1521 lines
46 KiB
C
1521 lines
46 KiB
C
/*-------------------------------------------------------------------------
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*
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* pathkeys.c
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* Utilities for matching and building path keys
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*
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* See src/backend/optimizer/README for a great deal of information about
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* the nature and use of path keys.
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*
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*
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* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.101 2010/02/26 02:00:45 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/skey.h"
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#include "catalog/pg_type.h"
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#include "nodes/makefuncs.h"
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#include "nodes/nodeFuncs.h"
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#include "nodes/plannodes.h"
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#include "optimizer/clauses.h"
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#include "optimizer/pathnode.h"
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#include "optimizer/paths.h"
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#include "optimizer/tlist.h"
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#include "parser/parsetree.h"
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#include "utils/lsyscache.h"
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static PathKey *makePathKey(EquivalenceClass *eclass, Oid opfamily,
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int strategy, bool nulls_first);
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static PathKey *make_canonical_pathkey(PlannerInfo *root,
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EquivalenceClass *eclass, Oid opfamily,
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int strategy, bool nulls_first);
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static bool pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys);
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static PathKey *make_pathkey_from_sortinfo(PlannerInfo *root,
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Expr *expr, Oid ordering_op,
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bool nulls_first,
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Index sortref,
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bool canonicalize);
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static Var *find_indexkey_var(PlannerInfo *root, RelOptInfo *rel,
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AttrNumber varattno);
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static bool right_merge_direction(PlannerInfo *root, PathKey *pathkey);
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/****************************************************************************
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* PATHKEY CONSTRUCTION AND REDUNDANCY TESTING
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****************************************************************************/
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/*
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* makePathKey
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* create a PathKey node
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*
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* This does not promise to create a canonical PathKey, it's merely a
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* convenience routine to build the specified node.
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*/
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static PathKey *
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makePathKey(EquivalenceClass *eclass, Oid opfamily,
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int strategy, bool nulls_first)
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{
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PathKey *pk = makeNode(PathKey);
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pk->pk_eclass = eclass;
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pk->pk_opfamily = opfamily;
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pk->pk_strategy = strategy;
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pk->pk_nulls_first = nulls_first;
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return pk;
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}
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/*
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* make_canonical_pathkey
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* Given the parameters for a PathKey, find any pre-existing matching
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* pathkey in the query's list of "canonical" pathkeys. Make a new
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* entry if there's not one already.
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*
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* Note that this function must not be used until after we have completed
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* merging EquivalenceClasses.
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*/
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static PathKey *
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make_canonical_pathkey(PlannerInfo *root,
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EquivalenceClass *eclass, Oid opfamily,
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int strategy, bool nulls_first)
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{
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PathKey *pk;
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ListCell *lc;
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MemoryContext oldcontext;
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/* The passed eclass might be non-canonical, so chase up to the top */
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while (eclass->ec_merged)
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eclass = eclass->ec_merged;
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foreach(lc, root->canon_pathkeys)
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{
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pk = (PathKey *) lfirst(lc);
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if (eclass == pk->pk_eclass &&
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opfamily == pk->pk_opfamily &&
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strategy == pk->pk_strategy &&
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nulls_first == pk->pk_nulls_first)
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return pk;
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}
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/*
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* Be sure canonical pathkeys are allocated in the main planning context.
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* Not an issue in normal planning, but it is for GEQO.
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*/
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oldcontext = MemoryContextSwitchTo(root->planner_cxt);
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pk = makePathKey(eclass, opfamily, strategy, nulls_first);
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root->canon_pathkeys = lappend(root->canon_pathkeys, pk);
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MemoryContextSwitchTo(oldcontext);
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return pk;
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}
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/*
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* pathkey_is_redundant
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* Is a pathkey redundant with one already in the given list?
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*
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* Both the given pathkey and the list members must be canonical for this
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* to work properly. We detect two cases:
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*
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* 1. If the new pathkey's equivalence class contains a constant, and isn't
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* below an outer join, then we can disregard it as a sort key. An example:
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* SELECT ... WHERE x = 42 ORDER BY x, y;
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* We may as well just sort by y. Note that because of opfamily matching,
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* this is semantically correct: we know that the equality constraint is one
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* that actually binds the variable to a single value in the terms of any
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* ordering operator that might go with the eclass. This rule not only lets
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* us simplify (or even skip) explicit sorts, but also allows matching index
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* sort orders to a query when there are don't-care index columns.
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*
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* 2. If the new pathkey's equivalence class is the same as that of any
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* existing member of the pathkey list, then it is redundant. Some examples:
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* SELECT ... ORDER BY x, x;
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* SELECT ... ORDER BY x, x DESC;
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* SELECT ... WHERE x = y ORDER BY x, y;
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* In all these cases the second sort key cannot distinguish values that are
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* considered equal by the first, and so there's no point in using it.
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* Note in particular that we need not compare opfamily (all the opfamilies
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* of the EC have the same notion of equality) nor sort direction.
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*
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* Because the equivclass.c machinery forms only one copy of any EC per query,
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* pointer comparison is enough to decide whether canonical ECs are the same.
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*/
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static bool
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pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys)
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{
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EquivalenceClass *new_ec = new_pathkey->pk_eclass;
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ListCell *lc;
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/* Assert we've been given canonical pathkeys */
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Assert(!new_ec->ec_merged);
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/* Check for EC containing a constant --- unconditionally redundant */
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if (EC_MUST_BE_REDUNDANT(new_ec))
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return true;
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/* If same EC already used in list, then redundant */
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foreach(lc, pathkeys)
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{
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PathKey *old_pathkey = (PathKey *) lfirst(lc);
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/* Assert we've been given canonical pathkeys */
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Assert(!old_pathkey->pk_eclass->ec_merged);
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if (new_ec == old_pathkey->pk_eclass)
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return true;
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}
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return false;
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}
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/*
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* canonicalize_pathkeys
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* Convert a not-necessarily-canonical pathkeys list to canonical form.
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*
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* Note that this function must not be used until after we have completed
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* merging EquivalenceClasses.
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*/
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List *
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canonicalize_pathkeys(PlannerInfo *root, List *pathkeys)
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{
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List *new_pathkeys = NIL;
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ListCell *l;
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foreach(l, pathkeys)
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{
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PathKey *pathkey = (PathKey *) lfirst(l);
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EquivalenceClass *eclass;
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PathKey *cpathkey;
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/* Find the canonical (merged) EquivalenceClass */
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eclass = pathkey->pk_eclass;
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while (eclass->ec_merged)
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eclass = eclass->ec_merged;
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/*
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* If we can tell it's redundant just from the EC, skip.
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* pathkey_is_redundant would notice that, but we needn't even bother
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* constructing the node...
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*/
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if (EC_MUST_BE_REDUNDANT(eclass))
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continue;
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/* OK, build a canonicalized PathKey struct */
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cpathkey = make_canonical_pathkey(root,
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eclass,
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pathkey->pk_opfamily,
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pathkey->pk_strategy,
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pathkey->pk_nulls_first);
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/* Add to list unless redundant */
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if (!pathkey_is_redundant(cpathkey, new_pathkeys))
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new_pathkeys = lappend(new_pathkeys, cpathkey);
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}
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return new_pathkeys;
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}
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/*
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* make_pathkey_from_sortinfo
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* Given an expression, a sortop, and a nulls-first flag, create
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* a PathKey. If canonicalize = true, the result is a "canonical"
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* PathKey, otherwise not. (But note it might be redundant anyway.)
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*
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* If the PathKey is being generated from a SortGroupClause, sortref should be
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* the SortGroupClause's SortGroupRef; otherwise zero.
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*
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* canonicalize should always be TRUE after EquivalenceClass merging has
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* been performed, but FALSE if we haven't done EquivalenceClass merging yet.
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*/
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static PathKey *
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make_pathkey_from_sortinfo(PlannerInfo *root,
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Expr *expr, Oid ordering_op,
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bool nulls_first,
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Index sortref,
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bool canonicalize)
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{
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Oid opfamily,
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opcintype;
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int16 strategy;
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Oid equality_op;
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List *opfamilies;
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EquivalenceClass *eclass;
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/*
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* An ordering operator fully determines the behavior of its opfamily, so
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* could only meaningfully appear in one family --- or perhaps two if one
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* builds a reverse-sort opfamily, but there's not much point in that
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* anymore. But EquivalenceClasses need to contain opfamily lists based
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* on the family membership of equality operators, which could easily be
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* bigger. So, look up the equality operator that goes with the ordering
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* operator (this should be unique) and get its membership.
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*/
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/* Find the operator in pg_amop --- failure shouldn't happen */
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if (!get_ordering_op_properties(ordering_op,
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&opfamily, &opcintype, &strategy))
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elog(ERROR, "operator %u is not a valid ordering operator",
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ordering_op);
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/* Get matching equality operator */
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equality_op = get_opfamily_member(opfamily,
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opcintype,
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opcintype,
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BTEqualStrategyNumber);
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if (!OidIsValid(equality_op)) /* shouldn't happen */
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elog(ERROR, "could not find equality operator for ordering operator %u",
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ordering_op);
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opfamilies = get_mergejoin_opfamilies(equality_op);
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if (!opfamilies) /* certainly should find some */
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elog(ERROR, "could not find opfamilies for ordering operator %u",
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ordering_op);
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/*
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* When dealing with binary-compatible opclasses, we have to ensure that
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* the exposed type of the expression tree matches the declared input type
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* of the opclass, except when that is a polymorphic type (compare the
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* behavior of parse_coerce.c). This ensures that we can correctly match
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* the indexkey or sortclause expression to other expressions we find in
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* the query, because arguments of ordinary operator expressions will be
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* cast that way. (We have to do this for indexkeys because they are
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* represented without any explicit relabel in pg_index, and for sort
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* clauses because the parser is likewise cavalier about putting relabels
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* on them.)
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*/
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if (exprType((Node *) expr) != opcintype &&
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!IsPolymorphicType(opcintype))
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{
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/* Strip any existing RelabelType, and add a new one if needed */
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while (expr && IsA(expr, RelabelType))
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expr = (Expr *) ((RelabelType *) expr)->arg;
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if (exprType((Node *) expr) != opcintype)
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expr = (Expr *) makeRelabelType(expr,
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opcintype,
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-1,
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COERCE_DONTCARE);
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}
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/* Now find or create a matching EquivalenceClass */
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eclass = get_eclass_for_sort_expr(root, expr, opcintype, opfamilies,
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sortref);
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/* And finally we can find or create a PathKey node */
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if (canonicalize)
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return make_canonical_pathkey(root, eclass, opfamily,
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strategy, nulls_first);
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else
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return makePathKey(eclass, opfamily, strategy, nulls_first);
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}
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/****************************************************************************
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* PATHKEY COMPARISONS
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****************************************************************************/
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/*
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* compare_pathkeys
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* Compare two pathkeys to see if they are equivalent, and if not whether
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* one is "better" than the other.
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*
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* This function may only be applied to canonicalized pathkey lists.
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* In the canonical representation, pathkeys can be checked for equality
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* by simple pointer comparison.
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*/
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PathKeysComparison
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compare_pathkeys(List *keys1, List *keys2)
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{
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ListCell *key1,
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*key2;
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/*
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* Fall out quickly if we are passed two identical lists. This mostly
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* catches the case where both are NIL, but that's common enough to
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* warrant the test.
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*/
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if (keys1 == keys2)
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return PATHKEYS_EQUAL;
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forboth(key1, keys1, key2, keys2)
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{
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PathKey *pathkey1 = (PathKey *) lfirst(key1);
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PathKey *pathkey2 = (PathKey *) lfirst(key2);
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/*
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* XXX would like to check that we've been given canonicalized input,
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* but PlannerInfo not accessible here...
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*/
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#ifdef NOT_USED
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Assert(list_member_ptr(root->canon_pathkeys, pathkey1));
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Assert(list_member_ptr(root->canon_pathkeys, pathkey2));
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#endif
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if (pathkey1 != pathkey2)
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return PATHKEYS_DIFFERENT; /* no need to keep looking */
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}
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/*
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* If we reached the end of only one list, the other is longer and
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* therefore not a subset.
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*/
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if (key1 != NULL)
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return PATHKEYS_BETTER1; /* key1 is longer */
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if (key2 != NULL)
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return PATHKEYS_BETTER2; /* key2 is longer */
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return PATHKEYS_EQUAL;
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}
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/*
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* pathkeys_contained_in
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* Common special case of compare_pathkeys: we just want to know
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* if keys2 are at least as well sorted as keys1.
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*/
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bool
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pathkeys_contained_in(List *keys1, List *keys2)
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{
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switch (compare_pathkeys(keys1, keys2))
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{
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case PATHKEYS_EQUAL:
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case PATHKEYS_BETTER2:
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return true;
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default:
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break;
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}
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return false;
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}
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/*
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* get_cheapest_path_for_pathkeys
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* Find the cheapest path (according to the specified criterion) that
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* satisfies the given pathkeys. Return NULL if no such path.
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*
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* 'paths' is a list of possible paths that all generate the same relation
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* 'pathkeys' represents a required ordering (already canonicalized!)
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* 'cost_criterion' is STARTUP_COST or TOTAL_COST
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*/
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Path *
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get_cheapest_path_for_pathkeys(List *paths, List *pathkeys,
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CostSelector cost_criterion)
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{
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Path *matched_path = NULL;
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ListCell *l;
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foreach(l, paths)
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{
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Path *path = (Path *) lfirst(l);
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/*
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* Since cost comparison is a lot cheaper than pathkey comparison, do
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* that first. (XXX is that still true?)
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*/
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if (matched_path != NULL &&
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compare_path_costs(matched_path, path, cost_criterion) <= 0)
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continue;
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if (pathkeys_contained_in(pathkeys, path->pathkeys))
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matched_path = path;
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}
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return matched_path;
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}
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/*
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* get_cheapest_fractional_path_for_pathkeys
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* Find the cheapest path (for retrieving a specified fraction of all
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* the tuples) that satisfies the given pathkeys.
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* Return NULL if no such path.
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*
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* See compare_fractional_path_costs() for the interpretation of the fraction
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* parameter.
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*
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* 'paths' is a list of possible paths that all generate the same relation
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* 'pathkeys' represents a required ordering (already canonicalized!)
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* 'fraction' is the fraction of the total tuples expected to be retrieved
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*/
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Path *
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get_cheapest_fractional_path_for_pathkeys(List *paths,
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List *pathkeys,
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double fraction)
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{
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Path *matched_path = NULL;
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ListCell *l;
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foreach(l, paths)
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{
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Path *path = (Path *) lfirst(l);
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/*
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* Since cost comparison is a lot cheaper than pathkey comparison, do
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* that first.
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*/
|
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if (matched_path != NULL &&
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compare_fractional_path_costs(matched_path, path, fraction) <= 0)
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continue;
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if (pathkeys_contained_in(pathkeys, path->pathkeys))
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matched_path = path;
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}
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return matched_path;
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}
|
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|
|
/****************************************************************************
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* NEW PATHKEY FORMATION
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****************************************************************************/
|
|
|
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/*
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* build_index_pathkeys
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* Build a pathkeys list that describes the ordering induced by an index
|
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* scan using the given index. (Note that an unordered index doesn't
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* induce any ordering; such an index will have no sortop OIDS in
|
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* its sortops arrays, and we will return NIL.)
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*
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* If 'scandir' is BackwardScanDirection, attempt to build pathkeys
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* representing a backwards scan of the index. Return NIL if can't do it.
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*
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* The result is canonical, meaning that redundant pathkeys are removed;
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* it may therefore have fewer entries than there are index columns.
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*
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* We generate the full pathkeys list whether or not all are useful for the
|
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* current query. Caller should do truncate_useless_pathkeys().
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*/
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List *
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build_index_pathkeys(PlannerInfo *root,
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IndexOptInfo *index,
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ScanDirection scandir)
|
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{
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List *retval = NIL;
|
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ListCell *indexprs_item = list_head(index->indexprs);
|
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int i;
|
|
|
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for (i = 0; i < index->ncolumns; i++)
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{
|
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Oid sortop;
|
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bool nulls_first;
|
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int ikey;
|
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Expr *indexkey;
|
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PathKey *cpathkey;
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|
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if (ScanDirectionIsBackward(scandir))
|
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{
|
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sortop = index->revsortop[i];
|
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nulls_first = !index->nulls_first[i];
|
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}
|
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else
|
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{
|
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sortop = index->fwdsortop[i];
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nulls_first = index->nulls_first[i];
|
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}
|
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|
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if (!OidIsValid(sortop))
|
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break; /* no more orderable columns */
|
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|
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ikey = index->indexkeys[i];
|
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if (ikey != 0)
|
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{
|
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/* simple index column */
|
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indexkey = (Expr *) find_indexkey_var(root, index->rel, ikey);
|
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}
|
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else
|
|
{
|
|
/* expression --- assume we need not copy it */
|
|
if (indexprs_item == NULL)
|
|
elog(ERROR, "wrong number of index expressions");
|
|
indexkey = (Expr *) lfirst(indexprs_item);
|
|
indexprs_item = lnext(indexprs_item);
|
|
}
|
|
|
|
/* OK, make a canonical pathkey for this sort key */
|
|
cpathkey = make_pathkey_from_sortinfo(root,
|
|
indexkey,
|
|
sortop,
|
|
nulls_first,
|
|
0,
|
|
true);
|
|
|
|
/* Add to list unless redundant */
|
|
if (!pathkey_is_redundant(cpathkey, retval))
|
|
retval = lappend(retval, cpathkey);
|
|
}
|
|
|
|
return retval;
|
|
}
|
|
|
|
/*
|
|
* Find or make a Var node for the specified attribute of the rel.
|
|
*
|
|
* We first look for the var in the rel's target list, because that's
|
|
* easy and fast. But the var might not be there (this should normally
|
|
* only happen for vars that are used in WHERE restriction clauses,
|
|
* but not in join clauses or in the SELECT target list). In that case,
|
|
* gin up a Var node the hard way.
|
|
*/
|
|
static Var *
|
|
find_indexkey_var(PlannerInfo *root, RelOptInfo *rel, AttrNumber varattno)
|
|
{
|
|
ListCell *temp;
|
|
Index relid;
|
|
Oid reloid,
|
|
vartypeid;
|
|
int32 type_mod;
|
|
|
|
foreach(temp, rel->reltargetlist)
|
|
{
|
|
Var *var = (Var *) lfirst(temp);
|
|
|
|
if (IsA(var, Var) &&
|
|
var->varattno == varattno)
|
|
return var;
|
|
}
|
|
|
|
relid = rel->relid;
|
|
reloid = getrelid(relid, root->parse->rtable);
|
|
get_atttypetypmod(reloid, varattno, &vartypeid, &type_mod);
|
|
|
|
return makeVar(relid, varattno, vartypeid, type_mod, 0);
|
|
}
|
|
|
|
/*
|
|
* convert_subquery_pathkeys
|
|
* Build a pathkeys list that describes the ordering of a subquery's
|
|
* result, in the terms of the outer query. This is essentially a
|
|
* task of conversion.
|
|
*
|
|
* 'rel': outer query's RelOptInfo for the subquery relation.
|
|
* 'subquery_pathkeys': the subquery's output pathkeys, in its terms.
|
|
*
|
|
* It is not necessary for caller to do truncate_useless_pathkeys(),
|
|
* because we select keys in a way that takes usefulness of the keys into
|
|
* account.
|
|
*/
|
|
List *
|
|
convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel,
|
|
List *subquery_pathkeys)
|
|
{
|
|
List *retval = NIL;
|
|
int retvallen = 0;
|
|
int outer_query_keys = list_length(root->query_pathkeys);
|
|
List *sub_tlist = rel->subplan->targetlist;
|
|
ListCell *i;
|
|
|
|
foreach(i, subquery_pathkeys)
|
|
{
|
|
PathKey *sub_pathkey = (PathKey *) lfirst(i);
|
|
EquivalenceClass *sub_eclass = sub_pathkey->pk_eclass;
|
|
PathKey *best_pathkey = NULL;
|
|
|
|
if (sub_eclass->ec_has_volatile)
|
|
{
|
|
/*
|
|
* If the sub_pathkey's EquivalenceClass is volatile, then it must
|
|
* have come from an ORDER BY clause, and we have to match it to
|
|
* that same targetlist entry.
|
|
*/
|
|
TargetEntry *tle;
|
|
|
|
if (sub_eclass->ec_sortref == 0) /* can't happen */
|
|
elog(ERROR, "volatile EquivalenceClass has no sortref");
|
|
tle = get_sortgroupref_tle(sub_eclass->ec_sortref, sub_tlist);
|
|
Assert(tle);
|
|
/* resjunk items aren't visible to outer query */
|
|
if (!tle->resjunk)
|
|
{
|
|
/* We can represent this sub_pathkey */
|
|
EquivalenceMember *sub_member;
|
|
Expr *outer_expr;
|
|
EquivalenceClass *outer_ec;
|
|
|
|
Assert(list_length(sub_eclass->ec_members) == 1);
|
|
sub_member = (EquivalenceMember *) linitial(sub_eclass->ec_members);
|
|
outer_expr = (Expr *)
|
|
makeVar(rel->relid,
|
|
tle->resno,
|
|
exprType((Node *) tle->expr),
|
|
exprTypmod((Node *) tle->expr),
|
|
0);
|
|
|
|
/*
|
|
* Note: it might look funny to be setting sortref = 0 for a
|
|
* reference to a volatile sub_eclass. However, the
|
|
* expression is *not* volatile in the outer query: it's just
|
|
* a Var referencing whatever the subquery emitted. (IOW, the
|
|
* outer query isn't going to re-execute the volatile
|
|
* expression itself.) So this is okay.
|
|
*/
|
|
outer_ec =
|
|
get_eclass_for_sort_expr(root,
|
|
outer_expr,
|
|
sub_member->em_datatype,
|
|
sub_eclass->ec_opfamilies,
|
|
0);
|
|
best_pathkey =
|
|
make_canonical_pathkey(root,
|
|
outer_ec,
|
|
sub_pathkey->pk_opfamily,
|
|
sub_pathkey->pk_strategy,
|
|
sub_pathkey->pk_nulls_first);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Otherwise, the sub_pathkey's EquivalenceClass could contain
|
|
* multiple elements (representing knowledge that multiple items
|
|
* are effectively equal). Each element might match none, one, or
|
|
* more of the output columns that are visible to the outer query.
|
|
* This means we may have multiple possible representations of the
|
|
* sub_pathkey in the context of the outer query. Ideally we
|
|
* would generate them all and put them all into an EC of the
|
|
* outer query, thereby propagating equality knowledge up to the
|
|
* outer query. Right now we cannot do so, because the outer
|
|
* query's EquivalenceClasses are already frozen when this is
|
|
* called. Instead we prefer the one that has the highest "score"
|
|
* (number of EC peers, plus one if it matches the outer
|
|
* query_pathkeys). This is the most likely to be useful in the
|
|
* outer query.
|
|
*/
|
|
int best_score = -1;
|
|
ListCell *j;
|
|
|
|
foreach(j, sub_eclass->ec_members)
|
|
{
|
|
EquivalenceMember *sub_member = (EquivalenceMember *) lfirst(j);
|
|
Expr *sub_expr = sub_member->em_expr;
|
|
Expr *sub_stripped;
|
|
ListCell *k;
|
|
|
|
/*
|
|
* We handle two cases: the sub_pathkey key can be either an
|
|
* exact match for a targetlist entry, or it could match after
|
|
* stripping RelabelType nodes. (We need that case since
|
|
* make_pathkey_from_sortinfo could add or remove
|
|
* RelabelType.)
|
|
*/
|
|
sub_stripped = sub_expr;
|
|
while (sub_stripped && IsA(sub_stripped, RelabelType))
|
|
sub_stripped = ((RelabelType *) sub_stripped)->arg;
|
|
|
|
foreach(k, sub_tlist)
|
|
{
|
|
TargetEntry *tle = (TargetEntry *) lfirst(k);
|
|
Expr *outer_expr;
|
|
EquivalenceClass *outer_ec;
|
|
PathKey *outer_pk;
|
|
int score;
|
|
|
|
/* resjunk items aren't visible to outer query */
|
|
if (tle->resjunk)
|
|
continue;
|
|
|
|
if (equal(tle->expr, sub_expr))
|
|
{
|
|
/* Exact match */
|
|
outer_expr = (Expr *)
|
|
makeVar(rel->relid,
|
|
tle->resno,
|
|
exprType((Node *) tle->expr),
|
|
exprTypmod((Node *) tle->expr),
|
|
0);
|
|
}
|
|
else
|
|
{
|
|
Expr *tle_stripped;
|
|
|
|
tle_stripped = tle->expr;
|
|
while (tle_stripped && IsA(tle_stripped, RelabelType))
|
|
tle_stripped = ((RelabelType *) tle_stripped)->arg;
|
|
|
|
if (equal(tle_stripped, sub_stripped))
|
|
{
|
|
/* Match after discarding RelabelType */
|
|
outer_expr = (Expr *)
|
|
makeVar(rel->relid,
|
|
tle->resno,
|
|
exprType((Node *) tle->expr),
|
|
exprTypmod((Node *) tle->expr),
|
|
0);
|
|
if (exprType((Node *) outer_expr) !=
|
|
exprType((Node *) sub_expr))
|
|
outer_expr = (Expr *)
|
|
makeRelabelType(outer_expr,
|
|
exprType((Node *) sub_expr),
|
|
-1,
|
|
COERCE_DONTCARE);
|
|
}
|
|
else
|
|
continue;
|
|
}
|
|
|
|
/* Found a representation for this sub_pathkey */
|
|
outer_ec = get_eclass_for_sort_expr(root,
|
|
outer_expr,
|
|
sub_member->em_datatype,
|
|
sub_eclass->ec_opfamilies,
|
|
0);
|
|
outer_pk = make_canonical_pathkey(root,
|
|
outer_ec,
|
|
sub_pathkey->pk_opfamily,
|
|
sub_pathkey->pk_strategy,
|
|
sub_pathkey->pk_nulls_first);
|
|
/* score = # of equivalence peers */
|
|
score = list_length(outer_ec->ec_members) - 1;
|
|
/* +1 if it matches the proper query_pathkeys item */
|
|
if (retvallen < outer_query_keys &&
|
|
list_nth(root->query_pathkeys, retvallen) == outer_pk)
|
|
score++;
|
|
if (score > best_score)
|
|
{
|
|
best_pathkey = outer_pk;
|
|
best_score = score;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If we couldn't find a representation of this sub_pathkey, we're
|
|
* done (we can't use the ones to its right, either).
|
|
*/
|
|
if (!best_pathkey)
|
|
break;
|
|
|
|
/*
|
|
* Eliminate redundant ordering info; could happen if outer query
|
|
* equivalences subquery keys...
|
|
*/
|
|
if (!pathkey_is_redundant(best_pathkey, retval))
|
|
{
|
|
retval = lappend(retval, best_pathkey);
|
|
retvallen++;
|
|
}
|
|
}
|
|
|
|
return retval;
|
|
}
|
|
|
|
/*
|
|
* build_join_pathkeys
|
|
* Build the path keys for a join relation constructed by mergejoin or
|
|
* nestloop join. This is normally the same as the outer path's keys.
|
|
*
|
|
* EXCEPTION: in a FULL or RIGHT join, we cannot treat the result as
|
|
* having the outer path's path keys, because null lefthand rows may be
|
|
* inserted at random points. It must be treated as unsorted.
|
|
*
|
|
* We truncate away any pathkeys that are uninteresting for higher joins.
|
|
*
|
|
* 'joinrel' is the join relation that paths are being formed for
|
|
* 'jointype' is the join type (inner, left, full, etc)
|
|
* 'outer_pathkeys' is the list of the current outer path's path keys
|
|
*
|
|
* Returns the list of new path keys.
|
|
*/
|
|
List *
|
|
build_join_pathkeys(PlannerInfo *root,
|
|
RelOptInfo *joinrel,
|
|
JoinType jointype,
|
|
List *outer_pathkeys)
|
|
{
|
|
if (jointype == JOIN_FULL || jointype == JOIN_RIGHT)
|
|
return NIL;
|
|
|
|
/*
|
|
* This used to be quite a complex bit of code, but now that all pathkey
|
|
* sublists start out life canonicalized, we don't have to do a darn thing
|
|
* here!
|
|
*
|
|
* We do, however, need to truncate the pathkeys list, since it may
|
|
* contain pathkeys that were useful for forming this joinrel but are
|
|
* uninteresting to higher levels.
|
|
*/
|
|
return truncate_useless_pathkeys(root, joinrel, outer_pathkeys);
|
|
}
|
|
|
|
/****************************************************************************
|
|
* PATHKEYS AND SORT CLAUSES
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* make_pathkeys_for_sortclauses
|
|
* Generate a pathkeys list that represents the sort order specified
|
|
* by a list of SortGroupClauses
|
|
*
|
|
* If canonicalize is TRUE, the resulting PathKeys are all in canonical form;
|
|
* otherwise not. canonicalize should always be TRUE after EquivalenceClass
|
|
* merging has been performed, but FALSE if we haven't done EquivalenceClass
|
|
* merging yet. (We provide this option because grouping_planner() needs to
|
|
* be able to represent requested pathkeys before the equivalence classes have
|
|
* been created for the query.)
|
|
*
|
|
* 'sortclauses' is a list of SortGroupClause nodes
|
|
* 'tlist' is the targetlist to find the referenced tlist entries in
|
|
*/
|
|
List *
|
|
make_pathkeys_for_sortclauses(PlannerInfo *root,
|
|
List *sortclauses,
|
|
List *tlist,
|
|
bool canonicalize)
|
|
{
|
|
List *pathkeys = NIL;
|
|
ListCell *l;
|
|
|
|
foreach(l, sortclauses)
|
|
{
|
|
SortGroupClause *sortcl = (SortGroupClause *) lfirst(l);
|
|
Expr *sortkey;
|
|
PathKey *pathkey;
|
|
|
|
sortkey = (Expr *) get_sortgroupclause_expr(sortcl, tlist);
|
|
Assert(OidIsValid(sortcl->sortop));
|
|
pathkey = make_pathkey_from_sortinfo(root,
|
|
sortkey,
|
|
sortcl->sortop,
|
|
sortcl->nulls_first,
|
|
sortcl->tleSortGroupRef,
|
|
canonicalize);
|
|
|
|
/* Canonical form eliminates redundant ordering keys */
|
|
if (canonicalize)
|
|
{
|
|
if (!pathkey_is_redundant(pathkey, pathkeys))
|
|
pathkeys = lappend(pathkeys, pathkey);
|
|
}
|
|
else
|
|
pathkeys = lappend(pathkeys, pathkey);
|
|
}
|
|
return pathkeys;
|
|
}
|
|
|
|
/****************************************************************************
|
|
* PATHKEYS AND MERGECLAUSES
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* cache_mergeclause_eclasses
|
|
* Make the cached EquivalenceClass links valid in a mergeclause
|
|
* restrictinfo.
|
|
*
|
|
* RestrictInfo contains fields in which we may cache pointers to
|
|
* EquivalenceClasses for the left and right inputs of the mergeclause.
|
|
* (If the mergeclause is a true equivalence clause these will be the
|
|
* same EquivalenceClass, otherwise not.)
|
|
*/
|
|
void
|
|
cache_mergeclause_eclasses(PlannerInfo *root, RestrictInfo *restrictinfo)
|
|
{
|
|
Assert(restrictinfo->mergeopfamilies != NIL);
|
|
|
|
/* the cached values should be either both set or both not */
|
|
if (restrictinfo->left_ec == NULL)
|
|
{
|
|
Expr *clause = restrictinfo->clause;
|
|
Oid lefttype,
|
|
righttype;
|
|
|
|
/* Need the declared input types of the operator */
|
|
op_input_types(((OpExpr *) clause)->opno, &lefttype, &righttype);
|
|
|
|
/* Find or create a matching EquivalenceClass for each side */
|
|
restrictinfo->left_ec =
|
|
get_eclass_for_sort_expr(root,
|
|
(Expr *) get_leftop(clause),
|
|
lefttype,
|
|
restrictinfo->mergeopfamilies,
|
|
0);
|
|
restrictinfo->right_ec =
|
|
get_eclass_for_sort_expr(root,
|
|
(Expr *) get_rightop(clause),
|
|
righttype,
|
|
restrictinfo->mergeopfamilies,
|
|
0);
|
|
}
|
|
else
|
|
Assert(restrictinfo->right_ec != NULL);
|
|
}
|
|
|
|
/*
|
|
* find_mergeclauses_for_pathkeys
|
|
* This routine attempts to find a set of mergeclauses that can be
|
|
* used with a specified ordering for one of the input relations.
|
|
* If successful, it returns a list of mergeclauses.
|
|
*
|
|
* 'pathkeys' is a pathkeys list showing the ordering of an input path.
|
|
* 'outer_keys' is TRUE if these keys are for the outer input path,
|
|
* FALSE if for inner.
|
|
* 'restrictinfos' is a list of mergejoinable restriction clauses for the
|
|
* join relation being formed.
|
|
*
|
|
* The restrictinfos must be marked (via outer_is_left) to show which side
|
|
* of each clause is associated with the current outer path. (See
|
|
* select_mergejoin_clauses())
|
|
*
|
|
* The result is NIL if no merge can be done, else a maximal list of
|
|
* usable mergeclauses (represented as a list of their restrictinfo nodes).
|
|
*/
|
|
List *
|
|
find_mergeclauses_for_pathkeys(PlannerInfo *root,
|
|
List *pathkeys,
|
|
bool outer_keys,
|
|
List *restrictinfos)
|
|
{
|
|
List *mergeclauses = NIL;
|
|
ListCell *i;
|
|
|
|
/* make sure we have eclasses cached in the clauses */
|
|
foreach(i, restrictinfos)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(i);
|
|
|
|
cache_mergeclause_eclasses(root, rinfo);
|
|
}
|
|
|
|
foreach(i, pathkeys)
|
|
{
|
|
PathKey *pathkey = (PathKey *) lfirst(i);
|
|
EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
|
|
List *matched_restrictinfos = NIL;
|
|
ListCell *j;
|
|
|
|
/*----------
|
|
* A mergejoin clause matches a pathkey if it has the same EC.
|
|
* If there are multiple matching clauses, take them all. In plain
|
|
* inner-join scenarios we expect only one match, because
|
|
* equivalence-class processing will have removed any redundant
|
|
* mergeclauses. However, in outer-join scenarios there might be
|
|
* multiple matches. An example is
|
|
*
|
|
* select * from a full join b
|
|
* on a.v1 = b.v1 and a.v2 = b.v2 and a.v1 = b.v2;
|
|
*
|
|
* Given the pathkeys ({a.v1}, {a.v2}) it is okay to return all three
|
|
* clauses (in the order a.v1=b.v1, a.v1=b.v2, a.v2=b.v2) and indeed
|
|
* we *must* do so or we will be unable to form a valid plan.
|
|
*
|
|
* We expect that the given pathkeys list is canonical, which means
|
|
* no two members have the same EC, so it's not possible for this
|
|
* code to enter the same mergeclause into the result list twice.
|
|
*
|
|
* It's possible that multiple matching clauses might have different
|
|
* ECs on the other side, in which case the order we put them into our
|
|
* result makes a difference in the pathkeys required for the other
|
|
* input path. However this routine hasn't got any info about which
|
|
* order would be best, so we don't worry about that.
|
|
*
|
|
* It's also possible that the selected mergejoin clauses produce
|
|
* a noncanonical ordering of pathkeys for the other side, ie, we
|
|
* might select clauses that reference b.v1, b.v2, b.v1 in that
|
|
* order. This is not harmful in itself, though it suggests that
|
|
* the clauses are partially redundant. Since it happens only with
|
|
* redundant query conditions, we don't bother to eliminate it.
|
|
* make_inner_pathkeys_for_merge() has to delete duplicates when
|
|
* it constructs the canonical pathkeys list, and we also have to
|
|
* deal with the case in create_mergejoin_plan().
|
|
*----------
|
|
*/
|
|
foreach(j, restrictinfos)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(j);
|
|
EquivalenceClass *clause_ec;
|
|
|
|
if (outer_keys)
|
|
clause_ec = rinfo->outer_is_left ?
|
|
rinfo->left_ec : rinfo->right_ec;
|
|
else
|
|
clause_ec = rinfo->outer_is_left ?
|
|
rinfo->right_ec : rinfo->left_ec;
|
|
if (clause_ec == pathkey_ec)
|
|
matched_restrictinfos = lappend(matched_restrictinfos, rinfo);
|
|
}
|
|
|
|
/*
|
|
* If we didn't find a mergeclause, we're done --- any additional
|
|
* sort-key positions in the pathkeys are useless. (But we can still
|
|
* mergejoin if we found at least one mergeclause.)
|
|
*/
|
|
if (matched_restrictinfos == NIL)
|
|
break;
|
|
|
|
/*
|
|
* If we did find usable mergeclause(s) for this sort-key position,
|
|
* add them to result list.
|
|
*/
|
|
mergeclauses = list_concat(mergeclauses, matched_restrictinfos);
|
|
}
|
|
|
|
return mergeclauses;
|
|
}
|
|
|
|
/*
|
|
* select_outer_pathkeys_for_merge
|
|
* Builds a pathkey list representing a possible sort ordering
|
|
* that can be used with the given mergeclauses.
|
|
*
|
|
* 'mergeclauses' is a list of RestrictInfos for mergejoin clauses
|
|
* that will be used in a merge join.
|
|
* 'joinrel' is the join relation we are trying to construct.
|
|
*
|
|
* The restrictinfos must be marked (via outer_is_left) to show which side
|
|
* of each clause is associated with the current outer path. (See
|
|
* select_mergejoin_clauses())
|
|
*
|
|
* Returns a pathkeys list that can be applied to the outer relation.
|
|
*
|
|
* Since we assume here that a sort is required, there is no particular use
|
|
* in matching any available ordering of the outerrel. (joinpath.c has an
|
|
* entirely separate code path for considering sort-free mergejoins.) Rather,
|
|
* it's interesting to try to match the requested query_pathkeys so that a
|
|
* second output sort may be avoided; and failing that, we try to list "more
|
|
* popular" keys (those with the most unmatched EquivalenceClass peers)
|
|
* earlier, in hopes of making the resulting ordering useful for as many
|
|
* higher-level mergejoins as possible.
|
|
*/
|
|
List *
|
|
select_outer_pathkeys_for_merge(PlannerInfo *root,
|
|
List *mergeclauses,
|
|
RelOptInfo *joinrel)
|
|
{
|
|
List *pathkeys = NIL;
|
|
int nClauses = list_length(mergeclauses);
|
|
EquivalenceClass **ecs;
|
|
int *scores;
|
|
int necs;
|
|
ListCell *lc;
|
|
int j;
|
|
|
|
/* Might have no mergeclauses */
|
|
if (nClauses == 0)
|
|
return NIL;
|
|
|
|
/*
|
|
* Make arrays of the ECs used by the mergeclauses (dropping any
|
|
* duplicates) and their "popularity" scores.
|
|
*/
|
|
ecs = (EquivalenceClass **) palloc(nClauses * sizeof(EquivalenceClass *));
|
|
scores = (int *) palloc(nClauses * sizeof(int));
|
|
necs = 0;
|
|
|
|
foreach(lc, mergeclauses)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
|
|
EquivalenceClass *oeclass;
|
|
int score;
|
|
ListCell *lc2;
|
|
|
|
/* get the outer eclass */
|
|
cache_mergeclause_eclasses(root, rinfo);
|
|
|
|
if (rinfo->outer_is_left)
|
|
oeclass = rinfo->left_ec;
|
|
else
|
|
oeclass = rinfo->right_ec;
|
|
|
|
/* reject duplicates */
|
|
for (j = 0; j < necs; j++)
|
|
{
|
|
if (ecs[j] == oeclass)
|
|
break;
|
|
}
|
|
if (j < necs)
|
|
continue;
|
|
|
|
/* compute score */
|
|
score = 0;
|
|
foreach(lc2, oeclass->ec_members)
|
|
{
|
|
EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
|
|
|
|
/* Potential future join partner? */
|
|
if (!em->em_is_const && !em->em_is_child &&
|
|
!bms_overlap(em->em_relids, joinrel->relids))
|
|
score++;
|
|
}
|
|
|
|
ecs[necs] = oeclass;
|
|
scores[necs] = score;
|
|
necs++;
|
|
}
|
|
|
|
/*
|
|
* Find out if we have all the ECs mentioned in query_pathkeys; if so we
|
|
* can generate a sort order that's also useful for final output. There is
|
|
* no percentage in a partial match, though, so we have to have 'em all.
|
|
*/
|
|
if (root->query_pathkeys)
|
|
{
|
|
foreach(lc, root->query_pathkeys)
|
|
{
|
|
PathKey *query_pathkey = (PathKey *) lfirst(lc);
|
|
EquivalenceClass *query_ec = query_pathkey->pk_eclass;
|
|
|
|
for (j = 0; j < necs; j++)
|
|
{
|
|
if (ecs[j] == query_ec)
|
|
break; /* found match */
|
|
}
|
|
if (j >= necs)
|
|
break; /* didn't find match */
|
|
}
|
|
/* if we got to the end of the list, we have them all */
|
|
if (lc == NULL)
|
|
{
|
|
/* copy query_pathkeys as starting point for our output */
|
|
pathkeys = list_copy(root->query_pathkeys);
|
|
/* mark their ECs as already-emitted */
|
|
foreach(lc, root->query_pathkeys)
|
|
{
|
|
PathKey *query_pathkey = (PathKey *) lfirst(lc);
|
|
EquivalenceClass *query_ec = query_pathkey->pk_eclass;
|
|
|
|
for (j = 0; j < necs; j++)
|
|
{
|
|
if (ecs[j] == query_ec)
|
|
{
|
|
scores[j] = -1;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Add remaining ECs to the list in popularity order, using a default sort
|
|
* ordering. (We could use qsort() here, but the list length is usually
|
|
* so small it's not worth it.)
|
|
*/
|
|
for (;;)
|
|
{
|
|
int best_j;
|
|
int best_score;
|
|
EquivalenceClass *ec;
|
|
PathKey *pathkey;
|
|
|
|
best_j = 0;
|
|
best_score = scores[0];
|
|
for (j = 1; j < necs; j++)
|
|
{
|
|
if (scores[j] > best_score)
|
|
{
|
|
best_j = j;
|
|
best_score = scores[j];
|
|
}
|
|
}
|
|
if (best_score < 0)
|
|
break; /* all done */
|
|
ec = ecs[best_j];
|
|
scores[best_j] = -1;
|
|
pathkey = make_canonical_pathkey(root,
|
|
ec,
|
|
linitial_oid(ec->ec_opfamilies),
|
|
BTLessStrategyNumber,
|
|
false);
|
|
/* can't be redundant because no duplicate ECs */
|
|
Assert(!pathkey_is_redundant(pathkey, pathkeys));
|
|
pathkeys = lappend(pathkeys, pathkey);
|
|
}
|
|
|
|
pfree(ecs);
|
|
pfree(scores);
|
|
|
|
return pathkeys;
|
|
}
|
|
|
|
/*
|
|
* make_inner_pathkeys_for_merge
|
|
* Builds a pathkey list representing the explicit sort order that
|
|
* must be applied to an inner path to make it usable with the
|
|
* given mergeclauses.
|
|
*
|
|
* 'mergeclauses' is a list of RestrictInfos for mergejoin clauses
|
|
* that will be used in a merge join.
|
|
* 'outer_pathkeys' are the already-known canonical pathkeys for the outer
|
|
* side of the join.
|
|
*
|
|
* The restrictinfos must be marked (via outer_is_left) to show which side
|
|
* of each clause is associated with the current outer path. (See
|
|
* select_mergejoin_clauses())
|
|
*
|
|
* Returns a pathkeys list that can be applied to the inner relation.
|
|
*
|
|
* Note that it is not this routine's job to decide whether sorting is
|
|
* actually needed for a particular input path. Assume a sort is necessary;
|
|
* just make the keys, eh?
|
|
*/
|
|
List *
|
|
make_inner_pathkeys_for_merge(PlannerInfo *root,
|
|
List *mergeclauses,
|
|
List *outer_pathkeys)
|
|
{
|
|
List *pathkeys = NIL;
|
|
EquivalenceClass *lastoeclass;
|
|
PathKey *opathkey;
|
|
ListCell *lc;
|
|
ListCell *lop;
|
|
|
|
lastoeclass = NULL;
|
|
opathkey = NULL;
|
|
lop = list_head(outer_pathkeys);
|
|
|
|
foreach(lc, mergeclauses)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
|
|
EquivalenceClass *oeclass;
|
|
EquivalenceClass *ieclass;
|
|
PathKey *pathkey;
|
|
|
|
cache_mergeclause_eclasses(root, rinfo);
|
|
|
|
if (rinfo->outer_is_left)
|
|
{
|
|
oeclass = rinfo->left_ec;
|
|
ieclass = rinfo->right_ec;
|
|
}
|
|
else
|
|
{
|
|
oeclass = rinfo->right_ec;
|
|
ieclass = rinfo->left_ec;
|
|
}
|
|
|
|
/* outer eclass should match current or next pathkeys */
|
|
/* we check this carefully for debugging reasons */
|
|
if (oeclass != lastoeclass)
|
|
{
|
|
if (!lop)
|
|
elog(ERROR, "too few pathkeys for mergeclauses");
|
|
opathkey = (PathKey *) lfirst(lop);
|
|
lop = lnext(lop);
|
|
lastoeclass = opathkey->pk_eclass;
|
|
if (oeclass != lastoeclass)
|
|
elog(ERROR, "outer pathkeys do not match mergeclause");
|
|
}
|
|
|
|
/*
|
|
* Often, we'll have same EC on both sides, in which case the outer
|
|
* pathkey is also canonical for the inner side, and we can skip a
|
|
* useless search.
|
|
*/
|
|
if (ieclass == oeclass)
|
|
pathkey = opathkey;
|
|
else
|
|
pathkey = make_canonical_pathkey(root,
|
|
ieclass,
|
|
opathkey->pk_opfamily,
|
|
opathkey->pk_strategy,
|
|
opathkey->pk_nulls_first);
|
|
|
|
/*
|
|
* Don't generate redundant pathkeys (can happen if multiple
|
|
* mergeclauses refer to same EC).
|
|
*/
|
|
if (!pathkey_is_redundant(pathkey, pathkeys))
|
|
pathkeys = lappend(pathkeys, pathkey);
|
|
}
|
|
|
|
return pathkeys;
|
|
}
|
|
|
|
/****************************************************************************
|
|
* PATHKEY USEFULNESS CHECKS
|
|
*
|
|
* We only want to remember as many of the pathkeys of a path as have some
|
|
* potential use, either for subsequent mergejoins or for meeting the query's
|
|
* requested output ordering. This ensures that add_path() won't consider
|
|
* a path to have a usefully different ordering unless it really is useful.
|
|
* These routines check for usefulness of given pathkeys.
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* pathkeys_useful_for_merging
|
|
* Count the number of pathkeys that may be useful for mergejoins
|
|
* above the given relation.
|
|
*
|
|
* We consider a pathkey potentially useful if it corresponds to the merge
|
|
* ordering of either side of any joinclause for the rel. This might be
|
|
* overoptimistic, since joinclauses that require different other relations
|
|
* might never be usable at the same time, but trying to be exact is likely
|
|
* to be more trouble than it's worth.
|
|
*
|
|
* To avoid doubling the number of mergejoin paths considered, we would like
|
|
* to consider only one of the two scan directions (ASC or DESC) as useful
|
|
* for merging for any given target column. The choice is arbitrary unless
|
|
* one of the directions happens to match an ORDER BY key, in which case
|
|
* that direction should be preferred, in hopes of avoiding a final sort step.
|
|
* right_merge_direction() implements this heuristic.
|
|
*/
|
|
int
|
|
pathkeys_useful_for_merging(PlannerInfo *root, RelOptInfo *rel, List *pathkeys)
|
|
{
|
|
int useful = 0;
|
|
ListCell *i;
|
|
|
|
foreach(i, pathkeys)
|
|
{
|
|
PathKey *pathkey = (PathKey *) lfirst(i);
|
|
bool matched = false;
|
|
ListCell *j;
|
|
|
|
/* If "wrong" direction, not useful for merging */
|
|
if (!right_merge_direction(root, pathkey))
|
|
break;
|
|
|
|
/*
|
|
* First look into the EquivalenceClass of the pathkey, to see if
|
|
* there are any members not yet joined to the rel. If so, it's
|
|
* surely possible to generate a mergejoin clause using them.
|
|
*/
|
|
if (rel->has_eclass_joins &&
|
|
eclass_useful_for_merging(pathkey->pk_eclass, rel))
|
|
matched = true;
|
|
else
|
|
{
|
|
/*
|
|
* Otherwise search the rel's joininfo list, which contains
|
|
* non-EquivalenceClass-derivable join clauses that might
|
|
* nonetheless be mergejoinable.
|
|
*/
|
|
foreach(j, rel->joininfo)
|
|
{
|
|
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(j);
|
|
|
|
if (restrictinfo->mergeopfamilies == NIL)
|
|
continue;
|
|
cache_mergeclause_eclasses(root, restrictinfo);
|
|
|
|
if (pathkey->pk_eclass == restrictinfo->left_ec ||
|
|
pathkey->pk_eclass == restrictinfo->right_ec)
|
|
{
|
|
matched = true;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If we didn't find a mergeclause, we're done --- any additional
|
|
* sort-key positions in the pathkeys are useless. (But we can still
|
|
* mergejoin if we found at least one mergeclause.)
|
|
*/
|
|
if (matched)
|
|
useful++;
|
|
else
|
|
break;
|
|
}
|
|
|
|
return useful;
|
|
}
|
|
|
|
/*
|
|
* right_merge_direction
|
|
* Check whether the pathkey embodies the preferred sort direction
|
|
* for merging its target column.
|
|
*/
|
|
static bool
|
|
right_merge_direction(PlannerInfo *root, PathKey *pathkey)
|
|
{
|
|
ListCell *l;
|
|
|
|
foreach(l, root->query_pathkeys)
|
|
{
|
|
PathKey *query_pathkey = (PathKey *) lfirst(l);
|
|
|
|
if (pathkey->pk_eclass == query_pathkey->pk_eclass &&
|
|
pathkey->pk_opfamily == query_pathkey->pk_opfamily)
|
|
{
|
|
/*
|
|
* Found a matching query sort column. Prefer this pathkey's
|
|
* direction iff it matches. Note that we ignore pk_nulls_first,
|
|
* which means that a sort might be needed anyway ... but we still
|
|
* want to prefer only one of the two possible directions, and we
|
|
* might as well use this one.
|
|
*/
|
|
return (pathkey->pk_strategy == query_pathkey->pk_strategy);
|
|
}
|
|
}
|
|
|
|
/* If no matching ORDER BY request, prefer the ASC direction */
|
|
return (pathkey->pk_strategy == BTLessStrategyNumber);
|
|
}
|
|
|
|
/*
|
|
* pathkeys_useful_for_ordering
|
|
* Count the number of pathkeys that are useful for meeting the
|
|
* query's requested output ordering.
|
|
*
|
|
* Unlike merge pathkeys, this is an all-or-nothing affair: it does us
|
|
* no good to order by just the first key(s) of the requested ordering.
|
|
* So the result is always either 0 or list_length(root->query_pathkeys).
|
|
*/
|
|
int
|
|
pathkeys_useful_for_ordering(PlannerInfo *root, List *pathkeys)
|
|
{
|
|
if (root->query_pathkeys == NIL)
|
|
return 0; /* no special ordering requested */
|
|
|
|
if (pathkeys == NIL)
|
|
return 0; /* unordered path */
|
|
|
|
if (pathkeys_contained_in(root->query_pathkeys, pathkeys))
|
|
{
|
|
/* It's useful ... or at least the first N keys are */
|
|
return list_length(root->query_pathkeys);
|
|
}
|
|
|
|
return 0; /* path ordering not useful */
|
|
}
|
|
|
|
/*
|
|
* truncate_useless_pathkeys
|
|
* Shorten the given pathkey list to just the useful pathkeys.
|
|
*/
|
|
List *
|
|
truncate_useless_pathkeys(PlannerInfo *root,
|
|
RelOptInfo *rel,
|
|
List *pathkeys)
|
|
{
|
|
int nuseful;
|
|
int nuseful2;
|
|
|
|
nuseful = pathkeys_useful_for_merging(root, rel, pathkeys);
|
|
nuseful2 = pathkeys_useful_for_ordering(root, pathkeys);
|
|
if (nuseful2 > nuseful)
|
|
nuseful = nuseful2;
|
|
|
|
/*
|
|
* Note: not safe to modify input list destructively, but we can avoid
|
|
* copying the list if we're not actually going to change it
|
|
*/
|
|
if (nuseful == 0)
|
|
return NIL;
|
|
else if (nuseful == list_length(pathkeys))
|
|
return pathkeys;
|
|
else
|
|
return list_truncate(list_copy(pathkeys), nuseful);
|
|
}
|
|
|
|
/*
|
|
* has_useful_pathkeys
|
|
* Detect whether the specified rel could have any pathkeys that are
|
|
* useful according to truncate_useless_pathkeys().
|
|
*
|
|
* This is a cheap test that lets us skip building pathkeys at all in very
|
|
* simple queries. It's OK to err in the direction of returning "true" when
|
|
* there really aren't any usable pathkeys, but erring in the other direction
|
|
* is bad --- so keep this in sync with the routines above!
|
|
*
|
|
* We could make the test more complex, for example checking to see if any of
|
|
* the joinclauses are really mergejoinable, but that likely wouldn't win
|
|
* often enough to repay the extra cycles. Queries with neither a join nor
|
|
* a sort are reasonably common, though, so this much work seems worthwhile.
|
|
*/
|
|
bool
|
|
has_useful_pathkeys(PlannerInfo *root, RelOptInfo *rel)
|
|
{
|
|
if (rel->joininfo != NIL || rel->has_eclass_joins)
|
|
return true; /* might be able to use pathkeys for merging */
|
|
if (root->query_pathkeys != NIL)
|
|
return true; /* might be able to use them for ordering */
|
|
return false; /* definitely useless */
|
|
}
|