Publications by Rachid Guerraoui

Asynchronous Byzantine Machine Learning (the case of SGD)

Rachid Guerraoui, El Mahdi El Mhamdi, Rhicheek Patra, Mahsa Taziki, Georgios Damaskinos

Asynchronous distributed machine learning solutions have proven very effective so far, but always assuming perfectly functioning workers. In practice, some of the workers can however exhibit Byzantine behavior, caused by hardware failures, software bugs, c ...

2018

TM 2 C: a software transactional memory for many-cores

Rachid Guerraoui, Vincent Gramoli, Vasileios Trigonakis

2018

The entropy of a distributed computation random number generation from memory interleaving

Patrick Blanchard, Rachid Guerraoui, Karolos Antoniadis, Julien Michel Stainer

2018

Locking Timestamps versus Locking Objects

Rachid Guerraoui, Tudor Alexandru David, Junxiong Wang

We present multiversion timestamp locking (MVTL), a new genre of multiversion concurrency control algorithms for serializable transactions. The key idea behind MVTL is simple: lock individual timestamps instead of locking objects. After presenting a generi ...

ASSOC COMPUTING MACHINERY2018

Causal Consistency and Latency Optimality: Friend or Foe? [Extended Version]

Rachid Guerraoui, Willy Zwaenepoel, Junxiong Wang, Diego Didona

Causal consistency is an attractive consistency model for geo-replicated data stores. It is provably the strongest model that tolerates network partitions. It avoids the long latencies associated with strong consistency, and, especially when using read-onl ...

2018

Log-Free Concurrent Data Structures

Rachid Guerraoui, Aleksandar Dragojevic, Mihail Igor Zablotchi, Tudor Alexandru David

Non-volatile RAM (NVRAM) makes it possible for data structures to tolerate transient failures, assuming however that programmers have designed these structures such that their consistency is preserved upon recovery. Previous ap- proaches are typically tran ...

USENIX Association2018

State Machine Replication is More Expensive than Consensus

Rachid Guerraoui, Karolos Antoniadis, Dragos-Adrian Seredinschi

Consensus and State Machine Replication (SMR) are generally considered to be equivalent problems. In certain system models, indeed, the two problems are computationally equivalent: any solution to the former problem leads to a solution to the latter, and v ...

2018

Causal Consistency and Latency Optimality: Friend or Foe?

Rachid Guerraoui, Willy Zwaenepoel, Junxiong Wang, Diego Didona

Causal consistency is an attractive consistency model for geo-replicated data stores. It is provably the strongest model that tolerates network partitions. It avoids the long latencies associated with strong consistency, and, especially when using read-onl ...

ASSOC COMPUTING MACHINERY2018

The Inherent Cost of Remembering Consistently

Rachid Guerraoui, Mihail Igor Zablotchi, Nachshon Cohen

Non-volatile memory (NVM) promises fast, byte-addressable and durable storage, with raw access latencies in the same order of magnitude as DRAM. But in order to take advantage of the durability of NVM, programmers need to design persistent objects which ma ...

2018

On the Unfairness of Blockchain

Rachid Guerraoui, Junxiong Wang

The success of Bitcoin largely relies on the perception of a fair underlying peer-to-peer protocol: blockchain. Fairness here essentially means that the reward (in bitcoins) given to any participant that helps maintain the consistency of the protocol by mi ...

Springer2018

Passing Messages while Sharing Memory

Rachid Guerraoui, Naama Ben David

We introduce a new distributed computing model called m&m that allows processes to both pass messages and share memory. Motivated by recent hardware trends, we find that this model improves the power of the pure message-passing and shared-memory models. As ...

ASSOC COMPUTING MACHINERY2018

Personalized and Private Peer-to-Peer Machine Learning

Rachid Guerraoui, Mahsa Taziki

2018

Collaborative Filtering Under a Sybil Attack: Similarity Metrics do Matter!

Rachid Guerraoui, Anne-Marie Kermarrec, Antoine Rault, Florestan Laurentin Marie De Moor, Davide Frey

Recommendation systems help users identify interesting content, but they also open new privacy threats. In this paper, we deeply analyze the effect of a Sybil attack that tries to infer information on users from a user-based collaborative-filtering recomme ...

IEEE2018

The Hidden Vulnerability of Distributed Learning in Byzantium

Rachid Guerraoui, El Mahdi El Mhamdi, Sébastien Louis Alexandre Rouault

While machine learning is going through an era of celebrated success, concerns have been raised about the vulnerability of its backbone: stochastic gradient descent (SGD). Recent approaches have been proposed to ensure the robustness of distributed SGD aga ...

2018

Monotonic Prefix Consistency in Distributed Systems

Rachid Guerraoui, Jad Hamza, Dragos-Adrian Seredinschi

We study the issue of data consistency in distributed systems. Specifically, we consider a distributed system that replicates its data at multiple sites, which is prone to partitions, and which is assumed to be available (in the sense that queries are alwa ...

2018

Distributed Transactions: Dissecting the Nightmare

Rachid Guerraoui, Willy Zwaenepoel, Junxiong Wang, Diego Didona

Many distributed storage systems are transactional and a lot of work has been devoted to optimizing their performance, especially the performance of read-only transactions that are considered the most frequent in practice. Yet, the results obtained so far ...

2018

On the Unfairness of Blockchain

Rachid Guerraoui, Junxiong Wang

The success of Bitcoin largely relies on the perception of a fair underlying peer-to-peer protocol: blockchain. Fairness here essentially means that the reward (in bitcoins) given to any participant that helps maintain the consistency of the protocol by mi ...

2018

The Inherent Cost of Remembering Consistently

Rachid Guerraoui, Mihail Igor Zablotchi, Nachshon Cohen

Non-volatile memory (NVM) promises fast, byte-addressable and durable storage, with raw access latencies in the same order of magnitude as DRAM. But in order to take advantage of the durability of NVM, programmers need to design persistent objects which ma ...

2018

Log-Free Concurrent Data Structures

Rachid Guerraoui, Aleksandar Dragojevic, Mihail Igor Zablotchi, Tudor Alexandru David

Non-volatile RAM (NVRAM) makes it possible for data structures to tolerate transient failures, assuming however that programmers have designed these structures such that their consistency is preserved upon recovery. Previous approaches are typically transa ...

USENIX ASSOC2018

ESTIMA: Extrapolating ScalabiliTy of In-Memory Applications

Rachid Guerraoui, Aleksandar Dragojevic, Georgios Chatzopoulos

This article presents ESTIMA, an easy-to-use tool for extrapolating the scalability of in-memory applications. ESTIMA is designed to perform a simple yet important task: Given the performance of an application on a small machine with a handful of cores, ES ...

2017