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, 4 deletions

diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index d73e7c0ab0f..894f9685e0f 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -114,7 +114,6 @@ query_planner(PlannerInfo *root, List *tlist,
 	root->right_join_clauses = NIL;
 	root->full_join_clauses = NIL;
 	root->join_info_list = NIL;
-	root->lateral_info_list = NIL;
 	root->placeholder_list = NIL;
 	root->initial_rels = NIL;
 
@@ -201,9 +200,8 @@ query_planner(PlannerInfo *root, List *tlist,
 	add_placeholders_to_base_rels(root);
 
 	/*
-	 * Create the LateralJoinInfo list now that we have finalized
-	 * PlaceHolderVar eval levels and made any necessary additions to the
-	 * lateral_vars lists for lateral references within PlaceHolderVars.
+	 * Construct the lateral reference sets now that we have finalized
+	 * PlaceHolderVar eval levels.
 	 */
 	create_lateral_join_info(root);