Since the two branches of the UNION produce disjoint sets, do a UNION…

… ALL

 so as to eliminate the need for a sort/eliminate duplicates step.

physical/postgresql/postgresql.go

@@ -96,7 +96,7 @@ func NewPostgreSQLBackend(conf map[string]string, logger log.Logger) (physical.B
 		get_query:    "SELECT value FROM " + quoted_table + " WHERE path = $1 AND key = $2",
 		delete_query: "DELETE FROM " + quoted_table + " WHERE path = $1 AND key = $2",
 		list_query: "SELECT key FROM " + quoted_table + " WHERE path = $1" +
-			"UNION SELECT DISTINCT substring(substr(path, length($1)+1) from '^.*?/') FROM " +
+			"UNION ALL SELECT DISTINCT substring(substr(path, length($1)+1) from '^.*?/') FROM " +
 			quoted_table + " WHERE parent_path LIKE $1 || '%'",
 		logger:     logger,
 		permitPool: physical.NewPermitPool(maxParInt),