Allow pushdown of reference table joins

CHANGELOG.md

@@ -42,6 +42,7 @@ Sooner to that time, we will announce the specific version of TimescaleDB in whi
 * #5262 Extend enabling compression on a continuous aggregrate with 'compress_segmentby' and 'compress_orderby' parameters
 * #5343 Set PortalContext when starting job
 * #5312 Add timeout support to the ping_data_node()
+* #5212 Allow pushdown of reference table joins 
 
 **Bugfixes**
 * #5214 Fix use of prepared statement in async module

src/cross_module_fn.c

@@ -402,6 +402,13 @@ ts_tsl_loaded(PG_FUNCTION_ARGS)
 	PG_RETURN_BOOL(ts_cm_functions != &ts_cm_functions_default);
 }
 
+static void
+mn_get_foreign_join_path_default_fn_pg_community(PlannerInfo *root, RelOptInfo *joinrel,
+												 RelOptInfo *outerrel, RelOptInfo *innerrel,
+												 JoinType jointype, JoinPathExtraData *extra)
+{
+}
+
 /*
  * Define cross-module functions' default values:
  * If the submodule isn't activated, using one of the cm functions will throw an
@@ -555,6 +562,7 @@ TSDLLEXPORT CrossModuleFunctions ts_cm_functions_default = {
 	.hypertable_distributed_set_replication_factor = error_no_default_fn_pg_community,
 	.update_compressed_chunk_relstats = update_compressed_chunk_relstats_default,
 	.health_check = error_no_default_fn_pg_community,
+	.mn_get_foreign_join_paths = mn_get_foreign_join_path_default_fn_pg_community,
 };
 
 TSDLLEXPORT CrossModuleFunctions *ts_cm_functions = &ts_cm_functions_default;

src/cross_module_fn.h

@@ -203,6 +203,9 @@ typedef struct CrossModuleFunctions
 	PGFunction chunks_drop_stale;
 	void (*update_compressed_chunk_relstats)(Oid uncompressed_relid, Oid compressed_relid);
 	PGFunction health_check;
+	void (*mn_get_foreign_join_paths)(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel,
+									  RelOptInfo *innerrel, JoinType jointype,
+									  JoinPathExtraData *extra);
 } CrossModuleFunctions;
 
 extern TSDLLEXPORT CrossModuleFunctions *ts_cm_functions;

src/planner/planner.c

@@ -110,6 +110,7 @@ void _planner_fini(void);
 
 static planner_hook_type prev_planner_hook;
 static set_rel_pathlist_hook_type prev_set_rel_pathlist_hook;
+static set_join_pathlist_hook_type prev_set_join_pathlist_hook;
 static get_relation_info_hook_type prev_get_relation_info_hook;
 static create_upper_paths_hook_type prev_create_upper_paths_hook;
 static void cagg_reorder_groupby_clause(RangeTblEntry *subq_rte, Index rtno, List *outer_sortcl,
@@ -1662,13 +1663,36 @@ cagg_reorder_groupby_clause(RangeTblEntry *subq_rte, Index rtno, List *outer_sor
 	}
 }
 
+/* Register our join pushdown hook. Becuase for PostgreSQL the tables we are operating
+ * on are local tables. So, the FDW hooks are not called. Register our join path
+ * generation as a generic planer hook.
+ */
+
+static void
+timescaledb_set_join_pathlist_hook(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel,
+								   RelOptInfo *innerrel, JoinType jointype,
+								   JoinPathExtraData *extra)
+{
+	/* Left table has to be a distributed hypertable */
+	TimescaleDBPrivate *outerrel_private = outerrel->fdw_private;
+	if (outerrel_private != NULL && outerrel_private->fdw_relation_info != NULL)
+		ts_cm_functions
+			->mn_get_foreign_join_paths(root, joinrel, outerrel, innerrel, jointype, extra);
+
+	/* Call next hook in chain */
+	if (prev_set_join_pathlist_hook != NULL)
+		(*prev_set_join_pathlist_hook)(root, joinrel, outerrel, innerrel, jointype, extra);
+}
+
 void
 _planner_init(void)
 {
 	prev_planner_hook = planner_hook;
 	planner_hook = timescaledb_planner;
 	prev_set_rel_pathlist_hook = set_rel_pathlist_hook;
+	prev_set_join_pathlist_hook = set_join_pathlist_hook;
 	set_rel_pathlist_hook = timescaledb_set_rel_pathlist;
+	set_join_pathlist_hook = timescaledb_set_join_pathlist_hook;
 
 	prev_get_relation_info_hook = get_relation_info_hook;
 	get_relation_info_hook = timescaledb_get_relation_info_hook;
@@ -1682,6 +1706,7 @@ _planner_fini(void)
 {
 	planner_hook = prev_planner_hook;
 	set_rel_pathlist_hook = prev_set_rel_pathlist_hook;
+	set_join_pathlist_hook = prev_set_join_pathlist_hook;
 	get_relation_info_hook = prev_get_relation_info_hook;
 	create_upper_paths_hook = prev_create_upper_paths_hook;
 }