summaryrefslogtreecommitdiff
path: root/src/backend/optimizer/path
diff options
context:
space:
mode:
authorTom Lane <tgl@sss.pgh.pa.us>2015-12-07 17:41:45 -0500
committerTom Lane <tgl@sss.pgh.pa.us>2015-12-07 17:41:45 -0500
commit0a34ff7e9a3a232d675fe03dba00d010c689f33c (patch)
tree17d39288c314c052b44c3668c9e71b111315b99d /src/backend/optimizer/path
parentfd52958856233bc3248db879c4241bdf08075c42 (diff)
Fix another oversight in checking if a join with LATERAL refs is legal.
It was possible for the planner to decide to join a LATERAL subquery to the outer side of an outer join before the outer join itself is completed. Normally that's fine because of the associativity rules, but it doesn't work if the subquery contains a lateral reference to the inner side of the outer join. In such a situation the outer join *must* be done first. join_is_legal() missed this consideration and would allow the join to be attempted, but the actual path-building code correctly decided that no valid join path could be made, sometimes leading to planner errors such as "failed to build any N-way joins". Per report from Andreas Seltenreich. Back-patch to 9.3 where LATERAL support was added.
Diffstat (limited to 'src/backend/optimizer/path')
-rw-r--r--src/backend/optimizer/path/joinrels.c30
1 files changed, 30 insertions, 0 deletions
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 125b33f48e7..7e2816aaec6 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -334,6 +334,7 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
bool must_be_leftjoin;
bool lateral_fwd;
bool lateral_rev;
+ Relids join_lateral_rels;
ListCell *l;
/*
@@ -569,6 +570,35 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
}
}
+ /*
+ * LATERAL references could also cause problems later on if we accept this
+ * join: if the join's minimum parameterization includes any rels that
+ * would have to be on the inside of an outer join with this join rel,
+ * then it's never going to be possible to build the complete query using
+ * this join. We should reject this join not only because it'll save
+ * work, but because if we don't, the clauseless-join heuristics might
+ * think that legality of this join means that some other join rel need
+ * not be formed, and that could lead to failure to find any plan at all.
+ * It seems best not to merge this check into the main loop above, because
+ * it is concerned with SJs that are not otherwise relevant to this join.
+ */
+ join_lateral_rels = min_join_parameterization(root, joinrelids);
+ if (join_lateral_rels)
+ {
+ foreach(l, root->join_info_list)
+ {
+ SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
+
+ if (bms_overlap(sjinfo->min_righthand, join_lateral_rels) &&
+ bms_overlap(sjinfo->min_lefthand, joinrelids))
+ return false; /* will not be able to join to min_righthand */
+ if (sjinfo->jointype == JOIN_FULL &&
+ bms_overlap(sjinfo->min_lefthand, join_lateral_rels) &&
+ bms_overlap(sjinfo->min_righthand, joinrelids))
+ return false; /* will not be able to join to min_lefthand */
+ }
+ }
+
/* Otherwise, it's a valid join */
*sjinfo_p = match_sjinfo;
*reversed_p = reversed;