Revisiting the Paxos algorithm

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 138-142).by Roberto de Prisco.M.S

From Formal Methods to Executable Code

Note: the cover page of this report shows an incorrect title. The title given on the first page of the document itself is correct.The objective of this work is the derivation of software that is verifiably correct. Our approach is to abstract system specifications and model these in a formal framework called Timed Input/Output Automata, which provides a notation for expressing distributed systems and mathematical support for reasoning about their properties. Although formal reasoning is easier at an abstract level, it is not clear how to transform these abstractions into executable code. During system implementation, when an abstract system specification is left up to human interpretation, then this opens a possibility of undesirable behaviors being introduced into the final code, thereby nullifying all formal efforts. This manuscript addresses this issue and presents a set of transformation methods for systems described as a network to timed automata into Java code for distributed platforms. We prove that the presented transformation methods preserve guarantees of the source specifications, and therefore, result in code that is correct by construction

Generalized Paxos Made Byzantine (and Less Complex)

One of the most recent members of the Paxos family of protocols is Generalized Paxos. This variant of Paxos has the characteristic that it departs from the original specification of consensus, allowing for a weaker safety condition where different processes can have a different views on a sequence being agreed upon. However, much like the original Paxos counterpart, Generalized Paxos does not have a simple implementation. Furthermore, with the recent practical adoption of Byzantine fault tolerant protocols, it is timely and important to understand how Generalized Paxos can be implemented in the Byzantine model. In this paper, we make two main contributions. First, we provide a description of Generalized Paxos that is easier to understand, based on a simpler specification and the pseudocode for a solution that can be readily implemented. Second, we extend the protocol to the Byzantine fault model

Consensus on Transaction Commit

The distributed transaction commit problem requires reaching agreement on whether a transaction is committed or aborted. The classic Two-Phase Commit protocol blocks if the coordinator fails. Fault-tolerant consensus algorithms also reach agreement, but do not block whenever any majority of the processes are working. Running a Paxos consensus algorithm on the commit/abort decision of each participant yields a transaction commit protocol that uses 2F +1 coordinators and makes progress if at least F +1 of them are working. In the fault-free case, this algorithm requires one extra message delay but has the same stable-storage write delay as Two-Phase Commit. The classic Two-Phase Commit algorithm is obtained as the special F = 0 case of the general Paxos Commit algorithm.Comment: Original at http://research.microsoft.com/research/pubs/view.aspx?tr_id=70

Performance comparison between the Paxos and Chandra-Toueg consensus algorithms

Protocols which solve agreement problems are essential building blocks for fault tolerant distributed applications. While many protocols have been published, little has been done to analyze their performance. This paper represents a starting point for such studies, by focusing on the consensus problem, a problem related to most other agreement problems. The paper compares the latency of two consensus algorithms designed for the asynchronous model with failure detectors: the Paxos algorithm and the Chandra-Toueg algorithm. We varied the number of processes which take part in the execution. Moreover, we evaluated the latency in different classes of runs: (1) runs with no failures nor failure suspicions, (2) runs with failures but no wrong suspicions. We determined the latency by measurements on a cluster of PCs interconnected with a 100 Mbps Ethernet network. We found that the Paxos algorithm is more efficient than the Chandra-Toueg algorithm when the process that coordinates the first round of the protocol crashes. The two algorithms have almost the same performance in all other cases