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, 1 insertions, 2 deletions

diff --git a/src/backend/optimizer/plan/planagg.c b/src/backend/optimizer/plan/planagg.c
index a761cfdb09b..02d38f15d1c 100644
--- a/src/backend/optimizer/plan/planagg.c
+++ b/src/backend/optimizer/plan/planagg.c
@@ -433,9 +433,8 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	subroot->plan_params = NIL;
 	subroot->outer_params = NULL;
 	subroot->init_plans = NIL;
-	/* There shouldn't be any OJ or LATERAL info to translate, as yet */
+	/* There shouldn't be any OJ info to translate, as yet */
 	Assert(subroot->join_info_list == NIL);
-	Assert(subroot->lateral_info_list == NIL);
 	/* and we haven't created PlaceHolderInfos, either */
 	Assert(subroot->placeholder_list == NIL);