Add support of postgres_fdw push-down.

Author: danolivo

Makefile

@@ -16,6 +16,8 @@ REGRESS =	aqo_disabled \
 			schema \
 			aqo_CVE-2020-14350
 
+fdw_srcdir = $(top_srcdir)/contrib/postgres_fdw
+PG_CPPFLAGS += -I$(libpq_srcdir) -I$(fdw_srcdir)
 EXTRA_REGRESS_OPTS=--temp-config=$(top_srcdir)/$(subdir)/conf.add
 
 DATA = aqo--1.0.sql aqo--1.0--1.1.sql aqo--1.1--1.2.sql aqo--1.2.sql

postprocessing.c

@@ -19,6 +19,7 @@
 #include "aqo.h"
 #include "access/parallel.h"
 #include "optimizer/optimizer.h"
+#include "postgres_fdw.h"
 #include "utils/queryenvironment.h"
 
 typedef struct
@@ -544,7 +545,7 @@ aqo_ExecutorEnd(QueryDesc *queryDesc)
 void
 aqo_copy_generic_path_info(PlannerInfo *root, Plan *dest, Path *src)
 {
-	bool		is_join_path;
+	bool is_join_path;
 
 	if (prev_copy_generic_path_info_hook)
 		prev_copy_generic_path_info_hook(root, dest, src);
@@ -569,6 +570,23 @@ aqo_copy_generic_path_info(PlannerInfo *root, Plan *dest, Path *src)
 		dest->path_clauses = ((JoinPath *) src)->joinrestrictinfo;
 		dest->path_jointype = ((JoinPath *) src)->jointype;
 	}
+	else if (src->type == T_ForeignPath)
+	{
+		ForeignPath *fpath = (ForeignPath *) src;
+		PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) fpath->path.parent->fdw_private;
+
+		/*
+		 * Pushed down foreign join keeps clauses in special fdw_private
+		 * structure.
+		 * I'm not sure what fpinfo structure keeps clauses for sufficient time.
+		 * So, copy clauses.
+		 */
+		dest->path_clauses = list_concat(list_copy(fpinfo->joinclauses),
+										 list_copy(fpinfo->remote_conds));
+		dest->path_clauses = list_concat(dest->path_clauses,
+										 list_copy(fpinfo->local_conds));
+		dest->path_jointype = ((JoinPath *) src)->jointype;
+	}
 	else
 	{
 		dest->path_clauses = list_concat(