mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-08-23 07:40:42 +02:00
1594 lines
49 KiB
C
1594 lines
49 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* pathkeys.c
|
|
* Utilities for matching and building path keys
|
|
*
|
|
* See src/backend/optimizer/README for a great deal of information about
|
|
* the nature and use of path keys.
|
|
*
|
|
*
|
|
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
* IDENTIFICATION
|
|
* $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.71 2005/07/28 22:27:00 tgl Exp $
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#include "postgres.h"
|
|
|
|
#include "nodes/makefuncs.h"
|
|
#include "optimizer/clauses.h"
|
|
#include "optimizer/pathnode.h"
|
|
#include "optimizer/paths.h"
|
|
#include "optimizer/planmain.h"
|
|
#include "optimizer/tlist.h"
|
|
#include "optimizer/var.h"
|
|
#include "parser/parsetree.h"
|
|
#include "parser/parse_expr.h"
|
|
#include "parser/parse_func.h"
|
|
#include "utils/lsyscache.h"
|
|
#include "utils/memutils.h"
|
|
|
|
|
|
static PathKeyItem *makePathKeyItem(Node *key, Oid sortop, bool checkType);
|
|
static void generate_outer_join_implications(PlannerInfo *root,
|
|
List *equi_key_set,
|
|
Relids *relids);
|
|
static void sub_generate_join_implications(PlannerInfo *root,
|
|
List *equi_key_set, Relids *relids,
|
|
Node *item1, Oid sortop1,
|
|
Relids item1_relids);
|
|
static void process_implied_const_eq(PlannerInfo *root,
|
|
List *equi_key_set, Relids *relids,
|
|
Node *item1, Oid sortop1,
|
|
Relids item1_relids,
|
|
bool delete_it);
|
|
static List *make_canonical_pathkey(PlannerInfo *root, PathKeyItem *item);
|
|
static Var *find_indexkey_var(PlannerInfo *root, RelOptInfo *rel,
|
|
AttrNumber varattno);
|
|
|
|
|
|
/*
|
|
* makePathKeyItem
|
|
* create a PathKeyItem node
|
|
*/
|
|
static PathKeyItem *
|
|
makePathKeyItem(Node *key, Oid sortop, bool checkType)
|
|
{
|
|
PathKeyItem *item = makeNode(PathKeyItem);
|
|
|
|
/*
|
|
* Some callers pass expressions that are not necessarily of the same
|
|
* type as the sort operator expects as input (for example when
|
|
* dealing with an index that uses binary-compatible operators). We
|
|
* must relabel these with the correct type so that the key
|
|
* expressions will be seen as equal() to expressions that have been
|
|
* correctly labeled.
|
|
*/
|
|
if (checkType)
|
|
{
|
|
Oid lefttype,
|
|
righttype;
|
|
|
|
op_input_types(sortop, &lefttype, &righttype);
|
|
if (exprType(key) != lefttype)
|
|
key = (Node *) makeRelabelType((Expr *) key,
|
|
lefttype, -1,
|
|
COERCE_DONTCARE);
|
|
}
|
|
|
|
item->key = key;
|
|
item->sortop = sortop;
|
|
return item;
|
|
}
|
|
|
|
/*
|
|
* add_equijoined_keys
|
|
* The given clause has a mergejoinable operator, so its two sides
|
|
* can be considered equal after restriction clause application; in
|
|
* particular, any pathkey mentioning one side (with the correct sortop)
|
|
* can be expanded to include the other as well. Record the exprs and
|
|
* associated sortops in the query's equi_key_list for future use.
|
|
*
|
|
* The query's equi_key_list field points to a list of sublists of PathKeyItem
|
|
* nodes, where each sublist is a set of two or more exprs+sortops that have
|
|
* been identified as logically equivalent (and, therefore, we may consider
|
|
* any two in a set to be equal). As described above, we will subsequently
|
|
* use direct pointers to one of these sublists to represent any pathkey
|
|
* that involves an equijoined variable.
|
|
*/
|
|
void
|
|
add_equijoined_keys(PlannerInfo *root, RestrictInfo *restrictinfo)
|
|
{
|
|
Expr *clause = restrictinfo->clause;
|
|
PathKeyItem *item1 = makePathKeyItem(get_leftop(clause),
|
|
restrictinfo->left_sortop,
|
|
false);
|
|
PathKeyItem *item2 = makePathKeyItem(get_rightop(clause),
|
|
restrictinfo->right_sortop,
|
|
false);
|
|
List *newset;
|
|
ListCell *cursetlink;
|
|
|
|
/* We might see a clause X=X; don't make a single-element list from it */
|
|
if (equal(item1, item2))
|
|
return;
|
|
|
|
/*
|
|
* Our plan is to make a two-element set, then sweep through the
|
|
* existing equijoin sets looking for matches to item1 or item2. When
|
|
* we find one, we remove that set from equi_key_list and union it
|
|
* into our new set. When done, we add the new set to the front of
|
|
* equi_key_list.
|
|
*
|
|
* It may well be that the two items we're given are already known to be
|
|
* equijoin-equivalent, in which case we don't need to change our data
|
|
* structure. If we find both of them in the same equivalence set to
|
|
* start with, we can quit immediately.
|
|
*
|
|
* This is a standard UNION-FIND problem, for which there exist better
|
|
* data structures than simple lists. If this code ever proves to be
|
|
* a bottleneck then it could be sped up --- but for now, simple is
|
|
* beautiful.
|
|
*/
|
|
newset = NIL;
|
|
|
|
/* cannot use foreach here because of possible lremove */
|
|
cursetlink = list_head(root->equi_key_list);
|
|
while (cursetlink)
|
|
{
|
|
List *curset = (List *) lfirst(cursetlink);
|
|
bool item1here = list_member(curset, item1);
|
|
bool item2here = list_member(curset, item2);
|
|
|
|
/* must advance cursetlink before lremove possibly pfree's it */
|
|
cursetlink = lnext(cursetlink);
|
|
|
|
if (item1here || item2here)
|
|
{
|
|
/*
|
|
* If find both in same equivalence set, no need to do any
|
|
* more
|
|
*/
|
|
if (item1here && item2here)
|
|
{
|
|
/* Better not have seen only one in an earlier set... */
|
|
Assert(newset == NIL);
|
|
return;
|
|
}
|
|
|
|
/* Build the new set only when we know we must */
|
|
if (newset == NIL)
|
|
newset = list_make2(item1, item2);
|
|
|
|
/* Found a set to merge into our new set */
|
|
newset = list_concat_unique(newset, curset);
|
|
|
|
/*
|
|
* Remove old set from equi_key_list.
|
|
*/
|
|
root->equi_key_list = list_delete_ptr(root->equi_key_list, curset);
|
|
list_free(curset); /* might as well recycle old cons cells */
|
|
}
|
|
}
|
|
|
|
/* Build the new set only when we know we must */
|
|
if (newset == NIL)
|
|
newset = list_make2(item1, item2);
|
|
|
|
root->equi_key_list = lcons(newset, root->equi_key_list);
|
|
}
|
|
|
|
/*
|
|
* generate_implied_equalities
|
|
* Scan the completed equi_key_list for the query, and generate explicit
|
|
* qualifications (WHERE clauses) for all the pairwise equalities not
|
|
* already mentioned in the quals; or remove qualifications found to be
|
|
* redundant.
|
|
*
|
|
* Adding deduced equalities is useful because the additional clauses help
|
|
* the selectivity-estimation code and may allow better joins to be chosen;
|
|
* and in fact it's *necessary* to ensure that sort keys we think are
|
|
* equivalent really are (see src/backend/optimizer/README for more info).
|
|
*
|
|
* If an equi_key_list set includes any constants then we adopt a different
|
|
* strategy: we record all the "var = const" deductions we can make, and
|
|
* actively remove all the "var = var" clauses that are implied by the set
|
|
* (including the clauses that originally gave rise to the set!). The reason
|
|
* is that given input like "a = b AND b = 42", once we have deduced "a = 42"
|
|
* there is no longer any need to apply the clause "a = b"; not only is
|
|
* it a waste of time to check it, but we will misestimate selectivity if the
|
|
* clause is left in. So we must remove it. For this purpose, any pathkey
|
|
* item that mentions no Vars of the current level can be taken as a constant.
|
|
* (The only case where this would be risky is if the item contains volatile
|
|
* functions; but we will never consider such an expression to be a pathkey
|
|
* at all, because check_mergejoinable() will reject it.)
|
|
*
|
|
* Also, when we have constants in an equi_key_list we can try to propagate
|
|
* the constants into outer joins; see generate_outer_join_implications
|
|
* for discussion.
|
|
*
|
|
* This routine just walks the equi_key_list to find all pairwise equalities.
|
|
* We call process_implied_equality (in plan/initsplan.c) to adjust the
|
|
* restrictinfo datastructures for each pair.
|
|
*/
|
|
void
|
|
generate_implied_equalities(PlannerInfo *root)
|
|
{
|
|
ListCell *cursetlink;
|
|
|
|
foreach(cursetlink, root->equi_key_list)
|
|
{
|
|
List *curset = (List *) lfirst(cursetlink);
|
|
int nitems = list_length(curset);
|
|
Relids *relids;
|
|
bool have_consts;
|
|
ListCell *ptr1;
|
|
int i1;
|
|
|
|
/*
|
|
* A set containing only two items cannot imply any equalities
|
|
* beyond the one that created the set, so we can skip it ---
|
|
* unless outer joins appear in the query.
|
|
*/
|
|
if (nitems < 3 && !root->hasOuterJoins)
|
|
continue;
|
|
|
|
/*
|
|
* Collect info about relids mentioned in each item. For this
|
|
* routine we only really care whether there are any at all in
|
|
* each item, but process_implied_equality() needs the exact sets,
|
|
* so we may as well pull them here.
|
|
*/
|
|
relids = (Relids *) palloc(nitems * sizeof(Relids));
|
|
have_consts = false;
|
|
i1 = 0;
|
|
foreach(ptr1, curset)
|
|
{
|
|
PathKeyItem *item1 = (PathKeyItem *) lfirst(ptr1);
|
|
|
|
relids[i1] = pull_varnos(item1->key);
|
|
if (bms_is_empty(relids[i1]))
|
|
have_consts = true;
|
|
i1++;
|
|
}
|
|
|
|
/*
|
|
* Match each item in the set with all that appear after it (it's
|
|
* sufficient to generate A=B, need not process B=A too).
|
|
*
|
|
* A set containing only two items cannot imply any equalities
|
|
* beyond the one that created the set, so we can skip this
|
|
* processing in that case.
|
|
*/
|
|
if (nitems >= 3)
|
|
{
|
|
i1 = 0;
|
|
foreach(ptr1, curset)
|
|
{
|
|
PathKeyItem *item1 = (PathKeyItem *) lfirst(ptr1);
|
|
bool i1_is_variable = !bms_is_empty(relids[i1]);
|
|
ListCell *ptr2;
|
|
int i2 = i1 + 1;
|
|
|
|
for_each_cell(ptr2, lnext(ptr1))
|
|
{
|
|
PathKeyItem *item2 = (PathKeyItem *) lfirst(ptr2);
|
|
bool i2_is_variable = !bms_is_empty(relids[i2]);
|
|
|
|
/*
|
|
* If it's "const = const" then just ignore it altogether.
|
|
* There is no place in the restrictinfo structure to
|
|
* store it. (If the two consts are in fact unequal, then
|
|
* propagating the comparison to Vars will cause us to
|
|
* produce zero rows out, as expected.)
|
|
*/
|
|
if (i1_is_variable || i2_is_variable)
|
|
{
|
|
/*
|
|
* Tell process_implied_equality to delete the clause,
|
|
* not add it, if it's "var = var" and we have
|
|
* constants present in the list.
|
|
*/
|
|
bool delete_it = (have_consts &&
|
|
i1_is_variable &&
|
|
i2_is_variable);
|
|
|
|
process_implied_equality(root,
|
|
item1->key, item2->key,
|
|
item1->sortop, item2->sortop,
|
|
relids[i1], relids[i2],
|
|
delete_it);
|
|
}
|
|
i2++;
|
|
}
|
|
i1++;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If we have constant(s) and outer joins, try to propagate the
|
|
* constants through outer-join quals.
|
|
*/
|
|
if (have_consts && root->hasOuterJoins)
|
|
generate_outer_join_implications(root, curset, relids);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* generate_outer_join_implications
|
|
* Generate clauses that can be deduced in outer-join situations.
|
|
*
|
|
* When we have mergejoinable clauses A = B that are outer-join clauses,
|
|
* we can't blindly combine them with other clauses A = C to deduce B = C,
|
|
* since in fact the "equality" A = B won't necessarily hold above the
|
|
* outer join (one of the variables might be NULL instead). Nonetheless
|
|
* there are cases where we can add qual clauses using transitivity.
|
|
*
|
|
* One case that we look for here is an outer-join clause OUTERVAR = INNERVAR
|
|
* combined with a pushed-down (valid everywhere) clause OUTERVAR = CONSTANT.
|
|
* It is safe and useful to push a clause INNERVAR = CONSTANT into the
|
|
* evaluation of the inner (nullable) relation, because any inner rows not
|
|
* meeting this condition will not contribute to the outer-join result anyway.
|
|
* (Any outer rows they could join to will be eliminated by the pushed-down
|
|
* clause.)
|
|
*
|
|
* Note that the above rule does not work for full outer joins, nor for
|
|
* pushed-down restrictions on an inner-side variable; nor is it very
|
|
* interesting to consider cases where the pushed-down clause involves
|
|
* relations entirely outside the outer join, since such clauses couldn't
|
|
* be pushed into the inner side's scan anyway. So the restriction to
|
|
* outervar = pseudoconstant is not really giving up anything.
|
|
*
|
|
* For full-join cases, we can only do something useful if it's a FULL JOIN
|
|
* USING and a merged column has a restriction MERGEDVAR = CONSTANT. By
|
|
* the time it gets here, the restriction will look like
|
|
* COALESCE(LEFTVAR, RIGHTVAR) = CONSTANT
|
|
* and we will have a join clause LEFTVAR = RIGHTVAR that we can match the
|
|
* COALESCE expression to. In this situation we can push LEFTVAR = CONSTANT
|
|
* and RIGHTVAR = CONSTANT into the input relations, since any rows not
|
|
* meeting these conditions cannot contribute to the join result.
|
|
*
|
|
* Again, there isn't any traction to be gained by trying to deal with
|
|
* clauses comparing a mergedvar to a non-pseudoconstant. So we can make
|
|
* use of the equi_key_lists to quickly find the interesting pushed-down
|
|
* clauses. The interesting outer-join clauses were accumulated for us by
|
|
* distribute_qual_to_rels.
|
|
*
|
|
* equi_key_set: a list of PathKeyItems that are known globally equivalent,
|
|
* at least one of which is a pseudoconstant.
|
|
* relids: an array of Relids sets showing the relation membership of each
|
|
* PathKeyItem in equi_key_set.
|
|
*/
|
|
static void
|
|
generate_outer_join_implications(PlannerInfo *root,
|
|
List *equi_key_set,
|
|
Relids *relids)
|
|
{
|
|
ListCell *l;
|
|
int i = 0;
|
|
|
|
/* Process each non-constant element of equi_key_set */
|
|
foreach(l, equi_key_set)
|
|
{
|
|
PathKeyItem *item1 = (PathKeyItem *) lfirst(l);
|
|
|
|
if (!bms_is_empty(relids[i]))
|
|
{
|
|
sub_generate_join_implications(root, equi_key_set, relids,
|
|
item1->key,
|
|
item1->sortop,
|
|
relids[i]);
|
|
}
|
|
i++;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* sub_generate_join_implications
|
|
* Propagate a constant equality through outer join clauses.
|
|
*
|
|
* The item described by item1/sortop1/item1_relids has been determined
|
|
* to be equal to the constant(s) listed in equi_key_set. Recursively
|
|
* trace out the implications of this.
|
|
*
|
|
* equi_key_set and relids are as for generate_outer_join_implications.
|
|
*/
|
|
static void
|
|
sub_generate_join_implications(PlannerInfo *root,
|
|
List *equi_key_set, Relids *relids,
|
|
Node *item1, Oid sortop1, Relids item1_relids)
|
|
|
|
{
|
|
ListCell *l;
|
|
|
|
/*
|
|
* Examine each mergejoinable outer-join clause with OUTERVAR on left,
|
|
* looking for an OUTERVAR identical to item1
|
|
*/
|
|
foreach(l, root->left_join_clauses)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
|
|
Node *leftop = get_leftop(rinfo->clause);
|
|
|
|
if (equal(leftop, item1) && rinfo->left_sortop == sortop1)
|
|
{
|
|
/*
|
|
* Match, so find constant member(s) of set and generate
|
|
* implied INNERVAR = CONSTANT
|
|
*/
|
|
Node *rightop = get_rightop(rinfo->clause);
|
|
|
|
process_implied_const_eq(root, equi_key_set, relids,
|
|
rightop,
|
|
rinfo->right_sortop,
|
|
rinfo->right_relids,
|
|
false);
|
|
/*
|
|
* We can remove explicit tests of this outer-join qual, too,
|
|
* since we now have tests forcing each of its sides
|
|
* to the same value.
|
|
*/
|
|
process_implied_equality(root,
|
|
leftop, rightop,
|
|
rinfo->left_sortop, rinfo->right_sortop,
|
|
rinfo->left_relids, rinfo->right_relids,
|
|
true);
|
|
/*
|
|
* And recurse to see if we can deduce anything from
|
|
* INNERVAR = CONSTANT
|
|
*/
|
|
sub_generate_join_implications(root, equi_key_set, relids,
|
|
rightop,
|
|
rinfo->right_sortop,
|
|
rinfo->right_relids);
|
|
}
|
|
}
|
|
|
|
/* The same, looking at clauses with OUTERVAR on right */
|
|
foreach(l, root->right_join_clauses)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
|
|
Node *rightop = get_rightop(rinfo->clause);
|
|
|
|
if (equal(rightop, item1) && rinfo->right_sortop == sortop1)
|
|
{
|
|
/*
|
|
* Match, so find constant member(s) of set and generate
|
|
* implied INNERVAR = CONSTANT
|
|
*/
|
|
Node *leftop = get_leftop(rinfo->clause);
|
|
|
|
process_implied_const_eq(root, equi_key_set, relids,
|
|
leftop,
|
|
rinfo->left_sortop,
|
|
rinfo->left_relids,
|
|
false);
|
|
/*
|
|
* We can remove explicit tests of this outer-join qual, too,
|
|
* since we now have tests forcing each of its sides
|
|
* to the same value.
|
|
*/
|
|
process_implied_equality(root,
|
|
leftop, rightop,
|
|
rinfo->left_sortop, rinfo->right_sortop,
|
|
rinfo->left_relids, rinfo->right_relids,
|
|
true);
|
|
/*
|
|
* And recurse to see if we can deduce anything from
|
|
* INNERVAR = CONSTANT
|
|
*/
|
|
sub_generate_join_implications(root, equi_key_set, relids,
|
|
leftop,
|
|
rinfo->left_sortop,
|
|
rinfo->left_relids);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Only COALESCE(x,y) items can possibly match full joins
|
|
*/
|
|
if (IsA(item1, CoalesceExpr))
|
|
{
|
|
CoalesceExpr *cexpr = (CoalesceExpr *) item1;
|
|
Node *cfirst;
|
|
Node *csecond;
|
|
|
|
if (list_length(cexpr->args) != 2)
|
|
return;
|
|
cfirst = (Node *) linitial(cexpr->args);
|
|
csecond = (Node *) lsecond(cexpr->args);
|
|
|
|
/*
|
|
* Examine each mergejoinable full-join clause, looking for a
|
|
* clause of the form "x = y" matching the COALESCE(x,y) expression
|
|
*/
|
|
foreach(l, root->full_join_clauses)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
|
|
Node *leftop = get_leftop(rinfo->clause);
|
|
Node *rightop = get_rightop(rinfo->clause);
|
|
|
|
/*
|
|
* We can assume the COALESCE() inputs are in the same order
|
|
* as the join clause, since both were automatically generated
|
|
* in the cases we care about.
|
|
*
|
|
* XXX currently this may fail to match in cross-type cases
|
|
* because the COALESCE will contain typecast operations while
|
|
* the join clause may not (if there is a cross-type mergejoin
|
|
* operator available for the two column types).
|
|
* Is it OK to strip implicit coercions from the COALESCE
|
|
* arguments? What of the sortops in such cases?
|
|
*/
|
|
if (equal(leftop, cfirst) &&
|
|
equal(rightop, csecond) &&
|
|
rinfo->left_sortop == sortop1 &&
|
|
rinfo->right_sortop == sortop1)
|
|
{
|
|
/*
|
|
* Match, so find constant member(s) of set and generate
|
|
* implied LEFTVAR = CONSTANT
|
|
*/
|
|
process_implied_const_eq(root, equi_key_set, relids,
|
|
leftop,
|
|
rinfo->left_sortop,
|
|
rinfo->left_relids,
|
|
false);
|
|
/* ... and RIGHTVAR = CONSTANT */
|
|
process_implied_const_eq(root, equi_key_set, relids,
|
|
rightop,
|
|
rinfo->right_sortop,
|
|
rinfo->right_relids,
|
|
false);
|
|
/* ... and remove COALESCE() = CONSTANT */
|
|
process_implied_const_eq(root, equi_key_set, relids,
|
|
item1,
|
|
sortop1,
|
|
item1_relids,
|
|
true);
|
|
/*
|
|
* We can remove explicit tests of this outer-join qual, too,
|
|
* since we now have tests forcing each of its sides
|
|
* to the same value.
|
|
*/
|
|
process_implied_equality(root,
|
|
leftop, rightop,
|
|
rinfo->left_sortop,
|
|
rinfo->right_sortop,
|
|
rinfo->left_relids,
|
|
rinfo->right_relids,
|
|
true);
|
|
/*
|
|
* And recurse to see if we can deduce anything from
|
|
* LEFTVAR = CONSTANT
|
|
*/
|
|
sub_generate_join_implications(root, equi_key_set, relids,
|
|
leftop,
|
|
rinfo->left_sortop,
|
|
rinfo->left_relids);
|
|
/* ... and RIGHTVAR = CONSTANT */
|
|
sub_generate_join_implications(root, equi_key_set, relids,
|
|
rightop,
|
|
rinfo->right_sortop,
|
|
rinfo->right_relids);
|
|
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* process_implied_const_eq
|
|
* Apply process_implied_equality with the given item and each
|
|
* pseudoconstant member of equi_key_set.
|
|
*
|
|
* equi_key_set and relids are as for generate_outer_join_implications,
|
|
* the other parameters as for process_implied_equality.
|
|
*/
|
|
static void
|
|
process_implied_const_eq(PlannerInfo *root, List *equi_key_set, Relids *relids,
|
|
Node *item1, Oid sortop1, Relids item1_relids,
|
|
bool delete_it)
|
|
{
|
|
ListCell *l;
|
|
bool found = false;
|
|
int i = 0;
|
|
|
|
foreach(l, equi_key_set)
|
|
{
|
|
PathKeyItem *item2 = (PathKeyItem *) lfirst(l);
|
|
|
|
if (bms_is_empty(relids[i]))
|
|
{
|
|
process_implied_equality(root,
|
|
item1, item2->key,
|
|
sortop1, item2->sortop,
|
|
item1_relids, NULL,
|
|
delete_it);
|
|
found = true;
|
|
}
|
|
i++;
|
|
}
|
|
/* Caller screwed up if no constants in list */
|
|
Assert(found);
|
|
}
|
|
|
|
/*
|
|
* exprs_known_equal
|
|
* Detect whether two expressions are known equal due to equijoin clauses.
|
|
*
|
|
* Note: does not bother to check for "equal(item1, item2)"; caller must
|
|
* check that case if it's possible to pass identical items.
|
|
*/
|
|
bool
|
|
exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2)
|
|
{
|
|
ListCell *cursetlink;
|
|
|
|
foreach(cursetlink, root->equi_key_list)
|
|
{
|
|
List *curset = (List *) lfirst(cursetlink);
|
|
bool item1member = false;
|
|
bool item2member = false;
|
|
ListCell *ptr;
|
|
|
|
foreach(ptr, curset)
|
|
{
|
|
PathKeyItem *pitem = (PathKeyItem *) lfirst(ptr);
|
|
|
|
if (equal(item1, pitem->key))
|
|
item1member = true;
|
|
else if (equal(item2, pitem->key))
|
|
item2member = true;
|
|
/* Exit as soon as equality is proven */
|
|
if (item1member && item2member)
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
|
|
/*
|
|
* make_canonical_pathkey
|
|
* Given a PathKeyItem, find the equi_key_list subset it is a member of,
|
|
* if any. If so, return a pointer to that sublist, which is the
|
|
* canonical representation (for this query) of that PathKeyItem's
|
|
* equivalence set. If it is not found, add a singleton "equivalence set"
|
|
* to the equi_key_list and return that --- see compare_pathkeys.
|
|
*
|
|
* Note that this function must not be used until after we have completed
|
|
* scanning the WHERE clause for equijoin operators.
|
|
*/
|
|
static List *
|
|
make_canonical_pathkey(PlannerInfo *root, PathKeyItem *item)
|
|
{
|
|
List *newset;
|
|
ListCell *cursetlink;
|
|
|
|
foreach(cursetlink, root->equi_key_list)
|
|
{
|
|
List *curset = (List *) lfirst(cursetlink);
|
|
|
|
if (list_member(curset, item))
|
|
return curset;
|
|
}
|
|
newset = list_make1(item);
|
|
root->equi_key_list = lcons(newset, root->equi_key_list);
|
|
return newset;
|
|
}
|
|
|
|
/*
|
|
* canonicalize_pathkeys
|
|
* Convert a not-necessarily-canonical pathkeys list to canonical form.
|
|
*
|
|
* Note that this function must not be used until after we have completed
|
|
* scanning the WHERE clause for equijoin operators.
|
|
*/
|
|
List *
|
|
canonicalize_pathkeys(PlannerInfo *root, List *pathkeys)
|
|
{
|
|
List *new_pathkeys = NIL;
|
|
ListCell *l;
|
|
|
|
foreach(l, pathkeys)
|
|
{
|
|
List *pathkey = (List *) lfirst(l);
|
|
PathKeyItem *item;
|
|
List *cpathkey;
|
|
|
|
/*
|
|
* It's sufficient to look at the first entry in the sublist; if
|
|
* there are more entries, they're already part of an equivalence
|
|
* set by definition.
|
|
*/
|
|
Assert(pathkey != NIL);
|
|
item = (PathKeyItem *) linitial(pathkey);
|
|
cpathkey = make_canonical_pathkey(root, item);
|
|
|
|
/*
|
|
* Eliminate redundant ordering requests --- ORDER BY A,A is the
|
|
* same as ORDER BY A. We want to check this only after we have
|
|
* canonicalized the keys, so that equivalent-key knowledge is
|
|
* used when deciding if an item is redundant.
|
|
*/
|
|
new_pathkeys = list_append_unique_ptr(new_pathkeys, cpathkey);
|
|
}
|
|
return new_pathkeys;
|
|
}
|
|
|
|
|
|
/*
|
|
* count_canonical_peers
|
|
* Given a PathKeyItem, find the equi_key_list subset it is a member of,
|
|
* if any. If so, return the number of other members of the set.
|
|
* If not, return 0 (without actually adding it to our equi_key_list).
|
|
*
|
|
* This is a hack to support the rather bogus heuristics in
|
|
* convert_subquery_pathkeys.
|
|
*/
|
|
static int
|
|
count_canonical_peers(PlannerInfo *root, PathKeyItem *item)
|
|
{
|
|
ListCell *cursetlink;
|
|
|
|
foreach(cursetlink, root->equi_key_list)
|
|
{
|
|
List *curset = (List *) lfirst(cursetlink);
|
|
|
|
if (list_member(curset, item))
|
|
return list_length(curset) - 1;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/****************************************************************************
|
|
* PATHKEY COMPARISONS
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* compare_pathkeys
|
|
* Compare two pathkeys to see if they are equivalent, and if not whether
|
|
* one is "better" than the other.
|
|
*
|
|
* This function may only be applied to canonicalized pathkey lists.
|
|
* In the canonical representation, sublists can be checked for equality
|
|
* by simple pointer comparison.
|
|
*/
|
|
PathKeysComparison
|
|
compare_pathkeys(List *keys1, List *keys2)
|
|
{
|
|
ListCell *key1,
|
|
*key2;
|
|
|
|
forboth(key1, keys1, key2, keys2)
|
|
{
|
|
List *subkey1 = (List *) lfirst(key1);
|
|
List *subkey2 = (List *) lfirst(key2);
|
|
|
|
/*
|
|
* XXX would like to check that we've been given canonicalized
|
|
* input, but PlannerInfo not accessible here...
|
|
*/
|
|
#ifdef NOT_USED
|
|
Assert(list_member_ptr(root->equi_key_list, subkey1));
|
|
Assert(list_member_ptr(root->equi_key_list, subkey2));
|
|
#endif
|
|
|
|
/*
|
|
* We will never have two subkeys where one is a subset of the
|
|
* other, because of the canonicalization process. Either they
|
|
* are equal or they ain't. Furthermore, we only need pointer
|
|
* comparison to detect equality.
|
|
*/
|
|
if (subkey1 != subkey2)
|
|
return PATHKEYS_DIFFERENT; /* no need to keep looking */
|
|
}
|
|
|
|
/*
|
|
* If we reached the end of only one list, the other is longer and
|
|
* therefore not a subset. (We assume the additional sublist(s) of
|
|
* the other list are not NIL --- no pathkey list should ever have a
|
|
* NIL sublist.)
|
|
*/
|
|
if (key1 == NULL && key2 == NULL)
|
|
return PATHKEYS_EQUAL;
|
|
if (key1 != NULL)
|
|
return PATHKEYS_BETTER1; /* key1 is longer */
|
|
return PATHKEYS_BETTER2; /* key2 is longer */
|
|
}
|
|
|
|
/*
|
|
* compare_noncanonical_pathkeys
|
|
* Compare two pathkeys to see if they are equivalent, and if not whether
|
|
* one is "better" than the other. This is used when we must compare
|
|
* non-canonicalized pathkeys.
|
|
*
|
|
* A pathkey can be considered better than another if it is a superset:
|
|
* it contains all the keys of the other plus more. For example, either
|
|
* ((A) (B)) or ((A B)) is better than ((A)).
|
|
*
|
|
* Currently, the only user of this routine is grouping_planner(),
|
|
* and it will only pass single-element sublists (from
|
|
* make_pathkeys_for_sortclauses). Therefore we don't have to do the
|
|
* full two-way-subset-inclusion test on each pair of sublists that is
|
|
* implied by the above statement. Instead we just verify they are
|
|
* singleton lists and then do an equal(). This could be improved if
|
|
* necessary.
|
|
*/
|
|
PathKeysComparison
|
|
compare_noncanonical_pathkeys(List *keys1, List *keys2)
|
|
{
|
|
ListCell *key1,
|
|
*key2;
|
|
|
|
forboth(key1, keys1, key2, keys2)
|
|
{
|
|
List *subkey1 = (List *) lfirst(key1);
|
|
List *subkey2 = (List *) lfirst(key2);
|
|
|
|
Assert(list_length(subkey1) == 1);
|
|
Assert(list_length(subkey2) == 1);
|
|
if (!equal(subkey1, subkey2))
|
|
return PATHKEYS_DIFFERENT; /* no need to keep looking */
|
|
}
|
|
|
|
/*
|
|
* If we reached the end of only one list, the other is longer and
|
|
* therefore not a subset. (We assume the additional sublist(s) of
|
|
* the other list are not NIL --- no pathkey list should ever have a
|
|
* NIL sublist.)
|
|
*/
|
|
if (key1 == NULL && key2 == NULL)
|
|
return PATHKEYS_EQUAL;
|
|
if (key1 != NULL)
|
|
return PATHKEYS_BETTER1; /* key1 is longer */
|
|
return PATHKEYS_BETTER2; /* key2 is longer */
|
|
}
|
|
|
|
/*
|
|
* pathkeys_contained_in
|
|
* Common special case of compare_pathkeys: we just want to know
|
|
* if keys2 are at least as well sorted as keys1.
|
|
*/
|
|
bool
|
|
pathkeys_contained_in(List *keys1, List *keys2)
|
|
{
|
|
switch (compare_pathkeys(keys1, keys2))
|
|
{
|
|
case PATHKEYS_EQUAL:
|
|
case PATHKEYS_BETTER2:
|
|
return true;
|
|
default:
|
|
break;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* noncanonical_pathkeys_contained_in
|
|
* The same, when we don't have canonical pathkeys.
|
|
*/
|
|
bool
|
|
noncanonical_pathkeys_contained_in(List *keys1, List *keys2)
|
|
{
|
|
switch (compare_noncanonical_pathkeys(keys1, keys2))
|
|
{
|
|
case PATHKEYS_EQUAL:
|
|
case PATHKEYS_BETTER2:
|
|
return true;
|
|
default:
|
|
break;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* get_cheapest_path_for_pathkeys
|
|
* Find the cheapest path (according to the specified criterion) that
|
|
* satisfies the given pathkeys. Return NULL if no such path.
|
|
*
|
|
* 'paths' is a list of possible paths that all generate the same relation
|
|
* 'pathkeys' represents a required ordering (already canonicalized!)
|
|
* 'cost_criterion' is STARTUP_COST or TOTAL_COST
|
|
*/
|
|
Path *
|
|
get_cheapest_path_for_pathkeys(List *paths, List *pathkeys,
|
|
CostSelector cost_criterion)
|
|
{
|
|
Path *matched_path = NULL;
|
|
ListCell *l;
|
|
|
|
foreach(l, paths)
|
|
{
|
|
Path *path = (Path *) lfirst(l);
|
|
|
|
/*
|
|
* Since cost comparison is a lot cheaper than pathkey comparison,
|
|
* do that first. (XXX is that still true?)
|
|
*/
|
|
if (matched_path != NULL &&
|
|
compare_path_costs(matched_path, path, cost_criterion) <= 0)
|
|
continue;
|
|
|
|
if (pathkeys_contained_in(pathkeys, path->pathkeys))
|
|
matched_path = path;
|
|
}
|
|
return matched_path;
|
|
}
|
|
|
|
/*
|
|
* get_cheapest_fractional_path_for_pathkeys
|
|
* Find the cheapest path (for retrieving a specified fraction of all
|
|
* the tuples) that satisfies the given pathkeys.
|
|
* Return NULL if no such path.
|
|
*
|
|
* See compare_fractional_path_costs() for the interpretation of the fraction
|
|
* parameter.
|
|
*
|
|
* 'paths' is a list of possible paths that all generate the same relation
|
|
* 'pathkeys' represents a required ordering (already canonicalized!)
|
|
* 'fraction' is the fraction of the total tuples expected to be retrieved
|
|
*/
|
|
Path *
|
|
get_cheapest_fractional_path_for_pathkeys(List *paths,
|
|
List *pathkeys,
|
|
double fraction)
|
|
{
|
|
Path *matched_path = NULL;
|
|
ListCell *l;
|
|
|
|
foreach(l, paths)
|
|
{
|
|
Path *path = (Path *) lfirst(l);
|
|
|
|
/*
|
|
* Since cost comparison is a lot cheaper than pathkey comparison,
|
|
* do that first.
|
|
*/
|
|
if (matched_path != NULL &&
|
|
compare_fractional_path_costs(matched_path, path, fraction) <= 0)
|
|
continue;
|
|
|
|
if (pathkeys_contained_in(pathkeys, path->pathkeys))
|
|
matched_path = path;
|
|
}
|
|
return matched_path;
|
|
}
|
|
|
|
/****************************************************************************
|
|
* NEW PATHKEY FORMATION
|
|
****************************************************************************/
|
|
|
|
/*
|
|
* build_index_pathkeys
|
|
* Build a pathkeys list that describes the ordering induced by an index
|
|
* scan using the given index. (Note that an unordered index doesn't
|
|
* induce any ordering; such an index will have no sortop OIDS in
|
|
* its "ordering" field, and we will return NIL.)
|
|
*
|
|
* If 'scandir' is BackwardScanDirection, attempt to build pathkeys
|
|
* representing a backwards scan of the index. Return NIL if can't do it.
|
|
*
|
|
* We generate the full pathkeys list whether or not all are useful for the
|
|
* current query. Caller should do truncate_useless_pathkeys().
|
|
*/
|
|
List *
|
|
build_index_pathkeys(PlannerInfo *root,
|
|
IndexOptInfo *index,
|
|
ScanDirection scandir)
|
|
{
|
|
List *retval = NIL;
|
|
int *indexkeys = index->indexkeys;
|
|
Oid *ordering = index->ordering;
|
|
ListCell *indexprs_item = list_head(index->indexprs);
|
|
|
|
while (*ordering != InvalidOid)
|
|
{
|
|
PathKeyItem *item;
|
|
Oid sortop;
|
|
Node *indexkey;
|
|
List *cpathkey;
|
|
|
|
sortop = *ordering;
|
|
if (ScanDirectionIsBackward(scandir))
|
|
{
|
|
sortop = get_commutator(sortop);
|
|
if (sortop == InvalidOid)
|
|
break; /* oops, no reverse sort operator? */
|
|
}
|
|
|
|
if (*indexkeys != 0)
|
|
{
|
|
/* simple index column */
|
|
indexkey = (Node *) find_indexkey_var(root, index->rel,
|
|
*indexkeys);
|
|
}
|
|
else
|
|
{
|
|
/* expression --- assume we need not copy it */
|
|
if (indexprs_item == NULL)
|
|
elog(ERROR, "wrong number of index expressions");
|
|
indexkey = (Node *) lfirst(indexprs_item);
|
|
indexprs_item = lnext(indexprs_item);
|
|
}
|
|
|
|
/* OK, make a sublist for this sort key */
|
|
item = makePathKeyItem(indexkey, sortop, true);
|
|
cpathkey = make_canonical_pathkey(root, item);
|
|
|
|
/*
|
|
* Eliminate redundant ordering info; could happen if query is
|
|
* such that index keys are equijoined...
|
|
*/
|
|
retval = list_append_unique_ptr(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(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)
|
|
{
|
|
List *sub_pathkey = (List *) lfirst(i);
|
|
ListCell *j;
|
|
PathKeyItem *best_item = NULL;
|
|
int best_score = 0;
|
|
List *cpathkey;
|
|
|
|
/*
|
|
* The sub_pathkey 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 a pathkey list of the outer query,
|
|
* thereby propagating equality knowledge up to the outer query.
|
|
* Right now we cannot do so, because the outer query's canonical
|
|
* pathkey sets are already frozen when this is called. Instead
|
|
* we prefer the one that has the highest "score" (number of
|
|
* canonical pathkey peers, plus one if it matches the outer
|
|
* query_pathkeys). This is the most likely to be useful in the
|
|
* outer query.
|
|
*/
|
|
foreach(j, sub_pathkey)
|
|
{
|
|
PathKeyItem *sub_item = (PathKeyItem *) lfirst(j);
|
|
Node *sub_key = sub_item->key;
|
|
ListCell *k;
|
|
|
|
foreach(k, sub_tlist)
|
|
{
|
|
TargetEntry *tle = (TargetEntry *) lfirst(k);
|
|
|
|
if (!tle->resjunk &&
|
|
equal(tle->expr, sub_key))
|
|
{
|
|
/* Found a representation for this sub_key */
|
|
Var *outer_var;
|
|
PathKeyItem *outer_item;
|
|
int score;
|
|
|
|
outer_var = makeVar(rel->relid,
|
|
tle->resno,
|
|
exprType((Node *) tle->expr),
|
|
exprTypmod((Node *) tle->expr),
|
|
0);
|
|
outer_item = makePathKeyItem((Node *) outer_var,
|
|
sub_item->sortop,
|
|
true);
|
|
/* score = # of mergejoin peers */
|
|
score = count_canonical_peers(root, outer_item);
|
|
/* +1 if it matches the proper query_pathkeys item */
|
|
if (retvallen < outer_query_keys &&
|
|
list_member(list_nth(root->query_pathkeys, retvallen), outer_item))
|
|
score++;
|
|
if (score > best_score)
|
|
{
|
|
best_item = outer_item;
|
|
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_item)
|
|
break;
|
|
|
|
/* Canonicalize the chosen item (we did not before) */
|
|
cpathkey = make_canonical_pathkey(root, best_item);
|
|
|
|
/*
|
|
* Eliminate redundant ordering info; could happen if outer query
|
|
* equijoins subquery keys...
|
|
*/
|
|
if (!list_member_ptr(retval, cpathkey))
|
|
{
|
|
retval = lappend(retval, cpathkey);
|
|
retvallen++;
|
|
}
|
|
}
|
|
|
|
return retval;
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
*
|
|
* 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.
|
|
*
|
|
* '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! 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;
|
|
ListCell *l;
|
|
|
|
foreach(l, sortclauses)
|
|
{
|
|
SortClause *sortcl = (SortClause *) lfirst(l);
|
|
Node *sortkey;
|
|
PathKeyItem *pathkey;
|
|
|
|
sortkey = get_sortgroupclause_expr(sortcl, tlist);
|
|
pathkey = makePathKeyItem(sortkey, sortcl->sortop, true);
|
|
|
|
/*
|
|
* The pathkey becomes a one-element sublist, for now;
|
|
* canonicalize_pathkeys() might replace it with a longer sublist
|
|
* later.
|
|
*/
|
|
pathkeys = lappend(pathkeys, list_make1(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.
|
|
*
|
|
* We have to be careful that the cached values are palloc'd in the same
|
|
* context the RestrictInfo node itself is in. This is not currently a
|
|
* problem for normal planning, but it is an issue for GEQO planning.
|
|
*/
|
|
void
|
|
cache_mergeclause_pathkeys(PlannerInfo *root, RestrictInfo *restrictinfo)
|
|
{
|
|
Node *key;
|
|
PathKeyItem *item;
|
|
MemoryContext oldcontext;
|
|
|
|
Assert(restrictinfo->mergejoinoperator != InvalidOid);
|
|
|
|
if (restrictinfo->left_pathkey == NIL)
|
|
{
|
|
oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(restrictinfo));
|
|
key = get_leftop(restrictinfo->clause);
|
|
item = makePathKeyItem(key, restrictinfo->left_sortop, false);
|
|
restrictinfo->left_pathkey = make_canonical_pathkey(root, item);
|
|
MemoryContextSwitchTo(oldcontext);
|
|
}
|
|
if (restrictinfo->right_pathkey == NIL)
|
|
{
|
|
oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(restrictinfo));
|
|
key = get_rightop(restrictinfo->clause);
|
|
item = makePathKeyItem(key, restrictinfo->right_sortop, false);
|
|
restrictinfo->right_pathkey = make_canonical_pathkey(root, item);
|
|
MemoryContextSwitchTo(oldcontext);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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(PlannerInfo *root,
|
|
List *pathkeys,
|
|
List *restrictinfos)
|
|
{
|
|
List *mergeclauses = NIL;
|
|
ListCell *i;
|
|
|
|
/* make sure we have pathkeys cached in the clauses */
|
|
foreach(i, restrictinfos)
|
|
{
|
|
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(i);
|
|
|
|
cache_mergeclause_pathkeys(root, restrictinfo);
|
|
}
|
|
|
|
foreach(i, pathkeys)
|
|
{
|
|
List *pathkey = (List *) lfirst(i);
|
|
List *matched_restrictinfos = NIL;
|
|
ListCell *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 = (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) &&
|
|
!list_member_ptr(mergeclauses, restrictinfo))
|
|
{
|
|
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 = list_concat(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(PlannerInfo *root,
|
|
List *mergeclauses,
|
|
RelOptInfo *rel)
|
|
{
|
|
List *pathkeys = NIL;
|
|
ListCell *l;
|
|
|
|
foreach(l, mergeclauses)
|
|
{
|
|
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);
|
|
List *pathkey;
|
|
|
|
cache_mergeclause_pathkeys(root, restrictinfo);
|
|
|
|
if (bms_is_subset(restrictinfo->left_relids, rel->relids))
|
|
{
|
|
/* Rel is left side of mergeclause */
|
|
pathkey = restrictinfo->left_pathkey;
|
|
}
|
|
else if (bms_is_subset(restrictinfo->right_relids, rel->relids))
|
|
{
|
|
/* Rel is right side of mergeclause */
|
|
pathkey = restrictinfo->right_pathkey;
|
|
}
|
|
else
|
|
{
|
|
elog(ERROR, "could not 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.
|
|
*/
|
|
pathkeys = list_append_unique_ptr(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 list).
|
|
*
|
|
* We consider a pathkey potentially useful if it corresponds to the merge
|
|
* ordering of either side of any joinclause for the rel. This might be
|
|
* overoptimistic, since joinclauses that require different other relations
|
|
* might never be usable at the same time, but trying to be exact is likely
|
|
* to be more trouble than it's worth.
|
|
*/
|
|
int
|
|
pathkeys_useful_for_merging(PlannerInfo *root, RelOptInfo *rel, List *pathkeys)
|
|
{
|
|
int useful = 0;
|
|
ListCell *i;
|
|
|
|
foreach(i, pathkeys)
|
|
{
|
|
List *pathkey = (List *) lfirst(i);
|
|
bool matched = false;
|
|
ListCell *j;
|
|
|
|
foreach(j, rel->joininfo)
|
|
{
|
|
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(j);
|
|
|
|
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 we didn't find a mergeclause, we're done --- any additional
|
|
* sort-key positions in the pathkeys are useless. (But we can
|
|
* still mergejoin if we found at least one mergeclause.)
|
|
*/
|
|
if (matched)
|
|
useful++;
|
|
else
|
|
break;
|
|
}
|
|
|
|
return useful;
|
|
}
|
|
|
|
/*
|
|
* pathkeys_useful_for_ordering
|
|
* Count the number of pathkeys that are useful for meeting the
|
|
* query's requested output ordering.
|
|
*
|
|
* Unlike merge pathkeys, this is an all-or-nothing affair: it does us
|
|
* no good to order by just the first key(s) of the requested ordering.
|
|
* So the result is always either 0 or list_length(root->query_pathkeys).
|
|
*/
|
|
int
|
|
pathkeys_useful_for_ordering(PlannerInfo *root, List *pathkeys)
|
|
{
|
|
if (root->query_pathkeys == NIL)
|
|
return 0; /* no special ordering requested */
|
|
|
|
if (pathkeys == NIL)
|
|
return 0; /* unordered path */
|
|
|
|
if (pathkeys_contained_in(root->query_pathkeys, pathkeys))
|
|
{
|
|
/* It's useful ... or at least the first N keys are */
|
|
return list_length(root->query_pathkeys);
|
|
}
|
|
|
|
return 0; /* path ordering not useful */
|
|
}
|
|
|
|
/*
|
|
* truncate_useless_pathkeys
|
|
* Shorten the given pathkey list to just the useful pathkeys.
|
|
*/
|
|
List *
|
|
truncate_useless_pathkeys(PlannerInfo *root,
|
|
RelOptInfo *rel,
|
|
List *pathkeys)
|
|
{
|
|
int nuseful;
|
|
int nuseful2;
|
|
|
|
nuseful = pathkeys_useful_for_merging(root, rel, pathkeys);
|
|
nuseful2 = pathkeys_useful_for_ordering(root, pathkeys);
|
|
if (nuseful2 > nuseful)
|
|
nuseful = nuseful2;
|
|
|
|
/*
|
|
* Note: not safe to modify input list destructively, but we can avoid
|
|
* copying the list if we're not actually going to change it
|
|
*/
|
|
if (nuseful == list_length(pathkeys))
|
|
return pathkeys;
|
|
else
|
|
return list_truncate(list_copy(pathkeys), nuseful);
|
|
}
|