/*
* join_search_one_level
* Consider ways to produce join relations containing exactly 'level'
* jointree items. (This is one step of the dynamic-programming method
* embodied in standard_join_search.) Join rel nodes for each feasible
* combination of lower-level rels are created and returned in a list.
* Implementation paths are created for each such joinrel, too.
*
* level: level of rels we want to make this time
* root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
*
* The result is returned in root->join_rel_level[level].
*/
void
join_search_one_level(PlannerInfo *root, int level)
{
List **joinrels = root->join_rel_level;
ListCell *r;
int k;
Assert(joinrels[level] == NIL);
/* Set join_cur_level so that new joinrels are added to proper list */
root->join_cur_level = level;
/*
* First, consider left-sided and right-sided plans, in which rels of
* exactly level-1 member relations are joined against initial relations.
* We prefer to join using join clauses, but if we find a rel of level-1
* members that has no join clauses, we will generate Cartesian-product
* joins against all initial rels not already contained in it.
*/
foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
has_join_restriction(root, old_rel))
{
/*
* There are join clauses or join order restrictions relevant to
* this rel, so consider joins between this rel and (only) those
* initial rels it is linked to by a clause or restriction.
*
* At level 2 this condition is symmetric, so there is no need to
* look at initial rels before this one in the list; we already
* considered such joins when we were at the earlier rel. (The
* mirror-image joins are handled automatically by make_join_rel.)
* In later passes (level > 2), we join rels of the previous level
* to each initial rel they don't already include but have a join
* clause or restriction with.
*/
ListCell *other_rels;
if (level == 2) /* consider remaining initial rels */
other_rels = lnext(r);
else /* consider all initial rels */
other_rels = list_head(joinrels[1]);
make_rels_by_clause_joins(root,
old_rel,
other_rels);
}
else
{
/*
* Oops, we have a relation that is not joined to any other
* relation, either directly or by join-order restrictions.
* Cartesian product time.
*
* We consider a cartesian product with each not-already-included
* initial rel, whether it has other join clauses or not. At
* level 2, if there are two or more clauseless initial rels, we
* will redundantly consider joining them in both directions; but
* such cases aren't common enough to justify adding complexity to
* avoid the duplicated effort.
*/
make_rels_by_clauseless_joins(root,
old_rel,
list_head(joinrels[1]));
}
}
/*
* join_search_one_level
* Consider ways to produce join relations containing exactly 'level'
* jointree items. (This is one step of the dynamic-programming method
* embodied in standard_join_search.) Join rel nodes for each feasible
* combination of lower-level rels are created and returned in a list.
* Implementation paths are created for each such joinrel, too.
*
* level: level of rels we want to make this time
* root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
*
* The result is returned in root->join_rel_level[level].
*/
void
join_search_one_level(PlannerInfo *root, int level)
{
List **joinrels = root->join_rel_level;
ListCell *r;
int k;
Assert(joinrels[level] == NIL);
/* Set join_cur_level so that new joinrels are added to proper list */
root->join_cur_level = level;
/*
* First, consider left-sided and right-sided plans, in which rels of
* exactly level-1 member relations are joined against initial relations.
* We prefer to join using join clauses, but if we find a rel of level-1
* members that has no join clauses, we will generate Cartesian-product
* joins against all initial rels not already contained in it.
*
* In the first pass (level == 2), we try to join each initial rel to each
* initial rel that appears later in joinrels[1]. (The mirror-image joins
* are handled automatically by make_join_rel.) In later passes, we try
* to join rels of size level-1 from joinrels[level-1] to each initial rel
* in joinrels[1].
*/
foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
if (level == 2)
other_rels = lnext(r); /* only consider remaining initial
* rels */
else
other_rels = list_head(joinrels[1]); /* consider all initial
* rels */
if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
has_join_restriction(root, old_rel))
{
/*
* Note that if all available join clauses for this rel require
* more than one other rel, we will fail to make any joins against
* it here. In most cases that's OK; it'll be considered by
* "bushy plan" join code in a higher-level pass where we have
* those other rels collected into a join rel.
*
* See also the last-ditch case below.
*/
make_rels_by_clause_joins(root,
old_rel,
other_rels);
}
else
{
/*
* Oops, we have a relation that is not joined to any other
* relation, either directly or by join-order restrictions.
* Cartesian product time.
*/
make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
}
}
/*
* join_search_one_level
* Consider ways to produce join relations containing exactly 'level'
* jointree items. (This is one step of the dynamic-programming method
* embodied in standard_join_search.) Join rel nodes for each feasible
* combination of lower-level rels are created and returned in a list.
* Implementation paths are created for each such joinrel, too.
*
* level: level of rels we want to make this time.
* joinrels[j], 1 <= j < level, is a list of rels containing j items.
*/
List *
join_search_one_level(PlannerInfo *root, int level, List **joinrels)
{
List *result_rels = NIL;
List *new_rels;
ListCell *r;
int k;
/*
* First, consider left-sided and right-sided plans, in which rels of
* exactly level-1 member relations are joined against initial relations.
* We prefer to join using join clauses, but if we find a rel of level-1
* members that has no join clauses, we will generate Cartesian-product
* joins against all initial rels not already contained in it.
*
* In the first pass (level == 2), we try to join each initial rel to each
* initial rel that appears later in joinrels[1]. (The mirror-image joins
* are handled automatically by make_join_rel.) In later passes, we try
* to join rels of size level-1 from joinrels[level-1] to each initial rel
* in joinrels[1].
*/
foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
if (level == 2)
other_rels = lnext(r); /* only consider remaining initial
* rels */
else
other_rels = list_head(joinrels[1]); /* consider all initial
* rels */
if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
has_join_restriction(root, old_rel))
{
/*
* Note that if all available join clauses for this rel require
* more than one other rel, we will fail to make any joins against
* it here. In most cases that's OK; it'll be considered by
* "bushy plan" join code in a higher-level pass where we have
* those other rels collected into a join rel.
*
* See also the last-ditch case below.
*/
new_rels = make_rels_by_clause_joins(root,
old_rel,
other_rels);
}
else
{
/*
* Oops, we have a relation that is not joined to any other
* relation, either directly or by join-order restrictions.
* Cartesian product time.
*/
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
}
/*
* At levels above 2 we will generate the same joined relation in
* multiple ways --- for example (a join b) join c is the same
* RelOptInfo as (b join c) join a, though the second case will add a
* different set of Paths to it. To avoid making extra work for
* subsequent passes, do not enter the same RelOptInfo into our output
* list multiple times.
*/
result_rels = list_concat_unique_ptr(result_rels, new_rels);
}