postgres_fdw: Avoid 'variable not found in subplan target list' error.

The tlist of the EvalPlanQual outer plan for a ForeignScan node is
adjusted to produce a tuple whose descriptor matches the scan tuple slot
for the ForeignScan node.  But in the case where the outer plan contains
an extra Sort node, if the new tlist contained columns required only for
evaluating PlaceHolderVars or columns required only for evaluating local
conditions, this would cause setrefs.c to fail with the error.

The cause of this is that when creating the outer plan by injecting the
Sort node into an alternative local join plan that could emit such extra
columns as well, we fail to arrange for the outer plan to propagate them
up through the Sort node, causing setrefs.c to fail to match up them in
the new tlist to what is available from the outer plan.  Repair.

Per report from Alexander Pyhalov.

Richard Guo and Etsuro Fujita, reviewed by Alexander Pyhalov and Tom Lane.
Backpatch to all supported versions.

Discussion: http://postgr.es/m/cfb17bf6dfdf876467bd5ef533852d18%40postgrespro.ru

1 files changed, 49 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 16320170cee..b76818f7fdb 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -5784,6 +5784,55 @@ add_paths_with_pathkeys_for_rel(PlannerInfo *root, RelOptInfo *rel,
 
 	useful_pathkeys_list = get_useful_pathkeys_for_relation(root, rel);
 
+	/*
+	 * Before creating sorted paths, arrange for the passed-in EPQ path, if
+	 * any, to return columns needed by the parent ForeignScan node so that
+	 * they will propagate up through Sort nodes injected below, if necessary.
+	 */
+	if (epq_path != NULL && useful_pathkeys_list != NIL)
+	{
+		PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+		PathTarget *target = copy_pathtarget(epq_path->pathtarget);
+
+		/* Include columns required for evaluating PHVs in the tlist. */
+		add_new_columns_to_pathtarget(target,
+									  pull_var_clause((Node *) target->exprs,
+													  PVC_RECURSE_PLACEHOLDERS));
+
+		/* Include columns required for evaluating the local conditions. */
+		foreach(lc, fpinfo->local_conds)
+		{
+			RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
+
+			add_new_columns_to_pathtarget(target,
+										  pull_var_clause((Node *) rinfo->clause,
+														  PVC_RECURSE_PLACEHOLDERS));
+		}
+
+		/*
+		 * If we have added any new columns, adjust the tlist of the EPQ path.
+		 *
+		 * Note: the plan created using this path will only be used to execute
+		 * EPQ checks, where accuracy of the plan cost and width estimates
+		 * would not be important, so we do not do set_pathtarget_cost_width()
+		 * for the new pathtarget here.  See also postgresGetForeignPlan().
+		 */
+		if (list_length(target->exprs) > list_length(epq_path->pathtarget->exprs))
+		{
+			/* The EPQ path is a join path, so it is projection-capable. */
+			Assert(is_projection_capable_path(epq_path));
+
+			/*
+			 * Use create_projection_path() here, so as to avoid modifying it
+			 * in place.
+			 */
+			epq_path = (Path *) create_projection_path(root,
+													   rel,
+													   epq_path,
+													   target);
+		}
+	}
+
 	/* Create one path for each set of pathkeys we found above. */
 	foreach(lc, useful_pathkeys_list)
 	{