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Fix miscomputation of direct_lateral_relids for join relations. 

If a PlaceHolderVar is to be evaluated at a join relation, but
its value is only needed there and not at higher levels, we neglected
to update the joinrel's direct_lateral_relids to include the PHV's
source rel.  This causes problems because join_is_legal() then won't
allow joining the joinrel to the PHV's source rel at all, leading
to "failed to build any N-way joins" planner failures.

Per report from Andreas Seltenreich.  Back-patch to 9.5
where the problem originated.

Discussion: https://postgr.es/m/87blfgqa4t.fsf@aurora.ydns.eu
This commit is contained in:
Tom Lane 2020-11-30 12:22:43 -05:00
parent e2d5de1500
commit 8c5da2d512
3 changed files with 118 additions and 12 deletions
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39
src/backend/optimizer/util/placeholder.c
View File

@ -400,10 +400,10 @@ add_placeholders_to_base_rels(PlannerInfo *root)
* and if they contain lateral references, add those references to the
* joinrel's direct_lateral_relids.
*
* A join rel should emit a PlaceHolderVar if (a) the PHV is needed above
* this join level and (b) the PHV can be computed at or below this level.
* At this time we do not need to distinguish whether the PHV will be
* computed here or copied up from below.
* A join rel should emit a PlaceHolderVar if (a) the PHV can be computed
* at or below this join level and (b) the PHV is needed above this level.
* However, condition (a) is sufficient to add to direct_lateral_relids,
* as explained below.
*/
void
add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel)
@ -415,21 +415,36 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
/* Is it still needed above this joinrel? */
if (bms_nonempty_difference(phinfo->ph_needed, relids))
/* Is it computable here? */
if (bms_is_subset(phinfo->ph_eval_at, relids))
{
/* Is it computable here? */
if (bms_is_subset(phinfo->ph_eval_at, relids))
/* Is it still needed above this joinrel? */
if (bms_nonempty_difference(phinfo->ph_needed, relids))
{
/* Yup, add it to the output */
joinrel->reltargetlist = lappend(joinrel->reltargetlist,
phinfo->ph_var);
joinrel->width += phinfo->ph_width;
/* Adjust joinrel's direct_lateral_relids as needed */
joinrel->direct_lateral_relids =
bms_add_members(joinrel->direct_lateral_relids,
phinfo->ph_lateral);
}
/*
* Also adjust joinrel's direct_lateral_relids to include the
* PHV's source rel(s). We must do this even if we're not
* actually going to emit the PHV, otherwise join_is_legal() will
* reject valid join orderings. (In principle maybe we could
* instead remove the joinrel's lateral_relids dependency; but
* that's complicated to get right, and cases where we're not
* going to emit the PHV are too rare to justify the work.)
*
* In principle we should only do this if the join doesn't yet
* include the PHV's source rel(s). But our caller
* build_join_rel() will clean things up by removing the join's
* own relids from its direct_lateral_relids, so we needn't
* account for that here.
*/
joinrel->direct_lateral_relids =
bms_add_members(joinrel->direct_lateral_relids,
phinfo->ph_lateral);
}
}
}

64
src/test/regress/expected/join.out
View File

@ -2972,6 +2972,70 @@ order by 1,2;
4567890123456789 | 4567890123456789 | 4567890123456789 | 42
(8 rows)
--
-- variant where a PlaceHolderVar is needed at a join, but not above the join
--
explain (costs off)
select * from
int4_tbl as i41,
lateral
(select 1 as x from
(select i41.f1 as lat,
i42.f1 as loc from
int8_tbl as i81, int4_tbl as i42) as ss1
right join int4_tbl as i43 on (i43.f1 > 1)
where ss1.loc = ss1.lat) as ss2
where i41.f1 > 0;
QUERY PLAN
--------------------------------------------------
Nested Loop
-> Nested Loop
-> Seq Scan on int4_tbl i41
Filter: (f1 > 0)
-> Nested Loop
Join Filter: (i41.f1 = i42.f1)
-> Seq Scan on int8_tbl i81
-> Materialize
-> Seq Scan on int4_tbl i42
-> Materialize
-> Seq Scan on int4_tbl i43
Filter: (f1 > 1)
(12 rows)
select * from
int4_tbl as i41,
lateral
(select 1 as x from
(select i41.f1 as lat,
i42.f1 as loc from
int8_tbl as i81, int4_tbl as i42) as ss1
right join int4_tbl as i43 on (i43.f1 > 1)
where ss1.loc = ss1.lat) as ss2
where i41.f1 > 0;
f1 | x
------------+---
123456 | 1
123456 | 1
123456 | 1
123456 | 1
123456 | 1
123456 | 1
123456 | 1
123456 | 1
123456 | 1
123456 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
2147483647 | 1
(20 rows)
--
-- test the corner cases FULL JOIN ON TRUE and FULL JOIN ON FALSE
--

27
src/test/regress/sql/join.sql
View File

@ -882,6 +882,33 @@ where
1 = (select 1 from int8_tbl t3 where ss.y is not null limit 1)
order by 1,2;
--
-- variant where a PlaceHolderVar is needed at a join, but not above the join
--
explain (costs off)
select * from
int4_tbl as i41,
lateral
(select 1 as x from
(select i41.f1 as lat,
i42.f1 as loc from
int8_tbl as i81, int4_tbl as i42) as ss1
right join int4_tbl as i43 on (i43.f1 > 1)
where ss1.loc = ss1.lat) as ss2
where i41.f1 > 0;
select * from
int4_tbl as i41,
lateral
(select 1 as x from
(select i41.f1 as lat,
i42.f1 as loc from
int8_tbl as i81, int4_tbl as i42) as ss1
right join int4_tbl as i43 on (i43.f1 > 1)
where ss1.loc = ss1.lat) as ss2
where i41.f1 > 0;
--
-- test the corner cases FULL JOIN ON TRUE and FULL JOIN ON FALSE
--