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Commit5613da4

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Optimize nested ConvertRowtypeExpr nodes.
A ConvertRowtypeExpr is used to translate a whole-row reference of achild to that of a parent. The planner produces nestedConvertRowtypeExpr while translating whole-row reference of a leafpartition in a multi-level partition hierarchy. Executor thentranslates the whole-row reference from the leaf partition into allthe intermediate parent's whole-row references before arriving at thefinal whole-row reference. It could instead translate the whole-rowreference from the leaf partition directly to the top-most parent'swhole-row reference skipping any intermediate translations.Ashutosh Bapat, with tests by Kyotaro Horiguchi and someeditorialization by me. Reviewed by Andres Freund, Pavel Stehule,Kyotaro Horiguchi, Dmitry Dolgov, Tom Lane.
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3 files changed

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‎src/backend/optimizer/util/clauses.c

Lines changed: 46 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3716,6 +3716,52 @@ eval_const_expressions_mutator(Node *node,
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context);
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}
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break;
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caseT_ConvertRowtypeExpr:
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{
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ConvertRowtypeExpr*cre=castNode(ConvertRowtypeExpr,node);
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Node*arg;
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ConvertRowtypeExpr*newcre;
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3725+
arg=eval_const_expressions_mutator((Node*)cre->arg,
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context);
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3728+
newcre=makeNode(ConvertRowtypeExpr);
3729+
newcre->resulttype=cre->resulttype;
3730+
newcre->convertformat=cre->convertformat;
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newcre->location=cre->location;
3732+
3733+
/*
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* In case of a nested ConvertRowtypeExpr, we can convert the
3735+
* leaf row directly to the topmost row format without any
3736+
* intermediate conversions. (This works because
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* ConvertRowtypeExpr is used only for child->parent
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* conversion in inheritance trees, which works by exact match
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* of column name, and a column absent in an intermediate
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* result can't be present in the final result.)
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*
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* No need to check more than one level deep, because the
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* above recursion will have flattened anything else.
3744+
*/
3745+
if (arg!=NULL&&IsA(arg,ConvertRowtypeExpr))
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{
3747+
ConvertRowtypeExpr*argcre= (ConvertRowtypeExpr*)arg;
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3749+
arg= (Node*)argcre->arg;
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/*
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* Make sure an outer implicit conversion can't hide an
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* inner explicit one.
3754+
*/
3755+
if (newcre->convertformat==COERCE_IMPLICIT_CAST)
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newcre->convertformat=argcre->convertformat;
3757+
}
3758+
3759+
newcre->arg= (Expr*)arg;
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3761+
if (arg!=NULL&&IsA(arg,Const))
3762+
returnece_evaluate_expr((Node*)newcre);
3763+
return (Node*)newcre;
3764+
}
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default:
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break;
37213767
}

‎src/test/regress/expected/inherit.out

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -764,6 +764,8 @@ NOTICE: drop cascades to table c1
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-- tables. See the pgsql-hackers thread beginning Dec. 4/04
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create table base (i integer);
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create table derived () inherits (base);
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create table more_derived (like derived, b int) inherits (derived);
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NOTICE: merging column "i" with inherited definition
767769
insert into derived (i) values (0);
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select derived::base from derived;
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derived
@@ -777,6 +779,22 @@ select NULL::derived::base;
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(1 row)
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782+
-- remove redundant conversions.
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explain (verbose on, costs off) select row(i, b)::more_derived::derived::base from more_derived;
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QUERY PLAN
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-------------------------------------------
786+
Seq Scan on public.more_derived
787+
Output: (ROW(i, b)::more_derived)::base
788+
(2 rows)
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explain (verbose on, costs off) select (1, 2)::more_derived::derived::base;
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QUERY PLAN
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-----------------------
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Result
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Output: '(1)'::base
795+
(2 rows)
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drop table more_derived;
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drop table derived;
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drop table base;
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create table p1(ff1 int);

‎src/test/regress/sql/inherit.sql

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -237,9 +237,14 @@ drop table p1 cascade;
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-- tables. See the pgsql-hackers thread beginning Dec. 4/04
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createtablebase (iinteger);
239239
createtablederived () inherits (base);
240+
createtablemore_derived (like derived, bint) inherits (derived);
240241
insert into derived (i)values (0);
241242
select derived::basefrom derived;
242243
selectNULL::derived::base;
244+
-- remove redundant conversions.
245+
explain (verboseon, costs off)select row(i, b)::more_derived::derived::basefrom more_derived;
246+
explain (verboseon, costs off)select (1,2)::more_derived::derived::base;
247+
droptable more_derived;
243248
droptable derived;
244249
droptable base;
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