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Optimize nested ConvertRowtypeExpr nodes.

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A ConvertRowtypeExpr is used to translate a whole-row reference of a
child to that of a parent. The planner produces nested
ConvertRowtypeExpr while translating whole-row reference of a leaf
partition in a multi-level partition hierarchy. Executor then
translates the whole-row reference from the leaf partition into all
the intermediate parent's whole-row references before arriving at the
final whole-row reference. It could instead translate the whole-row
reference from the leaf partition directly to the top-most parent's
whole-row reference skipping any intermediate translations.

Ashutosh Bapat, with tests by Kyotaro Horiguchi and some
editorialization by me. Reviewed by Andres Freund, Pavel Stehule,
Kyotaro Horiguchi, Dmitry Dolgov, Tom Lane.
This commit is contained in:
Andrew Gierth
2018-11-06 14:19:40 +00:00
parent c24dcd0cfd
commit 5613da4cc7
3 changed files with 69 additions and 0 deletions
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46
src/backend/optimizer/util/clauses.c
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@ -3716,6 +3716,52 @@ eval_const_expressions_mutator(Node *node,
context);
}
break;
case T_ConvertRowtypeExpr:
{
ConvertRowtypeExpr *cre = castNode(ConvertRowtypeExpr, node);
Node *arg;
ConvertRowtypeExpr *newcre;
arg = eval_const_expressions_mutator((Node *) cre->arg,
context);
newcre = makeNode(ConvertRowtypeExpr);
newcre->resulttype = cre->resulttype;
newcre->convertformat = cre->convertformat;
newcre->location = cre->location;
/*
* In case of a nested ConvertRowtypeExpr, we can convert the
* leaf row directly to the topmost row format without any
* intermediate conversions. (This works because
* ConvertRowtypeExpr is used only for child->parent
* conversion in inheritance trees, which works by exact match
* of column name, and a column absent in an intermediate
* result can't be present in the final result.)
*
* No need to check more than one level deep, because the
* above recursion will have flattened anything else.
*/
if (arg != NULL && IsA(arg, ConvertRowtypeExpr))
{
ConvertRowtypeExpr *argcre = (ConvertRowtypeExpr *) arg;
arg = (Node *) argcre->arg;
/*
* Make sure an outer implicit conversion can't hide an
* inner explicit one.
*/
if (newcre->convertformat == COERCE_IMPLICIT_CAST)
newcre->convertformat = argcre->convertformat;
}
newcre->arg = (Expr *) arg;
if (arg != NULL && IsA(arg, Const))
return ece_evaluate_expr((Node *) newcre);
return (Node *) newcre;
}
default:
break;
}