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Make equal() ignore CoercionForm fields for better planning with casts.

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This change ensures that the planner will see implicit and explicit casts
as equivalent for all purposes, except in the minority of cases where
there's actually a semantic difference (as reflected by having a 3-argument
cast function).  In particular, this fixes cases where the EquivalenceClass
machinery failed to consider two references to a varchar column as
equivalent if one was implicitly cast to text but the other was explicitly
cast to text, as seen in bug #7598 from Vaclav Juza.  We have had similar
bugs before in other parts of the planner, so I think it's time to fix this
problem at the core instead of continuing to band-aid around it.

Remove set_coercionform_dontcare(), which represents the band-aid
previously in use for allowing matching of index and constraint expressions
with inconsistent cast labeling.  (We can probably get rid of
COERCE_DONTCARE altogether, but I don't think removing that enum value in
back branches would be wise; it's possible there's third party code
referring to it.)

Back-patch to 9.2.  We could go back further, and might want to once this
has been tested more; but for the moment I won't risk destabilizing plan
choices in long-since-stable branches.
This commit is contained in:
Tom Lane
2012-10-12 12:10:49 -04:00
parent e583ffe947
commit 71e58dcfb9
6 changed files with 17 additions and 132 deletions
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42
src/backend/optimizer/util/clauses.c
View File

@ -98,7 +98,6 @@ static bool contain_leaky_functions_walker(Node *node, void *context);
static Relids find_nonnullable_rels_walker(Node *node, bool top_level);
static List *find_nonnullable_vars_walker(Node *node, bool top_level);
static bool is_strict_saop(ScalarArrayOpExpr *expr, bool falseOK);
static bool set_coercionform_dontcare_walker(Node *node, void *context);
static Node *eval_const_expressions_mutator(Node *node,
eval_const_expressions_context *context);
static List *simplify_or_arguments(List *args,
@ -2114,47 +2113,6 @@ strip_implicit_coercions(Node *node)
return node;
}
/*
* set_coercionform_dontcare: set all CoercionForm fields to COERCE_DONTCARE
*
* This is used to make index expressions and index predicates more easily
* comparable to clauses of queries. CoercionForm is not semantically
* significant (for cases where it does matter, the significant info is
* coded into the coercion function arguments) so we can ignore it during
* comparisons. Thus, for example, an index on "foo::int4" can match an
* implicit coercion to int4.
*
* Caution: the passed expression tree is modified in-place.
*/
void
set_coercionform_dontcare(Node *node)
{
(void) set_coercionform_dontcare_walker(node, NULL);
}
static bool
set_coercionform_dontcare_walker(Node *node, void *context)
{
if (node == NULL)
return false;
if (IsA(node, FuncExpr))
((FuncExpr *) node)->funcformat = COERCE_DONTCARE;
else if (IsA(node, RelabelType))
((RelabelType *) node)->relabelformat = COERCE_DONTCARE;
else if (IsA(node, CoerceViaIO))
((CoerceViaIO *) node)->coerceformat = COERCE_DONTCARE;
else if (IsA(node, ArrayCoerceExpr))
((ArrayCoerceExpr *) node)->coerceformat = COERCE_DONTCARE;
else if (IsA(node, ConvertRowtypeExpr))
((ConvertRowtypeExpr *) node)->convertformat = COERCE_DONTCARE;
else if (IsA(node, RowExpr))
((RowExpr *) node)->row_format = COERCE_DONTCARE;
else if (IsA(node, CoerceToDomain))
((CoerceToDomain *) node)->coercionformat = COERCE_DONTCARE;
return expression_tree_walker(node, set_coercionform_dontcare_walker,
context);
}
/*
* Helper for eval_const_expressions: check that datatype of an attribute
* is still what it was when the expression was parsed. This is needed to

6
src/backend/optimizer/util/plancat.c
View File

@ -665,12 +665,6 @@ get_relation_constraints(PlannerInfo *root,
cexpr = (Node *) canonicalize_qual((Expr *) cexpr);
/*
* Also mark any coercion format fields as "don't care", so that
* we can match to both explicit and implicit coercions.
*/
set_coercionform_dontcare(cexpr);
/* Fix Vars to have the desired varno */
if (varno != 1)
ChangeVarNodes(cexpr, 1, varno, 0);