Design and Analysis of a Logless Dynamic Reconfiguration Protocol

Distributed replication systems based on the replicated state machine model have become ubiquitous as the foundation of modern database systems. To ensure availability in the presence of faults, these systems must be able to dynamically replace failed nodes with healthy ones via dynamic reconfiguration. MongoDB is a document oriented database with a distributed replication mechanism derived from the Raft protocol. In this paper, we present MongoRaftReconfig, a novel dynamic reconfiguration protocol for the MongoDB replication system. MongoRaftReconfig utilizes a logless approach to managing configuration state and decouples the processing of configuration changes from the main database operation log. The protocol's design was influenced by engineering constraints faced when attempting to redesign an unsafe, legacy reconfiguration mechanism that existed previously in MongoDB. We provide a safety proof of MongoRaftReconfig, along with a formal specification in TLA+. To our knowledge, this is the first published safety proof and formal specification of a reconfiguration protocol for a Raft-based system. We also present results from model checking its safety properties on finite protocol instances. Finally, we discuss the conceptual novelties of MongoRaftReconfig, how it can be understood as an optimized and generalized version of the single server reconfiguration algorithm of Raft, and present an experimental evaluation of how its optimizations can provide performance benefits for reconfigurations.Comment: 35 pages, 2 figure

Safe Environmental Envelopes of Discrete Systems

A safety verification task involves verifying a system against a desired safety property under certain assumptions about the environment. However, these environmental assumptions may occasionally be violated due to modeling errors or faults. Ideally, the system guarantees its critical properties even under some of these violations, i.e., the system is \emph{robust} against environmental deviations. This paper proposes a notion of \emph{robustness} as an explicit, first-class property of a transition system that captures how robust it is against possible \emph{deviations} in the environment. We modeled deviations as a set of \emph{transitions} that may be added to the original environment. Our robustness notion then describes the safety envelope of this system, i.e., it captures all sets of extra environment transitions for which the system still guarantees a desired property. We show that being able to explicitly reason about robustness enables new types of system analysis and design tasks beyond the common verification problem stated above. We demonstrate the application of our framework on case studies involving a radiation therapy interface, an electronic voting machine, a fare collection protocol, and a medical pump device.Comment: Full version of CAV23 pape

Optimal management of asymptomatic carotid stenosis in 2021: the jury is still out. An International, multispecialty, expert review and position statement

Objectives: The recommendations of international guidelines for the management of asymptomatic carotid stenosis (ACS) often vary considerably and extend from a conservative approach with risk factor modification and best medical treatment (BMT) alone, to a more aggressive approach with a carotid intervention plus BMT. The aim of the current multispecialty position statement is to reconcile the conflicting views on the topic. Materials and methods: A literature review was performed with a focus on data from recent studies. Results: Several clinical and imaging high-risk features have been identified that are associated with an increased long-term ipsilateral ischemic stroke risk in patients with ACS. Such high-risk clinical/imaging features include intraplaque hemorrhage, impaired cerebrovascular reserve, carotid plaque echolucency/ulceration/ neovascularization, a lipid-rich necrotic core, a thin or ruptured fibrous cap, silent brain infarction, a contralateral transient ischemic attack/stroke episode, male patients <75 years and microembolic signals on transcranial Doppler. There is growing evidence that 80-99% ACS indicate a higher stroke risk than 50-79% stenoses. Conclusions: Although aggressive risk factor control and BMT should be implemented in all ACS patients, several high-risk features that may increase the risk of a future cerebrovascular event are now documented. Consequently, some guidelines recommend a prophylactic carotid intervention in high-risk patients to prevent future cerebrovascular events. Until the results of the much-anticipated randomized controlled trials emerge, the jury is still out regarding the optimal management of ACS patients

Optimal Management of Asymptomatic Carotid Stenosis in 2021:The Jury is Still Out. An International, Multispecialty, Expert Review and Position Statement

Objectives: The recommendations of international guidelines for the management of asymptomatic carotid stenosis (ACS) often vary considerably and extend from a conservative approach with risk factor modification and best medical treatment (BMT) alone, to a more aggressive approach with a carotid intervention plus BMT. The aim of the current multispecialty position statement is to reconcile the conflicting views on the topic. Materials and methods: A literature review was performed with a focus on data from recent studies. Results: Several clinical and imaging high-risk features have been identified that are associated with an increased long-term ipsilateral ischemic stroke risk in patients with ACS. Such high-risk clinical/imaging features include intraplaque hemorrhage, impaired cerebrovascular reserve, carotid plaque echolucency/ulceration/ neovascularization, a lipid-rich necrotic core, a thin or ruptured fibrous cap, silent brain infarction, a contralateral transient ischemic attack/stroke episode, male patients < 75 years and microembolic signals on transcranial Doppler. There is growing evidence that 80–99% ACS indicate a higher stroke risk than 50–79% stenoses. Conclusions: Although aggressive risk factor control and BMT should be implemented in all ACS patients, several high-risk features that may increase the risk of a future cerebrovascular event are now documented. Consequently, some guidelines recommend a prophylactic carotid intervention in high-risk patients to prevent future cerebrovascular events. Until the results of the much-anticipated randomized controlled trials emerge, the jury is still out regarding the optimal management of ACS patients

Plain and Simple Inductive Invariant Inference for Distributed Protocols in TLA+

We present a new technique for automatically inferring inductive invariants of parameterized distributed protocols specified in TLA+. Ours is the first such invariant inference technique to work directly on TLA+, an expressive, high level specification language. To achieve this, we present a new algorithm for invariant inference that is based around a core procedure for generating plain, potentially non-inductive lemma invariants that are used as candidate conjuncts of an overall inductive invariant. We couple this with a greedy lemma invariant selection procedure that selects lemmas that eliminate the largest number of counterexamples to induction at each round of our inference procedure. We have implemented our algorithm in a tool, endive, and evaluate it on a diverse set of distributed protocol benchmarks, demonstrating competitive performance and ability to uniquely solve an industrial scale reconfiguration protocol

Optimal periprocedural antithrombotic treatment in carotid interventions:An international, multispecialty, expert review and position statement

The optimal antithrombotic (antiplatelet or anticoagulant) treatment of patients undergoing extracranial carotid artery interventions is a subject of debate. The aim of this multidisciplinary document was to critically review the recommendations of current guidelines, taking into consideration the results of recently published studies

Benefits and drawbacks of statins and non-statin lipid lowering agents in carotid artery disease

none39si: International guidelines strongly recommend statins alone or in combination with other lipid-lowering agents to lower low-density lipoprotein cholesterol (LDL-C) levels for patients with asymptomatic/symptomatic carotid stenosis (AsxCS/SCS). Lowering LDL-C levels is associated with significant reductions in transient ischemic attack, stroke, cardiovascular (CV) event and death rates. The aim of this multi-disciplinary overview is to summarize the benefits and risks associated with lowering LDL-C with statins or non-statin medications for Asx/SCS patients. The cerebrovascular and CV beneficial effects associated with statins, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors and other non-statin lipid-lowering agents (e.g. fibrates, ezetimibe) are reviewed. The use of statins and PCSK9 inhibitors is associated with several beneficial effects for Asx/SCS patients, including carotid plaque stabilization and reduction of stroke rates. Ezetimibe and fibrates are associated with smaller reductions in stroke rates. The side-effects resulting from statin and PCSK9 inhibitor use are also highlighted. The benefits associated with lowering LDL-C with statins or non-statin lipid lowering agents (e.g. PCSK9 inhibitors) outweigh the risks and potential side-effects. Irrespective of their LDL-C levels, all Asx/SCS patients should receive high-dose statin treatment±ezetimibe or PCSK9 inhibitors for reduction not only of LDL-C levels, but also of stroke, cardiovascular mortality and coronary event rates.restrictedParaskevas, Kosmas I; Gloviczki, Peter; Antignani, Pier Luigi; Comerota, Anthony J; Dardik, Alan; Davies, Alun H; Eckstein, Hans-Henning; Faggioli, Gianluca; Fernandes, Jose Fernandes E; Fraedrich, Gustav; Geroulakos, George; Golledge, Jonathan; Gupta, Ajay; Gurevich, Victor S; Jawien, Arkadiusz; Jezovnik, Mateja K; Kakkos, Stavros K; Knoflach, Michael; Lanza, Gaetano; Liapis, Christos D; Loftus, Ian M; Mansilha, Armando; Nicolaides, Andrew N; Pini, Rodolfo; Poredos, Pavel; Proczka, Robert M; Ricco, Jean-Baptiste; Rundek, Tatjana; Saba, Luca; Schlachetzki, Felix; Silvestrini, Mauro; Spinelli, Francesco; Stilo, Francesco; Suri, Jasjit S; Svetlikov, Alexei V; Zeebregts, Clark J; Chaturvedi, Seemant; Veith, Frank J; Mikhailidis, Dimitri PParaskevas, Kosmas I; Gloviczki, Peter; Antignani, Pier Luigi; Comerota, Anthony J; Dardik, Alan; Davies, Alun H; Eckstein, Hans-Henning; Faggioli, Gianluca; Fernandes, Jose Fernandes E; Fraedrich, Gustav; Geroulakos, George; Golledge, Jonathan; Gupta, Ajay; Gurevich, Victor S; Jawien, Arkadiusz; Jezovnik, Mateja K; Kakkos, Stavros K; Knoflach, Michael; Lanza, Gaetano; Liapis, Christos D; Loftus, Ian M; Mansilha, Armando; Nicolaides, Andrew N; Pini, Rodolfo; Poredos, Pavel; Proczka, Robert M; Ricco, Jean-Baptiste; Rundek, Tatjana; Saba, Luca; Schlachetzki, Felix; Silvestrini, Mauro; Spinelli, Francesco; Stilo, Francesco; Suri, Jasjit S; Svetlikov, Alexei V; Zeebregts, Clark J; Chaturvedi, Seemant; Veith, Frank J; Mikhailidis, Dimitri

Optimal management of asymptomatic carotid stenosis in 2021: the jury is still out. An International, multispecialty, expert review and position statement.

OBJECTIVES: The recommendations of international guidelines for the management of asymptomatic carotid stenosis (ACS) often vary considerably and extend from a conservative approach with risk factor modification and best medical treatment (BMT) alone, to a more aggressive approach with a carotid intervention plus BMT. The aim of the current multispecialty position statement is to reconcile the conflicting views on the topic. MATERIALS AND METHODS: A literature review was performed with a focus on data from recent studies. RESULTS: Several clinical and imaging high-risk features have been identified that are associated with an increased long-term ipsilateral ischemic stroke risk in patients with ACS. Such high-risk clinical/imaging features include intraplaque hemorrhage, impaired cerebrovascular reserve, carotid plaque echolucency/ulceration/ neovascularization, a lipid-rich necrotic core, a thin or ruptured fibrous cap, silent brain infarction, a contralateral transient ischemic attack/stroke episode, male patients &lt;75 years and microembolic signals on transcranial Doppler. There is growing evidence that 80-99% ACS indicate a higher stroke risk than 50-79% stenoses. CONCLUSIONS: Although aggressive risk factor control and BMT should be implemented in all ACS patients, several high-risk features that may increase the risk of a future cerebrovascular event are now documented. Consequently, some guidelines recommend a prophylactic carotid intervention in high-risk patients to prevent future cerebrovascular events. Until the results of the much-anticipated randomized controlled trials emerge, the jury is still out regarding the optimal management of ACS patients