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, 30 insertions, 9 deletions

diff --git a/contrib/file_fdw/file_fdw.c b/contrib/file_fdw/file_fdw.c
index 46394a80e0..c2faa6235e 100644
--- a/contrib/file_fdw/file_fdw.c
+++ b/contrib/file_fdw/file_fdw.c
@@ -25,6 +25,7 @@
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "optimizer/cost.h"
+#include "optimizer/pathnode.h"
 #include "utils/rel.h"
 #include "utils/syscache.h"
 
@@ -93,7 +94,7 @@ PG_FUNCTION_INFO_V1(file_fdw_validator);
 /*
  * FDW callback routines
  */
-static FdwPlan *filePlanForeignScan(Oid foreigntableid,
+static void filePlanForeignScan(Oid foreigntableid,
 					PlannerInfo *root,
 					RelOptInfo *baserel);
 static void fileExplainForeignScan(ForeignScanState *node, ExplainState *es);
@@ -406,27 +407,44 @@ get_file_fdw_attribute_options(Oid relid)
 
 /*
  * filePlanForeignScan
- *		Create a FdwPlan for a scan on the foreign table
+ *		Create possible access paths for a scan on the foreign table
+ *
+ *		Currently we don't support any push-down feature, so there is only one
+ *		possible access path, which simply returns all records in the order in
+ *		the data file.
  */
-static FdwPlan *
+static void
 filePlanForeignScan(Oid foreigntableid,
 					PlannerInfo *root,
 					RelOptInfo *baserel)
 {
-	FdwPlan    *fdwplan;
 	char	   *filename;
 	List	   *options;
+	Cost		startup_cost;
+	Cost		total_cost;
 
 	/* Fetch options --- we only need filename at this point */
 	fileGetOptions(foreigntableid, &filename, &options);
 
-	/* Construct FdwPlan with cost estimates */
-	fdwplan = makeNode(FdwPlan);
+	/* Estimate costs and update baserel->rows */
 	estimate_costs(root, baserel, filename,
-				   &fdwplan->startup_cost, &fdwplan->total_cost);
-	fdwplan->fdw_private = NIL; /* not used */
+				   &startup_cost, &total_cost);
+
+	/* Create a ForeignPath node and add it as only possible path */
+	add_path(baserel, (Path *)
+			 create_foreignscan_path(root, baserel,
+									 baserel->rows,
+									 startup_cost,
+									 total_cost,
+									 NIL, /* no pathkeys */
+									 NULL, /* no outer rel either */
+									 NIL,
+									 NIL)); /* no fdw_private data */
 
-	return fdwplan;
+	/*
+	 * If data file was sorted, and we knew it somehow, we could insert
+	 * appropriate pathkeys into the ForeignPath node to tell the planner that.
+	 */
 }
 
 /*
@@ -576,6 +594,9 @@ fileReScanForeignScan(ForeignScanState *node)
 
 /*
  * Estimate costs of scanning a foreign table.
+ *
+ * In addition to setting *startup_cost and *total_cost, this should
+ * update baserel->rows.
  */
 static void
 estimate_costs(PlannerInfo *root, RelOptInfo *baserel,