database/postgres
database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-04-29 13:56:47 +03:00
Code
postgres/src/backend/optimizer/path/joinpath.c
Bruce Momjian 52f77df613 Ye-old pgindent run. Same 4-space tabs.
2000-04-12 17:17:23 +00:00

744 lines
24 KiB
C
Raw Blame History

/*-------------------------------------------------------------------------
*
* joinpath.c
* Routines to find all possible paths for processing a set of joins
*
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinpath.c,v 1.54 2000/04/12 17:15:19 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#include <sys/types.h>
#include <math.h>
#include "postgres.h"
#include "access/htup.h"
#include "catalog/pg_attribute.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/restrictinfo.h"
#include "parser/parsetree.h"
#include "utils/lsyscache.h"
static void sort_inner_and_outer(Query *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist, List *mergeclause_list);
static void match_unsorted_outer(Query *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist, List *mergeclause_list);
#ifdef NOT_USED
static void match_unsorted_inner(Query *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist, List *mergeclause_list);
#endif
static void hash_inner_and_outer(Query *root, RelOptInfo *joinrel,
RelOptInfo *outerrel, RelOptInfo *innerrel,
List *restrictlist);
static Path *best_innerjoin(List *join_paths, List *outer_relid);
static Selectivity estimate_disbursion(Query *root, Var *var);
static List *select_mergejoin_clauses(RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist);
/*
* 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.
*/
void
add_paths_to_joinrel(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist)
{
List *mergeclause_list = NIL;
/*
* Find potential mergejoin clauses.
*/
if (enable_mergejoin)
mergeclause_list = select_mergejoin_clauses(joinrel,
outerrel,
innerrel,
restrictlist);
/*
* 1. Consider mergejoin paths where both relations must be explicitly
* sorted.
*/
sort_inner_and_outer(root, joinrel, outerrel, innerrel,
restrictlist, mergeclause_list);
/*
* 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.
*/
match_unsorted_outer(root, joinrel, outerrel, innerrel,
restrictlist, mergeclause_list);
#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.
*/
match_unsorted_inner(root, joinrel, outerrel, innerrel,
restrictlist, mergeclause_list);
#endif
/*
* 4. Consider paths where both outer and inner relations must be
* hashed before being joined.
*/
if (enable_hashjoin)
hash_inner_and_outer(root, joinrel, outerrel, innerrel,
restrictlist);
}
/*
* 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
*/
static void
sort_inner_and_outer(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
List *mergeclause_list)
{
List *i;
/*
* 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. Generating a path here for *every*
* permutation of mergejoin clauses doesn't seem like a winning
* strategy, however; the cost in planning time is too high.
*
* For now, we generate one path for each mergejoin clause, listing that
* clause 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 clauses, we may end up evaluating
* clauses as qpquals when they could have been done as mergeclauses.
* We need to figure out a better way. (Two possible approaches: look
* at all the relevant index relations to suggest plausible sort
* orders, or make just one output path and somehow mark it as having
* a sort-order that can be rearranged freely.)
*/
foreach(i, mergeclause_list)
{
RestrictInfo *restrictinfo = lfirst(i);
List *curclause_list;
List *outerkeys;
List *innerkeys;
List *merge_pathkeys;
/* Make a mergeclause list with this guy first. */
if (i != mergeclause_list)
curclause_list = lcons(restrictinfo,
lremove(restrictinfo,
listCopy(mergeclause_list)));
else
curclause_list = mergeclause_list; /* no work at first one... */
/*
* Build sort pathkeys for both sides.
*
* 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.
*/
outerkeys = make_pathkeys_for_mergeclauses(root,
curclause_list,
outerrel->targetlist);
innerkeys = make_pathkeys_for_mergeclauses(root,
curclause_list,
innerrel->targetlist);
/* Build pathkeys representing output sort order. */
merge_pathkeys = build_join_pathkeys(outerkeys,
joinrel->targetlist,
root->equi_key_list);
/*
* And now we can make the path. 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.
*/
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
outerrel->cheapest_total_path,
innerrel->cheapest_total_path,
restrictlist,
merge_pathkeys,
curclause_list,
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 three: one on the cheapest-total-cost
* inner path, one on the cheapest-startup-cost inner path (if different),
* and one on the best inner-indexscan path (if any).
*
* 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
*/
static void
match_unsorted_outer(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
List *mergeclause_list)
{
Path *bestinnerjoin;
List *i;
/*
* Get the best innerjoin indexpath (if any) for this outer rel. It's
* the same for all outer paths.
*/
bestinnerjoin = best_innerjoin(innerrel->innerjoin, outerrel->relids);
foreach(i, outerrel->pathlist)
{
Path *outerpath = (Path *) lfirst(i);
List *merge_pathkeys;
List *mergeclauses;
List *innersortkeys;
List *trialsortkeys;
Path *cheapest_startup_inner;
Path *cheapest_total_inner;
int num_mergeclauses;
int clausecnt;
/*
* 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(outerpath->pathkeys,
joinrel->targetlist,
root->equi_key_list);
/*
* Always consider a nestloop join with this outer and cheapest-
* total-cost inner. Consider nestloops using the cheapest-
* startup-cost inner as well, and the best innerjoin indexpath.
*/
add_path(joinrel, (Path *)
create_nestloop_path(joinrel,
outerpath,
innerrel->cheapest_total_path,
restrictlist,
merge_pathkeys));
if (innerrel->cheapest_startup_path != innerrel->cheapest_total_path)
add_path(joinrel, (Path *)
create_nestloop_path(joinrel,
outerpath,
innerrel->cheapest_startup_path,
restrictlist,
merge_pathkeys));
if (bestinnerjoin != NULL)
add_path(joinrel, (Path *)
create_nestloop_path(joinrel,
outerpath,
bestinnerjoin,
restrictlist,
merge_pathkeys));
/* Look for useful mergeclauses (if any) */
mergeclauses = find_mergeclauses_for_pathkeys(outerpath->pathkeys,
mergeclause_list);
/* Done with this outer path if no chance for a mergejoin */
if (mergeclauses == NIL)
continue;
/* Compute the required ordering of the inner path */
innersortkeys = make_pathkeys_for_mergeclauses(root,
mergeclauses,
innerrel->targetlist);
/*
* Generate a mergejoin on the basis of sorting the cheapest
* inner. Since a sort will be needed, only cheapest total cost
* matters.
*/
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
outerpath,
innerrel->cheapest_total_path,
restrictlist,
merge_pathkeys,
mergeclauses,
NIL,
innersortkeys));
/*
* Look for presorted inner paths that satisfy the mergeclause
* list or any truncation thereof. Here, we consider both cheap
* startup cost and cheap total cost.
*/
trialsortkeys = listCopy(innersortkeys); /* modifiable copy */
cheapest_startup_inner = NULL;
cheapest_total_inner = NULL;
num_mergeclauses = length(mergeclauses);
for (clausecnt = num_mergeclauses; clausecnt > 0; clausecnt--)
{
Path *innerpath;
List *newclauses = NIL;
/*
* Look for an inner path ordered well enough to merge with
* the first 'clausecnt' mergeclauses. NB: trialsortkeys list
* is modified destructively, which is why we made a copy...
*/
trialsortkeys = ltruncate(clausecnt, trialsortkeys);
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 */
if (clausecnt < num_mergeclauses)
newclauses = ltruncate(clausecnt,
listCopy(mergeclauses));
else
newclauses = mergeclauses;
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
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 (clausecnt < num_mergeclauses)
newclauses = ltruncate(clausecnt,
listCopy(mergeclauses));
else
newclauses = mergeclauses;
}
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
outerpath,
innerpath,
restrictlist,
merge_pathkeys,
newclauses,
NIL,
NIL));
}
cheapest_startup_inner = innerpath;
}
}
}
}
#ifdef NOT_USED
/*
* match_unsorted_inner
* Generate mergejoin paths that use an explicit sort of the outer path
* with an already-ordered inner path.
*
* 'joinrel' is the join result 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
*/
static void
match_unsorted_inner(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist,
List *mergeclause_list)
{
List *i;
foreach(i, innerrel->pathlist)
{
Path *innerpath = (Path *) lfirst(i);
List *mergeclauses;
List *outersortkeys;
List *merge_pathkeys;
Path *totalouterpath;
Path *startupouterpath;
/* Look for useful mergeclauses (if any) */
mergeclauses = find_mergeclauses_for_pathkeys(innerpath->pathkeys,
mergeclause_list);
if (mergeclauses == NIL)
continue;
/* Compute the required ordering of the outer path */
outersortkeys = make_pathkeys_for_mergeclauses(root,
mergeclauses,
outerrel->targetlist);
/*
* Generate a mergejoin on the basis of sorting the cheapest
* outer. Since a sort will be needed, only cheapest total cost
* matters.
*/
merge_pathkeys = build_join_pathkeys(outersortkeys,
joinrel->targetlist,
root->equi_key_list);
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
outerrel->cheapest_total_path,
innerpath,
restrictlist,
merge_pathkeys,
mergeclauses,
outersortkeys,
NIL));
/*
* Now generate mergejoins based on already-sufficiently-ordered
* outer paths. There's likely to be some redundancy here with
* paths already generated by merge_unsorted_outer ... but since
* merge_unsorted_outer doesn't consider all permutations of the
* mergeclause list, it may fail to notice that this particular
* innerpath could have been used with this outerpath.
*/
totalouterpath = get_cheapest_path_for_pathkeys(outerrel->pathlist,
outersortkeys,
TOTAL_COST);
if (totalouterpath == NULL)
continue; /* there won't be a startup-cost path
* either */
merge_pathkeys = build_join_pathkeys(totalouterpath->pathkeys,
joinrel->targetlist,
root->equi_key_list);
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
totalouterpath,
innerpath,
restrictlist,
merge_pathkeys,
mergeclauses,
NIL,
NIL));
startupouterpath = get_cheapest_path_for_pathkeys(outerrel->pathlist,
outersortkeys,
STARTUP_COST);
if (startupouterpath != NULL && startupouterpath != totalouterpath)
{
merge_pathkeys = build_join_pathkeys(startupouterpath->pathkeys,
joinrel->targetlist,
root->equi_key_list);
add_path(joinrel, (Path *)
create_mergejoin_path(joinrel,
startupouterpath,
innerpath,
restrictlist,
merge_pathkeys,
mergeclauses,
NIL,
NIL));
}
}
}
#endif
/*
* hash_inner_and_outer
* Create hashjoin join paths by explicitly hashing both the outer and
* inner join relations 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
*/
static void
hash_inner_and_outer(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist)
{
Relids outerrelids = outerrel->relids;
Relids innerrelids = innerrel->relids;
List *i;
/*
* Scan the join's restrictinfo list to find hashjoinable clauses that
* are usable with this pair of sub-relations. Since we currently
* accept only var-op-var clauses as hashjoinable, we need only check
* the membership of the vars to determine whether a particular clause
* can be used with this pair of sub-relations. This code would need
* to be upgraded if we wanted to allow more-complex expressions in
* hash joins.
*/
foreach(i, restrictlist)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(i);
Expr *clause;
Var *left,
*right,
*inner;
List *hashclauses;
Selectivity innerdisbursion;
if (restrictinfo->hashjoinoperator == InvalidOid)
continue; /* not hashjoinable */
clause = restrictinfo->clause;
/* these must be OK, since check_hashjoinable accepted the clause */
left = get_leftop(clause);
right = get_rightop(clause);
/* check if clause is usable with these sub-rels, find inner var */
if (intMember(left->varno, outerrelids) &&
intMember(right->varno, innerrelids))
inner = right;
else if (intMember(left->varno, innerrelids) &&
intMember(right->varno, outerrelids))
inner = left;
else
continue; /* no good for these input relations */
/* always a one-element list of hash clauses */
hashclauses = lcons(restrictinfo, NIL);
/* estimate disbursion of inner var for costing purposes */
innerdisbursion = estimate_disbursion(root, inner);
/*
* 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.
*/
add_path(joinrel, (Path *)
create_hashjoin_path(joinrel,
outerrel->cheapest_total_path,
innerrel->cheapest_total_path,
restrictlist,
hashclauses,
innerdisbursion));
if (outerrel->cheapest_startup_path != outerrel->cheapest_total_path)
add_path(joinrel, (Path *)
create_hashjoin_path(joinrel,
outerrel->cheapest_startup_path,
innerrel->cheapest_total_path,
restrictlist,
hashclauses,
innerdisbursion));
}
}
/*
* best_innerjoin
* Find the cheapest index path that has already been identified by
* indexable_joinclauses() as being a possible inner path for the given
* outer relation(s) in a nestloop join.
*
* We compare indexpaths on total_cost only, assuming that they will all have
* zero or negligible startup_cost. We might have to think harder someday...
*
* 'join_paths' is a list of potential inner indexscan join paths
* 'outer_relids' is the relid list of the outer join relation
*
* Returns the pathnode of the best path, or NULL if there's no
* usable path.
*/
static Path *
best_innerjoin(List *join_paths, Relids outer_relids)
{
Path *cheapest = (Path *) NULL;
List *join_path;
foreach(join_path, join_paths)
{
Path *path = (Path *) lfirst(join_path);
Assert(IsA(path, IndexPath));
/*
* path->joinrelids is the set of base rels that must be part of
* outer_relids in order to use this inner path, because those
* rels are used in the index join quals of this inner path.
*/
if (is_subseti(((IndexPath *) path)->joinrelids, outer_relids) &&
(cheapest == NULL ||
compare_path_costs(path, cheapest, TOTAL_COST) < 0))
cheapest = path;
}
return cheapest;
}
/*
* Estimate disbursion of the specified Var
*
* We use a default of 0.1 if we can't figure out anything better.
* This will typically discourage use of a hash rather strongly,
* if the inner relation is large. We do not want to hash unless
* we know that the inner rel is well-dispersed (or the alternatives
* seem much worse).
*/
static Selectivity
estimate_disbursion(Query *root, Var *var)
{
Oid relid;
if (!IsA(var, Var))
return 0.1;
relid = getrelid(var->varno, root->rtable);
return (Selectivity) get_attdisbursion(relid, var->varattno, 0.1);
}
/*
* select_mergejoin_clauses
* Select mergejoin clauses that are usable for a particular join.
* Returns a list of RestrictInfo nodes for those clauses.
*
* 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.
*
* Since we currently allow only plain Vars as the left and right sides
* of mergejoin clauses, this test is relatively simple. This routine
* would need to be upgraded to support more-complex expressions
* as sides of mergejoins. In theory, we could allow arbitrarily complex
* expressions in mergejoins, so long as one side uses only vars from one
* sub-relation and the other side uses only vars from the other.
*/
static List *
select_mergejoin_clauses(RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
List *restrictlist)
{
List *result_list = NIL;
Relids outerrelids = outerrel->relids;
Relids innerrelids = innerrel->relids;
List *i;
foreach(i, restrictlist)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(i);
Expr *clause;
Var *left,
*right;
if (restrictinfo->mergejoinoperator == InvalidOid)
continue; /* not mergejoinable */
clause = restrictinfo->clause;
/* these must be OK, since check_mergejoinable accepted the clause */
left = get_leftop(clause);
right = get_rightop(clause);
if ((intMember(left->varno, outerrelids) &&
intMember(right->varno, innerrelids)) ||
(intMember(left->varno, innerrelids) &&
intMember(right->varno, outerrelids)))
result_list = lcons(restrictinfo, result_list);
}
return result_list;
}
View Git Blame Copy Permalink