Publications by Rachid Guerraoui

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Neural networks have been traditionally considered robust in the sense that their precision degrades gracefully with the failure of neurons and can be compensated by additional learning phases. Nevertheless, critical applications for which neural networks ...

Byzantine agreement enables n processes to agree on a common L-bit value, despite up to t > 0 arbitrary failures. A long line of work has been dedicated to improving the bit complexity of Byzantine agreement in synchrony. This has culminated in COOL, an er ...

When devising a distributed agreement algorithm, it is common to minimize the time complexity of global decisions, which is typically measured as the number of communication rounds needed for all correct processes to decide. In practice, what we might want to minimize is the time complexity of local decisions, which we define as the number of communication rounds needed for at least one correct process to decide. The motivation of this paper is to figure out whether there is any difference between local and

Gossip-based protocols have proven very efficient for disseminating high-bandwidth content such as video streams in a peer-to-peer fashion. However, for the protocols to work, nodes are required to collaborate by devoting a fraction of their upload bandwid ...

Concurrent implementations of abstract types usually rely on lock-free primitives or locks and are highly tuned to support a finite set of efficient operations. However, it is very hard to extend such types for specific needs by adding new operations. The synchronization based on memory transactions, which is generally less efficient than based on lock-free primitives or locks, has been proposed in part to address this issue by ensuring that any set of transactional operations can run concurrently. This pap

Gossip protocols (also called rumor spreading or epidemic protocols) are widely used to disseminate information in massive peer-to-peer networks. These protocols are often claimed to guarantee privacy because of the uncertainty they introduce on the node t ...

The atomic commit problem lies at the heart of distributed database systems. The problem consists for a set of processes (database nodes) to agree on whether to commit or abort a transaction (agreement property). The commit decision can only be taken if al ...

Distributed storage algorithms implement the abstraction of a shared register over distributed base objects. We study a specific class of storage algorithms, which we call amnesic: these have the pragmatic property that old values written in the implemente ...

Log-structured merge (LSM) data stores enable to store and process large volumes of data while maintaining good performance. They mitigate the I/O bottleneck by absorbing updates in a memory layer and transferring them to the disk layer in sequential batch ...

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 ...

This paper contributes to address the fundamental challenge of building Concurrent Data Types (CDT) that are reusable and scalable at the same time. We do so by proposing the abstraction of Polymorphic Transactions (PT): a new programming abstraction that offers different compatible transactions that can run concurrently in the same application. We outline the commonality of the problem in various object-oriented languages and implement PT and a reusable package in Java. With PT, annotating sequential ADTs

The vast majority of papers on distributed computing assume that processes are assigned unique identifiers before computation begins. But is this assumption necessary? What if processes do not have unique identifiers or do not wish to divulge them for reas ...

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 ...

With the recent advent of blockchains, we have witnessed a plethora of blockchain proposals. These proposals range from using work to using time, storage or stake in order to select blocks to be appended to the chain. As a drawback it makes it difficult fo ...

Transactional memory is an appealing paradigm for concurrent programming. Many software implementations of the paradigm were proposed in the last decades for both shared memory multi-core systems and clusters of distributed machines. However, chip manufacturers have started producing many-core architectures, with low network-on-chip communication latency and limited support for cache-coherence, rendering existing transactional memory implementations inapplicable. This paper presents TM2C, the first software

The perfectly-synchronized round-based model provides the powerful abstraction of crash-stop failures with atomic and synchronous message delivery. This abstraction makes distributed programming very easy.We describe a technique to automatically transform ...

In the k-set agreement problem, each processor starts with a private input value and eventually decides on an output value. At most k distinct output values may be chosen, and every processor's output value must be one of the proposed values. We consider a ...

The growing availability of distributed data has led to the increased use of machine learning (ML) algorithms in distributed topologies, where multiple nodes collaborate to train models under the coordination of a central server. However, distributed learn ...

The ability of a peer-to-peer (P2P) system to effectively host decentralized applications often relies on the availability of a peer-sampling service, which provides each participant with a random sample of other peers. Despite the practical effectiveness of existing peer samplers, their ability to produce random samples within a reasonable time frame remains poorly understood from a theoretical standpoint. This paper contributes to bridging this gap by introducing PeerSwap, a peer-sampling protocol with pr

Many distributed applications have a strong requirement for efficient dissemination of large amounts of information to widely spread consumers in large networks. These include applications in e-commerce and telecommunication. Publish/subscribe is considered one of the most important interaction styles to model communication at large scale. Producers publish information for a topic and consumers subscribe to the topics they wish to be informed of. The decoupling of producers and consumers in time, space, and

Rachid Guerraoui

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When Neurons Fail - Technical Report

Efficient Signature-Free Validated Agreement

Early Local Decisions in Distributed Agreement

Tracking freeriders in gossip-based content dissemination systems

Transaction Polymorphism

Who Started This Rumor? Quantifying the Natural Differential Privacy of Gossip Protocols

How Fast can a Distributed Transaction Commit?

Amnesic Distributed Storage

FloDB: Unlocking Memory in Persistent Key-Value Stores

The Inherent Cost of Remembering Consistently

Reusable Concurrent Data Types

What Can Be Implemented Anonymously?

The Hidden Vulnerability of Distributed Learning in Byzantium

DIABLO: A Benchmark Suite for Blockchains

TM2C: A software transactional memory for many-cores

The Perfectly-Synchronized Round-based Model of Distributed Computing

The Complexity Of Early Deciding Set Agreement

Towards Practical Homomorphic Aggregation in Byzantine-Resilient Distributed Learning

PeerSwap: A Peer-Sampler with Randomness Guarantees

Effective Multicast Programming in Large Scale Distributed Systems