Introduce custom path and scan providers.

This allows extension modules to define their own methods for
scanning a relation, and get the core code to use them.  It's
unclear as yet how much use this capability will find, but we
won't find out if we never commit it.

KaiGai Kohei, reviewed at various times and in various levels
of detail by Shigeru Hanada, Tom Lane, Andres Freund, Álvaro
Herrera, and myself.

1 files changed, 58 insertions, 2 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 4b641a2ca1f..8d9237ccac4 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -77,13 +77,15 @@ static WorkTableScan *create_worktablescan_plan(PlannerInfo *root, Path *best_pa
 						  List *tlist, List *scan_clauses);
 static ForeignScan *create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 						List *tlist, List *scan_clauses);
+static Plan *create_customscan_plan(PlannerInfo *root,
+									CustomPath *best_path,
+									List *tlist, List *scan_clauses);
 static NestLoop *create_nestloop_plan(PlannerInfo *root, NestPath *best_path,
 					 Plan *outer_plan, Plan *inner_plan);
 static MergeJoin *create_mergejoin_plan(PlannerInfo *root, MergePath *best_path,
 					  Plan *outer_plan, Plan *inner_plan);
 static HashJoin *create_hashjoin_plan(PlannerInfo *root, HashPath *best_path,
 					 Plan *outer_plan, Plan *inner_plan);
-static Node *replace_nestloop_params(PlannerInfo *root, Node *expr);
 static Node *replace_nestloop_params_mutator(Node *node, PlannerInfo *root);
 static void process_subquery_nestloop_params(PlannerInfo *root,
 								 List *subplan_params);
@@ -233,6 +235,7 @@ create_plan_recurse(PlannerInfo *root, Path *best_path)
 		case T_CteScan:
 		case T_WorkTableScan:
 		case T_ForeignScan:
+		case T_CustomScan:
 			plan = create_scan_plan(root, best_path);
 			break;
 		case T_HashJoin:
@@ -409,6 +412,13 @@ create_scan_plan(PlannerInfo *root, Path *best_path)
 													scan_clauses);
 			break;
 
+		case T_CustomScan:
+			plan = create_customscan_plan(root,
+										  (CustomPath *) best_path,
+										  tlist,
+										  scan_clauses);
+			break;
+
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) best_path->pathtype);
@@ -1072,6 +1082,52 @@ create_unique_plan(PlannerInfo *root, UniquePath *best_path)
 	return plan;
 }
 
+/*
+ * create_custom_plan
+ *
+ * Transform a CustomPath into a Plan.
+ */
+static Plan *
+create_customscan_plan(PlannerInfo *root, CustomPath *best_path,
+					   List *tlist, List *scan_clauses)
+{
+	Plan		   *plan;
+	RelOptInfo	   *rel = best_path->path.parent;
+
+	/*
+	 * Right now, all we can support is CustomScan node which is associated
+	 * with a particular base relation to be scanned.
+	 */
+	Assert(rel && rel->reloptkind == RELOPT_BASEREL);
+
+	/*
+	 * Sort clauses into the best execution order, although custom-scan
+	 * provider can reorder them again.
+	 */
+	scan_clauses = order_qual_clauses(root, scan_clauses);
+
+	/*
+	 * Create a CustomScan (or its inheritance) node according to
+	 * the supplied CustomPath.
+	 */
+	plan = best_path->methods->PlanCustomPath(root, rel, best_path, tlist,
+											  scan_clauses);
+
+	/*
+	 * NOTE: unlike create_foreignscan_plan(), it is responsibility of
+	 * the custom plan provider to replace outer-relation variables
+	 * with nestloop params, because we cannot know how many expression
+	 * trees are held in the private fields.
+	 */
+
+	/*
+	 * Copy cost data from Path to Plan; no need to make custom-plan
+	 * providers do this
+	 */
+	copy_path_costsize(plan, &best_path->path);
+
+	return plan;
+}
 
 /*****************************************************************************
  *
@@ -2540,7 +2596,7 @@ create_hashjoin_plan(PlannerInfo *root,
  * root->curOuterRels are replaced by Params, and entries are added to
  * root->curOuterParams if not already present.
  */
-static Node *
+Node *
 replace_nestloop_params(PlannerInfo *root, Node *expr)
 {
 	/* No setup needed for tree walk, so away we go */