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Commit6480c14

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Partially revert my patch of 2008-11-12 that installed a limit on the number
of AND/OR clause branches that predtest.c would attempt to deal with. Asnoted in bug #4721, that change disabled proof attempts for sizes of problemsthat people are actually expecting it to work for. The original complaintit was trying to solve was O(N^2) behavior for long IN-lists, so let's tryapplying the limit to just ScalarArrayOpExprs rather than everything.Another case of "foolish consistency" I fear.Back-patch to 8.2, same as the previous patch was.
1 parente54ec92 commit6480c14

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1 file changed

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‎src/backend/optimizer/util/predtest.c

Lines changed: 18 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@
99
*
1010
*
1111
* IDENTIFICATION
12-
* $PostgreSQL: pgsql/src/backend/optimizer/util/predtest.c,v 1.25 2009/05/10 22:45:28 tgl Exp $
12+
* $PostgreSQL: pgsql/src/backend/optimizer/util/predtest.c,v 1.26 2009/05/11 17:56:08 tgl Exp $
1313
*
1414
*-------------------------------------------------------------------------
1515
*/
@@ -31,13 +31,13 @@
3131

3232

3333
/*
34-
* Proof attempts involvingmany AND or OR branches are likely to require
35-
* O(N^2) time, and more often than not fail anyway. So we set an arbitrary
36-
* limit on the number ofbranches that we will allow at any one level of
37-
*clause. (Note that this is only effective because the trees have been
38-
*AND/OR flattened!)XXX is it worth exposing this as a GUC knob?
34+
* Proof attempts involvinglarge arrays in ScalarArrayOpExpr nodes are
35+
*likely to requireO(N^2) time, and more often than not fail anyway.
36+
*So we set an arbitrarylimit on the number ofarray elements that
37+
*we will allow to be treated as an AND or OR clause.
38+
* XXX is it worth exposing this as a GUC knob?
3939
*/
40-
#defineMAX_BRANCHES_TO_TEST100
40+
#defineMAX_SAOP_ARRAY_SIZE100
4141

4242
/*
4343
* To avoid redundant coding in predicate_implied_by_recurse and
@@ -735,12 +735,12 @@ predicate_refuted_by_recurse(Node *clause, Node *predicate)
735735
* If the expression is classified as AND- or OR-type, then *info is filled
736736
* in with the functions needed to iterate over its components.
737737
*
738-
* This function also implements enforcement ofMAX_BRANCHES_TO_TEST: ifan
739-
*AND/OR expression has too manybranches, we just classify it as an atom.
740-
* (This will result in its being passed as-is to the simple_clause functions,
741-
* which will fail to prove anything about it.) Note that we cannot just stop
742-
* after consideringMAX_BRANCHES_TO_TEST branches; in general that would
743-
* result in wrong proofs rather than failing to prove anything.
738+
* This function also implements enforcement ofMAX_SAOP_ARRAY_SIZE: ifa
739+
*ScalarArrayOpExpr's array has too manyelements, we just classify it as an
740+
*atom.(This will result in its being passed as-is to the simple_clause
741+
*functions,which will fail to prove anything about it.) Note that we
742+
*cannot just stopafter consideringMAX_SAOP_ARRAY_SIZE elements; in general
743+
*that wouldresult in wrong proofs, rather than failing to prove anything.
744744
*/
745745
staticPredClass
746746
predicate_classify(Node*clause,PredIterInfoinfo)
@@ -753,8 +753,7 @@ predicate_classify(Node *clause, PredIterInfo info)
753753
* If we see a List, assume it's an implicit-AND list; this is the correct
754754
* semantics for lists of RestrictInfo nodes.
755755
*/
756-
if (IsA(clause,List)&&
757-
list_length((List*)clause) <=MAX_BRANCHES_TO_TEST)
756+
if (IsA(clause,List))
758757
{
759758
info->startup_fn=list_startup_fn;
760759
info->next_fn=list_next_fn;
@@ -763,16 +762,14 @@ predicate_classify(Node *clause, PredIterInfo info)
763762
}
764763

765764
/* Handle normal AND and OR boolean clauses */
766-
if (and_clause(clause)&&
767-
list_length(((BoolExpr*)clause)->args) <=MAX_BRANCHES_TO_TEST)
765+
if (and_clause(clause))
768766
{
769767
info->startup_fn=boolexpr_startup_fn;
770768
info->next_fn=list_next_fn;
771769
info->cleanup_fn=list_cleanup_fn;
772770
returnCLASS_AND;
773771
}
774-
if (or_clause(clause)&&
775-
list_length(((BoolExpr*)clause)->args) <=MAX_BRANCHES_TO_TEST)
772+
if (or_clause(clause))
776773
{
777774
info->startup_fn=boolexpr_startup_fn;
778775
info->next_fn=list_next_fn;
@@ -800,7 +797,7 @@ predicate_classify(Node *clause, PredIterInfo info)
800797

801798
arrayval=DatumGetArrayTypeP(((Const*)arraynode)->constvalue);
802799
nelems=ArrayGetNItems(ARR_NDIM(arrayval),ARR_DIMS(arrayval));
803-
if (nelems <=MAX_BRANCHES_TO_TEST)
800+
if (nelems <=MAX_SAOP_ARRAY_SIZE)
804801
{
805802
info->startup_fn=arrayconst_startup_fn;
806803
info->next_fn=arrayconst_next_fn;
@@ -810,7 +807,7 @@ predicate_classify(Node *clause, PredIterInfo info)
810807
}
811808
elseif (arraynode&&IsA(arraynode,ArrayExpr)&&
812809
!((ArrayExpr*)arraynode)->multidims&&
813-
list_length(((ArrayExpr*)arraynode)->elements) <=MAX_BRANCHES_TO_TEST)
810+
list_length(((ArrayExpr*)arraynode)->elements) <=MAX_SAOP_ARRAY_SIZE)
814811
{
815812
info->startup_fn=arrayexpr_startup_fn;
816813
info->next_fn=arrayexpr_next_fn;

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