alternate build count strategy for postgres

store/datastore/sql/postgres/sql_gen.go

@@ -1,17 +1,3 @@
-// Copyright 2018 Drone.IO Inc.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
 package postgres
 
 // Lookup returns the named statement.
@@ -108,8 +94,7 @@ WHERE repo_active = true
 `
 
 var countBuilds = `
-SELECT reltuples
-FROM pg_class WHERE relname = 'builds'
+SELECT currval('builds_build_id_seq');
 `
 
 var feedLatestBuild = `