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postgres/src/backend/optimizer/path/joinpath.c
Tom Lane 45639a0525 Avoid invalidating all foreign-join cached plans when user mappings change. 
We must not push down a foreign join when the foreign tables involved
should be accessed under different user mappings.  Previously we tried
to enforce that rule literally during planning, but that meant that the
resulting plans were dependent on the current contents of the
pg_user_mapping catalog, and we had to blow away all cached plans
containing any remote join when anything at all changed in pg_user_mapping.
This could have been improved somewhat, but the fact that a syscache inval
callback has very limited info about what changed made it hard to do better
within that design.  Instead, let's change the planner to not consider user
mappings per se, but to allow a foreign join if both RTEs have the same
checkAsUser value.  If they do, then they necessarily will use the same
user mapping at runtime, and we don't need to know specifically which one
that is.  Post-plan-time changes in pg_user_mapping no longer require any
plan invalidation.

This rule does give up some optimization ability, to wit where two foreign
table references come from views with different owners or one's from a view
and one's directly in the query, but nonetheless the same user mapping
would have applied.  We'll sacrifice the first case, but to not regress
more than we have to in the second case, allow a foreign join involving
both zero and nonzero checkAsUser values if the nonzero one is the same as
the prevailing effective userID.  In that case, mark the plan as only
runnable by that userID.

The plancache code already had a notion of plans being userID-specific,
in order to support RLS.  It was a little confused though, in particular
lacking clarity of thought as to whether it was the rewritten query or just
the finished plan that's dependent on the userID.  Rearrange that code so
that it's clearer what depends on which, and so that the same logic applies
to both RLS-injected role dependency and foreign-join-injected role
dependency.

Note that this patch doesn't remove the other issue mentioned in the
original complaint, which is that while we'll reliably stop using a foreign
join if it's disallowed in a new context, we might fail to start using a
foreign join if it's now allowed, but we previously created a generic
cached plan that didn't use one.  It was agreed that the chance of winning
that way was not high enough to justify the much larger number of plan
invalidations that would have to occur if we tried to cause it to happen.

In passing, clean up randomly-varying spelling of EXPLAIN commands in
postgres_fdw.sql, and fix a COSTS ON example that had been allowed to
leak into the committed tests.

This reverts most of commits fbe5a3fb7 and 5d4171d1c, which were the
previous attempt at ensuring we wouldn't push down foreign joins that
span permissions contexts.

Etsuro Fujita and Tom Lane

Discussion: <d49c1e5b-f059-20f4-c132-e9752ee0113e@lab.ntt.co.jp>
2016-07-15 17:23:02 -04:00

1620 lines
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/*-------------------------------------------------------------------------
*
* joinpath.c
* Routines to find all possible paths for processing a set of joins
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/optimizer/path/joinpath.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <math.h>
#include "executor/executor.h"
#include "foreign/fdwapi.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
/* Hook for plugins to get control in add_paths_to_joinrel() */
set_join_pathlist_hook_type set_join_pathlist_hook = NULL;
#define PATH_PARAM_BY_REL(path, rel) \
((path)->param_info && bms_overlap(PATH_REQ_OUTER(path), (rel)->relids))
static void sort_inner_and_outer(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
JoinType jointype, JoinPathExtraData *extra);
static void match_unsorted_outer(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
JoinType jointype, JoinPathExtraData *extra);
static void consider_parallel_nestloop(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
JoinPathExtraData *extra);
static void hash_inner_and_outer(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
JoinType jointype, JoinPathExtraData *extra);
static List *select_mergejoin_clauses(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
JoinType jointype,
bool *mergejoin_allowed);
/*
* add_paths_to_joinrel
* Given a join relation and two component rels from which it can be made,
* consider all possible paths that use the two component rels as outer
* and inner rel respectively. Add these paths to the join rel's pathlist
* if they survive comparison with other paths (and remove any existing
* paths that are dominated by these paths).
*
* Modifies the pathlist field of the joinrel node to contain the best
* paths found so far.
*
* jointype is not necessarily the same as sjinfo->jointype; it might be
* "flipped around" if we are considering joining the rels in the opposite
* direction from what's indicated in sjinfo.
*
* Also, this routine and others in this module accept the special JoinTypes
* JOIN_UNIQUE_OUTER and JOIN_UNIQUE_INNER to indicate that we should
* unique-ify the outer or inner relation and then apply a regular inner
* join. These values are not allowed to propagate outside this module,
* however. Path cost estimation code may need to recognize that it's
* dealing with such a case --- the combination of nominal jointype INNER
* with sjinfo->jointype == JOIN_SEMI indicates that.
*/
void
add_paths_to_joinrel(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
SpecialJoinInfo *sjinfo,
List *restrictlist)
{
JoinPathExtraData extra;
bool mergejoin_allowed = true;
ListCell *lc;
extra.restrictlist = restrictlist;
extra.mergeclause_list = NIL;
extra.sjinfo = sjinfo;
extra.param_source_rels = NULL;
/*
* Find potential mergejoin clauses. We can skip this if we are not
* interested in doing a mergejoin. However, mergejoin may be our only
* way of implementing a full outer join, so override enable_mergejoin if
* it's a full join.
*/
if (enable_mergejoin || jointype == JOIN_FULL)
extra.mergeclause_list = select_mergejoin_clauses(root,
joinrel,
outerrel,
innerrel,
restrictlist,
jointype,
&mergejoin_allowed);
/*
* If it's SEMI or ANTI join, compute correction factors for cost
* estimation. These will be the same for all paths.
*/
if (jointype == JOIN_SEMI || jointype == JOIN_ANTI)
compute_semi_anti_join_factors(root, outerrel, innerrel,
jointype, sjinfo, restrictlist,
&extra.semifactors);
/*
* Decide whether it's sensible to generate parameterized paths for this
* joinrel, and if so, which relations such paths should require. There
* is usually no need to create a parameterized result path unless there
* is a join order restriction that prevents joining one of our input rels
* directly to the parameter source rel instead of joining to the other
* input rel. (But see allow_star_schema_join().) This restriction
* reduces the number of parameterized paths we have to deal with at
* higher join levels, without compromising the quality of the resulting
* plan. We express the restriction as a Relids set that must overlap the
* parameterization of any proposed join path.
*/
foreach(lc, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
/*
* SJ is relevant to this join if we have some part of its RHS
* (possibly not all of it), and haven't yet joined to its LHS. (This
* test is pretty simplistic, but should be sufficient considering the
* join has already been proven legal.) If the SJ is relevant, it
* presents constraints for joining to anything not in its RHS.
*/
if (bms_overlap(joinrel->relids, sjinfo->min_righthand) &&
!bms_overlap(joinrel->relids, sjinfo->min_lefthand))
extra.param_source_rels = bms_join(extra.param_source_rels,
bms_difference(root->all_baserels,
sjinfo->min_righthand));
/* full joins constrain both sides symmetrically */
if (sjinfo->jointype == JOIN_FULL &&
bms_overlap(joinrel->relids, sjinfo->min_lefthand) &&
!bms_overlap(joinrel->relids, sjinfo->min_righthand))
extra.param_source_rels = bms_join(extra.param_source_rels,
bms_difference(root->all_baserels,
sjinfo->min_lefthand));
}
/*
* However, when a LATERAL subquery is involved, there will simply not be
* any paths for the joinrel that aren't parameterized by whatever the
* subquery is parameterized by, unless its parameterization is resolved
* within the joinrel. So we might as well allow additional dependencies
* on whatever residual lateral dependencies the joinrel will have.
*/
extra.param_source_rels = bms_add_members(extra.param_source_rels,
joinrel->lateral_relids);
/*
* 1. Consider mergejoin paths where both relations must be explicitly
* sorted. Skip this if we can't mergejoin.
*/
if (mergejoin_allowed)
sort_inner_and_outer(root, joinrel, outerrel, innerrel,
jointype, &extra);
/*
* 2. Consider paths where the outer relation need not be explicitly
* sorted. This includes both nestloops and mergejoins where the outer
* path is already ordered. Again, skip this if we can't mergejoin.
* (That's okay because we know that nestloop can't handle right/full
* joins at all, so it wouldn't work in the prohibited cases either.)
*/
if (mergejoin_allowed)
match_unsorted_outer(root, joinrel, outerrel, innerrel,
jointype, &extra);
#ifdef NOT_USED
/*
* 3. Consider paths where the inner relation need not be explicitly
* sorted. This includes mergejoins only (nestloops were already built in
* match_unsorted_outer).
*
* Diked out as redundant 2/13/2000 -- tgl. There isn't any really
* significant difference between the inner and outer side of a mergejoin,
* so match_unsorted_inner creates no paths that aren't equivalent to
* those made by match_unsorted_outer when add_paths_to_joinrel() is
* invoked with the two rels given in the other order.
*/
if (mergejoin_allowed)
match_unsorted_inner(root, joinrel, outerrel, innerrel,
jointype, &extra);
#endif
/*
* 4. Consider paths where both outer and inner relations must be hashed
* before being joined. As above, disregard enable_hashjoin for full
* joins, because there may be no other alternative.
*/
if (enable_hashjoin || jointype == JOIN_FULL)
hash_inner_and_outer(root, joinrel, outerrel, innerrel,
jointype, &extra);
/*
* 5. If inner and outer relations are foreign tables (or joins) belonging
* to the same server and assigned to the same user to check access
* permissions as, give the FDW a chance to push down joins.
*/
if (joinrel->fdwroutine &&
joinrel->fdwroutine->GetForeignJoinPaths)
joinrel->fdwroutine->GetForeignJoinPaths(root, joinrel,
outerrel, innerrel,
jointype, &extra);
/*
* 6. Finally, give extensions a chance to manipulate the path list.
*/
if (set_join_pathlist_hook)
set_join_pathlist_hook(root, joinrel, outerrel, innerrel,
jointype, &extra);
}
/*
* We override the param_source_rels heuristic to accept nestloop paths in
* which the outer rel satisfies some but not all of the inner path's
* parameterization. This is necessary to get good plans for star-schema
* scenarios, in which a parameterized path for a large table may require
* parameters from multiple small tables that will not get joined directly to
* each other. We can handle that by stacking nestloops that have the small
* tables on the outside; but this breaks the rule the param_source_rels
* heuristic is based on, namely that parameters should not be passed down
* across joins unless there's a join-order-constraint-based reason to do so.
* So we ignore the param_source_rels restriction when this case applies.
*
* allow_star_schema_join() returns TRUE if the param_source_rels restriction
* should be overridden, ie, it's okay to perform this join.
*/
static inline bool
allow_star_schema_join(PlannerInfo *root,
Path *outer_path,
Path *inner_path)
{
Relids innerparams = PATH_REQ_OUTER(inner_path);
Relids outerrelids = outer_path->parent->relids;
/*
* It's a star-schema case if the outer rel provides some but not all of
* the inner rel's parameterization.
*/
return (bms_overlap(innerparams, outerrelids) &&
bms_nonempty_difference(innerparams, outerrelids));
}
/*
* try_nestloop_path
* Consider a nestloop join path; if it appears useful, push it into
* the joinrel's pathlist via add_path().
*/
static void
try_nestloop_path(PlannerInfo *root,
RelOptInfo *joinrel,
Path *outer_path,
Path *inner_path,
List *pathkeys,
JoinType jointype,
JoinPathExtraData *extra)
{
Relids required_outer;
JoinCostWorkspace workspace;
/*
* Check to see if proposed path is still parameterized, and reject if the
* parameterization wouldn't be sensible --- unless allow_star_schema_join
* says to allow it anyway. Also, we must reject if have_dangerous_phv
* doesn't like the look of it, which could only happen if the nestloop is
* still parameterized.
*/
required_outer = calc_nestloop_required_outer(outer_path,
inner_path);
if (required_outer &&
((!bms_overlap(required_outer, extra->param_source_rels) &&
!allow_star_schema_join(root, outer_path, inner_path)) ||
have_dangerous_phv(root,
outer_path->parent->relids,
PATH_REQ_OUTER(inner_path))))
{
/* Waste no memory when we reject a path here */
bms_free(required_outer);
return;
}
/*
* Do a precheck to quickly eliminate obviously-inferior paths. We
* calculate a cheap lower bound on the path's cost and then use
* add_path_precheck() to see if the path is clearly going to be dominated
* by some existing path for the joinrel. If not, do the full pushup with
* creating a fully valid path structure and submitting it to add_path().
* The latter two steps are expensive enough to make this two-phase
* methodology worthwhile.
*/
initial_cost_nestloop(root, &workspace, jointype,
outer_path, inner_path,
extra->sjinfo, &extra->semifactors);
if (add_path_precheck(joinrel,
workspace.startup_cost, workspace.total_cost,
pathkeys, required_outer))
{
add_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
&workspace,
extra->sjinfo,
&extra->semifactors,
outer_path,
inner_path,
extra->restrictlist,
pathkeys,
required_outer));
}
else
{
/* Waste no memory when we reject a path here */
bms_free(required_outer);
}
}
/*
* try_partial_nestloop_path
* Consider a partial nestloop join path; if it appears useful, push it into
* the joinrel's partial_pathlist via add_partial_path().
*/
static void
try_partial_nestloop_path(PlannerInfo *root,
RelOptInfo *joinrel,
Path *outer_path,
Path *inner_path,
List *pathkeys,
JoinType jointype,
JoinPathExtraData *extra)
{
JoinCostWorkspace workspace;
/*
* If the inner path is parameterized, the parameterization must be fully
* satisfied by the proposed outer path. Parameterized partial paths are
* not supported. The caller should already have verified that no
* extra_lateral_rels are required here.
*/
Assert(bms_is_empty(joinrel->lateral_relids));
if (inner_path->param_info != NULL)
{
Relids inner_paramrels = inner_path->param_info->ppi_req_outer;
if (!bms_is_subset(inner_paramrels, outer_path->parent->relids))
return;
}
/*
* Before creating a path, get a quick lower bound on what it is likely to
* cost. Bail out right away if it looks terrible.
*/
initial_cost_nestloop(root, &workspace, jointype,
outer_path, inner_path,
extra->sjinfo, &extra->semifactors);
if (!add_partial_path_precheck(joinrel, workspace.total_cost, pathkeys))
return;
/* Might be good enough to be worth trying, so let's try it. */
add_partial_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
&workspace,
extra->sjinfo,
&extra->semifactors,
outer_path,
inner_path,
extra->restrictlist,
pathkeys,
NULL));
}
/*
* try_mergejoin_path
* Consider a merge join path; if it appears useful, push it into
* the joinrel's pathlist via add_path().
*/
static void
try_mergejoin_path(PlannerInfo *root,
RelOptInfo *joinrel,
Path *outer_path,
Path *inner_path,
List *pathkeys,
List *mergeclauses,
List *outersortkeys,
List *innersortkeys,
JoinType jointype,
JoinPathExtraData *extra)
{
Relids required_outer;
JoinCostWorkspace workspace;
/*
* Check to see if proposed path is still parameterized, and reject if the
* parameterization wouldn't be sensible.
*/
required_outer = calc_non_nestloop_required_outer(outer_path,
inner_path);
if (required_outer &&
!bms_overlap(required_outer, extra->param_source_rels))
{
/* Waste no memory when we reject a path here */
bms_free(required_outer);
return;
}
/*
* If the given paths are already well enough ordered, we can skip doing
* an explicit sort.
*/
if (outersortkeys &&
pathkeys_contained_in(outersortkeys, outer_path->pathkeys))
outersortkeys = NIL;
if (innersortkeys &&
pathkeys_contained_in(innersortkeys, inner_path->pathkeys))
innersortkeys = NIL;
/*
* See comments in try_nestloop_path().
*/
initial_cost_mergejoin(root, &workspace, jointype, mergeclauses,
outer_path, inner_path,
outersortkeys, innersortkeys,
extra->sjinfo);
if (add_path_precheck(joinrel,
workspace.startup_cost, workspace.total_cost,
pathkeys, required_outer))
{
add_path(joinrel, (Path *)
create_mergejoin_path(root,
joinrel,
jointype,
&workspace,
extra->sjinfo,
outer_path,
inner_path,
extra->restrictlist,
pathkeys,
required_outer,
mergeclauses,
outersortkeys,
innersortkeys));
}
else
{
/* Waste no memory when we reject a path here */
bms_free(required_outer);
}
}
/*
* try_hashjoin_path
* Consider a hash join path; if it appears useful, push it into
* the joinrel's pathlist via add_path().
*/
static void
try_hashjoin_path(PlannerInfo *root,
RelOptInfo *joinrel,
Path *outer_path,
Path *inner_path,
List *hashclauses,
JoinType jointype,
JoinPathExtraData *extra)
{
Relids required_outer;
JoinCostWorkspace workspace;
/*
* Check to see if proposed path is still parameterized, and reject if the
* parameterization wouldn't be sensible.
*/
required_outer = calc_non_nestloop_required_outer(outer_path,
inner_path);
if (required_outer &&
!bms_overlap(required_outer, extra->param_source_rels))
{
/* Waste no memory when we reject a path here */
bms_free(required_outer);
return;
}
/*
* See comments in try_nestloop_path(). Also note that hashjoin paths
* never have any output pathkeys, per comments in create_hashjoin_path.
*/
initial_cost_hashjoin(root, &workspace, jointype, hashclauses,
outer_path, inner_path,
extra->sjinfo, &extra->semifactors);
if (add_path_precheck(joinrel,
workspace.startup_cost, workspace.total_cost,
NIL, required_outer))
{
add_path(joinrel, (Path *)
create_hashjoin_path(root,
joinrel,
jointype,
&workspace,
extra->sjinfo,
&extra->semifactors,
outer_path,
inner_path,
extra->restrictlist,
required_outer,
hashclauses));
}
else
{
/* Waste no memory when we reject a path here */
bms_free(required_outer);
}
}
/*
* try_partial_hashjoin_path
* Consider a partial hashjoin join path; if it appears useful, push it into
* the joinrel's partial_pathlist via add_partial_path().
*/
static void
try_partial_hashjoin_path(PlannerInfo *root,
RelOptInfo *joinrel,
Path *outer_path,
Path *inner_path,
List *hashclauses,
JoinType jointype,
JoinPathExtraData *extra)
{
JoinCostWorkspace workspace;
/*
* If the inner path is parameterized, the parameterization must be fully
* satisfied by the proposed outer path. Parameterized partial paths are
* not supported. The caller should already have verified that no
* extra_lateral_rels are required here.
*/
Assert(bms_is_empty(joinrel->lateral_relids));
if (inner_path->param_info != NULL)
{
Relids inner_paramrels = inner_path->param_info->ppi_req_outer;
if (!bms_is_empty(inner_paramrels))
return;
}
/*
* Before creating a path, get a quick lower bound on what it is likely to
* cost. Bail out right away if it looks terrible.
*/
initial_cost_hashjoin(root, &workspace, jointype, hashclauses,
outer_path, inner_path,
extra->sjinfo, &extra->semifactors);
if (!add_partial_path_precheck(joinrel, workspace.total_cost, NIL))
return;
/* Might be good enough to be worth trying, so let's try it. */
add_partial_path(joinrel, (Path *)
create_hashjoin_path(root,
joinrel,
jointype,
&workspace,
extra->sjinfo,
&extra->semifactors,
outer_path,
inner_path,
extra->restrictlist,
NULL,
hashclauses));
}
/*
* clause_sides_match_join
* Determine whether a join clause is of the right form to use in this join.
*
* We already know that the clause is a binary opclause referencing only the
* rels in the current join. The point here is to check whether it has the
* form "outerrel_expr op innerrel_expr" or "innerrel_expr op outerrel_expr",
* rather than mixing outer and inner vars on either side. If it matches,
* we set the transient flag outer_is_left to identify which side is which.
*/
static inline bool
clause_sides_match_join(RestrictInfo *rinfo, RelOptInfo *outerrel,
RelOptInfo *innerrel)
{
if (bms_is_subset(rinfo->left_relids, outerrel->relids) &&
bms_is_subset(rinfo->right_relids, innerrel->relids))
{
/* lefthand side is outer */
rinfo->outer_is_left = true;
return true;
}
else if (bms_is_subset(rinfo->left_relids, innerrel->relids) &&
bms_is_subset(rinfo->right_relids, outerrel->relids))
{
/* righthand side is outer */
rinfo->outer_is_left = false;
return true;
}
return false; /* no good for these input relations */
}
/*
* sort_inner_and_outer
* Create mergejoin join paths by explicitly sorting both the outer and
* inner join relations on each available merge ordering.
*
* 'joinrel' is the join relation
* 'outerrel' is the outer join relation
* 'innerrel' is the inner join relation
* 'jointype' is the type of join to do
* 'extra' contains additional input values
*/
static void
sort_inner_and_outer(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
JoinPathExtraData *extra)
{
Path *outer_path;
Path *inner_path;
List *all_pathkeys;
ListCell *l;
/*
* We only consider the cheapest-total-cost input paths, since we are
* assuming here that a sort is required. We will consider
* cheapest-startup-cost input paths later, and only if they don't need a
* sort.
*
* This function intentionally does not consider parameterized input
* paths, except when the cheapest-total is parameterized. If we did so,
* we'd have a combinatorial explosion of mergejoin paths of dubious
* value. This interacts with decisions elsewhere that also discriminate
* against mergejoins with parameterized inputs; see comments in
* src/backend/optimizer/README.
*/
outer_path = outerrel->cheapest_total_path;
inner_path = innerrel->cheapest_total_path;
/*
* If either cheapest-total path is parameterized by the other rel, we
* can't use a mergejoin. (There's no use looking for alternative input
* paths, since these should already be the least-parameterized available
* paths.)
*/
if (PATH_PARAM_BY_REL(outer_path, innerrel) ||
PATH_PARAM_BY_REL(inner_path, outerrel))
return;
/*
* If unique-ification is requested, do it and then handle as a plain
* inner join.
*/
if (jointype == JOIN_UNIQUE_OUTER)
{
outer_path = (Path *) create_unique_path(root, outerrel,
outer_path, extra->sjinfo);
Assert(outer_path);
jointype = JOIN_INNER;
}
else if (jointype == JOIN_UNIQUE_INNER)
{
inner_path = (Path *) create_unique_path(root, innerrel,
inner_path, extra->sjinfo);
Assert(inner_path);
jointype = JOIN_INNER;
}
/*
* Each possible ordering of the available mergejoin clauses will generate
* a differently-sorted result path at essentially the same cost. We have
* no basis for choosing one over another at this level of joining, but
* some sort orders may be more useful than others for higher-level
* mergejoins, so it's worth considering multiple orderings.
*
* Actually, it's not quite true that every mergeclause ordering will
* generate a different path order, because some of the clauses may be
* partially redundant (refer to the same EquivalenceClasses). Therefore,
* what we do is convert the mergeclause list to a list of canonical
* pathkeys, and then consider different orderings of the pathkeys.
*
* Generating a path for *every* permutation of the pathkeys doesn't seem
* like a winning strategy; the cost in planning time is too high. For
* now, we generate one path for each pathkey, listing that pathkey first
* and the rest in random order. This should allow at least a one-clause
* mergejoin without re-sorting against any other possible mergejoin
* partner path. But if we've not guessed the right ordering of secondary
* keys, we may end up evaluating clauses as qpquals when they could have
* been done as mergeclauses. (In practice, it's rare that there's more
* than two or three mergeclauses, so expending a huge amount of thought
* on that is probably not worth it.)
*
* The pathkey order returned by select_outer_pathkeys_for_merge() has
* some heuristics behind it (see that function), so be sure to try it
* exactly as-is as well as making variants.
*/
all_pathkeys = select_outer_pathkeys_for_merge(root,
extra->mergeclause_list,
joinrel);
foreach(l, all_pathkeys)
{
List *front_pathkey = (List *) lfirst(l);
List *cur_mergeclauses;
List *outerkeys;
List *innerkeys;
List *merge_pathkeys;
/* Make a pathkey list with this guy first */
if (l != list_head(all_pathkeys))
outerkeys = lcons(front_pathkey,
list_delete_ptr(list_copy(all_pathkeys),
front_pathkey));
else
outerkeys = all_pathkeys; /* no work at first one... */
/* Sort the mergeclauses into the corresponding ordering */
cur_mergeclauses = find_mergeclauses_for_pathkeys(root,
outerkeys,
true,
extra->mergeclause_list);
/* Should have used them all... */
Assert(list_length(cur_mergeclauses) == list_length(extra->mergeclause_list));
/* Build sort pathkeys for the inner side */
innerkeys = make_inner_pathkeys_for_merge(root,
cur_mergeclauses,
outerkeys);
/* Build pathkeys representing output sort order */
merge_pathkeys = build_join_pathkeys(root, joinrel, jointype,
outerkeys);
/*
* And now we can make the path.
*
* Note: it's possible that the cheapest paths will already be sorted
* properly. try_mergejoin_path will detect that case and suppress an
* explicit sort step, so we needn't do so here.
*/
try_mergejoin_path(root,
joinrel,
outer_path,
inner_path,
merge_pathkeys,
cur_mergeclauses,
outerkeys,
innerkeys,
jointype,
extra);
}
}
/*
* match_unsorted_outer
* Creates possible join paths for processing a single join relation
* 'joinrel' by employing either iterative substitution or
* mergejoining on each of its possible outer paths (considering
* only outer paths that are already ordered well enough for merging).
*
* We always generate a nestloop path for each available outer path.
* In fact we may generate as many as five: one on the cheapest-total-cost
* inner path, one on the same with materialization, one on the
* cheapest-startup-cost inner path (if different), one on the
* cheapest-total inner-indexscan path (if any), and one on the
* cheapest-startup inner-indexscan path (if different).
*
* We also consider mergejoins if mergejoin clauses are available. We have
* two ways to generate the inner path for a mergejoin: sort the cheapest
* inner path, or use an inner path that is already suitably ordered for the
* merge. If we have several mergeclauses, it could be that there is no inner
* path (or only a very expensive one) for the full list of mergeclauses, but
* better paths exist if we truncate the mergeclause list (thereby discarding
* some sort key requirements). So, we consider truncations of the
* mergeclause list as well as the full list. (Ideally we'd consider all
* subsets of the mergeclause list, but that seems way too expensive.)
*
* 'joinrel' is the join relation
* 'outerrel' is the outer join relation
* 'innerrel' is the inner join relation
* 'jointype' is the type of join to do
* 'extra' contains additional input values
*/
static void
match_unsorted_outer(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
JoinPathExtraData *extra)
{
JoinType save_jointype = jointype;
bool nestjoinOK;
bool useallclauses;
Path *inner_cheapest_total = innerrel->cheapest_total_path;
Path *matpath = NULL;
ListCell *lc1;
/*
* Nestloop only supports inner, left, semi, and anti joins. Also, if we
* are doing a right or full mergejoin, we must use *all* the mergeclauses
* as join clauses, else we will not have a valid plan. (Although these
* two flags are currently inverses, keep them separate for clarity and
* possible future changes.)
*/
switch (jointype)
{
case JOIN_INNER:
case JOIN_LEFT:
case JOIN_SEMI:
case JOIN_ANTI:
nestjoinOK = true;
useallclauses = false;
break;
case JOIN_RIGHT:
case JOIN_FULL:
nestjoinOK = false;
useallclauses = true;
break;
case JOIN_UNIQUE_OUTER:
case JOIN_UNIQUE_INNER:
jointype = JOIN_INNER;
nestjoinOK = true;
useallclauses = false;
break;
default:
elog(ERROR, "unrecognized join type: %d",
(int) jointype);
nestjoinOK = false; /* keep compiler quiet */
useallclauses = false;
break;
}
/*
* If inner_cheapest_total is parameterized by the outer rel, ignore it;
* we will consider it below as a member of cheapest_parameterized_paths,
* but the other possibilities considered in this routine aren't usable.
*/
if (PATH_PARAM_BY_REL(inner_cheapest_total, outerrel))
inner_cheapest_total = NULL;
/*
* If we need to unique-ify the inner path, we will consider only the
* cheapest-total inner.
*/
if (save_jointype == JOIN_UNIQUE_INNER)
{
/* No way to do this with an inner path parameterized by outer rel */
if (inner_cheapest_total == NULL)
return;
inner_cheapest_total = (Path *)
create_unique_path(root, innerrel, inner_cheapest_total, extra->sjinfo);
Assert(inner_cheapest_total);
}
else if (nestjoinOK)
{
/*
* Consider materializing the cheapest inner path, unless
* enable_material is off or the path in question materializes its
* output anyway.
*/
if (enable_material && inner_cheapest_total != NULL &&
!ExecMaterializesOutput(inner_cheapest_total->pathtype))
matpath = (Path *)
create_material_path(innerrel, inner_cheapest_total);
}
foreach(lc1, outerrel->pathlist)
{
Path *outerpath = (Path *) lfirst(lc1);
List *merge_pathkeys;
List *mergeclauses;
List *innersortkeys;
List *trialsortkeys;
Path *cheapest_startup_inner;
Path *cheapest_total_inner;
int num_sortkeys;
int sortkeycnt;
/*
* We cannot use an outer path that is parameterized by the inner rel.
*/
if (PATH_PARAM_BY_REL(outerpath, innerrel))
continue;
/*
* If we need to unique-ify the outer path, it's pointless to consider
* any but the cheapest outer. (XXX we don't consider parameterized
* outers, nor inners, for unique-ified cases. Should we?)
*/
if (save_jointype == JOIN_UNIQUE_OUTER)
{
if (outerpath != outerrel->cheapest_total_path)
continue;
outerpath = (Path *) create_unique_path(root, outerrel,
outerpath, extra->sjinfo);
Assert(outerpath);
}
/*
* The result will have this sort order (even if it is implemented as
* a nestloop, and even if some of the mergeclauses are implemented by
* qpquals rather than as true mergeclauses):
*/
merge_pathkeys = build_join_pathkeys(root, joinrel, jointype,
outerpath->pathkeys);
if (save_jointype == JOIN_UNIQUE_INNER)
{
/*
* Consider nestloop join, but only with the unique-ified cheapest
* inner path
*/
try_nestloop_path(root,
joinrel,
outerpath,
inner_cheapest_total,
merge_pathkeys,
jointype,
extra);
}
else if (nestjoinOK)
{
/*
* Consider nestloop joins using this outer path and various
* available paths for the inner relation. We consider the
* cheapest-total paths for each available parameterization of the
* inner relation, including the unparameterized case.
*/
ListCell *lc2;
foreach(lc2, innerrel->cheapest_parameterized_paths)
{
Path *innerpath = (Path *) lfirst(lc2);
try_nestloop_path(root,
joinrel,
outerpath,
innerpath,
merge_pathkeys,
jointype,
extra);
}
/* Also consider materialized form of the cheapest inner path */
if (matpath != NULL)
try_nestloop_path(root,
joinrel,
outerpath,
matpath,
merge_pathkeys,
jointype,
extra);
}
/* Can't do anything else if outer path needs to be unique'd */
if (save_jointype == JOIN_UNIQUE_OUTER)
continue;
/* Can't do anything else if inner rel is parameterized by outer */
if (inner_cheapest_total == NULL)
continue;
/* Look for useful mergeclauses (if any) */
mergeclauses = find_mergeclauses_for_pathkeys(root,
outerpath->pathkeys,
true,
extra->mergeclause_list);
/*
* Done with this outer path if no chance for a mergejoin.
*
* Special corner case: for "x FULL JOIN y ON true", there will be no
* join clauses at all. Ordinarily we'd generate a clauseless
* nestloop path, but since mergejoin is our only join type that
* supports FULL JOIN without any join clauses, it's necessary to
* generate a clauseless mergejoin path instead.
*/
if (mergeclauses == NIL)
{
if (jointype == JOIN_FULL)
/* okay to try for mergejoin */ ;
else
continue;
}
if (useallclauses && list_length(mergeclauses) != list_length(extra->mergeclause_list))
continue;
/* Compute the required ordering of the inner path */
innersortkeys = make_inner_pathkeys_for_merge(root,
mergeclauses,
outerpath->pathkeys);
/*
* Generate a mergejoin on the basis of sorting the cheapest inner.
* Since a sort will be needed, only cheapest total cost matters. (But
* try_mergejoin_path will do the right thing if inner_cheapest_total
* is already correctly sorted.)
*/
try_mergejoin_path(root,
joinrel,
outerpath,
inner_cheapest_total,
merge_pathkeys,
mergeclauses,
NIL,
innersortkeys,
jointype,
extra);
/* Can't do anything else if inner path needs to be unique'd */
if (save_jointype == JOIN_UNIQUE_INNER)
continue;
/*
* Look for presorted inner paths that satisfy the innersortkey list
* --- or any truncation thereof, if we are allowed to build a
* mergejoin using a subset of the merge clauses. Here, we consider
* both cheap startup cost and cheap total cost.
*
* Currently we do not consider parameterized inner paths here. This
* interacts with decisions elsewhere that also discriminate against
* mergejoins with parameterized inputs; see comments in
* src/backend/optimizer/README.
*
* As we shorten the sortkey list, we should consider only paths that
* are strictly cheaper than (in particular, not the same as) any path
* found in an earlier iteration. Otherwise we'd be intentionally
* using fewer merge keys than a given path allows (treating the rest
* as plain joinquals), which is unlikely to be a good idea. Also,
* eliminating paths here on the basis of compare_path_costs is a lot
* cheaper than building the mergejoin path only to throw it away.
*
* If inner_cheapest_total is well enough sorted to have not required
* a sort in the path made above, we shouldn't make a duplicate path
* with it, either. We handle that case with the same logic that
* handles the previous consideration, by initializing the variables
* that track cheapest-so-far properly. Note that we do NOT reject
* inner_cheapest_total if we find it matches some shorter set of
* pathkeys. That case corresponds to using fewer mergekeys to avoid
* sorting inner_cheapest_total, whereas we did sort it above, so the
* plans being considered are different.
*/
if (pathkeys_contained_in(innersortkeys,
inner_cheapest_total->pathkeys))
{
/* inner_cheapest_total didn't require a sort */
cheapest_startup_inner = inner_cheapest_total;
cheapest_total_inner = inner_cheapest_total;
}
else
{
/* it did require a sort, at least for the full set of keys */
cheapest_startup_inner = NULL;
cheapest_total_inner = NULL;
}
num_sortkeys = list_length(innersortkeys);
if (num_sortkeys > 1 && !useallclauses)
trialsortkeys = list_copy(innersortkeys); /* need modifiable copy */
else
trialsortkeys = innersortkeys; /* won't really truncate */
for (sortkeycnt = num_sortkeys; sortkeycnt > 0; sortkeycnt--)
{
Path *innerpath;
List *newclauses = NIL;
/*
* Look for an inner path ordered well enough for the first
* 'sortkeycnt' innersortkeys. NB: trialsortkeys list is modified
* destructively, which is why we made a copy...
*/
trialsortkeys = list_truncate(trialsortkeys, sortkeycnt);
innerpath = get_cheapest_path_for_pathkeys(innerrel->pathlist,
trialsortkeys,
NULL,
TOTAL_COST);
if (innerpath != NULL &&
(cheapest_total_inner == NULL ||
compare_path_costs(innerpath, cheapest_total_inner,
TOTAL_COST) < 0))
{
/* Found a cheap (or even-cheaper) sorted path */
/* Select the right mergeclauses, if we didn't already */
if (sortkeycnt < num_sortkeys)
{
newclauses =
find_mergeclauses_for_pathkeys(root,
trialsortkeys,
false,
mergeclauses);
Assert(newclauses != NIL);
}
else
newclauses = mergeclauses;
try_mergejoin_path(root,
joinrel,
outerpath,
innerpath,
merge_pathkeys,
newclauses,
NIL,
NIL,
jointype,
extra);
cheapest_total_inner = innerpath;
}
/* Same on the basis of cheapest startup cost ... */
innerpath = get_cheapest_path_for_pathkeys(innerrel->pathlist,
trialsortkeys,
NULL,
STARTUP_COST);
if (innerpath != NULL &&
(cheapest_startup_inner == NULL ||
compare_path_costs(innerpath, cheapest_startup_inner,
STARTUP_COST) < 0))
{
/* Found a cheap (or even-cheaper) sorted path */
if (innerpath != cheapest_total_inner)
{
/*
* Avoid rebuilding clause list if we already made one;
* saves memory in big join trees...
*/
if (newclauses == NIL)
{
if (sortkeycnt < num_sortkeys)
{
newclauses =
find_mergeclauses_for_pathkeys(root,
trialsortkeys,
false,
mergeclauses);
Assert(newclauses != NIL);
}
else
newclauses = mergeclauses;
}
try_mergejoin_path(root,
joinrel,
outerpath,
innerpath,
merge_pathkeys,
newclauses,
NIL,
NIL,
jointype,
extra);
}
cheapest_startup_inner = innerpath;
}
/*
* Don't consider truncated sortkeys if we need all clauses.
*/
if (useallclauses)
break;
}
}
/*
* If the joinrel is parallel-safe and the join type supports nested
* loops, we may be able to consider a partial nestloop plan. However, we
* can't handle JOIN_UNIQUE_OUTER, because the outer path will be partial,
* and therefore we won't be able to properly guarantee uniqueness. Nor
* can we handle extra_lateral_rels, since partial paths must not be
* parameterized.
*/
if (joinrel->consider_parallel && nestjoinOK &&
save_jointype != JOIN_UNIQUE_OUTER &&
bms_is_empty(joinrel->lateral_relids))
consider_parallel_nestloop(root, joinrel, outerrel, innerrel,
save_jointype, extra);
}
/*
* consider_parallel_nestloop
* Try to build partial paths for a joinrel by joining a partial path for the
* outer relation to a complete path for the inner relation.
*
* 'joinrel' is the join relation
* 'outerrel' is the outer join relation
* 'innerrel' is the inner join relation
* 'jointype' is the type of join to do
* 'extra' contains additional input values
*/
static void
consider_parallel_nestloop(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
JoinPathExtraData *extra)
{
ListCell *lc1;
foreach(lc1, outerrel->partial_pathlist)
{
Path *outerpath = (Path *) lfirst(lc1);
List *pathkeys;
ListCell *lc2;
/* Figure out what useful ordering any paths we create will have. */
pathkeys = build_join_pathkeys(root, joinrel, jointype,
outerpath->pathkeys);
/*
* Try the cheapest parameterized paths; only those which will produce
* an unparameterized path when joined to this outerrel will survive
* try_partial_nestloop_path. The cheapest unparameterized path is
* also in this list.
*/
foreach(lc2, innerrel->cheapest_parameterized_paths)
{
Path *innerpath = (Path *) lfirst(lc2);
/* Can't join to an inner path that is not parallel-safe */
if (!innerpath->parallel_safe)
continue;
/*
* Like match_unsorted_outer, we only consider a single nestloop
* path when the jointype is JOIN_UNIQUE_INNER. But we have to
* scan cheapest_parameterized_paths to find the one we want to
* consider, because cheapest_total_path might not be
* parallel-safe.
*/
if (jointype == JOIN_UNIQUE_INNER)
{
if (!bms_is_empty(PATH_REQ_OUTER(innerpath)))
continue;
innerpath = (Path *) create_unique_path(root, innerrel,
innerpath, extra->sjinfo);
Assert(innerpath);
}
try_partial_nestloop_path(root, joinrel, outerpath, innerpath,
pathkeys, jointype, extra);
}
}
}
/*
* hash_inner_and_outer
* Create hashjoin join paths by explicitly hashing both the outer and
* inner keys of each available hash clause.
*
* 'joinrel' is the join relation
* 'outerrel' is the outer join relation
* 'innerrel' is the inner join relation
* 'jointype' is the type of join to do
* 'extra' contains additional input values
*/
static void
hash_inner_and_outer(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
JoinPathExtraData *extra)
{
bool isouterjoin = IS_OUTER_JOIN(jointype);
List *hashclauses;
ListCell *l;
/*
* We need to build only one hashclauses list for any given pair of outer
* and inner relations; all of the hashable clauses will be used as keys.
*
* Scan the join's restrictinfo list to find hashjoinable clauses that are
* usable with this pair of sub-relations.
*/
hashclauses = NIL;
foreach(l, extra->restrictlist)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);
/*
* If processing an outer join, only use its own join clauses for
* hashing. For inner joins we need not be so picky.
*/
if (isouterjoin && restrictinfo->is_pushed_down)
continue;
if (!restrictinfo->can_join ||
restrictinfo->hashjoinoperator == InvalidOid)
continue; /* not hashjoinable */
/*
* Check if clause has the form "outer op inner" or "inner op outer".
*/
if (!clause_sides_match_join(restrictinfo, outerrel, innerrel))
continue; /* no good for these input relations */
hashclauses = lappend(hashclauses, restrictinfo);
}
/* If we found any usable hashclauses, make paths */
if (hashclauses)
{
/*
* We consider both the cheapest-total-cost and cheapest-startup-cost
* outer paths. There's no need to consider any but the
* cheapest-total-cost inner path, however.
*/
Path *cheapest_startup_outer = outerrel->cheapest_startup_path;
Path *cheapest_total_outer = outerrel->cheapest_total_path;
Path *cheapest_total_inner = innerrel->cheapest_total_path;
/*
* If either cheapest-total path is parameterized by the other rel, we
* can't use a hashjoin. (There's no use looking for alternative
* input paths, since these should already be the least-parameterized
* available paths.)
*/
if (PATH_PARAM_BY_REL(cheapest_total_outer, innerrel) ||
PATH_PARAM_BY_REL(cheapest_total_inner, outerrel))
return;
/* Unique-ify if need be; we ignore parameterized possibilities */
if (jointype == JOIN_UNIQUE_OUTER)
{
cheapest_total_outer = (Path *)
create_unique_path(root, outerrel,
cheapest_total_outer, extra->sjinfo);
Assert(cheapest_total_outer);
jointype = JOIN_INNER;
try_hashjoin_path(root,
joinrel,
cheapest_total_outer,
cheapest_total_inner,
hashclauses,
jointype,
extra);
/* no possibility of cheap startup here */
}
else if (jointype == JOIN_UNIQUE_INNER)
{
cheapest_total_inner = (Path *)
create_unique_path(root, innerrel,
cheapest_total_inner, extra->sjinfo);
Assert(cheapest_total_inner);
jointype = JOIN_INNER;
try_hashjoin_path(root,
joinrel,
cheapest_total_outer,
cheapest_total_inner,
hashclauses,
jointype,
extra);
if (cheapest_startup_outer != NULL &&
cheapest_startup_outer != cheapest_total_outer)
try_hashjoin_path(root,
joinrel,
cheapest_startup_outer,
cheapest_total_inner,
hashclauses,
jointype,
extra);
}
else
{
/*
* For other jointypes, we consider the cheapest startup outer
* together with the cheapest total inner, and then consider
* pairings of cheapest-total paths including parameterized ones.
* There is no use in generating parameterized paths on the basis
* of possibly cheap startup cost, so this is sufficient.
*/
ListCell *lc1;
ListCell *lc2;
if (cheapest_startup_outer != NULL)
try_hashjoin_path(root,
joinrel,
cheapest_startup_outer,
cheapest_total_inner,
hashclauses,
jointype,
extra);
foreach(lc1, outerrel->cheapest_parameterized_paths)
{
Path *outerpath = (Path *) lfirst(lc1);
/*
* We cannot use an outer path that is parameterized by the
* inner rel.
*/
if (PATH_PARAM_BY_REL(outerpath, innerrel))
continue;
foreach(lc2, innerrel->cheapest_parameterized_paths)
{
Path *innerpath = (Path *) lfirst(lc2);
/*
* We cannot use an inner path that is parameterized by
* the outer rel, either.
*/
if (PATH_PARAM_BY_REL(innerpath, outerrel))
continue;
if (outerpath == cheapest_startup_outer &&
innerpath == cheapest_total_inner)
continue; /* already tried it */
try_hashjoin_path(root,
joinrel,
outerpath,
innerpath,
hashclauses,
jointype,
extra);
}
}
}
/*
* If the joinrel is parallel-safe, we may be able to consider a
* partial hash join. However, we can't handle JOIN_UNIQUE_OUTER,
* because the outer path will be partial, and therefore we won't be
* able to properly guarantee uniqueness. Similarly, we can't handle
* JOIN_FULL and JOIN_RIGHT, because they can produce false null
* extended rows. Also, the resulting path must not be parameterized.
*/
if (joinrel->consider_parallel &&
jointype != JOIN_UNIQUE_OUTER &&
jointype != JOIN_FULL &&
jointype != JOIN_RIGHT &&
outerrel->partial_pathlist != NIL &&
bms_is_empty(joinrel->lateral_relids))
{
Path *cheapest_partial_outer;
Path *cheapest_safe_inner = NULL;
cheapest_partial_outer =
(Path *) linitial(outerrel->partial_pathlist);
/*
* Normally, given that the joinrel is parallel-safe, the cheapest
* total inner path will also be parallel-safe, but if not, we'll
* have to search cheapest_parameterized_paths for the cheapest
* unparameterized inner path.
*/
if (cheapest_total_inner->parallel_safe)
cheapest_safe_inner = cheapest_total_inner;
else
{
ListCell *lc;
foreach(lc, innerrel->cheapest_parameterized_paths)
{
Path *innerpath = (Path *) lfirst(lc);
if (innerpath->parallel_safe &&
bms_is_empty(PATH_REQ_OUTER(innerpath)))
{
cheapest_safe_inner = innerpath;
break;
}
}
}
if (cheapest_safe_inner != NULL)
try_partial_hashjoin_path(root, joinrel,
cheapest_partial_outer,
cheapest_safe_inner,
hashclauses, jointype, extra);
}
}
}
/*
* select_mergejoin_clauses
* Select mergejoin clauses that are usable for a particular join.
* Returns a list of RestrictInfo nodes for those clauses.
*
* *mergejoin_allowed is normally set to TRUE, but it is set to FALSE if
* this is a right/full join and there are nonmergejoinable join clauses.
* The executor's mergejoin machinery cannot handle such cases, so we have
* to avoid generating a mergejoin plan. (Note that this flag does NOT
* consider whether there are actually any mergejoinable clauses. This is
* correct because in some cases we need to build a clauseless mergejoin.
* Simply returning NIL is therefore not enough to distinguish safe from
* unsafe cases.)
*
* We also mark each selected RestrictInfo to show which side is currently
* being considered as outer. These are transient markings that are only
* good for the duration of the current add_paths_to_joinrel() call!
*
* We examine each restrictinfo clause known for the join to see
* if it is mergejoinable and involves vars from the two sub-relations
* currently of interest.
*/
static List *
select_mergejoin_clauses(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
JoinType jointype,
bool *mergejoin_allowed)
{
List *result_list = NIL;
bool isouterjoin = IS_OUTER_JOIN(jointype);
bool have_nonmergeable_joinclause = false;
ListCell *l;
foreach(l, restrictlist)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);
/*
* If processing an outer join, only use its own join clauses in the
* merge. For inner joins we can use pushed-down clauses too. (Note:
* we don't set have_nonmergeable_joinclause here because pushed-down
* clauses will become otherquals not joinquals.)
*/
if (isouterjoin && restrictinfo->is_pushed_down)
continue;
/* Check that clause is a mergeable operator clause */
if (!restrictinfo->can_join ||
restrictinfo->mergeopfamilies == NIL)
{
/*
* The executor can handle extra joinquals that are constants, but
* not anything else, when doing right/full merge join. (The
* reason to support constants is so we can do FULL JOIN ON
* FALSE.)
*/
if (!restrictinfo->clause || !IsA(restrictinfo->clause, Const))
have_nonmergeable_joinclause = true;
continue; /* not mergejoinable */
}
/*
* Check if clause has the form "outer op inner" or "inner op outer".
*/
if (!clause_sides_match_join(restrictinfo, outerrel, innerrel))
{
have_nonmergeable_joinclause = true;
continue; /* no good for these input relations */
}
/*
* Insist that each side have a non-redundant eclass. This
* restriction is needed because various bits of the planner expect
* that each clause in a merge be associatable with some pathkey in a
* canonical pathkey list, but redundant eclasses can't appear in
* canonical sort orderings. (XXX it might be worth relaxing this,
* but not enough time to address it for 8.3.)
*
* Note: it would be bad if this condition failed for an otherwise
* mergejoinable FULL JOIN clause, since that would result in
* undesirable planner failure. I believe that is not possible
* however; a variable involved in a full join could only appear in
* below_outer_join eclasses, which aren't considered redundant.
*
* This case *can* happen for left/right join clauses: the outer-side
* variable could be equated to a constant. Because we will propagate
* that constant across the join clause, the loss of ability to do a
* mergejoin is not really all that big a deal, and so it's not clear
* that improving this is important.
*/
update_mergeclause_eclasses(root, restrictinfo);
if (EC_MUST_BE_REDUNDANT(restrictinfo->left_ec) ||
EC_MUST_BE_REDUNDANT(restrictinfo->right_ec))
{
have_nonmergeable_joinclause = true;
continue; /* can't handle redundant eclasses */
}
result_list = lappend(result_list, restrictinfo);
}
/*
* Report whether mergejoin is allowed (see comment at top of function).
*/
switch (jointype)
{
case JOIN_RIGHT:
case JOIN_FULL:
*mergejoin_allowed = !have_nonmergeable_joinclause;
break;
default:
*mergejoin_allowed = true;
break;
}
return result_list;
}
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