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Commit39c8dd6

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committed
Invert and rename flag variable to improve code readability.
No change in functionality. Per discussion with Robert.
1 parent7b46401 commit39c8dd6

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1 file changed

+24
-23
lines changed

1 file changed

+24
-23
lines changed

‎src/backend/optimizer/path/joinpath.c

Lines changed: 24 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -42,7 +42,7 @@ static List *select_mergejoin_clauses(PlannerInfo *root,
4242
RelOptInfo*innerrel,
4343
List*restrictlist,
4444
JoinTypejointype,
45-
bool*have_nonmergeable_clause);
45+
bool*mergejoin_allowed);
4646

4747

4848
/*
@@ -78,7 +78,7 @@ add_paths_to_joinrel(PlannerInfo *root,
7878
List*restrictlist)
7979
{
8080
List*mergeclause_list=NIL;
81-
boolhave_nonmergeable_clause=false;
81+
boolmergejoin_allowed=true;
8282

8383
/*
8484
* Find potential mergejoin clauses. We can skip this if we are not
@@ -93,13 +93,13 @@ add_paths_to_joinrel(PlannerInfo *root,
9393
innerrel,
9494
restrictlist,
9595
jointype,
96-
&have_nonmergeable_clause);
96+
&mergejoin_allowed);
9797

9898
/*
9999
* 1. Consider mergejoin paths where both relations must be explicitly
100100
* sorted. Skip this if we can't mergejoin.
101101
*/
102-
if (!have_nonmergeable_clause)
102+
if (mergejoin_allowed)
103103
sort_inner_and_outer(root,joinrel,outerrel,innerrel,
104104
restrictlist,mergeclause_list,jointype,sjinfo);
105105

@@ -108,9 +108,9 @@ add_paths_to_joinrel(PlannerInfo *root,
108108
* sorted. This includes both nestloops and mergejoins where the outer
109109
* path is already ordered. Again, skip this if we can't mergejoin.
110110
* (That's okay because we know that nestloop can't handle right/full
111-
* joins at all, so it wouldn't work inthose cases either.)
111+
* joins at all, so it wouldn't work inthe prohibited cases either.)
112112
*/
113-
if (!have_nonmergeable_clause)
113+
if (mergejoin_allowed)
114114
match_unsorted_outer(root,joinrel,outerrel,innerrel,
115115
restrictlist,mergeclause_list,jointype,sjinfo);
116116

@@ -127,7 +127,7 @@ add_paths_to_joinrel(PlannerInfo *root,
127127
* those made by match_unsorted_outer when add_paths_to_joinrel() is
128128
* invoked with the two rels given in the other order.
129129
*/
130-
if (!have_nonmergeable_clause)
130+
if (mergejoin_allowed)
131131
match_unsorted_inner(root,joinrel,outerrel,innerrel,
132132
restrictlist,mergeclause_list,jointype,sjinfo);
133133
#endif
@@ -927,10 +927,14 @@ best_appendrel_indexscan(PlannerInfo *root, RelOptInfo *rel,
927927
* Select mergejoin clauses that are usable for a particular join.
928928
* Returns a list of RestrictInfo nodes for those clauses.
929929
*
930-
* *have_nonmergeable_clause is set TRUE if this is a right/full join and
931-
* there are nonmergejoinable join clauses. The executor's mergejoin
932-
* machinery cannot handle such cases, so we have to avoid generating a
933-
* mergejoin plan.
930+
* *mergejoin_allowed is normally set to TRUE, but it is set to FALSE if
931+
* this is a right/full join and there are nonmergejoinable join clauses.
932+
* The executor's mergejoin machinery cannot handle such cases, so we have
933+
* to avoid generating a mergejoin plan. (Note that this flag does NOT
934+
* consider whether there are actually any mergejoinable clauses. This is
935+
* correct because in some cases we need to build a clauseless mergejoin.
936+
* Simply returning NIL is therefore not enough to distinguish safe from
937+
* unsafe cases.)
934938
*
935939
* We also mark each selected RestrictInfo to show which side is currently
936940
* being considered as outer. These are transient markings that are only
@@ -947,22 +951,21 @@ select_mergejoin_clauses(PlannerInfo *root,
947951
RelOptInfo*innerrel,
948952
List*restrictlist,
949953
JoinTypejointype,
950-
bool*have_nonmergeable_clause)
954+
bool*mergejoin_allowed)
951955
{
952956
List*result_list=NIL;
953957
boolisouterjoin=IS_OUTER_JOIN(jointype);
958+
boolhave_nonmergeable_joinclause= false;
954959
ListCell*l;
955960

956-
*have_nonmergeable_clause= false;
957-
958961
foreach(l,restrictlist)
959962
{
960963
RestrictInfo*restrictinfo= (RestrictInfo*)lfirst(l);
961964

962965
/*
963966
* If processing an outer join, only use its own join clauses in the
964967
* merge. For inner joins we can use pushed-down clauses too. (Note:
965-
* we don't sethave_nonmergeable_clause here because pushed-down
968+
* we don't sethave_nonmergeable_joinclause here because pushed-down
966969
* clauses will become otherquals not joinquals.)
967970
*/
968971
if (isouterjoin&&restrictinfo->is_pushed_down)
@@ -979,7 +982,7 @@ select_mergejoin_clauses(PlannerInfo *root,
979982
* FALSE.)
980983
*/
981984
if (!restrictinfo->clause|| !IsA(restrictinfo->clause,Const))
982-
*have_nonmergeable_clause= true;
985+
have_nonmergeable_joinclause= true;
983986
continue;/* not mergejoinable */
984987
}
985988

@@ -988,7 +991,7 @@ select_mergejoin_clauses(PlannerInfo *root,
988991
*/
989992
if (!clause_sides_match_join(restrictinfo,outerrel,innerrel))
990993
{
991-
*have_nonmergeable_clause= true;
994+
have_nonmergeable_joinclause= true;
992995
continue;/* no good for these input relations */
993996
}
994997

@@ -1017,26 +1020,24 @@ select_mergejoin_clauses(PlannerInfo *root,
10171020
if (EC_MUST_BE_REDUNDANT(restrictinfo->left_ec)||
10181021
EC_MUST_BE_REDUNDANT(restrictinfo->right_ec))
10191022
{
1020-
*have_nonmergeable_clause= true;
1023+
have_nonmergeable_joinclause= true;
10211024
continue;/* can't handle redundant eclasses */
10221025
}
10231026

10241027
result_list=lappend(result_list,restrictinfo);
10251028
}
10261029

10271030
/*
1028-
* If it is not a right/full join then we don't need to insist on all the
1029-
* joinclauses being mergejoinable, so reset the flag. This simplifies
1030-
* the logic in add_paths_to_joinrel.
1031+
* Report whether mergejoin is allowed (see comment at top of function).
10311032
*/
10321033
switch (jointype)
10331034
{
10341035
caseJOIN_RIGHT:
10351036
caseJOIN_FULL:
1037+
*mergejoin_allowed= !have_nonmergeable_joinclause;
10361038
break;
10371039
default:
1038-
/* otherwise, it's OK to have nonmergeable join quals */
1039-
*have_nonmergeable_clause= false;
1040+
*mergejoin_allowed= true;
10401041
break;
10411042
}
10421043

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