docs: function (type, opts, cb) {
              var ret;
              var ds = this.metadataDataset.from("pg_class")
                  .filter({relkind: type}).select("relname")
                  .exclude({relname: {like: this.SYSTEM_TABLE_REGEXP}})
                  .join("pg_namespace", {oid: identifier("relnamespace")});
              ds = this.__filterSchema(ds, opts);
              var m = this.outputIdentifierFunc;
              if (cb) {
                  ret = when(cb(ds));
              } else {
                  ret = ds.map(function (r) {
                      return m(r.relname);
                  });
              }
              return ret.promise();
          }