Get rid of the planner's LateralJoinInfo data structure.

I originally modeled this data structure on SpecialJoinInfo, but after
commit acfcd45cacb6df23 that looks like a pretty poor decision.
All we really need is relid sets identifying laterally-referenced rels;
and most of the time, what we want to know about includes indirect lateral
references, a case the LateralJoinInfo data was unsuited to compute with
any efficiency.  The previous commit redefined RelOptInfo.lateral_relids
as the transitive closure of lateral references, so that it easily supports
checking indirect references.  For the places where we really do want just
direct references, add a new RelOptInfo field direct_lateral_relids, which
is easily set up as a copy of lateral_relids before we perform the
transitive closure calculation.  Then we can just drop lateral_info_list
and LateralJoinInfo and the supporting code.  This makes the planner's
handling of lateral references noticeably more efficient, and shorter too.

Such a change can't be back-patched into stable branches for fear of
breaking extensions that might be looking at the planner's data structures;
but it seems not too late to push it into 9.5, so I've done so.

1 files changed, 2 insertions, 7 deletions

diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 9bf1c662b53..39cce846024 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -1149,14 +1149,11 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 										subroot->append_rel_list);
 
 	/*
-	 * We don't have to do the equivalent bookkeeping for outer-join or
-	 * LATERAL info, because that hasn't been set up yet.  placeholder_list
-	 * likewise.
+	 * We don't have to do the equivalent bookkeeping for outer-join info,
+	 * because that hasn't been set up yet.  placeholder_list likewise.
 	 */
 	Assert(root->join_info_list == NIL);
 	Assert(subroot->join_info_list == NIL);
-	Assert(root->lateral_info_list == NIL);
-	Assert(subroot->lateral_info_list == NIL);
 	Assert(root->placeholder_list == NIL);
 	Assert(subroot->placeholder_list == NIL);
 
@@ -1641,7 +1638,6 @@ pull_up_simple_values(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte)
 	Assert(root->append_rel_list == NIL);
 	Assert(list_length(parse->rtable) == 1);
 	Assert(root->join_info_list == NIL);
-	Assert(root->lateral_info_list == NIL);
 	Assert(root->placeholder_list == NIL);
 
 	/*
@@ -2838,7 +2834,6 @@ substitute_multiple_relids_walker(Node *node,
 	}
 	/* Shouldn't need to handle planner auxiliary nodes here */
 	Assert(!IsA(node, SpecialJoinInfo));
-	Assert(!IsA(node, LateralJoinInfo));
 	Assert(!IsA(node, AppendRelInfo));
 	Assert(!IsA(node, PlaceHolderInfo));
 	Assert(!IsA(node, MinMaxAggInfo));