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postgresql/src/backend/optimizer/path/joinpath.c

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/*-------------------------------------------------------------------------
*
* joinpath.c
* Routines to find all possible paths for processing a set of joins
*
* Portions Copyright (c) 1996-2011, 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 "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
static void sort_inner_and_outer(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist, List *mergeclause_list,
JoinType jointype, SpecialJoinInfo *sjinfo);
static void match_unsorted_outer(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist, List *mergeclause_list,
JoinType jointype, SpecialJoinInfo *sjinfo);
static void hash_inner_and_outer(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist,
JoinType jointype, SpecialJoinInfo *sjinfo);
static Path *best_appendrel_indexscan(PlannerInfo *root, RelOptInfo *rel,
RelOptInfo *outer_rel, JoinType jointype);
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)
{
List *mergeclause_list = NIL;
bool mergejoin_allowed = true;
/*
* 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)
mergeclause_list = select_mergejoin_clauses(root,
joinrel,
outerrel,
innerrel,
restrictlist,
jointype,
&mergejoin_allowed);
/*
* 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,
restrictlist, mergeclause_list, jointype, sjinfo);
/*
* 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,
restrictlist, mergeclause_list, jointype, sjinfo);
#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,
restrictlist, mergeclause_list, jointype, sjinfo);
#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,
restrictlist, jointype, sjinfo);
}
/*
* 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
* 'restrictlist' contains all of the RestrictInfo nodes for restriction
* clauses that apply to this join
* 'mergeclause_list' is a list of RestrictInfo nodes for available
* mergejoin clauses in this join
* 'jointype' is the type of join to do
* 'sjinfo' is extra info about the join for selectivity estimation
*/
static void
sort_inner_and_outer(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
List *mergeclause_list,
JoinType jointype,
SpecialJoinInfo *sjinfo)
{
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.
*
* If unique-ification is requested, do it and then handle as a plain
* inner join.
*/
outer_path = outerrel->cheapest_total_path;
inner_path = innerrel->cheapest_total_path;
if (jointype == JOIN_UNIQUE_OUTER)
{
outer_path = (Path *) create_unique_path(root, outerrel,
outer_path, sjinfo);
Assert(outer_path);
jointype = JOIN_INNER;
}
else if (jointype == JOIN_UNIQUE_INNER)
{
inner_path = (Path *) create_unique_path(root, innerrel,
inner_path, 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,
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,
mergeclause_list);
/* Should have used them all... */
Assert(list_length(cur_mergeclauses) == list_length(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. create_mergejoin_path will detect that case and suppress
* an explicit sort step, so we needn't do so here.
*/
add_path(joinrel, (Path *)
create_mergejoin_path(root,
joinrel,
jointype,
sjinfo,
outer_path,
inner_path,
restrictlist,
merge_pathkeys,
cur_mergeclauses,
outerkeys,
innerkeys));
}
}
/*
* 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
* 'restrictlist' contains all of the RestrictInfo nodes for restriction
* clauses that apply to this join
* 'mergeclause_list' is a list of RestrictInfo nodes for available
* mergejoin clauses in this join
* 'jointype' is the type of join to do
* 'sjinfo' is extra info about the join for selectivity estimation
*/
static void
match_unsorted_outer(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
List *mergeclause_list,
JoinType jointype,
SpecialJoinInfo *sjinfo)
{
JoinType save_jointype = jointype;
bool nestjoinOK;
bool useallclauses;
Path *inner_cheapest_startup = innerrel->cheapest_startup_path;
Path *inner_cheapest_total = innerrel->cheapest_total_path;
Path *matpath = NULL;
Path *index_cheapest_startup = NULL;
Path *index_cheapest_total = NULL;
ListCell *l;
/*
* 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 we need to unique-ify the inner path, we will consider only the
* cheapest inner.
*/
if (save_jointype == JOIN_UNIQUE_INNER)
{
inner_cheapest_total = (Path *)
create_unique_path(root, innerrel, inner_cheapest_total, sjinfo);
Assert(inner_cheapest_total);
inner_cheapest_startup = 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 &&
!ExecMaterializesOutput(inner_cheapest_total->pathtype))
matpath = (Path *)
create_material_path(innerrel, inner_cheapest_total);
/*
* Get the best innerjoin indexpaths (if any) for this outer rel.
* They're the same for all outer paths.
*/
if (innerrel->reloptkind != RELOPT_JOINREL)
{
if (IsA(inner_cheapest_total, AppendPath))
index_cheapest_total = best_appendrel_indexscan(root,
innerrel,
outerrel,
jointype);
else if (innerrel->rtekind == RTE_RELATION)
best_inner_indexscan(root, innerrel, outerrel, jointype,
&index_cheapest_startup,
&index_cheapest_total);
}
}
foreach(l, outerrel->pathlist)
{
Path *outerpath = (Path *) lfirst(l);
List *merge_pathkeys;
List *mergeclauses;
List *innersortkeys;
List *trialsortkeys;
Path *cheapest_startup_inner;
Path *cheapest_total_inner;
int num_sortkeys;
int sortkeycnt;
/*
* If we need to unique-ify the outer path, it's pointless to consider
* any but the cheapest outer.
*/
if (save_jointype == JOIN_UNIQUE_OUTER)
{
if (outerpath != outerrel->cheapest_total_path)
continue;
outerpath = (Path *) create_unique_path(root, outerrel,
outerpath, 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 (nestjoinOK)
{
/*
* Always consider a nestloop join with this outer and
* cheapest-total-cost inner. When appropriate, also consider
* using the materialized form of the cheapest inner, the
* cheapest-startup-cost inner path, and the cheapest innerjoin
* indexpaths.
*/
add_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
inner_cheapest_total,
restrictlist,
merge_pathkeys));
if (matpath != NULL)
add_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
matpath,
restrictlist,
merge_pathkeys));
if (inner_cheapest_startup != inner_cheapest_total)
add_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
inner_cheapest_startup,
restrictlist,
merge_pathkeys));
if (index_cheapest_total != NULL)
add_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
index_cheapest_total,
restrictlist,
merge_pathkeys));
if (index_cheapest_startup != NULL &&
index_cheapest_startup != index_cheapest_total)
add_path(joinrel, (Path *)
create_nestloop_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
index_cheapest_startup,
restrictlist,
merge_pathkeys));
}
/* Can't do anything else if outer path needs to be unique'd */
if (save_jointype == JOIN_UNIQUE_OUTER)
continue;
/* Look for useful mergeclauses (if any) */
mergeclauses = find_mergeclauses_for_pathkeys(root,
outerpath->pathkeys,
true,
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(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
* create_mergejoin_path will do the right thing if
* inner_cheapest_total is already correctly sorted.)
*/
add_path(joinrel, (Path *)
create_mergejoin_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
inner_cheapest_total,
restrictlist,
merge_pathkeys,
mergeclauses,
NIL,
innersortkeys));
/* 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.
*
* 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,
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;
add_path(joinrel, (Path *)
create_mergejoin_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
innerpath,
restrictlist,
merge_pathkeys,
newclauses,
NIL,
NIL));
cheapest_total_inner = innerpath;
}
/* Same on the basis of cheapest startup cost ... */
innerpath = get_cheapest_path_for_pathkeys(innerrel->pathlist,
trialsortkeys,
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;
}
add_path(joinrel, (Path *)
create_mergejoin_path(root,
joinrel,
jointype,
sjinfo,
outerpath,
innerpath,
restrictlist,
merge_pathkeys,
newclauses,
NIL,
NIL));
}
cheapest_startup_inner = innerpath;
}
/*
* Don't consider truncated sortkeys if we need all clauses.
*/
if (useallclauses)
break;
}
}
}
/*
* 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
* 'restrictlist' contains all of the RestrictInfo nodes for restriction
* clauses that apply to this join
* 'jointype' is the type of join to do
* 'sjinfo' is extra info about the join for selectivity estimation
*/
static void
hash_inner_and_outer(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
JoinType jointype,
SpecialJoinInfo *sjinfo)
{
bool isouterjoin = IS_OUTER_JOIN(jointype);
List *hashclauses;
ListCell *l;
/*
* We need to build only one hashpath 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, 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 a path */
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;
/* Unique-ify if need be */
if (jointype == JOIN_UNIQUE_OUTER)
{
cheapest_total_outer = (Path *)
create_unique_path(root, outerrel,
cheapest_total_outer, sjinfo);
Assert(cheapest_total_outer);
cheapest_startup_outer = cheapest_total_outer;
jointype = JOIN_INNER;
}
else if (jointype == JOIN_UNIQUE_INNER)
{
cheapest_total_inner = (Path *)
create_unique_path(root, innerrel,
cheapest_total_inner, sjinfo);
Assert(cheapest_total_inner);
jointype = JOIN_INNER;
}
add_path(joinrel, (Path *)
create_hashjoin_path(root,
joinrel,
jointype,
sjinfo,
cheapest_total_outer,
cheapest_total_inner,
restrictlist,
hashclauses));
if (cheapest_startup_outer != cheapest_total_outer)
add_path(joinrel, (Path *)
create_hashjoin_path(root,
joinrel,
jointype,
sjinfo,
cheapest_startup_outer,
cheapest_total_inner,
restrictlist,
hashclauses));
}
}
/*
* best_appendrel_indexscan
* Finds the best available set of inner indexscans for a nestloop join
* with the given append relation on the inside and the given outer_rel
* outside. Returns an AppendPath comprising the best inner scans, or
* NULL if there are no possible inner indexscans.
*
* Note that we currently consider only cheapest-total-cost. It's not
* very clear what cheapest-startup-cost might mean for an AppendPath.
*/
static Path *
best_appendrel_indexscan(PlannerInfo *root, RelOptInfo *rel,
RelOptInfo *outer_rel, JoinType jointype)
{
int parentRTindex = rel->relid;
List *append_paths = NIL;
bool found_indexscan = false;
ListCell *l;
foreach(l, root->append_rel_list)
{
AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
int childRTindex;
RelOptInfo *childrel;
Path *index_cheapest_startup;
Path *index_cheapest_total;
/* append_rel_list contains all append rels; ignore others */
if (appinfo->parent_relid != parentRTindex)
continue;
childRTindex = appinfo->child_relid;
childrel = find_base_rel(root, childRTindex);
Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL);
/*
* Check to see if child was rejected by constraint exclusion. If so,
* it will have a cheapest_total_path that's a "dummy" path.
*/
if (IS_DUMMY_PATH(childrel->cheapest_total_path))
continue; /* OK, we can ignore it */
/*
* Get the best innerjoin indexpaths (if any) for this child rel.
*/
best_inner_indexscan(root, childrel, outer_rel, jointype,
&index_cheapest_startup, &index_cheapest_total);
/*
* If no luck on an indexpath for this rel, we'll still consider an
* Append substituting the cheapest-total inner path. However we must
* find at least one indexpath, else there's not going to be any
* improvement over the base path for the appendrel.
*/
if (index_cheapest_total)
found_indexscan = true;
else
index_cheapest_total = childrel->cheapest_total_path;
append_paths = lappend(append_paths, index_cheapest_total);
}
if (!found_indexscan)
return NULL;
/* Form and return the completed Append path. */
return (Path *) create_append_path(rel, append_paths);
}
/*
* 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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