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