Nested Transaction Concurrency Control in Parallel Real-Time Dat-abases

An integrated method for concurrency control in parallel real-time databases has been proposed in this paper. The nested transaction model has been investigated to offer more atomic execution units and finer grained control within in a transaction. Based on the classical nested locking protocol and the speculative concurrency control approach, a two-shadow adaptive concurrency control protocol, which combines the Sacrifice based Optimistic Concurrency Control (OPT-Sacrifice) and High Priority two-phase locking (HP2PL) algorithms together to support both optimistic and pessimistic shadow of each sub-transaction, has been proposed to increase the likelihood of successful timely commitment and to avoid unnecessary replication overload.

An Efficient Secure Real-Time Concurrency Control Protocol

Secure real-time databases must simultaneously satisfy two requirements in guaranteeing data security and minimizing the missing deadlines ratio of transactions. However, these two requirements can conflict with each other and achieve one requirement is to sacrifice the other. This paper presents a secure real-time concurrency control protocol based on optimistic method. The concurrency control protocol incorporates security constraints in a real-time optimistic concurrency control protocol and makes a suitable tradeoff between security and real-time requirements by introducing secure influence factor and real-time influence factor. The experimental results show the concurrency control protocol achieves data security without degrading real-time perform ance significantly.

Study on Agent Based Methods for Concurrency Control in CSCW

Concurrency control is a critical technology and one of the problems in CSCW systems. With the development of agent based technology, it has also been applied to research and development of CSCW systems. An Agent based method for concurrency control in CSCW is explored in this paper. This new way is achieved by making use of the thoughts of AOP (Agent Oriented Programming) to improve traditional locking method, on the basis of researching characteristics and functional requirements of concurrency control in CSCW, and analyzing various usually used concurrency control methods. All amendments to locking method are done on the basis of the analysis of limitations brought by locking. In this paper, a new algorithm supporting queue of locking request for Agent based concurrency control is also presented. All above aspects are discussed in some detail in this paper.

Weak Serializable Concurrency Control in Distributed Real-Time Database Systems

Most of the proposed concurrency control protocols for real time database systems are based on serializability theorem. Owing to the unique characteristics of real time database applications and the importance of satisfying the timing constraints of transactions, serializability is too strong as a correctness criterion and not suitable for real time databases in most cases. On the other hand, relaxed serializability including epsilon serializability and similarity serializability can allow more real time transactions to satisfy their timing constraints, but database consistency may be sacrificed to some extent. We thus propose the use of weak serializability(WSR) that is more relaxed than conflicting serializability while database consistency is maintained. In this paper, we first formally define the new notion of correctness called weak serializability. After the necessary and sufficient conditions for weak serializability are shown, corresponding concurrency control protocol WDHP(weak serializable distributed high priority protocol) is outlined for distributed real time databases, where a new lock mode called mask lock mode is proposed for simplifying the condition of global consistency. Finally, through a series of simulation studies, it is shown that using the new concurrency control protocol the performance of distributed real time databases can be greatly improved.

Similarity based mixed transaction concurrency control protocol

Due to the various performance requirements and data access restrictions of different types of real-time transactions, concurrency control protocols which had been designed for the systems with single type of transactions are not sufficient for mixed real-time database systems (MRTDBS), where different types of real-time transactions coexist in the systems concurrently. In this paper, a new concurrency control protocol MRTT_CC for mixed real-time transactions is proposed. The new strategy integrates with different concurrency control protocols to meet the deadline requirements of different types of real-time transactions. The data similarity concept is also explored in the new protocol to reduce the blocking time of soft real-time transactions, which increases their chances to meet the deadlines. Simulation experiments show that the new protocol has gained good performance.

Quasi serializable concurrency control in mobile broadcast environments

The problem of maintaining data consistency in mobile broadcast environments is researched. Quasi serializability is formally defined and analyzed at first. It was shown that quasi serializability is less stringent than serializability when database consistency is maintained for transactions. Then, corresponding concurrency control protocol that supports both update transactions and read-only transactions is outlined for mobile broadcast environments. Finally, the simulation results confirmed that the proposed protocol could improve the response time significantly.

Weak Serializable Concurrency Control in Real-time Broadcast Environments

Given the asymmetric communication capabilities in mobile real-time environments, traditional serializability-based approaches are too restrictive, unnecessary, and impractical. The new notion of correctness called weak serializability is given. After the necessary and sufficient conditions for weak serializability are shown, corresponding concurrency control protocol based on this criterion is outlined for real-time broadcast environments. The simulation results confirmed that the proposed techniques help mobile transactions to meet their deadlines and improve query response time.

Quasi Serializable Concurrency Control in Distributed Real-Time Database Systems

This paper formally defines and analyses the new notion of correctness called quasi serializability, and then outlines corresponding concurrency control protocol QDHP for distributed real-time databases. Finally, through a series of simulation studies, it shows that using the new concurrency control protocol the performance of distributed real-time databases can be much improved.

Adaptive Consistent Management to Prevent System Collapse on Shared Object Manipulation in Mixed Reality

A concurrency control mechanism for collaborative work is akey element in a mixed reality environment. However, conventional lockingmechanisms restrict potential tasks or the support of non-owners, thusincreasing the working time because of waiting to avoid conflicts. Herein, wepropose an adaptive concurrency control approach that can reduce conflictsand work time. We classify shared object manipulation in mixed reality intodetailed goals and tasks. Then, we model the relationships among goal,task, and ownership. As the collaborative work progresses, the proposedsystem adapts the different concurrency control mechanisms of shared objectmanipulation according to the modeling of goal–task–ownership. With theproposed concurrency control scheme, users can hold shared objects andmove and rotate together in a mixed reality environment similar to realindustrial sites. Additionally, this system provides MS Hololens and Myosensors to recognize inputs from a user and provides results in a mixed realityenvironment. The proposed method is applied to install an air conditioneras a case study. Experimental results and user studies show that, comparedwith the conventional approach, the proposed method reduced the number ofconflicts, waiting time, and total working time.

Hybrid concurrency control protocol for data sharing among heterogeneous blockchains

With the development of information technology and cloud computing,data sharing has become an important part of scientific research.In traditional data sharing,data is stored on a third-party storage platform,which causes the owner to lose control of the data.As a result,there are issues of intentional data leakage and tampering by third parties,and the private information contained in the data may lead to more significant issues.Furthermore,data is frequently maintained on multiple storage platforms,posing significant hurdles in terms of enlisting multiple parties to engage in data sharing while maintaining consistency.In this work,we propose a new architecture for applying blockchains to data sharing and achieve efficient and reliable data sharing among heterogeneous blockchains.We design a new data sharing transaction mechanism based on the system architecture to protect the security of the raw data and the processing process.We also design and implement a hybrid concurrency control protocol to overcome issues caused by the large differences in blockchain performance in our system and to improve the success rate of data sharing transactions.We took Ethereum and Hyperledger Fabric as examples to conduct crossblockchain data sharing experiments.The results show that our system achieves data sharing across heterogeneous blockchains with reasonable performance and has high scalability.

Gria:an efficient deterministic concurrency control protocol

Deterministic databases are able to reduce coordination costs in a replication.This property has fostered a significant interest in the design of efficient deterministic concurrency control protocols.However,the state-of-the-art deterministic concurrency control protocol Aria has three issues.First,it is impractical to configure a suitable batch size when the read-write set is unknown.Second,Aria running in low-concurrency scenarios,e.g.,a single-thread scenario,suffers from the same conflicts as running in high-concurrency scenarios.Third,the single-version schema brings write-after-write conflicts.To address these issues,we propose Gria,an efficient deterministic concurrency control protocol.Gria has the following properties.First,the batch size of Gria is auto-scaling.Second,Gria’s conflict probability in low-concurrency scenarios is lower than that in high-concurrency scenarios.Third,Gria has no write-after-write conflicts by adopting a multi-version structure.To further reduce conflicts,we propose two optimizations:a reordering mechanism as well as a rechecking strategy.The evaluation result on two popular benchmarks shows that Gria outperforms Aria by 13x.

An Interruptable Lock and Unlock Algorithm

Generally, Lock and Unlock statements are primitives that should be wholly imple- mented,i.e.,the test of lock state and the operation of locking must be executed continuously without being interrupted. Different from nmormal lock operations, the lock and Unlock algorithm Presented in this paper can be interrupted anywhere by other processes The value of the algorithm in the implementation of concurrent control and mutually-exclusive operations was elucidated with one application of the algorithm in a heterogeneous datedbase united system.

A NOVEL CONSISTENCY CONTROL ALGORITHM IN COOPERATIVE GRAPHICS EDITOR(CGE)

The research work presented in this paper is based on the concrete background ofthe Cooperative Graphics Editor (CGE), allowing two or more persons to remotely edit a graphicdocument simultaneously. A new concurrency control algorithm based on partial order set ispresented, which has fast response and less undo-redo operations as there are no lock mechanisms.It is used to solve inconsistency caused by operation on intersecting graphics concurrently. CGEalso possesses a mask strategy to solve inconsistency caused by operation on the same graphicconcurrently.

Scheduling transactions in mobile distributed real-time database systems

A DMVOCC-MVDA （distributed multiversion optimistic concurrency control with multiversion dynamic adjustment） protocol was presented to process mobile distributed real-time transaction in mobile broadcast environments. At the mobile hosts, all transactions perform local pre-validation. The local pre-validation process is carried out against the committed transactions at the server in the last broadcast cycle. Transactions that survive in local pre-validation must be submitted to the server for local final validation. The new protocol eliminates conflicts between mobile read-only and mobile update transactions, and resolves data conflicts flexibly by using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions. Mobile read-only transactions can be committed with no-blocking, and respond time of mobile read-only transactions is greatly shortened. The tolerance of mobile transactions of disconnections from the broadcast channel is increased. In global validation mobile distributed transactions have to do check to ensure distributed serializability in all participants. The simulation results show that the new concurrency control protocol proposed offers better performance than other protocols in terms of miss rate, restart rate, commit rate. Under high work load （think time is ls） the miss rate of DMVOCC-MVDA is only 14.6%, is significantly lower than that of other protocols. The restart rate of DMVOCC-MVDA is only 32.3%, showing that DMVOCC-MVDA can effectively reduce the restart rate of mobile transactions. And the commit rate of DMVOCC-MVDA is up to 61.2%, which is obviously higher than that of other protocols.

CRF:A Scheduling of Multi-Granularity Locks in Object-Oriented Database Systems

This paper introduces a multi-granularity locking model (MGL) for concurrency control in object-oriented database system briefiy, and presents a MGL model formally. Four lockingscheduling algorithms for MGL are proposed in the paper. The ideas of single queue scheduling(SQS) and dual queue scheduling (DQS) are proposed and the algorithm and the performance evaluation for these two scheduling are presented in some paper. This paper describes a new idea of thescheduling for MGL, compatible requests first (CRF). Combining the new idea with SQS and DQS,we propose two new scheduling algorithms called CRFS and CRFD. After describing the simulationmodel, this paper illustrates the comparisons of the performance among these four algorithms. Asshown in the experiments, DQS has better performance than SQS, CRFD is better than DQS, CRFSperforms better than SQS, and CRFS is the best one of these four scheduling algorithms.

Quanta-A platform for rapid control and monitoring of heterogeneous rbots

Rapid prototyping,real-time control and monitoring of various events in robots are crucial requirements for research in the fields of modular and swarm robotics.A large quantities of resources(time,man power,infrastructure,etc.)are often invested in programming,interfacing the sensors,debugging the response to algorithms during prototyping and operational phases of a robot development cycle.The cost of developing an optimal infrastructure to efficiently address such control and monitoring requirements increases significantly in the presence of mobile robots.Though numerous solutions have been developed for minimizing the resources spent on hardware prototyping and algorithm validation in both static and mobile scenarios,it can be observed that researchers have either chosen methodologies that conflict with the power and infrastructure constraints of the research field or generated constrained solutions whose applications are restricted to the field itself.This paper develops a solution for addressing the challenges in controlling heterogeneous mobile robots.A platform named Quanta-a cost effective,energy efficient and high-speed wireless infrastructure is prototyped as a part of the research in the field of modular robotics.Quanta is capable of controlling and monitoring various events in/using a robot with the help of a light-weight communication protocol independent of the robot hardware architecture(s).

oodOPT: A Semantics-Based Concurrency Control Framework for Fully-Replicated Architecture

Concurrency control has always been one of the most important issues in the design of synchronous groupware systems with fully-replicated architecture. An ideal strate- gy should be able to support natural and flexible human-to-computer and human-to-human interactions while maintaining the consistency of the system. This paper summarizes previ- ous researches on this topic and points out the deficiencies of the existing results. A novel semantics-based concurrency control framework, oodOPT is proposed. The main idea of the framework is to resolve conflicts by utilizing semantics of the operations and the accessed data objects. With this approach, complexities in concurrency control are shifted completely from application developers to the framework. Conflicts among operations on objects with different semantics and the strategies resolving these conflicts are analyzed. After describing the algo- rithm in full detail, the discussion ends up with a comparison with other related work and some considerations for open problems.

A Conflict Detection Scheme for Concurrency Control of R-tree

Despite extensive research on R-trees, most of the proposed schemes have notbeen integrated into existing DBMS owing to the lack of protocols of concurrency control. R-linktree is an acceptable data structure to deal with this issue, but problems like phantom still exist.In this paper, we focus on a conflict detection scheme based on R-link tree for completeconcurrency control. An in-memory operation control list is designed to suspend conflictingoperations . The main features of this approach are (1) it can be implemented easily and does notneed any extra information ; (2) No deadlocks are involved in locking scheme ; (3) Non-conflictingoperations are not restricted ; and (4) Phantom problems in R-link tree are avoided throughbeforehand predication . The experiment results show that this scheme is correct and gains bettersystem performance.

An Adaptive Strategy Integrating Locking with Optimistic Concurrency Control

This paper presents an adaptive strategy called K-locking algorithm for concurrency control in database system.The algorithm integrates an optimistic approach with the K-lock mechanism to control the degree of transaction interference.It is shown that the K-locking strategy is adaptive to the changes in transaction parameters and outperforms both an optimistic approach and a pessimistic approach.

Multi-Clock Snapshot Isolation Concurrency Control for NVM Database

Multi-Clock Snapshot Isolation(MCSI)is a concurrency control mechanism that implements snapshot isolation on a single-layer Non-Volatile Memory(NVM)database.It stores a single copy of data by using multi-version storage to ensure durability and runtime access.With multi-clock transaction timestamp assignment,MCSI can efficiently generate snapshots with vector clocks and use per-thread transaction status arrays to identify uncommitted versions in NVM.For evaluation,we compared MCSI with the PostgreSQL-style concurrency control used in the single-layer NVM database N2DB.The maximum transaction throughput of MCSI is 101%–195%higher than that of N2DB for the YCSB workloads,and 25%–49%higher for the TPC-C workloads.Moreover,the transaction latency of MCSI remains relatively stable as the thread count increases.With 18 worker threads,the average transaction latency of MCSI is 65%–84%lower than that of N2DB for the YCSB workloads and 16%–43%lower for the TPC-C workloads.