Redesign PlanForeignScan API to allow multiple paths for a foreign table.

The original API specification only allowed an FDW to create a single
access path, which doesn't seem like a terribly good idea in hindsight.
Instead, move the responsibility for building the Path node and calling
add_path() into the FDW's PlanForeignScan function.  Now, it can do that
more than once if appropriate.  There is no longer any need for the
transient FdwPlan struct, so get rid of that.

Etsuro Fujita, Shigeru Hanada, Tom Lane

1 files changed, 17 insertions, 23 deletions

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index d29b454f724..6d1545476df 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -16,7 +16,6 @@
 
 #include <math.h>
 
-#include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
@@ -1766,36 +1765,31 @@ create_worktablescan_path(PlannerInfo *root, RelOptInfo *rel)
  * create_foreignscan_path
  *	  Creates a path corresponding to a scan of a foreign table,
  *	  returning the pathnode.
+ *
+ * This function is never called from core Postgres; rather, it's expected
+ * to be called by the PlanForeignScan function of a foreign data wrapper.
+ * We make the FDW supply all fields of the path, since we do not have any
+ * way to calculate them in core.
  */
 ForeignPath *
-create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel)
+create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel,
+						double rows, Cost startup_cost, Cost total_cost,
+						List *pathkeys,
+						Relids required_outer, List *param_clauses,
+						List *fdw_private)
 {
 	ForeignPath *pathnode = makeNode(ForeignPath);
-	RangeTblEntry *rte;
-	FdwRoutine *fdwroutine;
-	FdwPlan    *fdwplan;
 
 	pathnode->path.pathtype = T_ForeignScan;
 	pathnode->path.parent = rel;
-	pathnode->path.pathkeys = NIL;		/* result is always unordered */
-	pathnode->path.required_outer = NULL;
-	pathnode->path.param_clauses = NIL;
+	pathnode->path.rows = rows;
+	pathnode->path.startup_cost = startup_cost;
+	pathnode->path.total_cost = total_cost;
+	pathnode->path.pathkeys = pathkeys;
+	pathnode->path.required_outer = required_outer;
+	pathnode->path.param_clauses = param_clauses;
 
-	/* Get FDW's callback info */
-	rte = planner_rt_fetch(rel->relid, root);
-	fdwroutine = GetFdwRoutineByRelId(rte->relid);
-
-	/* Let the FDW do its planning */
-	fdwplan = fdwroutine->PlanForeignScan(rte->relid, root, rel);
-	if (fdwplan == NULL || !IsA(fdwplan, FdwPlan))
-		elog(ERROR, "foreign-data wrapper PlanForeignScan function for relation %u did not return an FdwPlan struct",
-			 rte->relid);
-	pathnode->fdwplan = fdwplan;
-
-	/* use costs estimated by FDW */
-	pathnode->path.rows = rel->rows;
-	pathnode->path.startup_cost = fdwplan->startup_cost;
-	pathnode->path.total_cost = fdwplan->total_cost;
+	pathnode->fdw_private = fdw_private;
 
 	return pathnode;
 }