Pick & Mix Isolation Levels: Mixed Serialization Graph Testing

Distributed locking is commonly adopted for performing concurrency control in distributed systems. It incorporates additional steps for handling deadlocks. This activity is carried out by methods based on wait-for-graphs or probes. The present study examines detection of conflicts based on enhanced local processing for distributed concurrency control. In the proposed "edge detection" approach, a graph-based resolution of access conflicts has been adopted. The technique generates a uniform wait-for precedence order at distributed sites for transactions to execute. The earlier methods based on serialization graph testing are difficult to implement in a distributed environment. The edge detection approach is a fully distributed approach. It presents a unified technique for locking and deadlock detection exercises. The technique eliminates many deadlocks without incurring message overheads.

Distributed in-memory key-value stores (KVSs), such as memcached, have become a critical data serving layer in modern Internet-oriented datacenter infrastructure. Their performance and efficiency directly affect the QoS of web services and the efficiency of datacenters. Traditionally, these systems have had significant overheads from inefficient network processing, OS kernel involvement, and concurrency control. Two recent research thrusts have focused upon improving key-value performance. Hardware-centric research has started to explore specialized platforms including FPGAs for KVSs; results demonstrated an order of magnitude increase in throughput and energy efficiency over stock memcached. Software-centric research revisited the KVS application to address fundamental software bottlenecks and to exploit the full potential of modern commodity hardware; these efforts too showed orders of magnitude improvement over stock memcached. We aim at architecting high performance and efficient KVS platforms, and start with a rigorous architectural characterization across system stacks over a collection of representative KVS implementations. Our detailed full-system characterization not only identifies the critical hardware/software ingredients for high-performance KVS systems, but also leads to guided optimizations atop a recent design to achieve a record-setting throughput of 120 million requests per second (MRPS) on a single commodity server. Our implementation delivers 9.2X the performance (RPS) and 2.8X the system energy efficiency (RPS/watt) of the best-published FPGA-based claims. We craft a set of design principles for future platform architectures, and via detailed simulations demonstrate the capability of achieving a billion RPS with a single server constructed following our principles.

Building applications and information systems increasingly means dealing with concurrency and faults stemming from distribution of system components. Atomic transactions are a well-known method for transferring the responsibility for handling concurrency and faults from developers to the software's execution environment, but incur considerable execution overhead. This dissertation investigates methods that shift some of the burden of concurrency control into the network layer, to reduce response times and increase throughput. It anticipates future programmable network devices, enabling customized high-performance network protocols.\nWe propose Atomic Transfer (AT), a distributed algorithm to prevent race conditions due to messages crossing on a path of network switches. Switches check request messages for conflicts with response messages traveling in the opposite direction. Conflicting requests are dropped, obviating the request's receiving host from detecting and handling the conflict. AT is designed to perform well under high data contention, as concurrency control effort is balanced across a network instead of being handled by the contended endpoint hosts themselves.\nWe use AT as the basis for a new optimistic transactional cache consistency algorithm, supporting execution of atomic applications caching shared data. We then present a scalable refinement, allowing hierarchical consistent caches with predictable performance despite high data update rates.\nWe give detailed I/O Automata models of our algorithms along with correctness proofs. We begin with a simplified model, assuming static network paths and no message loss, and then refine it to support dynamic network paths and safe handling of message loss.\nWe present a trie-based data structure for accelerating conflict-checking on switches, with benchmarks suggesting the feasibility of our approach from a performance stand-point.

Many recent studies have suggested that the optimistic concurrency control (OCC) protocols outperform the locking-based protocols in real-time database systems (RTDBS). However, the OCC protocols suffer from the problem of unnecessary transaction restarts that is detrimental to transactions meeting their deadlines. The problem is more intensified in mixed transaction environments. Firm transactions are more vulnerable to restarts when they are in conflict with hard transactions on data access. In this paper, we addressed the problem and devised an effective OCC protocol with dynamic adjustment of serialization order, called OCC-DA, for RTDBS with mixed transactions. This protocol can avoid unnecessary transaction restarts by dynamically adjusting the serialization order of the conflicting transactions with respect to the validating transaction. As a result, much resource can be saved and more firm transactions can meet their deadlines without affecting the execution of hard transactions. The characteristics of the OCC-DA protocol were examined in detail by simulation. The results show that the performance of the OCC-DA protocol was consistently better than the other two popular protocols, OCC with forward validation and OCC with Wait-50, over a wide range of system settings. In particular, the OCC-DA protocol provides a more significant performance gain in mixed transaction environments.

In order to solve the concurrency and starvation control problems of distributed systems, the voting- and priority-based optimal and feasible solution is presented in this research work. In voting-based approach, a process getting the majority of votes will be only allowed to enter into the critical section (CS). But, this method has a disadvantage as if no process remains in the situation of achieving majority of votes then the system will remain in idle state although a considerable amount of minority processes will remain in waiting queue. In the prioritized distributed mutual exclusion-based algorithm, the process having highest priority amongst all the processes of distributed system is allowed to enter into the critical section (CS). Hence, leaving the other lower priority processes into the waiting queue which results an increase in the length of waiting queue. The proposed technique allows the creation of multiple critical sections in a distributed system and prevents the processors from entering into idle state which leads towards increase in throughput.

With the rapid growth of database applications, wireless networking technology and mobile computing devices, there is a demand for processing mobile transactions in Mobile Ad-hoc Network (MANET) databases, so that mobile users can access and manipulate data anytime and anywhere. However, in order to guarantee timely and correct results for multiple concurrent transactions, concurrency control (CC) techniques become critical. Due to the characteristics of MANET databases, existing CC algorithms cannot work effectively. In this paper, we propose a CC algorithm called Sequential Order with Dynamic Adjustment (SODA) for MANET databases. In the design of SODA, the major characteristics of MANET databases are taken into consideration. SODA is based on optimistic CC to offer high concurrency and avoid unbounded blocking time, utilizes the sequential order of committed transactions to improve response time, and dynamically adjusts the sequential order of committed transactions to reduce aborts. The simulation results confirm that SODA has lower abort rate than other existing techniques.

Laser peening has been demonstrated to be a unique and valuable method to increase the resistance of aircraft gas turbine engine compressor and fan blades to foreign object damage (FOD) and improve high cycle fatigue (HCF) life. Laser peening is also known as the LaserPeen process (LPP) or laser shock processing (LSP). LaserPeen processing’s high value as a surface enhancement process to mitigate high cycle fatigue failures is driving e fforts to expand its application from gas turbine engines to aircraft structures, land vehicles, weapon systems, and for general industrial use. One of the major impediments to the broad acceptance and use of the LaserPeen process has been high processing costs with relatively low throughput. Great strides are being made to significantly decrease laser peening costs and increase throughput, thanks to three important Air Force ManTech (manufacturing technology) programmes being conducted at LSP Technologies, Inc. (LSPT). Several key issues are being addressed to meet ManTech goals to lower costs and increase throughput, which include the development of production quality laser peening services and equipment and the expansion of the end user base for this technology. Additionally, a fourth ManTech programme is being conducted by Universal Technology Corporation (UTC) in conjunction with LSPT, Pratt & Whitney, and Howmet. The objective of this programme is to demonstrate that expensive wrought turbine engine blades can be replaced with low cost cast blades, which have been LaserPeen processed. SE / S214

This paper describes an efficient optimistic concurrency control scheme for use in distributed database systems in which objects are cached and manipulated at client machines while persistent storage and transactional support are provided by servers. The scheme provides both serializability and external consistency for committed transactions; it uses loosely synchronized clocks to achieve global serialization. It stores only a single version of each object, and avoids maintaining any concurrency control information on a per-object basis; instead, it tracks recent invalidations on a per-client basis, an approach that has low in-memory space overhead and no per-object disk overhead. In addition to its low space overheads, the scheme also performs well. The paper presents a simulation study that compares the scheme to adaptive callback locking, the best concurrency control scheme for client-server object-oriented database systems studied to date. The study shows that our scheme outperforms adaptive callback locking for low to moderate contention workloads, and scales better with the number of clients. For high contention workloads, optimism can result in a high abort rate; the scheme presented here is a first step toward a hybrid scheme that we expect to perform well across the full range of workloads.

The importance of multidimensional index structures to numerous emerging database applications is well established. However, before these index structures can be supported as access methods (AMs) in a “commercial-strength” database management system (DBMS), efficient techniques to provide transactional access to data via the index structure must be developed. Concurrent accesses to data via index structures introduce the problem of protecting ranges specified in the retrieval from phantom insertions and deletions (the phantom problem ). This paper presents a dynamic granular locking approach to phantom protection in Generalized Search Trees(GiSTs), an index structure supporting an extensible set of queries and data types. The granular locking technique offers a high degree of concurrency and has a low lock overhead. Our experiments show that the granular locking technique (1) scales well under various system loads and (2) similar to the B-tree case, provides a significantly more efficient implementation compared to predicate locking for multidimensional AMs as well. Since a wide variety of multidimensional index structures can be implemented using GiST, the developed algorithms provide a general solution to concurrency control in multidimensional AMs. To the best of our knowledge, this paper provides the first such solution based on granular locking.

Efficient validation of mobile transactions in wireless environments

Starvation-free secure multiversion concurrency control

Single-cell ATAC-seq has emerged as a powerful approach for revealing candidate cis-regulatory elements genome-wide at cell-type resolution. However, current single-cell methods suffer from limited throughput and high costs. Here, we present a novel technique called scifi-ATAC-seq, single-cell combinatorial fluidic indexing ATAC-sequencing, which combines a barcoded Tn5 pre-indexing step with droplet-based single-cell ATAC-seq using the 10X Genomics platform. With scifi-ATAC-seq, up to 200,000 nuclei across multiple samples can be indexed in a single emulsion reaction, representing an approximately 20-fold increase in throughput compared to the standard 10X Genomics workflow.

In many distributed systems concurrent access is required to a shared object, where abstract object servers may incorporate type-specific properties to define consistency requirements. Each operation and its outcome is treated as an event, and conflicts may occur between different event types. Hence concurrency control and synchronization are required at the granularity of conflicting event types. With such a fine granularity of locking, the occurrence of conflicts is likely to be lower than with whole-object locking, so optimistic techniques become more attractive. This work describes the design, implementation, and performance of servers for a shared atomic object, a semiqueue, where each server employs either pessimistic or optimistic locking techniques on each conflicting event type. We compare the performance of a purely optimistic server, a purely pessimistic server, and a hybrid server which treats certain event types optimistically and others pessimistically, to demonstrate the most appropriate environment for using pessimistic, optimistic, or hybrid control. We show that the advantages of low overhead on optimistic locking at low conflict levels is offset at higher conflict levels by the wasted work done by aborted transactions. To achieve optimum performance over the whole range of conflict levels, an adaptable server is required, whereby the treatment of conflicting event types can be changed dynamically between optimistic and pessimistic, according to various criteria depending on the expected frequency of conflict. We describe our implementations of adaptable servers which may allocate concurrency control strategy on the basis of state information, the history of conflicts encountered, or by using preset transaction priorities. We show that the adaptable servers perform almost as well as the best of the purely optimistic, pessimistic, or hybrid servers under the whole range of conflict levels, showing the versatility and efficiency of the dynamic servers. Finally we outline a general design methodology for implementing adaptable concurrency control in servers for atomic objects, illustrated using an atomic shared B-tree.

System-on-package: a broad perspective from system design to technology development

In recent years, the need for data collection and analysis is growing in many scientific disciplines. This is consequently causing an increase of research in automated data management and data mining to create reliable methods for data analysis. To deal with the need for smart environments and big computational resources, some previous works proposed to address the problem by moving on remote processing, with the aim of sharing supercomputer resources, algorithms and costs. Following this trend, in this work we propose an architecture for advanced remote data processing in a secure, smart and versatile client–server environment that is capable of integrating pre-existing local software. In order to assess the feasibility of our proposal, we developed a case study in the context of an image-based medical diagnostic environment. Our tests demonstrated that the proposed architecture has several benefits: increase of the system throughput, easy upgradability, maintainability and scalability. Moreover, for the scenario we have considered, the system showed a very low transmission overhead which settles on about 2.5 % for the widespread 10/100 mbps. Security has been achieved using client–server certificates and up-to-date standards.