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Allow planner to fold "stable" functions to constants when forming

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selectivity estimates, per recent discussion.
This commit is contained in:
Tom Lane 2004-11-09 21:42:53 +00:00
parent 8f6278d907
commit 9a633cbb6c
1 changed files with 33 additions and 16 deletions
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49
src/backend/optimizer/util/clauses.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.183 2004/10/22 17:20:05 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.184 2004/11/09 21:42:53 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@ -76,7 +76,8 @@ static Expr *simplify_function(Oid funcid, Oid result_type, List *args,
bool allow_inline,
eval_const_expressions_context *context);
static Expr *evaluate_function(Oid funcid, Oid result_type, List *args,
HeapTuple func_tuple);
HeapTuple func_tuple,
eval_const_expressions_context *context);
static Expr *inline_function(Oid funcid, Oid result_type, List *args,
HeapTuple func_tuple,
eval_const_expressions_context *context);
@ -1151,7 +1152,7 @@ eval_const_expressions(Node *node)
return eval_const_expressions_mutator(node, &context);
}
/*
/*--------------------
* estimate_expression_value
*
* This function attempts to estimate the value of an expression for
@ -1159,11 +1160,11 @@ eval_const_expressions(Node *node)
* eval_const_expressions(): we will perform constant reductions that are
* not necessarily 100% safe, but are reasonable for estimation purposes.
*
* Currently the only such transform is to substitute values for Params,
* when a bound Param value has been made available by the caller of planner().
* In future we might consider other things, such as reducing now() to current
* time. (XXX seems like there could be a lot of scope for ideas here...
* but we might need more volatility classifications ...)
* Currently the extra steps that are taken in this mode are:
* 1. Substitute values for Params, where a bound Param value has been made
* available by the caller of planner().
* 2. Fold stable, as well as immutable, functions to constants.
*--------------------
*/
Node *
estimate_expression_value(Node *node)
@ -1909,7 +1910,8 @@ simplify_function(Oid funcid, Oid result_type, List *args,
if (!HeapTupleIsValid(func_tuple))
elog(ERROR, "cache lookup failed for function %u", funcid);
newexpr = evaluate_function(funcid, result_type, args, func_tuple);
newexpr = evaluate_function(funcid, result_type, args,
func_tuple, context);
if (!newexpr && allow_inline)
newexpr = inline_function(funcid, result_type, args,
@ -1925,14 +1927,16 @@ simplify_function(Oid funcid, Oid result_type, List *args,
*
* We can do this if the function is strict and has any constant-null inputs
* (just return a null constant), or if the function is immutable and has all
* constant inputs (call it and return the result as a Const node).
* constant inputs (call it and return the result as a Const node). In
* estimation mode we are willing to pre-evaluate stable functions too.
*
* Returns a simplified expression if successful, or NULL if cannot
* simplify the function.
*/
static Expr *
evaluate_function(Oid funcid, Oid result_type, List *args,
HeapTuple func_tuple)
HeapTuple func_tuple,
eval_const_expressions_context *context)
{
Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
bool has_nonconst_input = false;
@ -1967,12 +1971,25 @@ evaluate_function(Oid funcid, Oid result_type, List *args,
return (Expr *) makeNullConst(result_type);
/*
* Otherwise, can simplify only if the function is immutable and all
* inputs are constants. (For a non-strict function, constant NULL
* inputs are treated the same as constant non-NULL inputs.)
* Otherwise, can simplify only if all inputs are constants. (For a
* non-strict function, constant NULL inputs are treated the same as
* constant non-NULL inputs.)
*/
if (funcform->provolatile != PROVOLATILE_IMMUTABLE ||
has_nonconst_input)
if (has_nonconst_input)
return NULL;
/*
* Ordinarily we are only allowed to simplify immutable functions.
* But for purposes of estimation, we consider it okay to simplify
* functions that are merely stable; the risk that the result might
* change from planning time to execution time is worth taking in
* preference to not being able to estimate the value at all.
*/
if (funcform->provolatile == PROVOLATILE_IMMUTABLE)
/* okay */ ;
else if (context->estimate && funcform->provolatile == PROVOLATILE_STABLE)
/* okay */ ;
else
return NULL;
/*