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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*-------------------------------------------------------------------------
*
* joinrels.c
* Routines to determine which relations should be joined
*
* Portions Copyright (c) 2006-2008, Greenplum inc
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.81.2.3 2007/02/16 00:14:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "miscadmin.h" /* CHECK_FOR_INTERRUPTS */
#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "cdb/cdbdef.h" /* CdbSwap */
static List *make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels);
static List *make_rels_by_clauseless_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels);
static void
cdb_add_subquery_join_paths(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *rel1,
RelOptInfo *rel2,
JoinType jointype,
JoinType swapjointype,
List *restrictlist);
static bool has_join_restriction(PlannerInfo *root, RelOptInfo *rel);
static bool has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel);
/*
* make_rels_by_joins
* Consider ways to produce join relations containing exactly 'level'
* jointree items. (This is one step of the dynamic-programming method
* embodied in make_one_rel_by_joins.) 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 *
make_rels_by_joins(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 || 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);
}
/*
* Now, consider "bushy plans" in which relations of k initial rels are
* joined to relations of level-k initial rels, for 2 <= k <= level-2.
*
* We only consider bushy-plan joins for pairs of rels where there is a
* suitable join clause (or join order restriction), in order to avoid
* unreasonable growth of planning time.
*/
for (k = 2;; k++)
{
int other_level = level - k;
/*
* Since make_join_rel(x, y) handles both x,y and y,x cases, we only
* need to go as far as the halfway point.
*/
if (k > other_level)
break;
foreach(r, joinrels[k])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
ListCell *r2;
/*
* We can ignore clauseless joins here, *except* when they
* participate in join-order restrictions --- then we might have
* to force a bushy join plan.
*/
if (old_rel->joininfo == NIL &&
!has_join_restriction(root, old_rel))
continue;
if (k == other_level)
other_rels = lnext(r); /* only consider remaining rels */
else
other_rels = list_head(joinrels[other_level]);
for_each_cell(r2, other_rels)
{
RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
if (!bms_overlap(old_rel->relids, new_rel->relids))
{
/*
* OK, we can build a rel of the right level from this
* pair of rels. Do so if there is at least one usable
* join clause or a relevant join restriction.
*/
if (have_relevant_joinclause(root, old_rel, new_rel) ||
have_join_order_restriction(root, old_rel, new_rel))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, new_rel);
/* Avoid making duplicate entries ... */
if (jrel)
result_rels = list_append_unique_ptr(result_rels,
jrel);
}
}
}
}
}
/*
* Last-ditch effort: if we failed to find any usable joins so far, force
* a set of cartesian-product joins to be generated. This handles the
* special case where all the available rels have join clauses but we
* cannot use any of the joins yet. An example is
*
* SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
*
* The join clause will be usable at level 3, but at level 2 we have no
* choice but to make cartesian joins. We consider only left-sided and
* right-sided cartesian joins in this case (no bushy).
*/
if (result_rels == NIL)
{
/*
* This loop is just like the first one, except we always call
* make_rels_by_clauseless_joins().
*/
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 */
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
result_rels = list_concat_unique_ptr(result_rels, new_rels);
}
/*----------
* When OJs or IN clauses are involved, there may be no legal way
* to make an N-way join for some values of N. For example consider
*
* SELECT ... FROM t1 WHERE
* x IN (SELECT ... FROM t2,t3 WHERE ...) AND
* y IN (SELECT ... FROM t4,t5 WHERE ...)
*
* We will flatten this query to a 5-way join problem, but there are
* no 4-way joins that join_is_legal() will consider legal. We have
* to accept failure at level 4 and go on to discover a workable
* bushy plan at level 5.
*
* However, if there are no such clauses then join_is_legal() should
* never fail, and so the following sanity check is useful.
*----------
*/
if (result_rels == NIL &&
root->oj_info_list == NIL && root->in_info_list == NIL)
elog(ERROR, "failed to build any %d-way joins", level);
}
return result_rels;
}
/*
* make_rels_by_clause_joins
* Build joins between the given relation 'old_rel' and other relations
* that participate in join clauses that 'old_rel' also participates in
* (or participate in join-order restrictions with it).
* The join rel nodes are returned in a list.
*
* 'old_rel' is the relation entry for the relation to be joined
* 'other_rels': the first cell in a linked list containing the other
* rels to be considered for joining
*
* Currently, this is only used with initial rels in other_rels, but it
* will work for joining to joinrels too.
*/
static List *
make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
List *result = NIL;
ListCell *l;
for_each_cell(l, other_rels)
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
if (!bms_overlap(old_rel->relids, other_rel->relids) &&
(have_relevant_joinclause(root, old_rel, other_rel) ||
have_join_order_restriction(root, old_rel, other_rel)))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, other_rel);
if (jrel)
result = lcons(jrel, result);
}
}
return result;
}
/*
* make_rels_by_clauseless_joins
* Given a relation 'old_rel' and a list of other relations
* 'other_rels', create a join relation between 'old_rel' and each
* member of 'other_rels' that isn't already included in 'old_rel'.
* The join rel nodes are returned in a list.
*
* 'old_rel' is the relation entry for the relation to be joined
* 'other_rels': the first cell of a linked list containing the
* other rels to be considered for joining
*
* Currently, this is only used with initial rels in other_rels, but it would
* work for joining to joinrels too.
*/
static List *
make_rels_by_clauseless_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
List *result = NIL;
ListCell *i;
for_each_cell(i, other_rels)
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(i);
if (!bms_overlap(other_rel->relids, old_rel->relids))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, other_rel);
/*
* As long as given other_rels are distinct, don't need to test to
* see if jrel is already part of output list.
*/
if (jrel)
result = lcons(jrel, result);
}
}
return result;
}
/*
* join_is_legal
* Determine whether a proposed join is legal given the query's
* join order constraints; and if it is, determine the join type.
*
* Caller must supply not only the two rels, but the union of their relids.
* (We could simplify the API by computing joinrelids locally, but this
* would be redundant work in the normal path through make_join_rel.)
*
* On success, *jointype_p is set to the required join type.
*/
static bool
join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
Relids joinrelids, JoinType *jointype_p)
{
JoinType jointype;
bool is_valid_inner;
ListCell *l;
/*
* Ensure *jointype_p is set on failure return. This is just to
* suppress uninitialized-variable warnings from overly anal compilers.
*/
*jointype_p = JOIN_INNER;
/*
* If we have any outer joins, the proposed join might be illegal; and in
* any case we have to determine its join type. Scan the OJ list for
* conflicts.
*/
jointype = JOIN_INNER; /* default if no match to an OJ */
is_valid_inner = true;
foreach(l, root->oj_info_list)
{
OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
/*
* This OJ is not relevant unless its RHS overlaps the proposed join.
* (Check this first as a fast path for dismissing most irrelevant OJs
* quickly.)
*/
if (!bms_overlap(ojinfo->min_righthand, joinrelids))
continue;
/*
* Also, not relevant if proposed join is fully contained within RHS
* (ie, we're still building up the RHS).
*/
if (bms_is_subset(joinrelids, ojinfo->min_righthand))
continue;
/*
* Also, not relevant if OJ is already done within either input.
*/
if (bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
bms_is_subset(ojinfo->min_righthand, rel1->relids))
continue;
if (bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
bms_is_subset(ojinfo->min_righthand, rel2->relids))
continue;
/*
* If one input contains min_lefthand and the other contains
* min_righthand, then we can perform the OJ at this join.
*
* Barf if we get matches to more than one OJ (is that possible?)
*/
if (bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
bms_is_subset(ojinfo->min_righthand, rel2->relids))
{
if (jointype != JOIN_INNER)
return false; /* invalid join path */
jointype = ojinfo->join_type;
if (jointype != JOIN_FULL && jointype != JOIN_LASJ && jointype != JOIN_LASJ_NOTIN)
jointype = JOIN_LEFT;
}
else if (bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
bms_is_subset(ojinfo->min_righthand, rel1->relids))
{
if (jointype != JOIN_INNER)
return false; /* invalid join path */
jointype = ojinfo->join_type;
if (jointype != JOIN_FULL && jointype != JOIN_LASJ && jointype != JOIN_LASJ_NOTIN)
jointype = JOIN_RIGHT;
}
else
{
/*----------
* Otherwise, the proposed join overlaps the RHS but isn't
* a valid implementation of this OJ. It might still be
* a legal join, however. If both inputs overlap the RHS,
* assume that it's OK. Since the inputs presumably got past
* this function's checks previously, they can't overlap the
* LHS and their violations of the RHS boundary must represent
* OJs that have been determined to commute with this one.
* We have to allow this to work correctly in cases like
* (a LEFT JOIN (b JOIN (c LEFT JOIN d)))
* when the c/d join has been determined to commute with the join
* to a, and hence d is not part of min_righthand for the upper
* join. It should be legal to join b to c/d but this will appear
* as a violation of the upper join's RHS.
* Furthermore, if one input overlaps the RHS and the other does
* not, we should still allow the join if it is a valid
* implementation of some other OJ. We have to allow this to
* support the associative identity
* (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab
* since joining B directly to C violates the lower OJ's RHS.
* We assume that make_outerjoininfo() set things up correctly
* so that we'll only match to some OJ if the join is valid.
* Set flag here to check at bottom of loop.
*----------
*/
if (bms_overlap(rel1->relids, ojinfo->min_righthand) &&
bms_overlap(rel2->relids, ojinfo->min_righthand))
{
/* seems OK */
Assert(!bms_overlap(joinrelids, ojinfo->min_lefthand));
}
else
is_valid_inner = false;
}
}
/* Fail if violated some OJ's RHS and didn't match to another OJ */
if (jointype == JOIN_INNER && !is_valid_inner)
return false; /* invalid join path */
/* Join is valid */
*jointype_p = jointype;
return true;
}
/*
* make_join_rel
* Find or create a join RelOptInfo that represents the join of
* the two given rels, and add to it path information for paths
* created with the two rels as outer and inner rel.
* (The join rel may already contain paths generated from other
* pairs of rels that add up to the same set of base rels.)
*
* NB: will return NULL if attempted join is not valid. This can happen
* when working with outer joins, or with IN clauses that have been turned
* into joins.
*/
RelOptInfo *
make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
{
Relids joinrelids;
JoinType jointype;
JoinType swapjointype;
RelOptInfo *joinrel;
List *restrictlist;
/* This is a convenient place to check for query cancel. */
CHECK_FOR_INTERRUPTS();
Insist(rel1 &&
rel2 &&
rel1->cheapest_total_path &&
rel2->cheapest_total_path);
/* We should never try to join two overlapping sets of rels. */
Assert(!bms_overlap(rel1->relids, rel2->relids));
/* Construct Relids set that identifies the joinrel. */
joinrelids = bms_union(rel1->relids, rel2->relids);
/* Check validity and determine join type. */
if (!join_is_legal(root, rel1, rel2, joinrelids, &jointype))
{
/* invalid join path */
bms_free(joinrelids);
return NULL;
}
/*
* Find or build the join RelOptInfo, and compute the restrictlist that
* goes with this particular joining.
*/
joinrel = build_join_rel(root, joinrelids, rel1, rel2, jointype,
&restrictlist);
/* Reversed jointype is useful when rel2 becomes outer and rel1 is inner. */
swapjointype = (jointype == JOIN_LEFT) ? JOIN_RIGHT
: (jointype == JOIN_RIGHT) ? JOIN_LEFT
: jointype;
/*
* CDB: Consider plans in which an upstream subquery's duplicate
* suppression is either postponed yet further downstream, or subsumed
* in this join by the use of the JOIN_IN technique on behalf of another
* subquery.
*/
if ((rel1->dedup_info && rel1->dedup_info->later_dedup_pathlist) ||
(rel2->dedup_info && rel2->dedup_info->later_dedup_pathlist))
cdb_add_subquery_join_paths(root,
joinrel,
rel1,
rel2,
jointype,
swapjointype,
restrictlist);
/*
* For antijoins, the outer and inner rel are fixed.
*/
else if (jointype == JOIN_LASJ || jointype == JOIN_LASJ_NOTIN)
{
add_paths_to_joinrel(root, joinrel, rel1, rel2, jointype, restrictlist);
}
/*
* Consider paths using each rel as both outer and inner.
*/
else
{
add_paths_to_joinrel(root, joinrel, rel1, rel2, jointype, restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, swapjointype, restrictlist);
}
bms_free(joinrelids);
return joinrel;
}
/*
* cdb_add_subquery_join_paths
*
* Each input rel may have a special pathlist containing paths in which some
* flattened subqueries have been completely evaluated except for duplicate
* suppression. Here we consider joins taking input from those paths. By
* postponing duplicate suppression until additional subqueries are brought
* into the join, a single duplicate suppression can cover multiple subqueries.
*/
void
cdb_add_subquery_join_paths(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *rel1,
RelOptInfo *rel2,
JoinType jointype,
JoinType swapjointype,
List *restrictlist)
{
CdbRelDedupInfo *dedup1 = rel1->dedup_info;
CdbRelDedupInfo *dedup2 = rel2->dedup_info;
List *save1_pathlist;
Path *save1_cheapest_startup;
Path *save1_cheapest_total;
List *save2_pathlist;
Path *save2_cheapest_startup;
Path *save2_cheapest_total;
/* If only one input's later_dedup_pathlist is nonempty, let it be rel2. */
if (!dedup2 ||
!dedup2->later_dedup_pathlist)
{
CdbSwap(RelOptInfo*, rel1, rel2);
CdbSwap(CdbRelDedupInfo*, dedup1, dedup2);
CdbSwap(JoinType, jointype, swapjointype);
Assert(dedup2 && dedup2->later_dedup_pathlist);
}
/* Consider joins between rel1's main paths and rel2's main paths. */
if (rel1->pathlist && rel2->pathlist)
{
add_paths_to_joinrel(root, joinrel, rel1, rel2, jointype, restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, swapjointype, restrictlist);
}
/* Save rel2's main pathlist ptrs. */
save2_pathlist = rel2->pathlist;
save2_cheapest_startup = rel2->cheapest_startup_path;
save2_cheapest_total = rel2->cheapest_total_path;
/* Swap in rel2's later_dedup_pathlist. */
rel2->pathlist = dedup2->later_dedup_pathlist;
rel2->cheapest_startup_path = dedup2->cheapest_startup_path;
rel2->cheapest_total_path = dedup2->cheapest_total_path;
/* Consider joins between rel1's main paths and rel2's later_dedup paths. */
if (rel1->pathlist)
{
add_paths_to_joinrel(root, joinrel, rel1, rel2, jointype, restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, swapjointype, restrictlist);
}
/* Finished if rel1 doesn't have later_dedup paths. */
if (!dedup1 ||
!dedup1->later_dedup_pathlist)
{
/* Restore rel2's main pathlist ptrs. */
rel2->pathlist = save2_pathlist;
rel2->cheapest_startup_path = save2_cheapest_startup;
rel2->cheapest_total_path = save2_cheapest_total;
return;
}
/* Save rel1's main pathlist ptrs. */
save1_pathlist = rel1->pathlist;
save1_cheapest_startup = rel1->cheapest_startup_path;
save1_cheapest_total = rel1->cheapest_total_path;
/* Swap in rel1's later_dedup_pathlist. */
rel1->pathlist = dedup1->later_dedup_pathlist;
rel1->cheapest_startup_path = dedup1->cheapest_startup_path;
rel1->cheapest_total_path = dedup1->cheapest_total_path;
/* Consider joins between later_dedup paths of both rel1 and rel2. */
add_paths_to_joinrel(root, joinrel, rel1, rel2, jointype, restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, swapjointype, restrictlist);
/* Restore rel2's main pathlist ptrs. */
rel2->pathlist = save2_pathlist;
rel2->cheapest_startup_path = save2_cheapest_startup;
rel2->cheapest_total_path = save2_cheapest_total;
/* Consider joins between rel1's later_dedup paths and rel2's main paths. */
if (rel2->pathlist)
{
add_paths_to_joinrel(root, joinrel, rel1, rel2, jointype, restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, swapjointype, restrictlist);
}
/* Restore rel1's main pathlist ptrs. */
rel1->pathlist = save1_pathlist;
rel1->cheapest_startup_path = save1_cheapest_startup;
rel1->cheapest_total_path = save1_cheapest_total;
} /* cdb_add_subquery_join_paths */
/*
* have_join_order_restriction
* Detect whether the two relations should be joined to satisfy
* a join-order restriction arising from outer joins or IN clauses.
*
* In practice this is always used with have_relevant_joinclause(), and so
* could be merged with that function, but it seems clearer to separate the
* two concerns. We need these tests because there are degenerate cases where
* a clauseless join must be performed to satisfy join-order restrictions.
*
* Note: this is only a problem if one side of a degenerate outer join
* contains multiple rels, or a clauseless join is required within an IN's
* RHS; else we will find a join path via the "last ditch" case in
* make_rels_by_joins(). We could dispense with this test if we were willing
* to try bushy plans in the "last ditch" case, but that seems much less
* efficient.
*/
bool
have_join_order_restriction(PlannerInfo *root,
RelOptInfo *rel1, RelOptInfo *rel2)
{
bool result = false;
ListCell *l;
/*
* It's possible that the rels correspond to the left and right sides
* of a degenerate outer join, that is, one with no joinclause mentioning
* the non-nullable side; in which case we should force the join to occur.
*
* Also, the two rels could represent a clauseless join that has to be
* completed to build up the LHS or RHS of an outer join.
*/
foreach(l, root->oj_info_list)
{
OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms handle them */
if (ojinfo->join_type == JOIN_FULL)
continue;
/* Can we perform the OJ with these rels? */
if (bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
bms_is_subset(ojinfo->min_righthand, rel2->relids))
{
result = true;
break;
}
if (bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
bms_is_subset(ojinfo->min_righthand, rel1->relids))
{
result = true;
break;
}
/*
* Might we need to join these rels to complete the RHS? We have
* to use "overlap" tests since either rel might include a lower OJ
* that has been proven to commute with this one.
*/
if (bms_overlap(ojinfo->min_righthand, rel1->relids) &&
bms_overlap(ojinfo->min_righthand, rel2->relids))
{
result = true;
break;
}
/* Likewise for the LHS. */
if (bms_overlap(ojinfo->min_lefthand, rel1->relids) &&
bms_overlap(ojinfo->min_lefthand, rel2->relids))
{
result = true;
break;
}
}
/*
* We do not force the join to occur if either input rel can legally
* be joined to anything else using joinclauses. This essentially
* means that clauseless bushy joins are put off as long as possible.
* The reason is that when there is a join order restriction high up
* in the join tree (that is, with many rels inside the LHS or RHS),
* we would otherwise expend lots of effort considering very stupid
* join combinations within its LHS or RHS.
*/
if (result)
{
if (has_legal_joinclause(root, rel1) ||
has_legal_joinclause(root, rel2))
result = false;
}
/*
* In CDB, unlike PostgreSQL, flattened subqueries do not restrict the
* join sequence; we aren't in danger of being unable to join all the
* tables. Still, an early cross-product (clauseless join) might
* sometimes enable the consideration of pre-join duplicate elimination
* (JOIN_IN or JOIN_UNIQUE). Someday we should consider a well-chosen
* set of early cross products. For now, limit the search space by
* means of a simple heuristic.
*/
foreach(l, root->in_info_list)
{
InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
/* Does the subquery RHS consist of exactly rel1 + rel2? */
if (bms_is_subset(rel1->relids, ininfo->righthand) &&
bms_is_subset(rel2->relids, ininfo->righthand) &&
bms_num_members(rel1->relids) + bms_num_members(rel2->relids) ==
bms_num_members(ininfo->righthand))
{
result = true;
break;
}
}
return result;
}
/*
* has_join_restriction
* Detect whether the specified relation has join-order restrictions
* due to being inside an outer join or an IN (sub-SELECT).
*
* Essentially, this tests whether have_join_order_restriction() could
* succeed with this rel and some other one. It's OK if we sometimes
* say "true" incorrectly. (Therefore, we don't bother with the relatively
* expensive has_legal_joinclause test.)
*/
static bool
has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
{
ListCell *l;
foreach(l, root->oj_info_list)
{
OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms preserve their ordering */
if (ojinfo->join_type == JOIN_FULL)
continue;
/* ignore if OJ is already contained in rel */
if (bms_is_subset(ojinfo->min_lefthand, rel->relids) &&
bms_is_subset(ojinfo->min_righthand, rel->relids))
continue;
/* restricted if it overlaps LHS or RHS, but doesn't contain OJ */
if (bms_overlap(ojinfo->min_lefthand, rel->relids) ||
bms_overlap(ojinfo->min_righthand, rel->relids))
return true;
}
foreach(l, root->in_info_list)
{
InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
/* CDB: Consider cross product if subquery RHS = rel + some other rel */
if (bms_is_subset(rel->relids, ininfo->righthand) &&
!bms_equal(rel->relids, ininfo->righthand))
return true;
}
return false;
}
/*
* has_legal_joinclause
* Detect whether the specified relation can legally be joined
* to any other rels using join clauses.
*
* We consider only joins to single other relations in the current
* initial_rels list. This is sufficient to get a "true" result in most real
* queries, and an occasional erroneous "false" will only cost a bit more
* planning time. The reason for this limitation is that considering joins to
* other joins would require proving that the other join rel can legally be
* formed, which seems like too much trouble for something that's only a
* heuristic to save planning time. (Note: we must look at initial_rels
* and not all of the query, since when we are planning a sub-joinlist we
* may be forced to make clauseless joins within initial_rels even though
* there are join clauses linking to other parts of the query.)
*/
static bool
has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel)
{
ListCell *lc;
foreach(lc, root->initial_rels)
{
RelOptInfo *rel2 = (RelOptInfo *) lfirst(lc);
/* ignore rels that are already in "rel" */
if (bms_overlap(rel->relids, rel2->relids))
continue;
if (have_relevant_joinclause(root, rel, rel2))
{
Relids joinrelids;
JoinType jointype;
/* join_is_legal needs relids of the union */
joinrelids = bms_union(rel->relids, rel2->relids);
if (join_is_legal(root, rel, rel2, joinrelids, &jointype))
{
/* Yes, this will work */
bms_free(joinrelids);
return true;
}
bms_free(joinrelids);
}
}
return false;
}