Three-phase commit protocol | EPFL Graph Search

In computer networking and databases, the three-phase commit protocol (3PC) is a distributed algorithm which lets all nodes in a distributed system agree to commit a transaction. It is a more failure-resilient refinement of the two-phase commit protocol (2PC). Motivation A two-phase commit protocol cannot dependably recover from a failure of both the coordinator and a cohort member during the Commit phase. If only the coordinator had failed, and no cohort members had received a commit message, it could safely be inferred that no commit had happened. If, however, both the coordinator and a cohort member failed, it is possible that the failed cohort member was the first to be notified, and had actually done the commit. Even if a new coordinator is selected, it cannot confidently proceed with the operation until it has received an agreement from all cohort members, and hence must block until all cohort members respond. The three-phase commit protocol eliminates this problem

The Complexity of Reliable and Secure Distributed Transactions

Junxiong Wang

The use of transactions in distributed systems dates back to the 70's. The last decade has also seen the proliferation of transactional systems. In the existing transactional systems, many protocols employ a centralized approach in executing a distributed transaction where one single process coordinates the participants of a transaction. The centralized approach is usually straightforward and efficient in the failure-free setting, yet the coordinator then turns to be a single point of failure, undermining reliability/security in the failure-prone setting, or even be a performance bottleneck in practice. In this dissertation, we explore the complexity of decentralized solutions for reliable and secure distributed transactions, which do not use a distinguished coordinator or use the coordinator as little as possible. We show that for some problems in reliable distributed transactions, there are decentralized solutions that perform as efficiently as the classical centralized one, while for some others, we determine the complexity limitations by proving lower and upper bounds to have a better understanding of the state-of-the-art solutions. We first study the complexity on two aspects of reliable transactions: atomicity and consistency. More specifically, we do a systematic study on the time and message complexity of non-blocking atomic commit of a distributed transaction, and investigate intrinsic limitations of causally consistent transactions. Our study of distributed transaction commit focuses on the complexity of the most frequent executions in practice, i.e., failure-free, and willing to commit. Through our systematic study, we close many open questions like the complexity of synchronous non-blocking atomic commit. We also present an effective protocol which solves what we call indulgent atomic commit that tolerates practical distributed database systems which are synchronous "most of the time", and can perform as efficiently as the two-phase commit protocol widely used in distributed database systems. Our investigation of causal transactions focuses on the limitations of read-only transactions, which are considered the most frequent in practice. We consider "fast" read-only transactions where operations are executed within one round-trip message exchange between a client seeking an object and the server storing it (in which no process can be a coordinator). We show two impossibility results regarding "fast" read-only transactions. By our impossibility results, when read-only transactions are "fast", they have to be "visible", i.e., they induce inherent updates on the servers. We also present a "fast" read-only transaction protocol that is "visible" as an upper bound on the complexity of inherent updates. We then study the complexity of secure transactions in the model of secure multiparty computation: even in the face of malicious parties, no party obtains the computation result unless all other parties obtain the same result. As it is impossible to achieve without any trusted party, we focus on optimism where if all parties are honest, they can obtain the computation result without resorting to a trusted third party, and the complexity of every optimistic execution where all parties are honest. We prove a tight lower bound on the message complexity by relating the number of messages to the length of the permutation sequence in combinatorics, a necessary pattern for messages in every optimistic execution.

EPFL2018

Non Blocking Atomic Commitment with an Unreliable Failure Detector

Rachid Guerraoui, André Schiper

In a transactional system, an {\em atomic commitment} protocol ensures that for any transaction, all {\em Data Manager} processes agree on the same outcome {\em (commit} or {\em abort)}. A {\em non-blocking atomic commitment} protocol enables an outcome to be decided at every correct process despite the failure of others. In this paper we apply, for the first time, the fundamental result of Chandra and Toueg on solving the abstract consensus problem, to non-blocking atomic commitment. More precisely, we present a non-blocking atomic commitment protocol in an asynchronous system augmented with an unreliable failure detector that can make an infinity of false failure suspicions. If no process is suspected to have failed, then our protocol is similar to a {\em three phase commit} protocol. In the case where processes are suspected, our protocol does not require any additionnal termination protocol: failure scenarios are handled within our regular protocol and are thus much simpler to manage.

1995

The Decentralized Non-Blocking Atomic Commitment Protocol

Rachid Guerraoui, André Schiper

In a transactional system, an atomic commitment protocol ensures that for any transaction, all data managers agree on the same outcome: commit or abort. A non-blocking atomic commitment protocol enables an outcome to be decided at every correct data manager despite the failure of others. It is well known that the famous Two Phase Commit protocol (2PC) is a blocking protocol, whereas the Three Phase Commit protocol (3PC) is a non-blocking protocol. Both protocols are centralized. In this paper, we discuss a Decentralized Non-Blocking Atomic Commitment protocol, named DNB-AC. In the absence of failures, the DNB-AC protocol requires the same number of steps to commit than the 2PC protocol (three steps). Performance measures show that the DNB-AC protocol is significantly faster that the 3PC and, in the case of a broadcast network, is almost as efficient as the 2PC. The DNB-AC protocol uses a uniform consensus protocol as a termination protocol. Using the recent results by Chandra and Toueg on solving consensus in an asynchronous system augmented with unreliable failure detectors, we give a precise characterization of the liveness of DNB-AC. We show that DNB-AC is non-blocking when a majority of data managers are correct and the failure detector is of class

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1995

The Decentralized Non-Blocking Atomic Commitment Protocol

Rachid Guerraoui, André Schiper

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1995