paxos-store

Practice on implementing paxos to realize fault-tolerant consensus amongst replicated servers.

I. Overview

This program builds upon RMI for client-server connections as well as Paxos operations. In the Paxos implementation, there are three entities/classes:

• Proposer: Receive requests from client and try to convince acceptors to accept the proposed values
• Acceptor: Accept certain proposed values from proposers and let proposers know if something else was accepted. A response from an acceptor represents a vote for a particular proposal.
• Learner: Announce the outcome and commit the final result.

During each request process, two phase are involved:

• Basically, the proposer interacts with the acceptors twice.
• In the Phase 1, a proposer asks all the working acceptors whether anyone already received a proposal. If the answer is no, propose a value.
• In the Phase 2, if a majority of acceptors agree to this value then that is consensus.

II. Implementation

Paxos Implementation:

• Proposer, Acceptor and Learner are implemented for paxos operations.
• 5 Server Class Server1 ~ Server5 are 5 servers running and processing requests as the kv store.
• User could select which server is the proposer via command, e.g., java -classpath paxos_store.jar Client localhost Server3. In this case, Server3 is the proposer.
• All paxos-based processes are displayed in the server log started with >>>

Acceptor Fault Tolerance:

• In the Proposer Class, fault testing functions has been implemented.
• For every 20 times process, a server would be shunt down (thread.sleep()) for 200 ms. Every server thread shares the same chance to sleep.
• SocketetTimeOut are used to continued the operation.
• Please check logs like ERR-FALT-TOLERANT-TEST: Server [1] has shut down for 200 milliseconds. in each server's log.

Others:

• Config file set a few basic constants for the program, such as server ports (8080~8084)

III. Testing

• Run 5 servers in 5 different terminal:

Terminal 1: java -classpath paxos_store.jar Server1
Terminal 2: java -classpath paxos_store.jar Server2
Terminal 3: java -classpath paxos_store.jar Server3
Terminal 4: java -classpath paxos_store.jar Server4
Terminal 5: java -classpath paxos_store.jar Server5

• Run Client in the 6th terminal, you could randomly select a server from Server1 to Server5 as the second argument

Terminal 6: java -classpath paxos_store.jar Client Server3

• Waiting for testing results, and then type in commands manually for further testing.