Don't test for system columns on join relations

create_foreignscan_plan needs to know whether any system columns are
requested from a relation (this flag is needed by ForeignNext during
execution).  However, for join relations this is a pointless test,
because it's not possible to request system columns from them, so
remove the check.

Author: Etsuro Fujita
Discussion: http://www.postgresql.org/message-id/56AA0FC5.9000207@lab.ntt.co.jp
Reviewed-by: David Rowley, Robert Haas

src/backend/optimizer/plan/createplan.c

@@ -2099,10 +2099,7 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 	RelOptInfo *rel = best_path->path.parent;
 	Index		scan_relid = rel->relid;
 	Oid			rel_oid = InvalidOid;
-	Bitmapset  *attrs_used = NULL;
 	Plan	   *outer_plan = NULL;
-	ListCell   *lc;
-	int			i;
 
 	Assert(rel->fdwroutine != NULL);
 
@@ -2180,36 +2177,48 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 	}
 
 	/*
-	 * Detect whether any system columns are requested from rel.  This is a
-	 * bit of a kluge and might go away someday, so we intentionally leave it
-	 * out of the API presented to FDWs.
-	 *
-	 * First, examine all the attributes needed for joins or final output.
-	 * Note: we must look at reltargetlist, not the attr_needed data, because
-	 * attr_needed isn't computed for inheritance child rels.
+	 * If rel is a base relation, detect whether any system columns are
+	 * requested from the rel.  (If rel is a join relation, rel->relid will be
+	 * 0, but there can be no Var with relid 0 in the reltargetlist or the
+	 * restriction clauses, so we skip this in that case.  Note that any such
+	 * columns in base relations that were joined are assumed to be contained
+	 * in fdw_scan_tlist.)  This is a bit of a kluge and might go away someday,
+	 * so we intentionally leave it out of the API presented to FDWs.
 	 */
-	pull_varattnos((Node *) rel->reltargetlist, rel->relid, &attrs_used);
-
-	/* Add all the attributes used by restriction clauses. */
-	foreach(lc, rel->baserestrictinfo)
+	scan_plan->fsSystemCol = false;
+	if (scan_relid > 0)
 	{
-		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+		Bitmapset  *attrs_used = NULL;
+		ListCell   *lc;
+		int			i;
 
-		pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used);
-	}
+		/*
+		 * First, examine all the attributes needed for joins or final output.
+		 * Note: we must look at reltargetlist, not the attr_needed data,
+		 * because attr_needed isn't computed for inheritance child rels.
+		 */
+		pull_varattnos((Node *) rel->reltargetlist, scan_relid, &attrs_used);
 
-	/* Now, are any system columns requested from rel? */
-	scan_plan->fsSystemCol = false;
-	for (i = FirstLowInvalidHeapAttributeNumber + 1; i < 0; i++)
-	{
-		if (bms_is_member(i - FirstLowInvalidHeapAttributeNumber, attrs_used))
+		/* Add all the attributes used by restriction clauses. */
+		foreach(lc, rel->baserestrictinfo)
 		{
-			scan_plan->fsSystemCol = true;
-			break;
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+			pull_varattnos((Node *) rinfo->clause, scan_relid, &attrs_used);
 		}
-	}
 
-	bms_free(attrs_used);
+		/* Now, are any system columns requested from rel? */
+		for (i = FirstLowInvalidHeapAttributeNumber + 1; i < 0; i++)
+		{
+			if (bms_is_member(i - FirstLowInvalidHeapAttributeNumber, attrs_used))
+			{
+				scan_plan->fsSystemCol = true;
+				break;
+			}
+		}
+
+		bms_free(attrs_used);
+	}
 
 	return scan_plan;
 }