284 research outputs found
Speculative Concurrency Control for Real-Time Databases
In this paper, we propose a new class of Concurrency Control Algorithms that is especially suited for real-time database applications. Our approach relies on the use of (potentially) redundant computations to ensure that serializable schedules are found and executed as early as possible, thus, increasing the chances of a timely commitment of transactions with strict timing constraints. Due to its nature, we term our concurrency control algorithms Speculative. The aforementioned description encompasses many algorithms that we call collectively Speculative Concurrency Control (SCC) algorithms. SCC algorithms combine the advantages of both Pessimistic and Optimistic Concurrency Control (PCC and OCC) algorithms, while avoiding their disadvantages. On the one hand, SCC resembles PCC in that conflicts are detected as early as possible, thus making alternative schedules available in a timely fashion in case they are needed. On the other hand, SCC resembles OCC in that it allows conflicting transactions to proceed concurrently, thus avoiding unnecessary delays that may jeopardize their timely commitment
AN ENERGY-EFFICIENT CONCURRENCY CONTROL ALGORITHM FOR MOBILE AD-HOC NETWORK DATABASES
With the rapid growth of the wireless networking technology and mobile computing devices, there is an increasing demand for processing mobile database transactions in mission-critical applications such as disaster rescue and military operations that do not require a fixed infrastructure, so that mobile users can access and manipulate the database anytime and anywhere. A Mobile Ad-hoc Network (MANET) is a collection of mobile, wireless and battery-powered nodes without a fixed infrastructure; therefore it fits well in such applications. However, when a node runs out of energy or has insufficient energy to function, communication may fail, disconnections may happen, execution of transactions may be prolonged, and thus time-critical transactions may be aborted if they missed their deadlines. In order to guarantee timely and correct results for multiple concurrent transactions, energy-efficient database concurrency control (CC) techniques become critical. Due to the characteristics of MANET databases, existing CC algorithms cannot work effectively.In this dissertation, an energy-efficient CC algorithm, called Sequential Order with Dynamic Adjustment (SODA), is developed for mission-critical MANET databases in a clustered network architecture where nodes are divided into clusters, each of which has a node, called a cluster head, responsible for the processing of all nodes in the cluster. The cluster structure is constructed using a novel weighted clustering algorithm, called MEW (Mobility, Energy, and Workload), that uses node mobility, remaining energy and workload to group nodes into clusters and select cluster heads. In SODA, in order to conserve energy and balance energy consumption among servers so that the lifetime of the network is prolonged, cluster heads are elected to work as coordinating servers. SODA is based on optimistic CC to offer high transaction concurrency and avoid unbounded blocking time. It utilizes the sequential order of committed transactions to simplify the validation process and dynamically adjusts the sequential order of committed transactions to reduce transaction aborts and improve system throughput.Besides correctness proof and theoretical analysis, comprehensive simulation experiments were conducted to study the performance of MEW and SODA. The simulation results confirm that MEW prolongs the lifetime of MANETs and has a lower cluster head change rate and re-affiliation rate than the existing algorithm MOBIC. The simulation results also show the superiority of SODA over the existing techniques, SESAMO and S2PL, in terms of transaction abort rate, system throughput, total energy consumption by all servers, and degree of balancing energy consumption among servers
Oze: Decentralized Graph-based Concurrency Control for Real-world Long Transactions on BoM Benchmark
In this paper, we propose Oze, a new concurrency control protocol that
handles heterogeneous workloads which include long-running update transactions.
Oze explores a large scheduling space using a fully precise multi-version
serialization graph to reduce false positives. Oze manages the graph in a
decentralized manner to exploit many cores in modern servers. We also propose a
new OLTP benchmark, BoMB (Bill of Materials Benchmark), based on a use case in
an actual manufacturing company. BoMB consists of one long-running update
transaction and five short transactions that conflict with each other.
Experiments using BoMB show that Oze keeps the abort rate of the long-running
update transaction at zero while reaching up to 1.7 Mtpm for short transactions
with near linear scalability, whereas state-of-the-art protocols cannot commit
the long transaction or experience performance degradation in short transaction
throughput
Research issues in real-time database systems
Cataloged from PDF version of article.Today's real-time systems are characterized by managing large volumes of data.
Efficient database management algorithms for accessing and manipulating data are
required to satisfy timing constraints of supported applications. Real-time database
systems involve a new research area investigating possible ways of applying database
systems technology to real-time systems. Management of real-time information through
a database system requires the integration of concepts from both real-time systems and
database systems. Some new criteria need to be developed to involve timing constraints
of real-time applications in many database systems design issues, such as
transaction/query processing, data buffering, CPU, and IO scheduling. In this paper, a
basic understanding of the issues in real-time database systems is provided and the
research efforts in this area are introduced. Different approaches to various problems of
real-time database systems are briefly described, and possible future research directions
are discussed
ORPE -- A Data Semantics Driven Concurrency Control
This paper presents a concurrency control mechanism that does not follow a
'one concurrency control mechanism fits all needs' strategy. With the presented
mechanism a transaction runs under several concurrency control mechanisms and
the appropriate one is chosen based on the accessed data. For this purpose, the
data is divided into four classes based on its access type and usage
(semantics). Class (the optimistic class) implements a first-committer-wins
strategy, class (the reconciliation class) implements a
first-n-committers-win strategy, class (the pessimistic class) implements a
first-reader-wins strategy, and class (the escrow class) implements a
first-n-readers-win strategy. Accordingly, the model is called \PeFS. The
selected concurrency control mechanism may be automatically adapted at run-time
according to the current load or a known usage profile. This run-time
adaptation allows \Pe to balance the commit rate and the response time even
under changing conditions. \Pe outperforms the Snapshot Isolation concurrency
control in terms of response time by a factor of approximately 4.5 under heavy
transactional load (4000 concurrent transactions). As consequence, the degree
of concurrency is 3.2 times higher.Comment: 20 pages, 7 tables, 15 figure
\u3cem\u3eRTC\u3c/em\u3e: Language Support for Real-Time Concurrency
This paper presents language constructs for the expression of timing and concurrency requirements in distributed real-time programs. Our programming paradigm combines an object-based paradigm for the specification of shared resources, and a distributed transaction-based paradigm for the specification of application processes. Resources provide abstract views of shared system entities, such as devices and data structures. Each resource has a state and defines a set of actions that can be invoked by processes to examine or change its state. A resource also specifies scheduling constraints on the execution of its actions to ensure the maintenance of its state\u27s consistency. Processes access resources by invoking actions and express precedence, consistency. Processes access resources by invoking actions and express precedence, consistency and timing constraints on action invocations. The implementation of our language constructs with real-time scheduling and locking for concurrency control is also described
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