used to change a rel into dummy state after we already made * paths for it.) */ static void set_dummy_rel_pathlist(RelOptInfo *rel) { /* Set dummy size estimates --- we leave attr_widths[] as zeroes */ rel->rows = 0; rel->reltarget->width = 0; /* Discard any pre-existing paths; no further need for them */ rel->pathlist = NIL; rel->partial_pathlist = NIL; /* Set up the dummy path */ add_path(rel, (Path *) create_append_path(NULL, rel, NIL, NIL, NIL, rel->lateral_relids, 0, false, -1)); /* * We set the cheapest-path fields immediately, just in case they were * pointing at some discarded path. This is redundant in current usage * because set_rel_pathlist will do it later, but it's cheap so we keep it * for safety and consistency with mark_dummy_rel. */ set_cheapest(rel); } /* * find_window_run_conditions * Determine if 'wfunc' is really a WindowFunc and call its prosupport * function to determine the function's monotonic properties. We then * see if 'opexpr' can be used to short-circuit execution. * * For example row_number() over (order by ...) always produces a value one * higher than the previous. If someone has a window function in a subquery * and has a WHERE clause in the outer query to filter rows <= 10, then we may * as well stop processing the windowagg once the row number reaches 11. Here * we check if 'opexpr' might help us to stop doing needless extra processing * in WindowAgg nodes. * * '*keep_original' is set to true if the caller should also use 'opexpr' for * its original purpose. This is set to false if the caller can assume that * the run condition will handle all of the required filtering. * * Returns true if 'opexpr' was found to be useful and was added to the * WindowFunc's runCondition. We also set *keep_original accordingly and add * 'attno' to *run_cond_attrs offset by FirstLowInvalidHeapAttributeNumber. * If the 'opexpr' cannot be used then we set *keep_original to true and * return false. */ static bool find_window_run_conditions(Query *subquery, RangeTblEntry *rte, Index rti, AttrNumber attno, WindowFunc *wfunc, OpExpr *opexpr, bool wfunc_left, bool *keep_original, Bitmapset **run_cond_attrs) { Oid prosupport; Expr *otherexpr; SupportRequestWFuncMonotonic req; SupportRequestWFuncMonotonic *res; WindowClause *wclause; List *opinfos; OpExpr *runopexpr; Oid runoperator; ListCell *lc; *keep_original = true; while (IsA(wfunc, RelabelType)) wfunc = (WindowFunc *) ((RelabelType *) wfunc)->arg; /* we can only work with window functions */ if (!IsA(wfunc, WindowFunc)) return false; /* can't use it if there are subplans in the WindowFunc */ if (contain_subplans((Node *) wfunc)) return false; prosupport = get_func_support(wfunc->winfnoid); /* Check if there's a support function for 'wfunc' */ if (!OidIsValid(prosupport)) return false; /* get the Expr from the other side of the OpExpr */ if (wfunc_left) otherexpr = lsecond(opexpr->args); else otherexpr = linitial(opexpr->args); /* * The value being compared must not change during the evaluation of the * window partition. */ if (!is_pseudo_constant_clause((Node *) otherexpr)) return false; /* find the window clause belonging to the window function */ wclause = (WindowClause *) list_nth(subquery->windowClause, wfunc->winref - 1); req.type = T_SupportRequestWFuncMonotonic; req.window_func = wfunc; req.window_clause = wclause; /* call the support function */ res = (SupportRequestWFuncMonotonic *) DatumGetPointer(OidFunctionCall1(prosupport, PointerGetDatum(&req))); /* * Nothing to do if the function is neither monotonically increasing nor * monotonically decreasing. */ if (res == NULL || res->monotonic == MONOTONICFUNC_NONE) return false; runopexpr = NULL; runoperator = InvalidOid; opinfos = get_op_index_interpretation(opexpr->opno); foreach(lc, opinfos) { OpIndexInterpretation *opinfo = (OpIndexInterpretation *) lfirst(lc); CompareType cmptype = opinfo->cmptype; /* handle < / <= */ if (cmptype == COMPARE_LT || cmptype == COMPARE_LE) { /* * < / <= is supported for monotonically increasing functions in * the form op and op * for monotonically decreasing functions. */ if ((wfunc_left && (res->monotonic & MONOTONICFUNC_INCREASING)) || (!wfunc_left && (res->monotonic & MONOTONICFUNC_DECREASING))) { *keep_original = false; runopexpr = opexpr; runoperator = opexpr->opno; } break; } /* handle > / >= */ else if (cmptype == COMPARE_GT || cmptype == COMPARE_GE) { /* * > / >= is supported for monotonically decreasing functions in * the form op and op * for monotonically increasing functions. */ if ((wfunc_left && (res->monotonic & MONOTONICFUNC_DECREASING)) || (!wfunc_left && (res->monotonic & MONOTONICFUNC_INCREASING))) { *keep_original = false; runopexpr = opexpr; runoperator = opexpr->opno; } break; } /* handle = */ else if (cmptype == COMPARE_EQ) { CompareType newcmptype; /* * When both monotonically increasing and decreasing then the * return value of the window function will be the same each time. * We can simply use 'opexpr' as the run condition without * modifying it. */ if ((res->monotonic & MONOTONICFUNC_BOTH) == MONOTONICFUNC_BOTH) { *keep_original = false; runopexpr = opexpr; runoperator = opexpr->opno; break; } /* * When monotonically increasing we make a qual with <= * or >= in order to filter out values * which are above the value in the equality condition. For * monotonically decreasing functions we want to filter values * below the value in the equality condition. */ if (res->monotonic & MONOTONICFUNC_INCREASING) newcmptype = wfunc_left ? COMPARE_LE : COMPARE_GE; else newcmptype = wfunc_left ? COMPARE_GE : COMPARE_LE; /* We must keep the original equality qual */ *keep_original = true; runopexpr = opexpr; /* determine the operator to use for the WindowFuncRunCondition */ runoperator = get_opfamily_member_for_cmptype(opinfo->opfamily_id, opinfo->oplefttype, opinfo->oprighttype, newcmptype); break; } } if (runopexpr != NULL) { WindowFuncRunCondition *wfuncrc; wfuncrc = makeNode(WindowFuncRunCondition); wfuncrc->opno = runoperator; wfuncrc->inputcollid = runopexpr->inputcollid; wfuncrc->wfunc_left = wfunc_left; wfuncrc->arg = copyObject(otherexpr); wfunc->runCondition = lappend(wfunc->runCondition, wfuncrc); /* record that this attno was used in a run condition */ *run_cond_attrs = bms_add_member(*run_cond_attrs, attno - FirstLowInvalidHeapAttributeNumber); return true; } /* unsupported OpExpr */ return false; } /* * check_and_push_window_quals * Check if 'clause' is a qual that can be pushed into a WindowFunc * as a 'runCondition' qual. These, when present, allow some unnecessary * work to be skipped during execution. * * 'run_cond_attrs' will be populated with all targetlist resnos of subquery * targets (offset by FirstLowInvalidHeapAttributeNumber) that we pushed * window quals for. * * Returns true if the caller still must keep the original qual or false if * the caller can safely ignore the original qual because the WindowAgg node * will use the runCondition to stop returning tuples. */ static bool check_and_push_window_quals(Query *subquery, RangeTblEntry *rte, Index rti, Node *clause, Bitmapset **run_cond_attrs) { OpExpr *opexpr = (OpExpr *) clause; bool keep_original = true; Var *var1; Var *var2; /* We're only able to use OpExprs with 2 operands */ if (!IsA(opexpr, OpExpr)) return true; if (list_length(opexpr->args) != 2) return true; /* * Currently, we restrict this optimization to strict OpExprs. The reason * for this is that during execution, once the runcondition becomes false, * we stop evaluating WindowFuncs. To avoid leaving around stale window * function result values, we set them to NULL. Having only strict * OpExprs here ensures that we properly filter out the tuples with NULLs * in the top-level WindowAgg. */ set_opfuncid(opexpr); if (!func_strict(opexpr->opfuncid)) return true; /* * Check for plain Vars that reference window functions in the subquery. * If we find any, we'll ask find_window_run_conditions() if 'opexpr' can * be used as part of the run condition. */ /* Check the left side of the OpExpr */ var1 = linitial(opexpr->args); if (IsA(var1, Var) && var1->varattno > 0) { TargetEntry *tle = list_nth(subquery->targetList, var1->varattno - 1); WindowFunc *wfunc = (WindowFunc *) tle->expr; if (find_window_run_conditions(subquery, rte, rti, tle->resno, wfunc, opexpr, true, &keep_original, run_cond_attrs)) return keep_original; } /* and check the right side */ var2 = lsecond(opexpr->args); if (IsA(var2, Var) && var2->varattno > 0) { TargetEntry *tle = list_nth(subquery->targetList, var2->varattno - 1); WindowFunc *wfunc = (WindowFunc *) tle->expr; if (find_window_run_conditions(subquery, rte, rti, tle->resno, wfunc, opexpr, false, &keep_original, run_cond_attrs)) return keep_original; } return true; } /* * set_subquery_pathlist * Generate SubqueryScan access paths for a subquery RTE * * We don't currently support generating parameterized paths for subqueries * by pushing join clauses down into them; it seems too expensive to re-plan * the subquery multiple times to consider different alternatives. * (XXX that could stand to be reconsidered, now that we use Paths.) * So the paths made here will be parameterized if the subquery contains * LATERAL references, otherwise not. As long as that's true, there's no need * for a separate set_subquery_size phase: just make the paths right away. */ static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte) { Query *parse = root->parse; Query *subquery = rte->subquery; bool trivial_pathtarget; Relids required_outer; pushdown_safety_info safetyInfo; double tuple_fraction; RelOptInfo *sub_final_rel; Bitmapset *run_cond_attrs = NULL; ListCell *lc; /* * Must copy the Query so that planning doesn't mess up the RTE contents * (really really need to fix the planner to not scribble on its input, * someday ... but see remove_unused_subquery_outputs to start with). */ subquery = copyObject(subquery); /* * If it's a LATERAL subquery, it might contain some Vars of the current * query level, requiring it to be treated as parameterized, even though * we don't support pushing down join quals into subqueries. */ required_outer = rel->lateral_relids; /* * Zero out result area for subquery_is_pushdown_safe, so that it can set * flags as needed while recursing. In particular, we need a workspace * for keeping track of the reasons why columns are unsafe to reference. * These reasons are stored in the bits inside unsafeFlags[i] when we * discover reasons that column i of the subquery is unsafe to be used in * a pushed-down qual. */ memset(&safetyInfo, 0, sizeof(safetyInfo)); safetyInfo.unsafeFlags = (unsigned char *) palloc0((list_length(subquery->targetList) + 1) * sizeof(unsigned char)); /* * If the subquery has the "security_barrier" flag, it means the subquery * originated from a view that must enforce row-level security. Then we * must not push down quals that contain leaky functions. (Ideally this * would be checked inside subquery_is_pushdown_safe, but since we don't * currently pass the RTE to that function, we must do it here.) */ safetyInfo.unsafeLeaky = rte->security_barrier; /* * If there are any restriction clauses that have been attached to the * subquery relation, consider pushing them down to become WHERE or HAVING * quals of the subquery itself. This transformation is useful because it * may allow us to generate a better plan for the subquery than evaluating * all the subquery output rows and then filtering them. * * There are several cases where we cannot push down clauses. Restrictions * involving the subquery are checked by subquery_is_pushdown_safe(). * Restrictions on individual clauses are checked by * qual_is_pushdown_safe(). Also, we don't want to push down * pseudoconstant clauses; better to have the gating node above the * subquery. * * Non-pushed-down clauses will get evaluated as qpquals of the * SubqueryScan node. * * XXX Are there any cases where we want to make a policy decision not to * push down a pushable qual, because it'd result in a worse plan? */ if (rel->baserestrictinfo != NIL && subquery_is_pushdown_safe(subquery, subquery, &safetyInfo)) { /* OK to consider pushing down individual quals */ List *upperrestrictlist = NIL; ListCell *l; foreach(l, rel->baserestrictinfo) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(l); Node *clause = (Node *) rinfo->clause; if (rinfo->pseudoconstant) { upperrestrictlist = lappend(upperrestrictlist, rinfo); continue; } switch (qual_is_pushdown_safe(subquery, rti, rinfo, &safetyInfo)) { case PUSHDOWN_SAFE: /* Push it down */ subquery_push_qual(subquery, rte, rti, clause); break; case PUSHDOWN_WINDOWCLAUSE_RUNCOND: /* * Since we can't push the qual down into the subquery, * check if it happens to reference a window function. If * so then it might be useful to use for the WindowAgg's * runCondition. */ if (!subquery->hasWindowFuncs || check_and_push_window_quals(subquery, rte, rti, clause, &run_cond_attrs)) { /* * subquery has no window funcs or the clause is not a * suitable window run condition qual or it is, but * the original must also be kept in the upper query. */ upperrestrictlist = lappend(upperrestrictlist, rinfo); } break; case PUSHDOWN_UNSAFE: upperrestrictlist = lappend(upperrestrictlist, rinfo); break; } } rel->baserestrictinfo = upperrestrictlist; /* We don't bother recomputing baserestrict_min_security */ } pfree(safetyInfo.unsafeFlags); /* * The upper query might not use all the subquery's output columns; if * not, we can simplify. Pass the attributes that were pushed down into * WindowAgg run conditions to ensure we don't accidentally think those * are unused. */ remove_unused_subquery_outputs(subquery, rel, run_cond_attrs); /* * We can safely pass the outer tuple_fraction down to the subquery if the * outer level has no joining, aggregation, or sorting to do. Otherwise * we'd better tell the subquery to plan for full retrieval. (XXX This * could probably be made more intelligent ...) */ if (parse->hasAggs || parse->groupClause || parse->groupingSets || root->hasHavingQual || parse->distinctClause || parse->sortClause || bms_membership(root->all_baserels) == BMS_MULTIPLE) tuple_fraction = 0.0; /* default case */ else tuple_fraction = root->tuple_fraction; /* plan_params should not be in use in current query level */ Assert(root->plan_params == NIL); /* Generate a subroot and Paths for the subquery */ rel->subroot = subquery_planner(root->glob, subquery, root, false, tuple_fraction, NULL); /* Isolate the params needed by this specific subplan */ rel->subplan_params = root->plan_params; root->plan_params = NIL; /* * It's possible that constraint exclusion proved the subquery empty. If * so, it's desirable to produce an unadorned dummy path so that we will * recognize appropriate optimizations at this query level. */ sub_final_rel = fetch_upper_rel(rel->subroot, UPPERREL_FINAL, NULL); if (IS_DUMMY_REL(sub_final_rel)) { set_dummy_rel_pathlist(rel); return; } /* * Mark rel with estimated output rows, width, etc. Note that we have to * do this before generating outer-query paths, else cost_subqueryscan is * not happy. */ set_subquery_size_estimates(root, rel); /* * Also detect whether the reltarget is trivial, so that we can pass that * info to cost_subqueryscan (rather than re-deriving it multiple times). * It's trivial if it fetches all the subplan output columns in order. */ if (list_length(rel->reltarget->exprs) != list_length(subquery->targetList)) trivial_pathtarget = false; else { trivial_pathtarget = true; foreach(lc, rel->reltarget->exprs) { Node *node = (Node *) lfirst(lc); Var *var; if (!IsA(node, Var)) { trivial_pathtarget = false; break; } var = (Var *) node; if (var->varno != rti || var->varattno != foreach_current_index(lc) + 1) { trivial_pathtarget = false; break; } } } /* * For each Path that subquery_planner produced, make a SubqueryScanPath * in the outer query. */ foreach(lc, sub_final_rel->pathlist) { Path *subpath = (Path *) lfirst(lc); List *pathkeys; /* Convert subpath's pathkeys to outer representation */ pathkeys = convert_subquery_pathkeys(root, rel, subpath->pathkeys, make_tlist_from_pathtarget(subpath->pathtarget)); /* Generate outer path using this subpath */ add_path(rel, (Path *) create_subqueryscan_path(root, rel, subpath, trivial_pathtarget, pathkeys, required_outer)); } /* If outer rel allows parallelism, do same for partial paths. */ if (rel->consider_parallel && bms_is_empty(required_outer)) { /* If consider_parallel is false, there should be no partial paths. */ Assert(sub_final_rel->consider_parallel || sub_final_rel->partial_pathlist == NIL); /* Same for partial paths. */ foreach(lc, sub_final_rel->partial_pathlist) { Path *subpath = (Path *) lfirst(lc); List *pathkeys; /* Convert subpath's pathkeys to outer representation */ pathkeys = convert_subquery_pathkeys(root, rel, subpath->pathkeys, make_tlist_from_pathtarget(subpath->pathtarget)); /* Generate outer path using this subpath */ add_partial_path(rel, (Path *) create_subqueryscan_path(root, rel, subpath, trivial_pathtarget, pathkeys, required_outer)); } } } /* * set_function_pathlist * Build the (single) access path for a function RTE */ static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; List *pathkeys = NIL; /* * We don't support pushing join clauses into the quals of a function * scan, but it could still have required parameterization due to LATERAL * refs in the function expression. */ required_outer = rel->lateral_relids; /* * The result is considered unordered unless ORDINALITY was used, in which * case it is ordered by the ordinal column (the last one). See if we * care, by checking for uses of that Var in equivalence classes. */ if (rte->funcordinality) { AttrNumber ordattno = rel->max_attr; Var *var = NULL; ListCell *lc; /* * Is there a Var for it in rel's targetlist? If not, the query did * not reference the ordinality column, or at least not in any way * that would be interesting for sorting. */ foreach(lc, rel->reltarget->exprs) { Var *node = (Var *) lfirst(lc); /* checking varno/varlevelsup is just paranoia */ if (IsA(node, Var) && node->varattno == ordattno && node->varno == rel->relid && node->varlevelsup == 0) { var = node; break; } } /* * Try to build pathkeys for this Var with int8 sorting. We tell * build_expression_pathkey not to build any new equivalence class; if * the Var isn't already mentioned in some EC, it means that nothing * cares about the ordering. */ if (var) pathkeys = build_expression_pathkey(root, (Expr *) var, Int8LessOperator, rel->relids, false); } /* Generate appropriate path */ add_path(rel, create_functionscan_path(root, rel, pathkeys, required_outer)); } /* * set_values_pathlist * Build the (single) access path for a VALUES RTE */ static void set_values_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; /* * We don't support pushing join clauses into the quals of a values scan, * but it could still have required parameterization due to LATERAL refs * in the values expressions. */ required_outer = rel->lateral_relids; /* Generate appropriate path */ add_path(rel, create_valuesscan_path(root, rel, required_outer)); } /* * set_tablefunc_pathlist * Build the (single) access path for a table func RTE */ static void set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; /* * We don't support pushing join clauses into the quals of a tablefunc * scan, but it could still have required parameterization due to LATERAL * refs in the function expression. */ required_outer = rel->lateral_relids; /* Generate appropriate path */ add_path(rel, create_tablefuncscan_path(root, rel, required_outer)); } /* * set_cte_pathlist * Build the (single) access path for a non-self-reference CTE RTE * * There's no need for a separate set_cte_size phase, since we don't * support join-qual-parameterized paths for CTEs. */ static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Path *ctepath; Plan *cteplan; PlannerInfo *cteroot; Index levelsup; List *pathkeys; int ndx; ListCell *lc; int plan_id; Relids required_outer; /* * Find the referenced CTE, and locate the path and plan previously made * for it. */ levelsup = rte->ctelevelsup; cteroot = root; while (levelsup-- > 0) { cteroot = cteroot->parent_root; if (!cteroot) /* shouldn't happen */ elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename); } /* * Note: cte_plan_ids can be shorter than cteList, if we are still working * on planning the CTEs (ie, this is a side-reference from another CTE). * So we mustn't use forboth here. */ ndx = 0; foreach(lc, cteroot->parse->cteList) { CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc); if (strcmp(cte->ctename, rte->ctename) == 0) break; ndx++; } if (lc == NULL) /* shouldn't happen */ elog(ERROR, "could not find CTE \"%s\"", rte->ctename); if (ndx >= list_length(cteroot->cte_plan_ids)) elog(ERROR, "could not find plan for CTE \"%s\"", rte->ctename); plan_id = list_nth_int(cteroot->cte_plan_ids, ndx); if (plan_id <= 0) elog(ERROR, "no plan was made for CTE \"%s\"", rte->ctename); Assert(list_length(root->glob->subpaths) == list_length(root->glob->subplans)); ctepath = (Path *) list_nth(root->glob->subpaths, plan_id - 1); cteplan = (Plan *) list_nth(root->glob->subplans, plan_id - 1); /* Mark rel with estimated output rows, width, etc */ set_cte_size_estimates(root, rel, cteplan->plan_rows); /* Convert the ctepath's pathkeys to outer query's representation */ pathkeys = convert_subquery_pathkeys(root, rel, ctepath->pathkeys, cteplan->targetlist); /* * We don't support pushing join clauses into the quals of a CTE scan, but * it could still have required parameterization due to LATERAL refs in * its tlist. */ required_outer = rel->lateral_relids; /* Generate appropriate path */ add_path(rel, create_ctescan_path(root, rel, pathkeys, required_outer)); } /* * set_namedtuplestore_pathlist * Build the (single) access path for a named tuplestore RTE * * There's no need for a separate set_namedtuplestore_size phase, since we * don't support join-qual-parameterized paths for tuplestores. */ static void set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; /* Mark rel with estimated output rows, width, etc */ set_namedtuplestore_size_estimates(root, rel); /* * We don't support pushing join clauses into the quals of a tuplestore * scan, but it could still have required parameterization due to LATERAL * refs in its tlist. */ required_outer = rel->lateral_relids; /* Generate appropriate path */ add_path(rel, create_namedtuplestorescan_path(root, rel, required_outer)); } /* * set_result_pathlist * Build the (single) access path for an RTE_RESULT RTE * * There's no need for a separate set_result_size phase, since we * don't support join-qual-parameterized paths for these RTEs. */ static void set_result_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Relids required_outer; /* Mark rel with estimated output rows, width, etc */ set_result_size_estimates(root, rel); /* * We don't support pushing join clauses into the quals of a Result scan, * but it could still have required parameterization due to LATERAL refs * in its tlist. */ required_outer = rel->lateral_relids; /* Generate appropriate path */ add_path(rel, create_resultscan_path(root, rel, required_outer)); } /* * set_worktable_pathlist * Build the (single) access path for a self-reference CTE RTE * * There's no need for a separate set_worktable_size phase, since we don't * support join-qual-parameterized paths for CTEs. */ static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) { Path *ctepath; PlannerInfo *cteroot; Index levelsup; Relids required_outer; /* * We need to find the non-recursive term's path, which is in the plan * level that's processing the recursive UNION, which is one level *below* * where the CTE comes from. */ levelsup = rte->ctelevelsup; if (levelsup == 0) /* shouldn't happen */ elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename); levelsup--; cteroot = root; while (levelsup-- > 0) { cteroot = cteroot->parent_root; if (!cteroot) /* shouldn't happen */ elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename); } ctepath = cteroot->non_recursive_path; if (!ctepath) /* shouldn't happen */ elog(ERROR, "could not find path for CTE \"%s\"", rte->ctename); /* Mark rel with estimated output rows, width, etc */ set_cte_size_estimates(root, rel, ctepath->rows); /* * We don't support pushing join clauses into the quals of a worktable * scan, but it could still have required parameterization due to LATERAL * refs in its tlist. (I'm not sure this is actually possible given the * restrictions on recursive references, but it's easy enough to support.) */ required_outer = rel->lateral_relids; /* Generate appropriate path */ add_path(rel, create_worktablescan_path(root, rel, required_outer)); } /* * generate_gather_paths * Generate parallel access paths for a relation by pushing a Gather or * Gather Merge on top of a partial path. * * This must not be called until after we're done creating all partial paths * for the specified relation. (Otherwise, add_partial_path might delete a * path that some GatherPath or GatherMergePath has a reference to.) * * If we're generating paths for a scan or join relation, override_rows will * be false, and we'll just use the relation's size estimate. When we're * being called for a partially-grouped or partially-distinct path, though, we * need to override the rowcount estimate. (It's not clear that the * particular value we're using here is actually best, but the underlying rel * has no estimate so we must do something.) */ void generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows) { Path *cheapest_partial_path; Path *simple_gather_path; ListCell *lc; double rows; double *rowsp = NULL; /* If there are no partial paths, there's nothing to do here. */ if (rel->partial_pathlist == NIL) return; /* Should we override the rel's rowcount estimate? */ if (override_rows) rowsp = &rows; /* * The output of Gather is always unsorted, so there's only one partial * path of interest: the cheapest one. That will be the one at the front * of partial_pathlist because of the way add_partial_path works. */ cheapest_partial_path = linitial(rel->partial_pathlist); rows = compute_gather_rows(cheapest_partial_path); simple_gather_path = (Path *) create_gather_path(root, rel, cheapest_partial_path, rel->reltarget, NULL, rowsp); add_path(rel, simple_gather_path); /* * For each useful ordering, we can consider an order-preserving Gather * Merge. */ foreach(lc, rel->partial_pathlist) { Path *subpath = (Path *) lfirst(lc); GatherMergePath *path; if (subpath->pathkeys == NIL) continue; rows = compute_gather_rows(subpath); path = create_gather_merge_path(root, rel, subpath, rel->reltarget, subpath->pathkeys, NULL, rowsp); add_path(rel, &path->path); } } /* * get_useful_pathkeys_for_relation * Determine which orderings of a relation might be useful. * * Getting data in sorted order can be useful either because the requested * order matches the final output ordering for the overall query we're * planning, or because it enables an efficient merge join. Here, we try * to figure out which pathkeys to consider. * * This allows us to do incremental sort on top of an index scan under a gather * merge node, i.e. parallelized. * * If the require_parallel_safe is true, we also require the expressions to * be parallel safe (which allows pushing the sort below Gather Merge). * * XXX At the moment this can only ever return a list with a single element, * because it looks at query_pathkeys only. So we might return the pathkeys * directly, but it seems plausible we'll want to consider other orderings * in the future. For example, we might want to consider pathkeys useful for * merge joins. */ static List * get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel, bool require_parallel_safe) { List *useful_pathkeys_list = NIL; /* * Considering query_pathkeys is always worth it, because it might allow * us to avoid a total sort when we have a partially presorted path * available or to push the total sort into the parallel portion of the * query. */ if (root->query_pathkeys) { ListCell *lc; int npathkeys = 0; /* useful pathkeys */ foreach(lc, root->query_pathkeys) { PathKey *pathkey = (PathKey *) lfirst(lc); EquivalenceClass *pathkey_ec = pathkey->pk_eclass; /* * We can only build a sort for pathkeys that contain a * safe-to-compute-early EC member computable from the current * relation's reltarget, so ignore the remainder of the list as * soon as we find a pathkey without such a member. * * It's still worthwhile to return any prefix of the pathkeys list * that meets this requirement, as we may be able to do an * incremental sort. * * If requested, ensure the sort expression is parallel-safe too. */ if (!relation_can_be_sorted_early(root, rel, pathkey_ec, require_parallel_safe)) break; npathkeys++; } /* * The whole query_pathkeys list matches, so append it directly, to * allow comparing pathkeys easily by comparing list pointer. If we * have to truncate the pathkeys, we gotta do a copy though. */ if (npathkeys == list_length(root->query_pathkeys)) useful_pathkeys_list = lappend(useful_pathkeys_list, root->query_pathkeys); else if (npathkeys > 0) useful_pathkeys_list = lappend(useful_pathkeys_list, list_copy_head(root->query_pathkeys, npathkeys)); } return useful_pathkeys_list; } /* * generate_useful_gather_paths * Generate parallel access paths for a relation by pushing a Gather or * Gather Merge on top of a partial path. * * Unlike plain generate_gather_paths, this looks both at pathkeys of input * paths (aiming to preserve the ordering), but also considers ordering that * might be useful for nodes above the gather merge node, and tries to add * a sort (regular or incremental) to provide that. */ void generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows) { ListCell *lc; double rows; double *rowsp = NULL; List *useful_pathkeys_list = NIL; Path *cheapest_partial_path = NULL; /* If there are no partial paths, there's nothing to do here. */ if (rel->partial_pathlist == NIL) return; /* Should we override the rel's rowcount estimate? */ if (override_rows) rowsp = &rows; /* generate the regular gather (merge) paths */ generate_gather_paths(root, rel, override_rows); /* consider incremental sort for interesting orderings */ useful_pathkeys_list = get_useful_pathkeys_for_relation(root, rel, true); /* used for explicit (full) sort paths */ cheapest_partial_path = linitial(rel->partial_pathlist); /* * Consider sorted paths for each interesting ordering. We generate both * incremental and full sort. */ foreach(lc, useful_pathkeys_list) { List *useful_pathkeys = lfirst(lc); ListCell *lc2; bool is_sorted; int presorted_keys; foreach(lc2, rel->partial_pathlist) { Path *subpath = (Path *) lfirst(lc2); GatherMergePath *path; is_sorted = pathkeys_count_contained_in(useful_pathkeys, subpath->pathkeys, &presorted_keys); /* * We don't need to consider the case where a subpath is already * fully sorted because generate_gather_paths already creates a * gather merge path for every subpath that has pathkeys present. * * But since the subpath is already sorted, we know we don't need * to consider adding a sort (full or incremental) on top of it, * so we can continue here. */ if (is_sorted) continue; /* * Try at least sorting the cheapest path and also try * incrementally sorting any path which is partially sorted * already (no need to deal with paths which have presorted keys * when incremental sort is disabled unless it's the cheapest * input path). */ if (subpath != cheapest_partial_path && (presorted_keys == 0 || !enable_incremental_sort)) continue; /* * Consider regular sort for any path that's not presorted or if * incremental sort is disabled. We've no need to consider both * sort and incremental sort on the same path. We assume that * incremental sort is always faster when there are presorted * keys. * * This is not redundant with the gather paths created in * generate_gather_paths, because that doesn't generate ordered * output. Here we add an explicit sort to match the useful * ordering. */ if (presorted_keys == 0 || !enable_incremental_sort) { subpath = (Path *) create_sort_path(root, rel, subpath, useful_pathkeys, -1.0); } else subpath = (Path *) create_incremental_sort_path(root, rel, subpath, useful_pathkeys, presorted_keys, -1); rows = compute_gather_rows(subpath); path = create_gather_merge_path(root, rel, subpath, rel->reltarget, subpath->pathkeys, NULL, rowsp); add_path(rel, &path->path); } } } /* * make_rel_from_joinlist * Build access paths using a "joinlist" to guide the join path search. * * See comments for deconstruct_jointree() for definition of the joinlist * data structure. */ static RelOptInfo * make_rel_from_joinlist(PlannerInfo *root, List *joinlist) { int levels_needed; List *initial_rels; ListCell *jl; /* * Count the number of child joinlist nodes. This is the depth of the * dynamic-programming algorithm we must employ to consider all ways of * joining the child nodes. */ levels_needed = list_length(joinlist); if (levels_needed <= 0) return NULL; /* nothing to do? */ /* * Construct a list of rels corresponding to the child joinlist nodes. * This may contain both base rels and rels constructed according to * sub-joinlists. */ initial_rels = NIL; foreach(jl, joinlist) { Node *jlnode = (Node *) lfirst(jl); RelOptInfo *thisrel; if (IsA(jlnode, RangeTblRef)) { int varno = ((RangeTblRef *) jlnode)->rtindex; thisrel = find_base_rel(root, varno); } else if (IsA(jlnode, List)) { /* Recurse to handle subproblem */ thisrel = make_rel_from_joinlist(root, (List *) jlnode); } else { elog(ERROR, "unrecognized joinlist node type: %d", (int) nodeTag(jlnode)); thisrel = NULL; /* keep compiler quiet */ } initial_rels = lappend(initial_rels, thisrel); } if (levels_needed == 1) { /* * Single joinlist node, so we're done. */ return (RelOptInfo *) linitial(initial_rels); } else { /* * Consider the different orders in which we could join the rels, * using a plugin, GEQO, or the regular join search code. * * We put the initial_rels list into a PlannerInfo field because * has_legal_joinclause() needs to look at it (ugly :-(). */ root->initial_rels = initial_rels; if (join_search_hook) return (*join_search_hook) (root, levels_needed, initial_rels); else if (enable_geqo && levels_needed >= geqo_threshold) return geqo(root, levels_needed, initial_rels); else return standard_join_search(root, levels_needed, initial_rels); } } /* * standard_join_search * Find possible joinpaths for a query by successively finding ways * to join component relations into join relations. * * 'levels_needed' is the number of iterations needed, ie, the number of * independent jointree items in the query. This is > 1. * * 'initial_rels' is a list of RelOptInfo nodes for each independent * jointree item. These are the components to be joined together. * Note that levels_needed == list_length(initial_rels). * * Returns the final level of join relations, i.e., the relation that is * the result of joining all the original relations together. * At least one implementation path must be provided for this relation and * all required sub-relations. * * To support loadable plugins that modify planner behavior by changing the * join searching algorithm, we provide a hook variable that lets a plugin * replace or supplement this function. Any such hook must return the same * final join relation as the standard code would, but it might have a * different set of implementation paths attached, and only the sub-joinrels * needed for these paths need have been instantiated. * * Note to plugin authors: the functions invoked during standard_join_search() * modify root->join_rel_list and root->join_rel_hash. If you want to do more * than one join-order search, you'll probably need to save and restore the * original states of those data structures. See geqo_eval() for an example. */ RelOptInfo * standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels) { int lev; RelOptInfo *rel; /* * This function cannot be invoked recursively within any one planning * problem, so join_rel_level[] can't be in use already. */ Assert(root->join_rel_level == NULL); /* * We employ a simple "dynamic programming" algorithm: we first find all * ways to build joins of two jointree items, then all ways to build joins * of three items (from two-item joins and single items), then four-item * joins, and so on until we have considered all ways to join all the * items into one rel. * * root->join_rel_level[j] is a list of all the j-item rels. Initially we * set root->join_rel_level[1] to represent all the single-jointree-item * relations. */ root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *)); root->join_rel_level[1] = initial_rels; for (lev = 2; lev <= levels_needed; lev++) { ListCell *lc; /* * Determine all possible pairs of relations to be joined at this * level, and build paths for making each one from every available * pair of lower-level relations. */ join_search_one_level(root, lev); /* * Run generate_partitionwise_join_paths() and * generate_useful_gather_paths() for each just-processed joinrel. We * could not do this earlier because both regular and partial paths * can get added to a particular joinrel at multiple times within * join_search_one_level. * * After that, we're done creating paths for the joinrel, so run * set_cheapest(). */ foreach(lc, root->join_rel_level[lev]) { rel = (RelOptInfo *) lfirst(lc); /* Create paths for partitionwise joins. */ generate_partitionwise_join_paths(root, rel); /* * Except for the topmost scan/join rel, consider gathering * partial paths. We'll do the same for the topmost scan/join rel * once we know the final targetlist (see grouping_planner's and * its call to apply_scanjoin_target_to_paths). */ if (!bms_equal(rel->relids, root->all_query_rels)) generate_useful_gather_paths(root, rel, false); /* Find and save the cheapest paths for this rel */ set_cheapest(rel); #ifdef OPTIMIZER_DEBUG pprint(rel); #endif } } /* * We should have a single rel at the final level. */ if (root->join_rel_level[levels_needed] == NIL) elog(ERROR, "failed to build any %d-way joins", levels_needed); Assert(list_length(root->join_rel_level[levels_needed]) == 1); rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]); root->join_rel_level = NULL; return rel; } /***************************************************************************** * PUSHING QUALS DOWN INTO SUBQUERIES *****************************************************************************/ /* * subquery_is_pushdown_safe - is a subquery safe for pushing down quals? * * subquery is the particular component query being checked. topquery * is the top component of a set-operations tree (the same Query if no * set-op is involved). * * Conditions checked here: * * 1. If the subquery has a LIMIT clause, we must not push down any quals, * since that could change the set of rows returned. * * 2. If the subquery contains EXCEPT or EXCEPT ALL set ops we cannot push * quals into it, because that could change the results. * * 3. If the subquery uses DISTINCT, we cannot push volatile quals into it. * This is because upper-level quals should semantically be evaluated only * once per distinct row, not once per original row, and if the qual is * volatile then extra evaluations could change the results. (This issue * does not apply to other forms of aggregation such as GROUP BY, because * when those are present we push into HAVING not WHERE, so that the quals * are still applied after aggregation.) * * 4. If the subquery contains window functions, we cannot push volatile quals * into it. The issue here is a bit different from DISTINCT: a volatile qual * might succeed for some rows of a window partition and fail for others, * thereby changing the partition contents and thus the window functions' * results for rows that remain. * * 5. If the subquery contains any set-returning functions in its targetlist, * we cannot push volatile quals into it. That would push them below the SRFs * and thereby change the number of times they are evaluated. Also, a * volatile qual could succeed for some SRF output rows and fail for others, * a behavior that cannot occur if it's evaluated before SRF expansion. * * 6. If the subquery has nonempty grouping sets, we cannot push down any * quals. The concern here is that a qual referencing a "constant" grouping * column could get constant-folded, which would be improper because the value * is potentially nullable by grouping-set expansion. This restriction could * be removed if we had a parsetree representation that shows that such * grouping columns are not really constant. (There are other ideas that * could be used to relax this restriction, but that's the approach most * likely to get taken in the future. Note that there's not much to be gained * so long as subquery_planner can't move HAVING clauses to WHERE within such * a subquery.) * * In addition, we make several checks on the subquery's output columns to see * if it is safe to reference them in pushed-down quals. If output column k * is found to be unsafe to reference, we set the reason for that inside * safetyInfo->unsafeFlags[k], but we don't reject the subquery overall since * column k might not be referenced by some/all quals. The unsafeFlags[] * array will be consulted later by qual_is_pushdown_safe(). It's better to * do it this way than to make the checks directly in qual_is_pushdown_safe(), * because when the subquery involves set operations we have to check the * output expressions in each arm of the set op. * * Note: pushing quals into a DISTINCT subquery is theoretically dubious: * we're effectively assuming that the quals cannot distinguish values that * the DISTINCT's equality operator sees as equal, yet there are many * counterexamples to that assumption. However use of such a qual with a * DISTINCT subquery would be unsafe anyway, since there's no guarantee which * "equal" value will be chosen as the output value by the DISTINCT operation. * So we don't worry too much about that. Another objection is that if the * qual is expensive to evaluate, running it for each original row might cost * more than we save by eliminating rows before the DISTINCT step. But it * would be very hard to estimate that at this stage, and in practice pushdown * seldom seems to make things worse, so we ignore that problem too. * * Note: likewise, pushing quals into a subquery with window functions is a * bit dubious: the quals might remove some rows of a window partition while * leaving others, causing changes in the window functions' results for the * surviving rows. We insist that such a qual reference only partitioning * columns, but again that only protects us if the qual does not distinguish * values that the partitioning equality operator sees as equal. The risks * here are perhaps larger than for DISTINCT, since no de-duplication of rows * occurs and thus there is no theoretical problem with such a qual. But * we'll do this anyway because the potential performance benefits are very * large, and we've seen no field complaints about the longstanding comparable * behavior with DISTINCT. */ static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery, pushdown_safety_info *safetyInfo) { SetOperationStmt *topop; /* Check point 1 */ if (subquery->limitOffset != NULL || subquery->limitCount != NULL) return false; /* Check point 6 */ if (subquery->groupClause && subquery->groupingSets) return false; /* Check points 3, 4, and 5 */ if (subquery->distinctClause || subquery->hasWindowFuncs || subquery->hasTargetSRFs) safetyInfo->unsafeVolatile = true; /* * If we're at a leaf query, check for unsafe expressions in its target * list, and mark any reasons why they're unsafe in unsafeFlags[]. * (Non-leaf nodes in setop trees have only simple Vars in their tlists, * so no need to check them.) */ if (subquery->setOperations == NULL) check_output_expressions(subquery, safetyInfo); /* Are we at top level, or looking at a setop component? */ if (subquery == topquery) { /* Top level, so check any component queries */ if (subquery->setOperations != NULL) if (!recurse_pushdown_safe(subquery->setOperations, topquery, safetyInfo)) return false; } else { /* Setop component must not have more components (too weird) */ if (subquery->setOperations != NULL) return false; /* Check whether setop component output types match top level */ topop = castNode(SetOperationStmt, topquery->setOperations); Assert(topop); compare_tlist_datatypes(subquery->targetList, topop->colTypes, safetyInfo); } return true; } /* * Helper routine to recurse through setOperations tree */ static bool recurse_pushdown_safe(Node *setOp, Query *topquery, pushdown_safety_info *safetyInfo) { if (IsA(setOp, RangeTblRef)) { RangeTblRef *rtr = (RangeTblRef *) setOp; RangeTblEntry *rte = rt_fetch(rtr->rtindex, topquery->rtable); Query *subquery = rte->subquery; Assert(subquery != NULL); return subquery_is_pushdown_safe(subquery, topquery, safetyInfo); } else if (IsA(setOp, SetOperationStmt)) { SetOperationStmt *op = (SetOperationStmt *) setOp; /* EXCEPT is no good (point 2 for subquery_is_pushdown_safe) */ if (op->op == SETOP_EXCEPT) return false; /* Else recurse */ if (!recurse_pushdown_safe(op->larg, topquery, safetyInfo)) return false; if (!recurse_pushdown_safe(op->rarg, topquery, safetyInfo)) return false; } else { elog(ERROR, "unrecognized node type: %d", (int) nodeTag(setOp)); } return true; } /* * check_output_expressions - check subquery's output expressions for safety * * There are several cases in which it's unsafe to push down an upper-level * qual if it references a particular output column of a subquery. We check * each output column of the subquery and set flags in unsafeFlags[k] when we * see that column is unsafe for a pushed-down qual to reference. The * conditions checked here are: * * 1. We must not push down any quals that refer to subselect outputs that * return sets, else we'd introduce functions-returning-sets into the * subquery's WHERE/HAVING quals. * * 2. We must not push down any quals that refer to subselect outputs that * contain volatile functions, for fear of introducing strange results due * to multiple evaluation of a volatile function. * * 3. If the subquery uses DISTINCT ON, we must not push down any quals that * refer to non-DISTINCT output columns, because that could change the set * of rows returned. (This condition is vacuous for DISTINCT, because then * there are no non-DISTINCT output columns, so we needn't check. Note that * subquery_is_pushdown_safe already reported that we can't use volatile * quals if there's DISTINCT or DISTINCT ON.) * * 4. If the subquery has any window functions, we must not push down quals * that reference any output columns that are not listed in all the subquery's * window PARTITION BY clauses. We can push down quals that use only * partitioning columns because they should succeed or fail identically for * every row of any one window partition, and totally excluding some * partitions will not change a window function's results for remaining * partitions. (Again, this also requires nonvolatile quals, but * subquery_is_pushdown_safe handles that.). Subquery columns marked as * unsafe for this reason can still have WindowClause run conditions pushed * down. */ static void check_output_expressions(Query *subquery, pushdown_safety_info *safetyInfo) { ListCell *lc; foreach(lc, subquery->targetList) { TargetEntry *tle = (TargetEntry *) lfirst(lc); if (tle->resjunk) continue; /* ignore resjunk columns */ /* Functions returning sets are unsafe (point 1) */ if (subquery->hasTargetSRFs && (safetyInfo->unsafeFlags[tle->resno] & UNSAFE_HAS_SET_FUNC) == 0 && expression_returns_set((Node *) tle->expr)) { safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_HAS_SET_FUNC; continue; } /* Volatile functions are unsafe (point 2) */ if ((safetyInfo->unsafeFlags[tle->resno] & UNSAFE_HAS_VOLATILE_FUNC) == 0 && contain_volatile_functions((Node *) tle->expr)) { safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_HAS_VOLATILE_FUNC; continue; } /* If subquery uses DISTINCT ON, check point 3 */ if (subquery->hasDistinctOn && (safetyInfo->unsafeFlags[tle->resno] & UNSAFE_NOTIN_DISTINCTON_CLAUSE) == 0 && !targetIsInSortList(tle, InvalidOid, subquery->distinctClause)) { /* non-DISTINCT column, so mark it unsafe */ safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_NOTIN_DISTINCTON_CLAUSE; continue; } /* If subquery uses window functions, check point 4 */ if (subquery->hasWindowFuncs && (safetyInfo->unsafeFlags[tle->resno] & UNSAFE_NOTIN_DISTINCTON_CLAUSE) == 0 && !targetIsInAllPartitionLists(tle, subquery)) { /* not present in all PARTITION BY clauses, so mark it unsafe */ safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_NOTIN_PARTITIONBY_CLAUSE; continue; } } } /* * For subqueries using UNION/UNION ALL/INTERSECT/INTERSECT ALL, we can * push quals into each component query, but the quals can only reference * subquery columns that suffer no type coercions in the set operation. * Otherwise there are possible semantic gotchas. So, we check the * component queries to see if any of them have output types different from * the top-level setop outputs. We set the UNSAFE_TYPE_MISMATCH bit in * unsafeFlags[k] if column k has different type in any component. * * We don't have to care about typmods here: the only allowed difference * between set-op input and output typmods is input is a specific typmod * and output is -1, and that does not require a coercion. * * tlist is a subquery tlist. * colTypes is an OID list of the top-level setop's output column types. * safetyInfo is the pushdown_safety_info to set unsafeFlags[] for. */ static void compare_tlist_datatypes(List *tlist, List *colTypes, pushdown_safety_info *safetyInfo) { ListCell *l; ListCell *colType = list_head(colTypes); foreach(l, tlist) { TargetEntry *tle = (TargetEntry *) lfirst(l); if (tle->resjunk) continue; /* ignore resjunk columns */ if (colType == NULL) elog(ERROR, "wrong number of tlist entries"); if (exprType((Node *) tle->expr) != lfirst_oid(colType)) safetyInfo->unsafeFlags[tle->resno] |= UNSAFE_TYPE_MISMATCH; colType = lnext(colTypes, colType); } if (colType != NULL) elog(ERROR, "wrong number of tlist entries"); } /* * targetIsInAllPartitionLists * True if the TargetEntry is listed in the PARTITION BY clause * of every window defined in the query. * * It would be safe to ignore windows not actually used by any window * function, but it's not easy to get that info at this stage; and it's * unlikely to be useful to spend any extra cycles getting it, since * unreferenced window definitions are probably infrequent in practice. */ static bool targetIsInAllPartitionLists(TargetEntry *tle, Query *query) { ListCell *lc; foreach(lc, query->windowClause) { WindowClause *wc = (WindowClause *) lfirst(lc); if (!targetIsInSortList(tle, InvalidOid, wc->partitionClause)) return false; } return true; } /* * qual_is_pushdown_safe - is a particular rinfo safe to push down? * * rinfo is a restriction clause applying to the given subquery (whose RTE * has index rti in the parent query). * * Conditions checked here: * * 1. rinfo's clause must not contain any SubPlans (mainly because it's * unclear that it will work correctly: SubLinks will already have been * transformed into SubPlans in the qual, but not in the subquery). Note that * SubLinks that transform to initplans are safe, and will be accepted here * because what we'll see in the qual is just a Param referencing the initplan * output. * * 2. If unsafeVolatile is set, rinfo's clause must not contain any volatile * functions. * * 3. If unsafeLeaky is set, rinfo's clause must not contain any leaky * functions that are passed Var nodes, and therefore might reveal values from * the subquery as side effects. * * 4. rinfo's clause must not refer to the whole-row output of the subquery * (since there is no easy way to name that within the subquery itself). * * 5. rinfo's clause must not refer to any subquery output columns that were * found to be unsafe to reference by subquery_is_pushdown_safe(). */ static pushdown_safe_type qual_is_pushdown_safe(Query *subquery, Index rti, RestrictInfo *rinfo, pushdown_safety_info *safetyInfo) { pushdown_safe_type safe = PUSHDOWN_SAFE; Node *qual = (Node *) rinfo->clause; List *vars; ListCell *vl; /* Refuse subselects (point 1) */ if (contain_subplans(qual)) return PUSHDOWN_UNSAFE; /* Refuse volatile quals if we found they'd be unsafe (point 2) */ if (safetyInfo->unsafeVolatile && contain_volatile_functions((Node *) rinfo)) return PUSHDOWN_UNSAFE; /* Refuse leaky quals if told to (point 3) */ if (safetyInfo->unsafeLeaky && contain_leaked_vars(qual)) return PUSHDOWN_UNSAFE; /* * Examine all Vars used in clause. Since it's a restriction clause, all * such Vars must refer to subselect output columns ... unless this is * part of a LATERAL subquery, in which case there could be lateral * references. * * By omitting the relevant flags, this also gives us a cheap sanity check * that no aggregates or window functions appear in the qual. Those would * be unsafe to push down, but at least for the moment we could never see * any in a qual anyhow. */ vars = pull_var_clause(qual, PVC_INCLUDE_PLACEHOLDERS); foreach(vl, vars) { Var *var = (Var *) lfirst(vl); /* * XXX Punt if we find any PlaceHolderVars in the restriction clause. * It's not clear whether a PHV could safely be pushed down, and even * less clear whether such a situation could arise in any cases of * practical interest anyway. So for the moment, just refuse to push * down. */ if (!IsA(var, Var)) { safe = PUSHDOWN_UNSAFE; break; } /* * Punt if we find any lateral references. It would be safe to push * these down, but we'd have to convert them into outer references, * which subquery_push_qual lacks the infrastructure to do. The case * arises so seldom that it doesn't seem worth working hard on. */ if (var->varno != rti) { safe = PUSHDOWN_UNSAFE; break; } /* Subqueries have no system columns */ Assert(var->varattno >= 0); /* Check point 4 */ if (var->varattno == 0) { safe = PUSHDOWN_UNSAFE; break; } /* Check point 5 */ if (safetyInfo->unsafeFlags[var->varattno] != 0) { if (safetyInfo->unsafeFlags[var->varattno] & (UNSAFE_HAS_VOLATILE_FUNC | UNSAFE_HAS_SET_FUNC | UNSAFE_NOTIN_DISTINCTON_CLAUSE | UNSAFE_TYPE_MISMATCH)) { safe = PUSHDOWN_UNSAFE; break; } else { /* UNSAFE_NOTIN_PARTITIONBY_CLAUSE is ok for run conditions */ safe = PUSHDOWN_WINDOWCLAUSE_RUNCOND; /* don't break, we might find another Var that's unsafe */ } } } list_free(vars); return safe; } /* * subquery_push_qual - push down a qual that we have determined is safe */ static void subquery_push_qual(Query *subquery, RangeTblEntry *rte, Index rti, Node *qual) { if (subquery->setOperations != NULL) { /* Recurse to push it separately to each component query */ recurse_push_qual(subquery->setOperations, subquery, rte, rti, qual); } else { /* * We need to replace Vars in the qual (which must refer to outputs of * the subquery) with copies of the subquery's targetlist expressions. * Note that at this point, any uplevel Vars in the qual should have * been replaced with Params, so they need no work. * * This step also ensures that when we are pushing into a setop tree, * each component query gets its own copy of the qual. */ qual = ReplaceVarsFromTargetList(qual, rti, 0, rte, subquery->targetList, subquery->resultRelation, REPLACEVARS_REPORT_ERROR, 0, &subquery->hasSubLinks); /* * Now attach the qual to the proper place: normally WHERE, but if the * subquery uses grouping or aggregation, put it in HAVING (since the * qual really refers to the group-result rows). */ if (subquery->hasAggs || subquery->groupClause || subquery->groupingSets || subquery->havingQual) subquery->havingQual = make_and_qual(subquery->havingQual, qual); else subquery->jointree->quals = make_and_qual(subquery->jointree->quals, qual); /* * We need not change the subquery's hasAggs or hasSubLinks flags, * since we can't be pushing down any aggregates that weren't there * before, and we don't push down subselects at all. */ } } /* * Helper routine to recurse through setOperations tree */ static void recurse_push_qual(Node *setOp, Query *topquery, RangeTblEntry *rte, Index rti, Node *qual) { if (IsA(setOp, RangeTblRef)) { RangeTblRef *rtr = (RangeTblRef *) setOp; RangeTblEntry *subrte = rt_fetch(rtr->rtindex, topquery->rtable); Query *subquery = subrte->subquery; Assert(subquery != NULL); subquery_push_qual(subquery, rte, rti, qual); } else if (IsA(setOp, SetOperationStmt)) { SetOperationStmt *op = (SetOperationStmt *) setOp; recurse_push_qual(op->larg, topquery, rte, rti, qual); recurse_push_qual(op->rarg, topquery, rte, rti, qual); } else { elog(ERROR, "unrecognized node type: %d", (int) nodeTag(setOp)); } } /***************************************************************************** * SIMPLIFYING SUBQUERY TARGETLISTS *****************************************************************************/ /* * remove_unused_subquery_outputs * Remove subquery targetlist items we don't need * * It's possible, even likely, that the upper query does not read all the * output columns of the subquery. We can remove any such outputs that are * not needed by the subquery itself (e.g., as sort/group columns) and do not * affect semantics otherwise (e.g., volatile functions can't be removed). * This is useful not only because we might be able to remove expensive-to- * compute expressions, but because deletion of output columns might allow * optimizations such as join removal to occur within the subquery. * * extra_used_attrs can be passed as non-NULL to mark any columns (offset by * FirstLowInvalidHeapAttributeNumber) that we should not remove. This * parameter is modified by the function, so callers must make a copy if they * need to use the passed in Bitmapset after calling this function. * * To avoid affecting column numbering in the targetlist, we don't physically * remove unused tlist entries, but rather replace their expressions with NULL * constants. This is implemented by modifying subquery->targetList. */ static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel, Bitmapset *extra_used_attrs) { Bitmapset *attrs_used; ListCell *lc; /* * Just point directly to extra_used_attrs. No need to bms_copy as none of * the current callers use the Bitmapset after calling this function. */ attrs_used = extra_used_attrs; /* * Do nothing if subquery has UNION/INTERSECT/EXCEPT: in principle we * could update all the child SELECTs' tlists, but it seems not worth the * trouble presently. */ if (subquery->setOperations) return; /* * If subquery has regular DISTINCT (not DISTINCT ON), we're wasting our * time: all its output columns must be used in the distinctClause. */ if (subquery->distinctClause && !subquery->hasDistinctOn) return; /* * Collect a bitmap of all the output column numbers used by the upper * query. * * Add all the attributes needed for joins or final output. Note: we must * look at rel's targetlist, not the attr_needed data, because attr_needed * isn't computed for inheritance child rels, cf set_append_rel_size(). * (XXX might be worth changing that sometime.) */ pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used); /* Add all the attributes used by un-pushed-down restriction clauses. */ foreach(lc, rel->baserestrictinfo) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc); pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used); } /* * If there's a whole-row reference to the subquery, we can't remove * anything. */ if (bms_is_member(0 - FirstLowInvalidHeapAttributeNumber, attrs_used)) return; /* * Run through the tlist and zap entries we don't need. It's okay to * modify the tlist items in-place because set_subquery_pathlist made a * copy of the subquery. */ foreach(lc, subquery->targetList) { TargetEntry *tle = (TargetEntry *) lfirst(lc); Node *texpr = (Node *) tle->expr; /* * If it has a sortgroupref number, it's used in some sort/group * clause so we'd better not remove it. Also, don't remove any * resjunk columns, since their reason for being has nothing to do * with anybody reading the subquery's output. (It's likely that * resjunk columns in a sub-SELECT would always have ressortgroupref * set, but even if they don't, it seems imprudent to remove them.) */ if (tle->ressortgroupref || tle->resjunk) continue; /* * If it's used by the upper query, we can't remove it. */ if (bms_is_member(tle->resno - FirstLowInvalidHeapAttributeNumber, attrs_used)) continue; /* * If it contains a set-returning function, we can't remove it since * that could change the number of rows returned by the subquery. */ if (subquery->hasTargetSRFs && expression_returns_set(texpr)) continue; /* * If it contains volatile functions, we daren't remove it for fear * that the user is expecting their side-effects to happen. */ if (contain_volatile_functions(texpr)) continue; /* * OK, we don't need it. Replace the expression with a NULL constant. * Preserve the exposed type of the expression, in case something * looks at the rowtype of the subquery's result. */ tle->expr = (Expr *) makeNullConst(exprType(texpr), exprTypmod(texpr), exprCollation(texpr)); } } /* * create_partial_bitmap_paths * Build partial bitmap heap path for the relation */ void create_partial_bitmap_paths(PlannerInfo *root, RelOptInfo *rel, Path *bitmapqual) { int parallel_workers; double pages_fetched; /* Compute heap pages for bitmap heap scan */ pages_fetched = compute_bitmap_pages(root, rel, bitmapqual, 1.0, NULL, NULL); parallel_workers = compute_parallel_worker(rel, pages_fetched, -1, max_parallel_workers_per_gather); if (parallel_workers <= 0) return; add_partial_path(rel, (Path *) create_bitmap_heap_path(root, rel, bitmapqual, rel->lateral_relids, 1.0, parallel_workers)); } /* * Compute the number of parallel workers that should be used to scan a * relation. We compute the parallel workers based on the size of the heap to * be scanned and the size of the index to be scanned, then choose a minimum * of those. * * "heap_pages" is the number of pages from the table that we expect to scan, or * -1 if we don't expect to scan any. * * "index_pages" is the number of pages from the index that we expect to scan, or * -1 if we don't expect to scan any. * * "max_workers" is caller's limit on the number of workers. This typically * comes from a GUC. */ int compute_parallel_worker(RelOptInfo *rel, double heap_pages, double index_pages, int max_workers) { int parallel_workers = 0; /* * If the user has set the parallel_workers reloption, use that; otherwise * select a default number of workers. */ if (rel->rel_parallel_workers != -1) parallel_workers = rel->rel_parallel_workers; else { /* * If the number of pages being scanned is insufficient to justify a * parallel scan, just return zero ... unless it's an inheritance * child. In that case, we want to generate a parallel path here * anyway. It might not be worthwhile just for this relation, but * when combined with all of its inheritance siblings it may well pay * off. */ if (rel->reloptkind == RELOPT_BASEREL && ((heap_pages >= 0 && heap_pages < min_parallel_table_scan_size) || (index_pages >= 0 && index_pages < min_parallel_index_scan_size))) return 0; if (heap_pages >= 0) { int heap_parallel_threshold; int heap_parallel_workers = 1; /* * Select the number of workers based on the log of the size of * the relation. This probably needs to be a good deal more * sophisticated, but we need something here for now. Note that * the upper limit of the min_parallel_table_scan_size GUC is * chosen to prevent overflow here. */ heap_parallel_threshold = Max(min_parallel_table_scan_size, 1); while (heap_pages >= (BlockNumber) (heap_parallel_threshold * 3)) { heap_parallel_workers++; heap_parallel_threshold *= 3; if (heap_parallel_threshold > INT_MAX / 3) break; /* avoid overflow */ } parallel_workers = heap_parallel_workers; } if (index_pages >= 0) { int index_parallel_workers = 1; int index_parallel_threshold; /* same calculation as for heap_pages above */ index_parallel_threshold = Max(min_parallel_index_scan_size, 1); while (index_pages >= (BlockNumber) (index_parallel_threshold * 3)) { index_parallel_workers++; index_parallel_threshold *= 3; if (index_parallel_threshold > INT_MAX / 3) break; /* avoid overflow */ } if (parallel_workers > 0) parallel_workers = Min(parallel_workers, index_parallel_workers); else parallel_workers = index_parallel_workers; } } /* In no case use more than caller supplied maximum number of workers */ parallel_workers = Min(parallel_workers, max_workers); return parallel_workers; } /* * generate_partitionwise_join_paths * Create paths representing partitionwise join for given partitioned * join relation. * * This must not be called until after we are done adding paths for all * child-joins. Otherwise, add_path might delete a path to which some path * generated here has a reference. */ void generate_partitionwise_join_paths(PlannerInfo *root, RelOptInfo *rel) { List *live_children = NIL; int cnt_parts; int num_parts; RelOptInfo **part_rels; /* Handle only join relations here. */ if (!IS_JOIN_REL(rel)) return; /* We've nothing to do if the relation is not partitioned. */ if (!IS_PARTITIONED_REL(rel)) return; /* The relation should have consider_partitionwise_join set. */ Assert(rel->consider_partitionwise_join); /* Guard against stack overflow due to overly deep partition hierarchy. */ check_stack_depth(); num_parts = rel->nparts; part_rels = rel->part_rels; /* Collect non-dummy child-joins. */ for (cnt_parts = 0; cnt_parts < num_parts; cnt_parts++) { RelOptInfo *child_rel = part_rels[cnt_parts]; /* If it's been pruned entirely, it's certainly dummy. */ if (child_rel == NULL) continue; /* Make partitionwise join paths for this partitioned child-join. */ generate_partitionwise_join_paths(root, child_rel); /* If we failed to make any path for this child, we must give up. */ if (child_rel->pathlist == NIL) { /* * Mark the parent joinrel as unpartitioned so that later * functions treat it correctly. */ rel->nparts = 0; return; } /* Else, identify the cheapest path for it. */ set_cheapest(child_rel); /* Dummy children need not be scanned, so ignore those. */ if (IS_DUMMY_REL(child_rel)) continue; #ifdef OPTIMIZER_DEBUG pprint(child_rel); #endif live_children = lappend(live_children, child_rel); } /* If all child-joins are dummy, parent join is also dummy. */ if (!live_children) { mark_dummy_rel(rel); return; } /* Build additional paths for this rel from child-join paths. */ add_paths_to_append_rel(root, rel, live_children); list_free(live_children); }