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Commit9a633cb

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committed
Allow planner to fold "stable" functions to constants when forming
selectivity estimates, per recent discussion.
1 parent8f6278d commit9a633cb

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1 file changed

+33
-16
lines changed

1 file changed

+33
-16
lines changed

‎src/backend/optimizer/util/clauses.c

Lines changed: 33 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.183 2004/10/22 17:20:05 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.184 2004/11/09 21:42:53 tgl Exp $
1212
*
1313
* HISTORY
1414
* AUTHORDATEMAJOR EVENT
@@ -76,7 +76,8 @@ static Expr *simplify_function(Oid funcid, Oid result_type, List *args,
7676
boolallow_inline,
7777
eval_const_expressions_context*context);
7878
staticExpr*evaluate_function(Oidfuncid,Oidresult_type,List*args,
79-
HeapTuplefunc_tuple);
79+
HeapTuplefunc_tuple,
80+
eval_const_expressions_context*context);
8081
staticExpr*inline_function(Oidfuncid,Oidresult_type,List*args,
8182
HeapTuplefunc_tuple,
8283
eval_const_expressions_context*context);
@@ -1151,19 +1152,19 @@ eval_const_expressions(Node *node)
11511152
returneval_const_expressions_mutator(node,&context);
11521153
}
11531154

1154-
/*
1155+
/*--------------------
11551156
* estimate_expression_value
11561157
*
11571158
* This function attempts to estimate the value of an expression for
11581159
* planning purposes. It is in essence a more aggressive version of
11591160
* eval_const_expressions(): we will perform constant reductions that are
11601161
* not necessarily 100% safe, but are reasonable for estimation purposes.
11611162
*
1162-
* Currently theonly such transform is to substitute values for Params,
1163-
*whena bound Param value has been made available by the caller of planner().
1164-
*In future we might consider other things, such as reducing now() to current
1165-
*time. (XXX seems like there could be a lot of scope for ideas here...
1166-
* but we might need more volatility classifications ...)
1163+
* Currently theextra steps that are taken in this mode are:
1164+
*1. Substitute values for Params, wherea bound Param value has been made
1165+
* available by the caller of planner().
1166+
*2. Fold stable, as well as immutable, functions to constants.
1167+
*--------------------
11671168
*/
11681169
Node*
11691170
estimate_expression_value(Node*node)
@@ -1909,7 +1910,8 @@ simplify_function(Oid funcid, Oid result_type, List *args,
19091910
if (!HeapTupleIsValid(func_tuple))
19101911
elog(ERROR,"cache lookup failed for function %u",funcid);
19111912

1912-
newexpr=evaluate_function(funcid,result_type,args,func_tuple);
1913+
newexpr=evaluate_function(funcid,result_type,args,
1914+
func_tuple,context);
19131915

19141916
if (!newexpr&&allow_inline)
19151917
newexpr=inline_function(funcid,result_type,args,
@@ -1925,14 +1927,16 @@ simplify_function(Oid funcid, Oid result_type, List *args,
19251927
*
19261928
* We can do this if the function is strict and has any constant-null inputs
19271929
* (just return a null constant), or if the function is immutable and has all
1928-
* constant inputs (call it and return the result as a Const node).
1930+
* constant inputs (call it and return the result as a Const node). In
1931+
* estimation mode we are willing to pre-evaluate stable functions too.
19291932
*
19301933
* Returns a simplified expression if successful, or NULL if cannot
19311934
* simplify the function.
19321935
*/
19331936
staticExpr*
19341937
evaluate_function(Oidfuncid,Oidresult_type,List*args,
1935-
HeapTuplefunc_tuple)
1938+
HeapTuplefunc_tuple,
1939+
eval_const_expressions_context*context)
19361940
{
19371941
Form_pg_procfuncform= (Form_pg_proc)GETSTRUCT(func_tuple);
19381942
boolhas_nonconst_input= false;
@@ -1967,12 +1971,25 @@ evaluate_function(Oid funcid, Oid result_type, List *args,
19671971
return (Expr*)makeNullConst(result_type);
19681972

19691973
/*
1970-
* Otherwise, can simplify only ifthe function is immutable and all
1971-
*inputs are constants. (For anon-strict function, constant NULL
1972-
*inputs are treated the same asconstant non-NULL inputs.)
1974+
* Otherwise, can simplify only ifall inputs are constants. (For a
1975+
* non-strict function, constant NULL inputs are treated the same as
1976+
* constant non-NULL inputs.)
19731977
*/
1974-
if (funcform->provolatile!=PROVOLATILE_IMMUTABLE||
1975-
has_nonconst_input)
1978+
if (has_nonconst_input)
1979+
returnNULL;
1980+
1981+
/*
1982+
* Ordinarily we are only allowed to simplify immutable functions.
1983+
* But for purposes of estimation, we consider it okay to simplify
1984+
* functions that are merely stable; the risk that the result might
1985+
* change from planning time to execution time is worth taking in
1986+
* preference to not being able to estimate the value at all.
1987+
*/
1988+
if (funcform->provolatile==PROVOLATILE_IMMUTABLE)
1989+
/* okay */ ;
1990+
elseif (context->estimate&&funcform->provolatile==PROVOLATILE_STABLE)
1991+
/* okay */ ;
1992+
else
19761993
returnNULL;
19771994

19781995
/*

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