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the cons cell it's deleting from the list. Do this, and fix a few callers that were bogusly assuming it wouldn't free the cons cell.
1029 lines
30 KiB
C
1029 lines
30 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) 1996-2002, 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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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.43 2002/12/17 01:18:22 tgl 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 "nodes/makefuncs.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/planmain.h"
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#include "optimizer/tlist.h"
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#include "parser/parsetree.h"
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#include "parser/parse_func.h"
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#include "utils/lsyscache.h"
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static PathKeyItem *makePathKeyItem(Node *key, Oid sortop);
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static List *make_canonical_pathkey(Query *root, PathKeyItem *item);
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static Var *find_indexkey_var(Query *root, RelOptInfo *rel,
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AttrNumber varattno);
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/*
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* makePathKeyItem
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* create a PathKeyItem node
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*/
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static PathKeyItem *
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makePathKeyItem(Node *key, Oid sortop)
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{
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PathKeyItem *item = makeNode(PathKeyItem);
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item->key = key;
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item->sortop = sortop;
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return item;
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}
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/*
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* add_equijoined_keys
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* The given clause has a mergejoinable operator, so its two sides
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* can be considered equal after restriction clause application; in
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* particular, any pathkey mentioning one side (with the correct sortop)
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* can be expanded to include the other as well. Record the vars and
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* associated sortops in the query's equi_key_list for future use.
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*
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* The query's equi_key_list field points to a list of sublists of PathKeyItem
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* nodes, where each sublist is a set of two or more vars+sortops that have
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* been identified as logically equivalent (and, therefore, we may consider
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* any two in a set to be equal). As described above, we will subsequently
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* use direct pointers to one of these sublists to represent any pathkey
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* that involves an equijoined variable.
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*
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* This code would actually work fine with expressions more complex than
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* a single Var, but currently it won't see any because check_mergejoinable
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* won't accept such clauses as mergejoinable.
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*/
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void
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add_equijoined_keys(Query *root, RestrictInfo *restrictinfo)
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{
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Expr *clause = restrictinfo->clause;
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PathKeyItem *item1 = makePathKeyItem((Node *) get_leftop(clause),
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restrictinfo->left_sortop);
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PathKeyItem *item2 = makePathKeyItem((Node *) get_rightop(clause),
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restrictinfo->right_sortop);
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List *newset,
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*cursetlink;
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/* We might see a clause X=X; don't make a single-element list from it */
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if (equal(item1, item2))
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return;
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/*
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* Our plan is to make a two-element set, then sweep through the
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* existing equijoin sets looking for matches to item1 or item2. When
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* we find one, we remove that set from equi_key_list and union it
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* into our new set. When done, we add the new set to the front of
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* equi_key_list.
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*
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* It may well be that the two items we're given are already known to be
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* equijoin-equivalent, in which case we don't need to change our data
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* structure. If we find both of them in the same equivalence set to
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* start with, we can quit immediately.
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*
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* This is a standard UNION-FIND problem, for which there exist better
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* data structures than simple lists. If this code ever proves to be
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* a bottleneck then it could be sped up --- but for now, simple is
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* beautiful.
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*/
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newset = NIL;
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/* cannot use foreach here because of possible lremove */
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cursetlink = root->equi_key_list;
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while (cursetlink)
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{
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List *curset = lfirst(cursetlink);
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bool item1here = member(item1, curset);
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bool item2here = member(item2, curset);
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/* must advance cursetlink before lremove possibly pfree's it */
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cursetlink = lnext(cursetlink);
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if (item1here || item2here)
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{
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/*
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* If find both in same equivalence set, no need to do any
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* more
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*/
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if (item1here && item2here)
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{
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/* Better not have seen only one in an earlier set... */
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Assert(newset == NIL);
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return;
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}
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/* Build the new set only when we know we must */
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if (newset == NIL)
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newset = makeList2(item1, item2);
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/* Found a set to merge into our new set */
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newset = set_union(newset, curset);
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/*
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* Remove old set from equi_key_list.
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*/
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root->equi_key_list = lremove(curset, root->equi_key_list);
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freeList(curset); /* might as well recycle old cons cells */
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}
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}
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/* Build the new set only when we know we must */
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if (newset == NIL)
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newset = makeList2(item1, item2);
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root->equi_key_list = lcons(newset, root->equi_key_list);
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}
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/*
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* generate_implied_equalities
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* Scan the completed equi_key_list for the query, and generate explicit
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* qualifications (WHERE clauses) for all the pairwise equalities not
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* already mentioned in the quals. This is useful because the additional
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* clauses help the selectivity-estimation code, and in fact it's
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* *necessary* to ensure that sort keys we think are equivalent really
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* are (see src/backend/optimizer/README for more info).
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*
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* This routine just walks the equi_key_list to find all pairwise equalities.
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* We call process_implied_equality (in plan/initsplan.c) to determine whether
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* each is already known and add it to the proper restrictinfo list if not.
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*/
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void
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generate_implied_equalities(Query *root)
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{
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List *cursetlink;
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foreach(cursetlink, root->equi_key_list)
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{
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List *curset = lfirst(cursetlink);
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List *ptr1;
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/*
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* A set containing only two items cannot imply any equalities
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* beyond the one that created the set, so we can skip it.
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*/
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if (length(curset) < 3)
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continue;
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/*
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* Match each item in the set with all that appear after it (it's
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* sufficient to generate A=B, need not process B=A too).
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*/
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foreach(ptr1, curset)
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{
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PathKeyItem *item1 = (PathKeyItem *) lfirst(ptr1);
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List *ptr2;
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foreach(ptr2, lnext(ptr1))
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{
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PathKeyItem *item2 = (PathKeyItem *) lfirst(ptr2);
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process_implied_equality(root, item1->key, item2->key,
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item1->sortop, item2->sortop);
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}
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}
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}
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}
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/*
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* make_canonical_pathkey
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* Given a PathKeyItem, find the equi_key_list subset it is a member of,
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* if any. If so, return a pointer to that sublist, which is the
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* canonical representation (for this query) of that PathKeyItem's
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* equivalence set. If it is not found, add a singleton "equivalence set"
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* to the equi_key_list and return that --- see compare_pathkeys.
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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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* scanning the WHERE clause for equijoin operators.
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*/
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static List *
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make_canonical_pathkey(Query *root, PathKeyItem *item)
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{
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List *cursetlink;
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List *newset;
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foreach(cursetlink, root->equi_key_list)
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{
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List *curset = lfirst(cursetlink);
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if (member(item, curset))
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return curset;
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}
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newset = makeList1(item);
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root->equi_key_list = lcons(newset, root->equi_key_list);
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return newset;
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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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* scanning the WHERE clause for equijoin operators.
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*/
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List *
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canonicalize_pathkeys(Query *root, List *pathkeys)
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{
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List *new_pathkeys = NIL;
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List *i;
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foreach(i, pathkeys)
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{
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List *pathkey = (List *) lfirst(i);
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PathKeyItem *item;
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List *cpathkey;
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/*
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* It's sufficient to look at the first entry in the sublist; if
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* there are more entries, they're already part of an equivalence
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* set by definition.
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*/
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Assert(pathkey != NIL);
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item = (PathKeyItem *) lfirst(pathkey);
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cpathkey = make_canonical_pathkey(root, item);
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/*
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* Eliminate redundant ordering requests --- ORDER BY A,A is the
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* same as ORDER BY A. We want to check this only after we have
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* canonicalized the keys, so that equivalent-key knowledge is
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* used when deciding if an item is redundant.
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*/
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if (!ptrMember(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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* 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, sublists 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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List *key1,
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*key2;
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for (key1 = keys1, key2 = keys2;
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key1 != NIL && key2 != NIL;
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key1 = lnext(key1), key2 = lnext(key2))
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{
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List *subkey1 = lfirst(key1);
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List *subkey2 = lfirst(key2);
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/*
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* XXX would like to check that we've been given canonicalized
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* input, but query root not accessible here...
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*/
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#ifdef NOT_USED
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Assert(ptrMember(subkey1, root->equi_key_list));
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Assert(ptrMember(subkey2, root->equi_key_list));
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#endif
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/*
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* We will never have two subkeys where one is a subset of the
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* other, because of the canonicalization process. Either they
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* are equal or they ain't. Furthermore, we only need pointer
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* comparison to detect equality.
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*/
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if (subkey1 != subkey2)
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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. (We assume the additional sublist(s) of
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* the other list are not NIL --- no pathkey list should ever have a
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* NIL sublist.)
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*/
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if (key1 == NIL && key2 == NIL)
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return PATHKEYS_EQUAL;
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if (key1 != NIL)
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return PATHKEYS_BETTER1; /* key1 is longer */
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return PATHKEYS_BETTER2; /* key2 is longer */
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}
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/*
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* compare_noncanonical_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. This is used when we must compare
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* non-canonicalized pathkeys.
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*
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* A pathkey can be considered better than another if it is a superset:
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* it contains all the keys of the other plus more. For example, either
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* ((A) (B)) or ((A B)) is better than ((A)).
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*
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* Currently, the only user of this routine is grouping_planner(),
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* and it will only pass single-element sublists (from
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* make_pathkeys_for_sortclauses). Therefore we don't have to do the
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* full two-way-subset-inclusion test on each pair of sublists that is
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* implied by the above statement. Instead we just verify they are
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* singleton lists and then do an equal(). This could be improved if
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* necessary.
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*/
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PathKeysComparison
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compare_noncanonical_pathkeys(List *keys1, List *keys2)
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{
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List *key1,
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*key2;
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for (key1 = keys1, key2 = keys2;
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key1 != NIL && key2 != NIL;
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key1 = lnext(key1), key2 = lnext(key2))
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{
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List *subkey1 = lfirst(key1);
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List *subkey2 = lfirst(key2);
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Assert(length(subkey1) == 1);
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Assert(length(subkey2) == 1);
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if (!equal(subkey1, subkey2))
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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. (We assume the additional sublist(s) of
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* the other list are not NIL --- no pathkey list should ever have a
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* NIL sublist.)
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*/
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if (key1 == NIL && key2 == NIL)
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return PATHKEYS_EQUAL;
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if (key1 != NIL)
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return PATHKEYS_BETTER1; /* key1 is longer */
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return PATHKEYS_BETTER2; /* key2 is longer */
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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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* noncanonical_pathkeys_contained_in
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* The same, when we don't have canonical pathkeys.
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*/
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bool
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noncanonical_pathkeys_contained_in(List *keys1, List *keys2)
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{
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switch (compare_noncanonical_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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List *i;
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foreach(i, paths)
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{
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Path *path = (Path *) lfirst(i);
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/*
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* Since cost comparison is a lot cheaper than pathkey comparison,
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* do 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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List *i;
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foreach(i, paths)
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{
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Path *path = (Path *) lfirst(i);
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/*
|
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* Since cost comparison is a lot cheaper than pathkey comparison,
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* do 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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/****************************************************************************
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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 "ordering" field, 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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List *
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build_index_pathkeys(Query *root,
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RelOptInfo *rel,
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IndexOptInfo *index,
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ScanDirection scandir)
|
|
{
|
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List *retval = NIL;
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int *indexkeys = index->indexkeys;
|
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Oid *ordering = index->ordering;
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PathKeyItem *item;
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Oid sortop;
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if (!indexkeys || indexkeys[0] == 0 ||
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!ordering || ordering[0] == InvalidOid)
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return NIL; /* unordered index? */
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|
|
if (index->indproc)
|
|
{
|
|
/* Functional index: build a representation of the function call */
|
|
Expr *funcnode;
|
|
List *funcargs = NIL;
|
|
|
|
sortop = *ordering;
|
|
if (ScanDirectionIsBackward(scandir))
|
|
{
|
|
sortop = get_commutator(sortop);
|
|
if (sortop == InvalidOid)
|
|
return NIL; /* oops, no reverse sort operator? */
|
|
}
|
|
|
|
while (*indexkeys != 0)
|
|
{
|
|
funcargs = lappend(funcargs,
|
|
find_indexkey_var(root, rel, *indexkeys));
|
|
indexkeys++;
|
|
}
|
|
|
|
funcnode = make_funcclause(index->indproc,
|
|
get_func_rettype(index->indproc),
|
|
false, /* cannot be a set */
|
|
COERCE_DONTCARE, /* to match any user expr */
|
|
funcargs);
|
|
|
|
/* Make a one-sublist pathkeys list for the function expression */
|
|
item = makePathKeyItem((Node *) funcnode, sortop);
|
|
retval = makeList1(make_canonical_pathkey(root, item));
|
|
}
|
|
else
|
|
{
|
|
/* Normal non-functional index */
|
|
while (*indexkeys != 0 && *ordering != InvalidOid)
|
|
{
|
|
Var *relvar = find_indexkey_var(root, rel, *indexkeys);
|
|
List *cpathkey;
|
|
|
|
sortop = *ordering;
|
|
if (ScanDirectionIsBackward(scandir))
|
|
{
|
|
sortop = get_commutator(sortop);
|
|
if (sortop == InvalidOid)
|
|
break; /* oops, no reverse sort operator? */
|
|
}
|
|
|
|
/* OK, make a sublist for this sort key */
|
|
item = makePathKeyItem((Node *) relvar, sortop);
|
|
cpathkey = make_canonical_pathkey(root, item);
|
|
|
|
/*
|
|
* Eliminate redundant ordering info; could happen if query is
|
|
* such that index keys are equijoined...
|
|
*/
|
|
if (!ptrMember(cpathkey, retval))
|
|
retval = lappend(retval, cpathkey);
|
|
indexkeys++;
|
|
ordering++;
|
|
}
|
|
}
|
|
|
|
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(Query *root, RelOptInfo *rel, AttrNumber varattno)
|
|
{
|
|
List *temp;
|
|
int relid;
|
|
Oid reloid,
|
|
vartypeid;
|
|
int32 type_mod;
|
|
|
|
foreach(temp, rel->targetlist)
|
|
{
|
|
Var *tle_var = get_expr(lfirst(temp));
|
|
|
|
if (IsA(tle_var, Var) &&tle_var->varattno == varattno)
|
|
return tle_var;
|
|
}
|
|
|
|
relid = lfirsti(rel->relids);
|
|
reloid = getrelid(relid, root->rtable);
|
|
vartypeid = get_atttype(reloid, varattno);
|
|
type_mod = get_atttypmod(reloid, varattno);
|
|
|
|
return makeVar(relid, varattno, vartypeid, type_mod, 0);
|
|
}
|
|
|
|
/*
|
|
* build_join_pathkeys
|
|
* Build the path keys for a join relation constructed by mergejoin or
|
|
* nestloop join. These keys should include all the path key vars of the
|
|
* outer path (since the join will retain the ordering of the outer path)
|
|
* plus any vars of the inner path that are equijoined to the outer vars.
|
|
*
|
|
* Per the discussion in backend/optimizer/README, equijoined inner vars
|
|
* can be considered path keys of the result, just the same as the outer
|
|
* vars they were joined with; furthermore, it doesn't matter what kind
|
|
* of join algorithm is actually used.
|
|
*
|
|
* 'joinrel' is the join relation that paths are being formed for
|
|
* 'outer_pathkeys' is the list of the current outer path's path keys
|
|
*
|
|
* Returns the list of new path keys.
|
|
*/
|
|
List *
|
|
build_join_pathkeys(Query *root,
|
|
RelOptInfo *joinrel,
|
|
List *outer_pathkeys)
|
|
{
|
|
/*
|
|
* 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! The inner-rel vars we used to need to add are
|
|
* *already* part of the outer pathkey!
|
|
*
|
|
* We do, however, need to truncate the pathkeys list, since it may
|
|
* contain pathkeys that were useful for forming this joinrel but are
|
|
* uninteresting to higher levels.
|
|
*/
|
|
return truncate_useless_pathkeys(root, joinrel, outer_pathkeys);
|
|
}
|
|
|
|
/****************************************************************************
|
|
* PATHKEYS AND SORT CLAUSES
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* make_pathkeys_for_sortclauses
|
|
* Generate a pathkeys list that represents the sort order specified
|
|
* by a list of SortClauses (GroupClauses will work too!)
|
|
*
|
|
* NB: the result is NOT in canonical form, but must be passed through
|
|
* canonicalize_pathkeys() before it can be used for comparisons or
|
|
* labeling relation sort orders. (We do things this way because
|
|
* grouping_planner needs to be able to construct requested pathkeys
|
|
* before the pathkey equivalence sets have been created for the query.)
|
|
*
|
|
* 'sortclauses' is a list of SortClause or GroupClause nodes
|
|
* 'tlist' is the targetlist to find the referenced tlist entries in
|
|
*/
|
|
List *
|
|
make_pathkeys_for_sortclauses(List *sortclauses,
|
|
List *tlist)
|
|
{
|
|
List *pathkeys = NIL;
|
|
List *i;
|
|
|
|
foreach(i, sortclauses)
|
|
{
|
|
SortClause *sortcl = (SortClause *) lfirst(i);
|
|
Node *sortkey;
|
|
PathKeyItem *pathkey;
|
|
|
|
sortkey = get_sortgroupclause_expr(sortcl, tlist);
|
|
pathkey = makePathKeyItem(sortkey, sortcl->sortop);
|
|
|
|
/*
|
|
* The pathkey becomes a one-element sublist, for now;
|
|
* canonicalize_pathkeys() might replace it with a longer sublist
|
|
* later.
|
|
*/
|
|
pathkeys = lappend(pathkeys, makeList1(pathkey));
|
|
}
|
|
return pathkeys;
|
|
}
|
|
|
|
/****************************************************************************
|
|
* PATHKEYS AND MERGECLAUSES
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* cache_mergeclause_pathkeys
|
|
* Make the cached pathkeys valid in a mergeclause restrictinfo.
|
|
*
|
|
* RestrictInfo contains fields in which we may cache the result
|
|
* of looking up the canonical pathkeys for the left and right sides
|
|
* of the mergeclause. (Note that in normal cases they will be the
|
|
* same, but not if the mergeclause appears above an OUTER JOIN.)
|
|
* This is a worthwhile savings because these routines will be invoked
|
|
* many times when dealing with a many-relation query.
|
|
*/
|
|
void
|
|
cache_mergeclause_pathkeys(Query *root, RestrictInfo *restrictinfo)
|
|
{
|
|
Node *key;
|
|
PathKeyItem *item;
|
|
|
|
Assert(restrictinfo->mergejoinoperator != InvalidOid);
|
|
|
|
if (restrictinfo->left_pathkey == NIL)
|
|
{
|
|
key = (Node *) get_leftop(restrictinfo->clause);
|
|
item = makePathKeyItem(key, restrictinfo->left_sortop);
|
|
restrictinfo->left_pathkey = make_canonical_pathkey(root, item);
|
|
}
|
|
if (restrictinfo->right_pathkey == NIL)
|
|
{
|
|
key = (Node *) get_rightop(restrictinfo->clause);
|
|
item = makePathKeyItem(key, restrictinfo->right_sortop);
|
|
restrictinfo->right_pathkey = make_canonical_pathkey(root, item);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
* It doesn't matter whether it is for the inner or outer path.
|
|
* 'restrictinfos' is a list of mergejoinable restriction clauses for the
|
|
* join relation being formed.
|
|
*
|
|
* 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).
|
|
*
|
|
* XXX Ideally we ought to be considering context, ie what path orderings
|
|
* are available on the other side of the join, rather than just making
|
|
* an arbitrary choice among the mergeclauses that will work for this side
|
|
* of the join.
|
|
*/
|
|
List *
|
|
find_mergeclauses_for_pathkeys(Query *root,
|
|
List *pathkeys,
|
|
List *restrictinfos)
|
|
{
|
|
List *mergeclauses = NIL;
|
|
List *i;
|
|
|
|
/* make sure we have pathkeys cached in the clauses */
|
|
foreach(i, restrictinfos)
|
|
{
|
|
RestrictInfo *restrictinfo = lfirst(i);
|
|
|
|
cache_mergeclause_pathkeys(root, restrictinfo);
|
|
}
|
|
|
|
foreach(i, pathkeys)
|
|
{
|
|
List *pathkey = lfirst(i);
|
|
List *matched_restrictinfos = NIL;
|
|
List *j;
|
|
|
|
/*
|
|
* We can match a pathkey against either left or right side of any
|
|
* mergejoin clause. (We examine both sides since we aren't told
|
|
* if the given pathkeys are for inner or outer input path; no
|
|
* confusion is possible.) Furthermore, if there are multiple
|
|
* matching clauses, take them all. In plain inner-join scenarios
|
|
* we expect only one match, because redundant-mergeclause
|
|
* elimination will have removed any redundant mergeclauses from
|
|
* the input list. 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.
|
|
*/
|
|
foreach(j, restrictinfos)
|
|
{
|
|
RestrictInfo *restrictinfo = lfirst(j);
|
|
|
|
/*
|
|
* We can compare canonical pathkey sublists by simple pointer
|
|
* equality; see compare_pathkeys.
|
|
*/
|
|
if ((pathkey == restrictinfo->left_pathkey ||
|
|
pathkey == restrictinfo->right_pathkey) &&
|
|
!ptrMember(restrictinfo, mergeclauses))
|
|
{
|
|
matched_restrictinfos = lappend(matched_restrictinfos,
|
|
restrictinfo);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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 = nconc(mergeclauses, matched_restrictinfos);
|
|
}
|
|
|
|
return mergeclauses;
|
|
}
|
|
|
|
/*
|
|
* make_pathkeys_for_mergeclauses
|
|
* Builds a pathkey list representing the explicit sort order that
|
|
* must be applied to a path in order to make it usable for the
|
|
* given mergeclauses.
|
|
*
|
|
* 'mergeclauses' is a list of RestrictInfos for mergejoin clauses
|
|
* that will be used in a merge join.
|
|
* 'rel' is the relation the pathkeys will apply to (ie, either the inner
|
|
* or outer side of the proposed join rel).
|
|
*
|
|
* Returns a pathkeys list that can be applied to the indicated 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_pathkeys_for_mergeclauses(Query *root,
|
|
List *mergeclauses,
|
|
RelOptInfo *rel)
|
|
{
|
|
List *pathkeys = NIL;
|
|
List *i;
|
|
|
|
foreach(i, mergeclauses)
|
|
{
|
|
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(i);
|
|
Node *key;
|
|
List *pathkey;
|
|
|
|
cache_mergeclause_pathkeys(root, restrictinfo);
|
|
|
|
key = (Node *) get_leftop(restrictinfo->clause);
|
|
if (IsA(key, Var) &&
|
|
VARISRELMEMBER(((Var *) key)->varno, rel))
|
|
{
|
|
/* Rel is left side of mergeclause */
|
|
pathkey = restrictinfo->left_pathkey;
|
|
}
|
|
else
|
|
{
|
|
key = (Node *) get_rightop(restrictinfo->clause);
|
|
if (IsA(key, Var) &&
|
|
VARISRELMEMBER(((Var *) key)->varno, rel))
|
|
{
|
|
/* Rel is right side of mergeclause */
|
|
pathkey = restrictinfo->right_pathkey;
|
|
}
|
|
else
|
|
{
|
|
elog(ERROR, "make_pathkeys_for_mergeclauses: can't identify which side of mergeclause to use");
|
|
pathkey = NIL; /* keep compiler quiet */
|
|
}
|
|
}
|
|
|
|
/*
|
|
* When we are given multiple merge clauses, it's possible that
|
|
* some clauses refer to the same vars as earlier clauses. There's
|
|
* no reason for us to specify sort keys like (A,B,A) when (A,B)
|
|
* will do --- and adding redundant sort keys makes add_path think
|
|
* that this sort order is different from ones that are really the
|
|
* same, so don't do it. Since we now have a canonicalized
|
|
* pathkey, a simple ptrMember test is sufficient to detect
|
|
* redundant keys.
|
|
*/
|
|
if (!ptrMember(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 (by looking at its joininfo lists).
|
|
*
|
|
* 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 appear in different join lists
|
|
* might never be usable at the same time, but trying to be exact is likely
|
|
* to be more trouble than it's worth.
|
|
*/
|
|
int
|
|
pathkeys_useful_for_merging(Query *root, RelOptInfo *rel, List *pathkeys)
|
|
{
|
|
int useful = 0;
|
|
List *i;
|
|
|
|
foreach(i, pathkeys)
|
|
{
|
|
List *pathkey = lfirst(i);
|
|
bool matched = false;
|
|
List *j;
|
|
|
|
foreach(j, rel->joininfo)
|
|
{
|
|
JoinInfo *joininfo = (JoinInfo *) lfirst(j);
|
|
List *k;
|
|
|
|
foreach(k, joininfo->jinfo_restrictinfo)
|
|
{
|
|
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(k);
|
|
|
|
if (restrictinfo->mergejoinoperator == InvalidOid)
|
|
continue;
|
|
cache_mergeclause_pathkeys(root, restrictinfo);
|
|
|
|
/*
|
|
* We can compare canonical pathkey sublists by simple
|
|
* pointer equality; see compare_pathkeys.
|
|
*/
|
|
if (pathkey == restrictinfo->left_pathkey ||
|
|
pathkey == restrictinfo->right_pathkey)
|
|
{
|
|
matched = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (matched)
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* If we didn't find a mergeclause, we're done --- any additional
|
|
* sort-key positions in the pathkeys are useless. (But we can
|
|
* still mergejoin if we found at least one mergeclause.)
|
|
*/
|
|
if (matched)
|
|
useful++;
|
|
else
|
|
break;
|
|
}
|
|
|
|
return useful;
|
|
}
|
|
|
|
/*
|
|
* pathkeys_useful_for_ordering
|
|
* Count the number of pathkeys that are useful for meeting the
|
|
* query's requested output ordering.
|
|
*
|
|
* Unlike merge pathkeys, this is an all-or-nothing affair: it does us
|
|
* no good to order by just the first key(s) of the requested ordering.
|
|
* So the result is always either 0 or length(root->query_pathkeys).
|
|
*/
|
|
int
|
|
pathkeys_useful_for_ordering(Query *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 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(Query *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 == length(pathkeys))
|
|
return pathkeys;
|
|
else
|
|
return ltruncate(nuseful, listCopy(pathkeys));
|
|
}
|