<!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you 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. //-->

ZooKeeper's System Specification of TLA+

Overview

ZooKeeper's system specification of TLA+ focuses on the implementation of the Zookeeper Atomic Broadcast(ZAB) consensus protocol (or, ZAB1.0).

As is shown by the informal description of ZAB1.0, the implementation of ZAB that used in ZooKeeper production differs a lot from its original design.

We make this system specification to grasp the core logic of the ZAB's implementation especially.

The sysetm specification written in TLA+ is precise without ambiguity, and testable with existed tools like the TLC model checker. (We have done a certain scale of model checking to verify its correctness!)

The system specification can serve as the super-doc supplementing detailed system documentation for the ZooKeeper developers. It can evolve incrementally without high cost as the system develops over time, continually ensuring correctness for both the design and the implementation.

We have also made a formal specification for Fast Leader Election in Zab since ZAB 1.0 depends on FLE to complete the election phase.

If you have any question or find any problem of the specification, please contact us.