List the points of difference in the design philosophy of Chubby and Zookeeper? How Zookeeper ensures wait-freedom and event-ordering?

Chubby →

1. Strong Consistency: Chubby emphasizes strong consistency, ensuring that all clients see the same state at any given time. This is achieved through a single master server and a quorum-based approach for replication.
2. File System Interface: Chubby provides a file system-like interface, allowing clients to create, read, write, and lock files within the Chubby namespace. This makes it suitable for coordinating distributed applications that require file-like abstractions.
3. Use of Paxos for Consensus: Chubby uses the Paxos algorithm for achieving consensus among replicas. Paxos ensures that only one master is active at any given time and that updates are committed in a coordinated and consistent manner.

ZooKeeper →

1. Emphasis on Coordination: ZooKeeper focuses on providing primitives for coordination and synchronization among distributed applications. It offers a simple hierarchical namespace and a set of operations for creating, updating, and watching nodes in the namespace.
2. ZAB (ZooKeeper Atomic Broadcast) Protocol: ZooKeeper uses the ZAB protocol, which is similar to Paxos but optimized for read-heavy workloads and high throughput. ZAB ensures that updates are ordered and propagated to all replicas in a consistent manner.
3. Sequential Consistency Guarantees: ZooKeeper provides sequential consistency guarantees, ensuring that updates are applied in the order they were received. This makes it suitable for implementing distributed coordination protocols and maintaining shared state across distributed systems.

ZooKeeper’s Approach to Wait-Freedom and Event-Ordering:

1. Wait-Freedom: ZooKeeper ensures wait-freedom by providing bounded response times for all operations, regardless of the number of clients or the state of the system. This is achieved through the use of efficient algorithms and data structures, as well as careful system design to minimize contention and latency.
2. Event-Ordering: ZooKeeper guarantees event-ordering by maintaining a strict order of operations within the system. Clients can register watches on nodes in the ZooKeeper namespace, and they receive notifications in the order that changes occur. This ensures that clients can observe consistent and predictable behavior, even in the presence of concurrent updates and failures.