Detect case where an outer join can be reduced to a plain inner join
because there are WHERE clauses that will reject the null-extended rows. Per suggestion from Brandon Craig Rhodes, 19-Nov-02.
This commit is contained in:
Tom Lane
parent
43785a434e
commit
b5956a2f22
|
|
@ -8,7 +8,7 @@
|
|||
*
|
||||
*
|
||||
* IDENTIFICATION
|
||||
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.145 2003/02/09 00:30:39 tgl Exp $
|
||||
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.146 2003/02/09 23:57:19 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
|
|
@ -144,6 +144,7 @@ subquery_planner(Query *parse, double tuple_fraction)
|
|||
{
|
||||
List *saved_initplan = PlannerInitPlan;
|
||||
int saved_planid = PlannerPlanId;
|
||||
bool hasOuterJoins;
|
||||
Plan *plan;
|
||||
List *newHaving;
|
||||
List *lst;
|
||||
|
|
@ -172,10 +173,12 @@ subquery_planner(Query *parse, double tuple_fraction)
|
|||
|
||||
/*
|
||||
* Detect whether any rangetable entries are RTE_JOIN kind; if not,
|
||||
* we can avoid the expense of doing flatten_join_alias_vars().
|
||||
* we can avoid the expense of doing flatten_join_alias_vars(). Also
|
||||
* check for outer joins --- if none, we can skip reduce_outer_joins().
|
||||
* This must be done after we have done pull_up_subqueries, of course.
|
||||
*/
|
||||
parse->hasJoinRTEs = false;
|
||||
hasOuterJoins = false;
|
||||
foreach(lst, parse->rtable)
|
||||
{
|
||||
RangeTblEntry *rte = (RangeTblEntry *) lfirst(lst);
|
||||
|
|
@ -183,7 +186,12 @@ subquery_planner(Query *parse, double tuple_fraction)
|
|||
if (rte->rtekind == RTE_JOIN)
|
||||
{
|
||||
parse->hasJoinRTEs = true;
|
||||
break;
|
||||
if (IS_OUTER_JOIN(rte->jointype))
|
||||
{
|
||||
hasOuterJoins = true;
|
||||
/* Can quit scanning once we find an outer join */
|
||||
break;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
|
|
@ -244,15 +252,23 @@ subquery_planner(Query *parse, double tuple_fraction)
|
|||
}
|
||||
parse->havingQual = (Node *) newHaving;
|
||||
|
||||
/*
|
||||
* If we have any outer joins, try to reduce them to plain inner joins.
|
||||
* This step is most easily done after we've done expression preprocessing.
|
||||
*/
|
||||
if (hasOuterJoins)
|
||||
reduce_outer_joins(parse);
|
||||
|
||||
/*
|
||||
* See if we can simplify the jointree; opportunities for this may come
|
||||
* from having pulled up subqueries, or from flattening explicit JOIN
|
||||
* syntax. We must do this after flattening JOIN alias variables, since
|
||||
* eliminating explicit JOIN nodes from the jointree will cause
|
||||
* get_relids_for_join() to fail.
|
||||
* get_relids_for_join() to fail. But it should happen after
|
||||
* reduce_outer_joins, anyway.
|
||||
*/
|
||||
parse->jointree = (FromExpr *)
|
||||
preprocess_jointree(parse, (Node *) parse->jointree);
|
||||
simplify_jointree(parse, (Node *) parse->jointree);
|
||||
|
||||
/*
|
||||
* Do the main planning. If we have an inherited target relation,
|
||||
|
|
|
|||
|
|
@ -3,13 +3,20 @@
|
|||
* prepjointree.c
|
||||
* Planner preprocessing for subqueries and join tree manipulation.
|
||||
*
|
||||
* NOTE: the intended sequence for invoking these operations is
|
||||
* pull_up_IN_clauses
|
||||
* pull_up_subqueries
|
||||
* do expression preprocessing (including flattening JOIN alias vars)
|
||||
* reduce_outer_joins
|
||||
* simplify_jointree
|
||||
*
|
||||
*
|
||||
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
|
||||
* Portions Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
*
|
||||
* IDENTIFICATION
|
||||
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.4 2003/02/09 00:35:55 tgl Exp $
|
||||
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.5 2003/02/09 23:57:19 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
|
|
@ -21,6 +28,7 @@
|
|||
#include "optimizer/var.h"
|
||||
#include "parser/parsetree.h"
|
||||
#include "rewrite/rewriteManip.h"
|
||||
#include "utils/lsyscache.h"
|
||||
|
||||
|
||||
/* These parameters are set by GUC */
|
||||
|
|
@ -28,9 +36,22 @@ int from_collapse_limit;
|
|||
int join_collapse_limit;
|
||||
|
||||
|
||||
typedef struct reduce_outer_joins_state
|
||||
{
|
||||
Relids relids; /* base relids within this subtree */
|
||||
bool contains_outer; /* does subtree contain outer join(s)? */
|
||||
List *sub_states; /* List of states for subtree components */
|
||||
} reduce_outer_joins_state;
|
||||
|
||||
static bool is_simple_subquery(Query *subquery);
|
||||
static bool has_nullable_targetlist(Query *subquery);
|
||||
static void resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist);
|
||||
static reduce_outer_joins_state *reduce_outer_joins_pass1(Node *jtnode);
|
||||
static void reduce_outer_joins_pass2(Node *jtnode,
|
||||
reduce_outer_joins_state *state,
|
||||
Query *parse,
|
||||
Relids nonnullable_rels);
|
||||
static Relids find_nonnullable_rels(Node *node, bool top_level);
|
||||
static void fix_in_clause_relids(List *in_info_list, int varno,
|
||||
Relids subrelids);
|
||||
static Node *find_jointree_node_for_rel(Node *jtnode, int relid);
|
||||
|
|
@ -463,7 +484,332 @@ resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist)
|
|||
}
|
||||
|
||||
/*
|
||||
* preprocess_jointree
|
||||
* reduce_outer_joins
|
||||
* Attempt to reduce outer joins to plain inner joins.
|
||||
*
|
||||
* The idea here is that given a query like
|
||||
* SELECT ... FROM a LEFT JOIN b ON (...) WHERE b.y = 42;
|
||||
* we can reduce the LEFT JOIN to a plain JOIN if the "=" operator in WHERE
|
||||
* is strict. The strict operator will always return NULL, causing the outer
|
||||
* WHERE to fail, on any row where the LEFT JOIN filled in NULLs for b's
|
||||
* columns. Therefore, there's no need for the join to produce null-extended
|
||||
* rows in the first place --- which makes it a plain join not an outer join.
|
||||
* (This scenario may not be very likely in a query written out by hand, but
|
||||
* it's reasonably likely when pushing quals down into complex views.)
|
||||
*
|
||||
* More generally, an outer join can be reduced in strength if there is a
|
||||
* strict qual above it in the qual tree that constrains a Var from the
|
||||
* nullable side of the join to be non-null. (For FULL joins this applies
|
||||
* to each side separately.)
|
||||
*
|
||||
* To ease recognition of strict qual clauses, we require this routine to be
|
||||
* run after expression preprocessing (i.e., qual canonicalization and JOIN
|
||||
* alias-var expansion).
|
||||
*/
|
||||
void
|
||||
reduce_outer_joins(Query *parse)
|
||||
{
|
||||
reduce_outer_joins_state *state;
|
||||
|
||||
/*
|
||||
* To avoid doing strictness checks on more quals than necessary,
|
||||
* we want to stop descending the jointree as soon as there are no
|
||||
* outer joins below our current point. This consideration forces
|
||||
* a two-pass process. The first pass gathers information about which
|
||||
* base rels appear below each side of each join clause, and about
|
||||
* whether there are outer join(s) below each side of each join clause.
|
||||
* The second pass examines qual clauses and changes join types as
|
||||
* it descends the tree.
|
||||
*/
|
||||
state = reduce_outer_joins_pass1((Node *) parse->jointree);
|
||||
|
||||
/* planner.c shouldn't have called me if no outer joins */
|
||||
if (state == NULL || !state->contains_outer)
|
||||
elog(ERROR, "reduce_outer_joins: so where are the outer joins?");
|
||||
|
||||
reduce_outer_joins_pass2((Node *) parse->jointree, state, parse, NULL);
|
||||
}
|
||||
|
||||
/*
|
||||
* reduce_outer_joins_pass1 - phase 1 data collection
|
||||
*
|
||||
* Returns a state node describing the given jointree node.
|
||||
*/
|
||||
static reduce_outer_joins_state *
|
||||
reduce_outer_joins_pass1(Node *jtnode)
|
||||
{
|
||||
reduce_outer_joins_state *result;
|
||||
|
||||
result = (reduce_outer_joins_state *)
|
||||
palloc(sizeof(reduce_outer_joins_state));
|
||||
result->relids = NULL;
|
||||
result->contains_outer = false;
|
||||
result->sub_states = NIL;
|
||||
|
||||
if (jtnode == NULL)
|
||||
return result;
|
||||
if (IsA(jtnode, RangeTblRef))
|
||||
{
|
||||
int varno = ((RangeTblRef *) jtnode)->rtindex;
|
||||
|
||||
result->relids = bms_make_singleton(varno);
|
||||
}
|
||||
else if (IsA(jtnode, FromExpr))
|
||||
{
|
||||
FromExpr *f = (FromExpr *) jtnode;
|
||||
List *l;
|
||||
|
||||
foreach(l, f->fromlist)
|
||||
{
|
||||
reduce_outer_joins_state *sub_state;
|
||||
|
||||
sub_state = reduce_outer_joins_pass1(lfirst(l));
|
||||
result->relids = bms_add_members(result->relids,
|
||||
sub_state->relids);
|
||||
result->contains_outer |= sub_state->contains_outer;
|
||||
result->sub_states = lappend(result->sub_states, sub_state);
|
||||
}
|
||||
}
|
||||
else if (IsA(jtnode, JoinExpr))
|
||||
{
|
||||
JoinExpr *j = (JoinExpr *) jtnode;
|
||||
reduce_outer_joins_state *sub_state;
|
||||
|
||||
/* join's own RT index is not wanted in result->relids */
|
||||
if (IS_OUTER_JOIN(j->jointype))
|
||||
result->contains_outer = true;
|
||||
|
||||
sub_state = reduce_outer_joins_pass1(j->larg);
|
||||
result->relids = bms_add_members(result->relids,
|
||||
sub_state->relids);
|
||||
result->contains_outer |= sub_state->contains_outer;
|
||||
result->sub_states = lappend(result->sub_states, sub_state);
|
||||
|
||||
sub_state = reduce_outer_joins_pass1(j->rarg);
|
||||
result->relids = bms_add_members(result->relids,
|
||||
sub_state->relids);
|
||||
result->contains_outer |= sub_state->contains_outer;
|
||||
result->sub_states = lappend(result->sub_states, sub_state);
|
||||
}
|
||||
else
|
||||
elog(ERROR, "reduce_outer_joins_pass1: unexpected node type %d",
|
||||
nodeTag(jtnode));
|
||||
return result;
|
||||
}
|
||||
|
||||
/*
|
||||
* reduce_outer_joins_pass2 - phase 2 processing
|
||||
*
|
||||
* jtnode: current jointree node
|
||||
* state: state data collected by phase 1 for this node
|
||||
* parse: toplevel Query
|
||||
* nonnullable_rels: set of base relids forced non-null by upper quals
|
||||
*/
|
||||
static void
|
||||
reduce_outer_joins_pass2(Node *jtnode,
|
||||
reduce_outer_joins_state *state,
|
||||
Query *parse,
|
||||
Relids nonnullable_rels)
|
||||
{
|
||||
/*
|
||||
* pass 2 should never descend as far as an empty subnode or base rel,
|
||||
* because it's only called on subtrees marked as contains_outer.
|
||||
*/
|
||||
if (jtnode == NULL)
|
||||
elog(ERROR, "reduce_outer_joins_pass2: reached empty jointree");
|
||||
if (IsA(jtnode, RangeTblRef))
|
||||
{
|
||||
elog(ERROR, "reduce_outer_joins_pass2: reached base rel");
|
||||
}
|
||||
else if (IsA(jtnode, FromExpr))
|
||||
{
|
||||
FromExpr *f = (FromExpr *) jtnode;
|
||||
List *l;
|
||||
List *s;
|
||||
Relids pass_nonnullable;
|
||||
|
||||
/* Scan quals to see if we can add any nonnullability constraints */
|
||||
pass_nonnullable = find_nonnullable_rels(f->quals, true);
|
||||
pass_nonnullable = bms_add_members(pass_nonnullable,
|
||||
nonnullable_rels);
|
||||
/* And recurse --- but only into interesting subtrees */
|
||||
s = state->sub_states;
|
||||
foreach(l, f->fromlist)
|
||||
{
|
||||
reduce_outer_joins_state *sub_state = lfirst(s);
|
||||
|
||||
if (sub_state->contains_outer)
|
||||
reduce_outer_joins_pass2(lfirst(l), sub_state, parse,
|
||||
pass_nonnullable);
|
||||
s = lnext(s);
|
||||
}
|
||||
bms_free(pass_nonnullable);
|
||||
}
|
||||
else if (IsA(jtnode, JoinExpr))
|
||||
{
|
||||
JoinExpr *j = (JoinExpr *) jtnode;
|
||||
int rtindex = j->rtindex;
|
||||
JoinType jointype = j->jointype;
|
||||
reduce_outer_joins_state *left_state = lfirst(state->sub_states);
|
||||
reduce_outer_joins_state *right_state = lsecond(state->sub_states);
|
||||
|
||||
/* Can we simplify this join? */
|
||||
switch (jointype)
|
||||
{
|
||||
case JOIN_LEFT:
|
||||
if (bms_overlap(nonnullable_rels, right_state->relids))
|
||||
jointype = JOIN_INNER;
|
||||
break;
|
||||
case JOIN_RIGHT:
|
||||
if (bms_overlap(nonnullable_rels, left_state->relids))
|
||||
jointype = JOIN_INNER;
|
||||
break;
|
||||
case JOIN_FULL:
|
||||
if (bms_overlap(nonnullable_rels, left_state->relids))
|
||||
{
|
||||
if (bms_overlap(nonnullable_rels, right_state->relids))
|
||||
jointype = JOIN_INNER;
|
||||
else
|
||||
jointype = JOIN_LEFT;
|
||||
}
|
||||
else
|
||||
{
|
||||
if (bms_overlap(nonnullable_rels, right_state->relids))
|
||||
jointype = JOIN_RIGHT;
|
||||
}
|
||||
break;
|
||||
default:
|
||||
break;
|
||||
}
|
||||
if (jointype != j->jointype)
|
||||
{
|
||||
/* apply the change to both jointree node and RTE */
|
||||
RangeTblEntry *rte = rt_fetch(rtindex, parse->rtable);
|
||||
|
||||
Assert(rte->rtekind == RTE_JOIN);
|
||||
Assert(rte->jointype == j->jointype);
|
||||
rte->jointype = j->jointype = jointype;
|
||||
}
|
||||
|
||||
/* Only recurse if there's more to do below here */
|
||||
if (left_state->contains_outer || right_state->contains_outer)
|
||||
{
|
||||
Relids pass_nonnullable;
|
||||
|
||||
/*
|
||||
* Scan join quals to see if we can add any nonnullability
|
||||
* constraints. (Okay to do this even if join is still outer.)
|
||||
*/
|
||||
pass_nonnullable = find_nonnullable_rels(j->quals, true);
|
||||
pass_nonnullable = bms_add_members(pass_nonnullable,
|
||||
nonnullable_rels);
|
||||
/* And recurse as needed */
|
||||
if (left_state->contains_outer)
|
||||
reduce_outer_joins_pass2(j->larg, left_state, parse,
|
||||
pass_nonnullable);
|
||||
if (right_state->contains_outer)
|
||||
reduce_outer_joins_pass2(j->rarg, right_state, parse,
|
||||
pass_nonnullable);
|
||||
bms_free(pass_nonnullable);
|
||||
}
|
||||
}
|
||||
else
|
||||
elog(ERROR, "reduce_outer_joins_pass2: unexpected node type %d",
|
||||
nodeTag(jtnode));
|
||||
}
|
||||
|
||||
/*
|
||||
* find_nonnullable_rels
|
||||
* Determine which base rels are forced nonnullable by given quals
|
||||
*
|
||||
* We don't use expression_tree_walker here because we don't want to
|
||||
* descend through very many kinds of nodes; only the ones we can be sure
|
||||
* are strict. We can descend through the top level of implicit AND'ing,
|
||||
* but not through any explicit ANDs (or ORs) below that, since those are not
|
||||
* strict constructs. The List case handles the top-level implicit AND list
|
||||
* as well as lists of arguments to strict operators/functions.
|
||||
*/
|
||||
static Relids
|
||||
find_nonnullable_rels(Node *node, bool top_level)
|
||||
{
|
||||
Relids result = NULL;
|
||||
|
||||
if (node == NULL)
|
||||
return NULL;
|
||||
if (IsA(node, Var))
|
||||
{
|
||||
Var *var = (Var *) node;
|
||||
|
||||
if (var->varlevelsup == 0)
|
||||
result = bms_make_singleton(var->varno);
|
||||
}
|
||||
else if (IsA(node, List))
|
||||
{
|
||||
List *l;
|
||||
|
||||
foreach(l, (List *) node)
|
||||
{
|
||||
result = bms_join(result, find_nonnullable_rels(lfirst(l),
|
||||
top_level));
|
||||
}
|
||||
}
|
||||
else if (IsA(node, FuncExpr))
|
||||
{
|
||||
FuncExpr *expr = (FuncExpr *) node;
|
||||
|
||||
if (func_strict(expr->funcid))
|
||||
result = find_nonnullable_rels((Node *) expr->args, false);
|
||||
}
|
||||
else if (IsA(node, OpExpr))
|
||||
{
|
||||
OpExpr *expr = (OpExpr *) node;
|
||||
|
||||
if (op_strict(expr->opno))
|
||||
result = find_nonnullable_rels((Node *) expr->args, false);
|
||||
}
|
||||
else if (IsA(node, BoolExpr))
|
||||
{
|
||||
BoolExpr *expr = (BoolExpr *) node;
|
||||
|
||||
/* NOT is strict, others are not */
|
||||
if (expr->boolop == NOT_EXPR)
|
||||
result = find_nonnullable_rels((Node *) expr->args, false);
|
||||
}
|
||||
else if (IsA(node, RelabelType))
|
||||
{
|
||||
RelabelType *expr = (RelabelType *) node;
|
||||
|
||||
result = find_nonnullable_rels((Node *) expr->arg, top_level);
|
||||
}
|
||||
else if (IsA(node, NullTest))
|
||||
{
|
||||
NullTest *expr = (NullTest *) node;
|
||||
|
||||
/*
|
||||
* IS NOT NULL can be considered strict, but only at top level;
|
||||
* else we might have something like NOT (x IS NOT NULL).
|
||||
*/
|
||||
if (top_level && expr->nulltesttype == IS_NOT_NULL)
|
||||
result = find_nonnullable_rels((Node *) expr->arg, false);
|
||||
}
|
||||
else if (IsA(node, BooleanTest))
|
||||
{
|
||||
BooleanTest *expr = (BooleanTest *) node;
|
||||
|
||||
/*
|
||||
* Appropriate boolean tests are strict at top level.
|
||||
*/
|
||||
if (top_level &&
|
||||
(expr->booltesttype == IS_TRUE ||
|
||||
expr->booltesttype == IS_FALSE ||
|
||||
expr->booltesttype == IS_NOT_UNKNOWN))
|
||||
result = find_nonnullable_rels((Node *) expr->arg, false);
|
||||
}
|
||||
return result;
|
||||
}
|
||||
|
||||
/*
|
||||
* simplify_jointree
|
||||
* Attempt to simplify a query's jointree.
|
||||
*
|
||||
* If we succeed in pulling up a subquery then we might form a jointree
|
||||
|
|
@ -487,7 +833,7 @@ resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist)
|
|||
* work reliably --- see comments for pull_up_subqueries().
|
||||
*/
|
||||
Node *
|
||||
preprocess_jointree(Query *parse, Node *jtnode)
|
||||
simplify_jointree(Query *parse, Node *jtnode)
|
||||
{
|
||||
if (jtnode == NULL)
|
||||
return NULL;
|
||||
|
|
@ -506,7 +852,7 @@ preprocess_jointree(Query *parse, Node *jtnode)
|
|||
Node *child = (Node *) lfirst(l);
|
||||
|
||||
/* Recursively simplify this child... */
|
||||
child = preprocess_jointree(parse, child);
|
||||
child = simplify_jointree(parse, child);
|
||||
/* Now, is it a FromExpr? */
|
||||
if (child && IsA(child, FromExpr))
|
||||
{
|
||||
|
|
@ -546,8 +892,8 @@ preprocess_jointree(Query *parse, Node *jtnode)
|
|||
JoinExpr *j = (JoinExpr *) jtnode;
|
||||
|
||||
/* Recursively simplify the children... */
|
||||
j->larg = preprocess_jointree(parse, j->larg);
|
||||
j->rarg = preprocess_jointree(parse, j->rarg);
|
||||
j->larg = simplify_jointree(parse, j->larg);
|
||||
j->rarg = simplify_jointree(parse, j->rarg);
|
||||
/*
|
||||
* If it is an outer join, we must not flatten it. An inner join
|
||||
* is semantically equivalent to a FromExpr; we convert it to one,
|
||||
|
|
@ -605,7 +951,7 @@ preprocess_jointree(Query *parse, Node *jtnode)
|
|||
}
|
||||
}
|
||||
else
|
||||
elog(ERROR, "preprocess_jointree: unexpected node type %d",
|
||||
elog(ERROR, "simplify_jointree: unexpected node type %d",
|
||||
nodeTag(jtnode));
|
||||
return jtnode;
|
||||
}
|
||||
|
|
@ -684,7 +1030,7 @@ get_relids_in_jointree(Node *jtnode)
|
|||
/*
|
||||
* get_relids_for_join: get set of base RT indexes making up a join
|
||||
*
|
||||
* NB: this will not work reliably after preprocess_jointree() is run,
|
||||
* NB: this will not work reliably after simplify_jointree() is run,
|
||||
* since that may eliminate join nodes from the jointree.
|
||||
*/
|
||||
Relids
|
||||
|
|
|
|||
|
|
@ -7,7 +7,7 @@
|
|||
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
|
||||
* Portions Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
* $Id: prep.h,v 1.36 2003/02/08 20:20:55 tgl Exp $
|
||||
* $Id: prep.h,v 1.37 2003/02/09 23:57:19 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
|
|
@ -28,7 +28,8 @@ extern int join_collapse_limit;
|
|||
extern Node *pull_up_IN_clauses(Query *parse, Node *node);
|
||||
extern Node *pull_up_subqueries(Query *parse, Node *jtnode,
|
||||
bool below_outer_join);
|
||||
extern Node *preprocess_jointree(Query *parse, Node *jtnode);
|
||||
extern void reduce_outer_joins(Query *parse);
|
||||
extern Node *simplify_jointree(Query *parse, Node *jtnode);
|
||||
extern Relids get_relids_in_jointree(Node *jtnode);
|
||||
extern Relids get_relids_for_join(Query *parse, int joinrelid);
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue