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Commit8d3c4aa

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Fix an oversight in join-removal optimization: we have to check not only for
plain Vars that are generated in the inner rel and used above the join, butalso for PlaceHolderVars. Per report from Oleg K.
1 parentecac5e6 commit8d3c4aa

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3 files changed

+89
-2
lines changed

3 files changed

+89
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lines changed

‎src/backend/optimizer/path/joinpath.c

Lines changed: 17 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.130 2010/02/26 02:00:44 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.131 2010/03/22 13:57:15 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -192,7 +192,9 @@ clause_sides_match_join(RestrictInfo *rinfo, RelOptInfo *outerrel,
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*
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* This is true for a left join for which the join condition cannot match
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* more than one inner-side row. (There are other possibly interesting
195-
* cases, but we don't have the infrastructure to prove them.)
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* cases, but we don't have the infrastructure to prove them.) We also
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* have to check that the inner side doesn't generate any variables needed
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* above the join.
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*
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* Note: there is no need to consider the symmetrical case of duplicating the
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* right input, because add_paths_to_joinrel() will be called with each rel
@@ -245,6 +247,19 @@ join_is_removable(PlannerInfo *root,
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return false;
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}
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/*
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* Similarly check that the inner rel doesn't produce any PlaceHolderVars
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* that will be used above the join.
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*/
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foreach(l,root->placeholder_list)
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{
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PlaceHolderInfo*phinfo= (PlaceHolderInfo*)lfirst(l);
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if (bms_is_subset(phinfo->ph_eval_at,innerrel->relids)&&
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!bms_is_subset(phinfo->ph_needed,joinrel->relids))
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return false;
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}
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/*
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* Search for mergejoinable clauses that constrain the inner rel against
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* either the outer rel or a pseudoconstant. If an operator is

‎src/test/regress/expected/join.out

Lines changed: 49 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2491,3 +2491,52 @@ select * from int4_tbl a full join int4_tbl b on false;
24912491
-2147483647 |
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(10 rows)
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--
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-- test join removal
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--
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create temp table parent (k int primary key, pd int);
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NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "parent_pkey" for table "parent"
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create temp table child (k int unique, cd int);
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NOTICE: CREATE TABLE / UNIQUE will create implicit index "child_k_key" for table "child"
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insert into parent values (1, 10), (2, 20), (3, 30);
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insert into child values (1, 100), (4, 400);
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-- this case is optimizable
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select p.* from parent p left join child c on (p.k = c.k);
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k | pd
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---+----
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1 | 10
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2 | 20
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3 | 30
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(3 rows)
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explain (costs off)
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select p.* from parent p left join child c on (p.k = c.k);
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QUERY PLAN
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----------------------
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Seq Scan on parent p
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(1 row)
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-- this case is not
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select p.*, linked from parent p
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left join (select c.*, true as linked from child c) as ss
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on (p.k = ss.k);
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k | pd | linked
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---+----+--------
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1 | 10 | t
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2 | 20 |
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3 | 30 |
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(3 rows)
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explain (costs off)
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select p.*, linked from parent p
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left join (select c.*, true as linked from child c) as ss
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on (p.k = ss.k);
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QUERY PLAN
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---------------------------------
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Hash Left Join
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Hash Cond: (p.k = c.k)
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-> Seq Scan on parent p
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-> Hash
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-> Seq Scan on child c
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(5 rows)
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‎src/test/regress/sql/join.sql

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -567,3 +567,26 @@ group by t1.q2 order by 1;
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--
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select*from int4_tbl a fulljoin int4_tbl bon true;
569569
select*from int4_tbl a fulljoin int4_tbl bon false;
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--
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-- test join removal
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--
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create temp table parent (kintprimary key, pdint);
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create temp table child (kint unique, cdint);
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insert into parentvalues (1,10), (2,20), (3,30);
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insert into childvalues (1,100), (4,400);
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-- this case is optimizable
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select p.*from parent pleft join child con (p.k=c.k);
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explain (costs off)
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select p.*from parent pleft join child con (p.k=c.k);
584+
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-- this case is not
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select p.*, linkedfrom parent p
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left join (select c.*, trueas linkedfrom child c)as ss
588+
on (p.k=ss.k);
589+
explain (costs off)
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select p.*, linkedfrom parent p
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left join (select c.*, trueas linkedfrom child c)as ss
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on (p.k=ss.k);

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