Designing the replication layer of a general-purpose datacenter key-value store

Online services and cloud applications such as graph applications, messaging systems, coordination services, HPC applications, social networks and deep learning rely on key-value stores (KVSes), in order to reliably store and quickly retrieve data. KVSes are NoSQL Databases with a read/write/read-modify-write API. KVSes replicate their dataset in a few servers, such that the KVS can continue operating in the presence of faults (availability). To allow programmers to reason about replication, KVSes specify a set of rules (consistency), which are enforced through the use of replication protocols. These rules must be intuitive to facilitate programmer productivity (programmability). A general-purpose KVS must maximize the number of operations executed per unit of time within a predetermined latency (performance) without compromising on consistency, availability or programmability. However, all three of these guarantees are at odds with performance. In this thesis, we explore the design of the replication layer of a general-purpose KVS, which is responsible for navigating this trade-off, by specifying and enforcing the consistency and availability guarantees of the KVS. We start the exploration by observing that modern, server-grade hardware with manycore servers and RDMA-capable networks, challenges conventional wisdom in protocol design. In order to investigate the impact of these advances on protocols and their design, we first create an informal taxonomy of strongly-consistent replication protocols. We focus on strong consistency semantics because they are necessary for a general-purpose KVS and they are at odds with performance. Based on this taxonomy we carefully select 10 protocols for analysis. Secondly, we present Odyssey, a frame-work tailored towards protocol implementation for multi-threaded, RDMA-enabled, in-memory, replicated KVSes. Using Odyssey, we characterize the design space of strongly-consistent replication protocols, by building, evaluating and comparing the 10 protocols. Our evaluation demonstrates that some of the protocols that were efficient in yesterday’s hardware are not so today because they cannot take advantage of the abundant parallelism and fast networking present in modern hardware. Conversely, some protocols that were inefficient in yesterday’s hardware are very attractive today. We distil our findings in a concise set of general guidelines and recommendations for protocol selection and design in the era of modern hardware. The second step of our exploration focuses on the tension between consistency and performance. The problem is that expensive strongly-consistent primitives are necessary to achieve synchronization, but in typical applications only a small fraction of accesses is actually used for synchronization. To navigate this trade-off, we advocate the adoption of Release Consistency (RC) for KVSes. We argue that RC’s one-sided barriers are ideal for capturing the ordering relationship between synchronization and non-synchronization accesses while enabling high performance. We present Kite, a general-purpose, replicated KVS that enforces RC through a novel fast/slow path mechanism that leverages the absence of failures in the typical case to maximize performance, while relying on the slow path for progress. In ad dition, Kite leverages our study of replication protocols to select the most suitable protocols for its primitives and is implemented over Odyssey to make the most out of modern hardware. Finally, Kite does not compromise on consistency, availability or programmability, as it provides sufficient primitives to implement any algorithm (consistency), does not interrupt its operation on a failure (availability), and offers the RC API that programmers are already familiar with (programmability)

The Role of High Sensitivity Troponin: More Acute Coronary Syndromes or More False Positive Results?

Cardiac troponins (cTn) are the most sensitive and specific biomarkers of myocardial damage. Troponin has both diagnostic and prognostic significance for acute coronary syndrome (ACS). The joint European Society of Cardiology/American College of Cardiology Foundation/American Heart Association/World Heart Federation task force recommendations for a universal definition of acute myocardial infarction (AMI) in 2007 are based on detection of cTn and associated clinical evidence. Although the clinical introduction of new generation high sensitivity cTnT and cTnI assays is certainly valuable in the appropriate setting, its widespread use in a variety of clinical situations may lead to the detection of cTn elevation in absence of thrombotic ACS. Until now there is no clarity between “sensitive” and “high sensitive” cTn assays something that raises concerns regarding the interpretation of the latest clinical studies. The increased analytical sensitivity against compromised specifity may increase ‘‘false positive’’ results in patients with cardiovascular disease or apparently healthy subjects with previously undetected cTn levels. A cTn rise in the absence of ACS should prompt for an assessment for a different, non-ischemic mechanism of troponin elevation and direct management at the primary cause. The role of the clinician is to apply clinical doubts where abnormal cTn levels are not due to myocardial injury. The current strategy of management of such patients is based on established algorithms and clinical knowledge

Advances in Post Resuscitation Care:Mild Therapeutic Hypothermia

Out of hospital cardiac arrest remains a major cause of mortality and morbidity despite progress in resuscitative practices. The number of survivors with severe neurologicalimpairment at hospital discharge is similarly dismal. Recently, much attention has been directed toward the use of mild therapeutic hypothermia in postresuscitation care of comatose survivors of cardiac arrest. Two randomized, controlled clinical trials published in the New England Journal of Medicine showed that after resuscitation mild hypothermia lowers mortality, improves neurological outcome after successfully treated cardiac arrest, and is recommended by the 2005 update guidelines of International Liaison Committee on Resuscitation and European Resuscitation Council (ERC). In the present article pathophysiological mechanisms of hypothermia, cooling methods and potential side effects are briefly discussed. Questions regarding implementation of therapeutic hypothermia recommendations in every day clinical practice and future investigation are also addressed

Acute post cardiac injury syndrome occurring immediately after a demanding percutaneous coronary intervention.

Postcardiac injury syndrome (PCIS) occurs as a complication of myocardial infarction (Dressler's syndrome), of cardiac surgery (post-pericardiotomy syndrome), or post-traumatic (either iatrogenic or non-iatrogenic) and involves a pericardial or myocardial injury. There is scarce data regarding occurrence and pathogenesis of PCIS after invasive procedures. Herein, we describe a unique case of acute PCIS with typical clinical, laboratory, echocardiographic findings that occurred one hour after a demanding multi-stenting percutaneous coronary intervention. Possible pathogenetic mechanisms and treatment options are being discussed

Development of Brugada Syndrome Following Photodynamic Therapy in a Patient with Cholangiocarcinoma

Brugada syndrome can be unmasked by several conditions including a febrile state, marked leukocytosis, and electrolyte disturbances. Herein, we describe a 62-year-old man with cholangiocarcinoma in the first reported case of Brugada syndrome onset following photodynamic therapy