Concurrency and dynamic protocol update for group communication middleware

The last three decades have seen computers invading our society: computers are now present at work to improve productivity and at home to enlarge the scope of our hobbies and to communicate. Furthermore, computers have been involved in many critical systems such as anti-locking braking systems (ABS) in our cars, airplane control systems, space rockets, nuclear power plants, banking and trading systems, medical care systems, and so on. The importance of these systems requires a high level of trust in computer-based systems. For example, a failure in a trading system (even if it is temporary) may result in severe economical losses. Hence coping with failures is a key aspect of computer systems. A common approach to tolerate failures is to replicate a system that provides a critical service, so that once a failure occurs on a given replica, the requests to the critical service are still executed by other replicas. This approach has the advantage of masking failures, i.e., requests to the service are continuously executed even in the presence of failures. However, replication introduces a performance cost, mainly because the execution of the service requests must be coordinated among all replicas. Furthermore, despite its apparent simplicity, replication is rather complex to implement. Replication is made easier by group communication which defines several abstractions that can be used by the designer of replicated systems. The group communication abstractions are implemented by distributed protocols that compose a group communication middleware. The aim of the thesis is to study two techniques to improve the performance of group communication middleware, and thus, reduce the cost of replication. First, we study dynamic protocol update, which allows group communication middleware to adapt to environment changes. More particularly, dynamic protocol update consists in replacing at runtime a given protocol composing the group communication middleware with a similar but more efficient protocol. The thesis provides several solutions to dynamic protocol update. For instance, we describe two algorithms to dynamically replace consensus and atomic broadcast, two essential protocols of a group communication middleware. Second, we propose solutions to introduce concurrency within a group communication middleware in order to benefit from the advantages offered by multiprocessor (or multicore) computers

On the Cost of Modularity in Atomic Broadcast

Modularity is a desirable property of complex software systems, since it simplifies code reuse, verification, maintenance, etc. However, the use of loosely coupled modules introduces a performance overhead. This overhead is often considered negligible, but this is not always the case. This paper aims at casting some light on the cost, in terms of performance, that is incurred when designing a relevant group communication protocol with modularity in mind: atomic broadcast. We conduct our experiments using two versions of atomic broadcast: a modular version and a monolithic one. We then measure the performance of both implementations under different system loads. Our results show that the overhead introduced by modularity is strongly related to the level of stress to which the system is subjected, and in the worst cases, reaches approximately 50%

Generic construction of consensus algorithms for benign and Byzantine faults

The paper proposes a generic consensus algorithm that highlights the basic and common features of known consensus algorithms. The parameters of the generic algorithm encapsulate the core differences between various consensus algorithms, including leader-based and leader-free algorithms, addressing benign faults, authenticated Byzantine faults and Byzantine faults. This leads to the identification of three classes of consensus algorithms. With the proposed classification, Paxos and PBFT indeed belong to the same class, while FaB Paxos belongs to a different class. Interestingly, the classification allowed us to identify a new Byzantine consensus algorithm that requires n>4b, where b is the maximum number of Byzantine processes

Structural and Algorithmic Issues of Dynamic Protocol Update

In this paper, we study dynamic protocol update (DPU). Contrary to local code updates on-the-fly, DPU requires global coordination of local code replacements. We propose a novel solution to DPU. The key idea is to add a level of indirection between the service callers and the service provider. This indirection level facilitates implementation of simple and efficient algorithms for DPU. We also describe an experimental implementation of adaptable group communication middleware. It can switch between different atomic broadcast protocols on-the-fly. All middleware services, including those that depend on the updated protocols, provide service correctly and with negligible delay while the global update takes places. The switching algorithm introduces very low overhead, that we illustrate by showing example measurement results

Isoform-specific AMPK association with TBC1D1 is reduced by a mutation associated with severe obesity

AMP-activated protein kinase (AMPK) is a key regulator of cellular and systemic energy homeostasis which achieves this through the phosphorylation of a myriad of downstream targets. One target is TBC1D1 a Rab-GTPase-activating protein that regulates glucose uptake in muscle cells by integrating insulin signalling with that promoted by muscle contraction. Ser237 in TBC1D1 is a target for phosphorylation by AMPK, an event which may be important in regulating glucose uptake. Here, we show AMPK heterotrimers containing the α1, but not the α2, isoform of the catalytic subunit form an unusual and stable association with TBC1D1, but not its paralogue AS160. The interaction between the two proteins is direct, involves a dual interaction mechanism employing both phosphotyrosinebinding (PTB) domains of TBC1D1 and is increased by two different pharmacological activators of AMPK (AICAR and A769962). The interaction enhances the efficiency by which AMPK phosphorylates TBC1D1 on its key regulatory site, Ser237. Furthermore, the interaction is reduced by a naturally occurring R125W mutation in the PTB1 domain of TBC1D1, previously found to be associated with severe familial obesity in females, with a concomitant reduction in Ser237 phosphorylation. Our observations provide evidence for a functional difference between AMPK α-subunits and extend the repertoire of protein kinases that interact with substrates via stabilisation mechanisms that modify the efficacy of substrate phosphorylation

Triglyceride-rich lipoproteins and high-density lipoprotein cholesterol in patients at high risk of cardiovascular disease: evidence and guidance for management

Even at low-density lipoprotein cholesterol (LDL-C) goal, patients with cardiometabolic abnormalities remain at high risk of cardiovascular events. This paper aims (i) to critically appraise evidence for elevated levels of triglyceride-rich lipoproteins (TRLs) and low levels of high-density lipoprotein cholesterol (HDL-C) as cardiovascular risk factors, and (ii) to advise on therapeutic strategies for management. Current evidence supports a causal association between elevated TRL and their remnants, low HDL-C, and cardiovascular risk. This interpretation is based on mechanistic and genetic studies for TRL and remnants, together with the epidemiological data suggestive of the association for circulating triglycerides and cardiovascular disease. For HDL, epidemiological, mechanistic, and clinical intervention data are consistent with the view that low HDL-C contributes to elevated cardiovascular risk; genetic evidence is unclear however, potentially reflecting the complexity of HDL metabolism. The Panel believes that therapeutic targeting of elevated triglycerides (≥1.7 mmol/L or 150 mg/dL), a marker of TRL and their remnants, and/or low HDL-C (<1.0 mmol/L or 40 mg/dL) may provide further benefit. The first step should be lifestyle interventions together with consideration of compliance with pharmacotherapy and secondary causes of dyslipidaemia. If inadequately corrected, adding niacin or a fibrate, or intensifying LDL-C lowering therapy may be considered. Treatment decisions regarding statin combination therapy should take into account relevant safety concerns, i.e. the risk of elevation of blood glucose, uric acid or liver enzymes with niacin, and myopathy, increased serum creatinine and cholelithiasis with fibrates. These recommendations will facilitate reduction in the substantial cardiovascular risk that persists in patients with cardiometabolic abnormalities at LDL-C goal

Service Interface: A New Abstraction for Implementing and Composing Protocols

In this paper we compare two approaches to the design of protocol frameworks – tools for implementing modular network protocols. The most common approach uses events as the main abstraction for a local interaction between protocol modules. We argue that an alternative approach, that is based on service abstraction, is more suitable for expressing modular protocols. It also facilitates advanced features in the design of protocols, such as dynamic update of distributed protocols. We then describe an experimental implementation of a service-based protocol framework in Java