Cache table AM in Chunk struct

src/chunk.c

@@ -1620,6 +1620,7 @@ chunk_tuple_found(TupleInfo *ti, void *arg)
 	chunk->hypertable_relid = ts_hypertable_id_to_relid(chunk->fd.hypertable_id, false);
 
 	chunk->relkind = get_rel_relkind(chunk->table_id);
+	chunk->amoid = ts_get_rel_am(chunk->table_id);
 
 	Ensure(chunk->relkind > 0,
 		   "relkind for chunk \"%s\".\"%s\" is invalid",

src/chunk.h

@@ -66,6 +66,7 @@ typedef struct Chunk
 	char relkind;
 	Oid table_id;
 	Oid hypertable_relid;
+	Oid amoid; /* Table access method used by chunk */
 
 	/*
 	 * The hypercube defines the chunks position in the N-dimensional space.

src/utils.c

@@ -1748,3 +1748,25 @@ ts_update_placeholder(PG_FUNCTION_ARGS)
 	elog(ERROR, "this stub function is used only as placeholder during extension updates");
 	PG_RETURN_NULL();
 }
+
+/*
+ * Get the table access method Oid for a relation.
+ */
+Oid
+ts_get_rel_am(Oid relid)
+{
+	HeapTuple tuple;
+	Form_pg_class cform;
+	Oid amoid;
+
+	tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
+
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for relation %u", relid);
+
+	cform = (Form_pg_class) GETSTRUCT(tuple);
+	amoid = cform->relam;
+	ReleaseSysCache(tuple);
+
+	return amoid;
+}

src/utils.h

@@ -371,3 +371,5 @@ ts_datum_set_objectid(const AttrNumber attno, NullableDatum *datums, const Oid v
 	else
 		datums[AttrNumberGetAttrOffset(attno)].isnull = true;
 }
+
+extern Oid ts_get_rel_am(Oid relid);