40372826
Caching and Concurrency Control in Mobile Client/Server Database Systems
3189771
Revisiting Transaction Management in Multidatabase Systems
A lot of research efforts have focused on global serializability, global atomicity, and global deadlocks in multidatabase systems. Surprisingly, however, very few transaction processing model exists that ensures global serializability, global atomicity, and freedom from global deadlocks in a uniform manner. In this paper, we examine previous transaction processing models and propose a new transaction processing model that generates globally serializable and deadlock-free schedules in failure-prone multidatabase systems. A new transaction processing model adopts rigid conflict serializability as a correctness criterion on global serializability, and follows an emulated 2PC, criteria for global commitment, and an abort-based multidatabase recovery scheme for global serializability in failure-prone multidatabase systems. In addition, a deadlock-free policy is suggested where rigid conflict serializability is enforced when each subtransaction, including redo transactions, begins its execution. To practically support a new transaction processing model, Rigid Ticket Ordering (RTO) methods are designed. The proposed transaction processing model has the following improvements: (a) it resolves abnormal direct conflicts identified in this paper, (b) it imposes no restrictions on the execution of local transactions, and (c) it relaxes the restrictions on the execution of global transactions.
31039691
Hybrid checkpointing protocol based on selective-sender-based message logging
This paper presents a hybrid checkpointing protocol-an asynchronous checkpointing protocol using a message sending/receiving state change for reducing the overhead of failure-free operation combined with a selective sender-based message logging protocol for reducing the cascade rollback of asynchronous checkpointing protocol. The selective sender-based message logging protocol records only potential orphan messages when taking a checkpoint. And this paper presents a message dependency tree recording the inter-process message sending/receiving information on a volatile storage for reducing the search time of inter-process information during the failure recovery.
28648006
Molecular dynamics simulations of liquid methanol and methanol-water mixtures with polarizable models
A polarizable model for simulation of liquid methanol, compatible with the COS/G2 water model, has been developed using the Charge-on-Spring (COS) technique. The model consists of three point charges, with one polarizable center on the oxygen atom. The Lennard-Jones parameters on the oxygen atom together with the molecular polarizability were varied to reproduce the experimental heat of vaporization and density of liquid methanol at ambient conditions. We examined the energies of various methanol dimers in the gas phase and compared them with values obtained from ab initio calculations. The model was then used to study the thermodynamic, dynamic, structural, and dielectric properties of liquid methanol as well as of a methanol-water mixture. A microscopic picture of the structure of pure liquid methanol and of the methanol-water mixture is provided. Good agreement was found between the results from our model simulations and available experimental and ab initio calculation data. In particular, the experimental dielectric permittivity of 32 could be reproduced, which had been shown to be difficult when using nonpolarizable models.
2617895
Overcoming the Majority Barrier in Large-Scale Systems
In asynchronous environments, the majority barrier prevents us from achieving consensus when more than half of the nodes fail. We argue that the majority barrier significantly limits the availability of practical systems such as peer-to-peer systems. To overcome the barrier realistically, this paper proposes a witness model that probabilistically strengthens the traditional asynchronous model for large-scale systems. The model is motivated by the prevalence of fuzzy partitions in today’s Internet, namely, reachability is far from transitive. Our assumptions in the model are strictly weaker than those in previous approaches. To show that the model is realistic, we carefully use real Internet measurements to validate our strengthening assumptions. On the other hand, we design three consensus protocols under the witness model that can tolerate n-1 failures, showing that the model is strong enough to overcome the majority barrier.
14427569
Design and evaluation of a continuous consistency model for replicated services
The tradeoffs between consistency, performance, and availability are well understood. Traditionally, however, designers of replicated systems have been forced to choose from either strong consistency guarantees or none at all. This paper explores the semantic space between traditional strong and optimistic consistency models for replicated services. We argue that an important class of applications can tolerate relaxed consistency, but benefit from bounding the maximum rate of inconsistent access in an application-specific manner. Thus, we develop a set of metrics, Numerical Error, Order Error, and Staleness, to capture the consistency spectrum. We then present the design and implementation of TACT, a middleware layer that enforces arbitrary consistency bounds among replicas using these metrics. Finally, we show that three replicated applications demonstrate significant semantic and performance benefits from using our framework.
14421655
Signed quorum systems
With n servers that independently fail with probability of p < 0.5, it is well known that the majority quorum system achieves the best availability among all quorum systems. However, even this optimal construction requires (n+1)/2 functioning servers out of n. Furthermore, the number of probes needed to acquire a quorum is also lower bounded by (n+1)/2.Motivated by the need for a highly available and low probe complexity quorum system in the Internet, this paper proposes signed quorum systems (SQS) that can be available as long as any O(1) servers are available, and simultaneously have O(1) probe complexity. SQS provides probabilistic intersection guarantees and exploits the property of independent mismatches in today's Internet. Such key property has been validated previously under multiple Internet measurement traces. This paper then extensively studies the availability, probe complexity, and load of SQS, derives lower bounds for all three metrics, and constructs matching upper bounds. We show that in addition to the qualitatively superior availability and probe complexity, SQS also decouples availability from load and probe complexity, so that optimal availability can be achieved under most probe complexity and load values.
15030041
Adaptive reduction parallelization techniques
In this paper, we propose to adapt parallelizing transformations, more specifically, reduction parallelizations, to the actual reference pattern executed by a loop, i.e., to the particular input data and dynamic phase of a program. More precisely we will show how, after validating a reduction at run-time (when this is not possible at compile time) we can dynamically characterize its reference pattern and choose the most appropriate method for parallelizing it. For this purpose, we develop a library of parallel reduction algorithms, including both previously known and novel schemes, which includes algorithms specialized for different classes of access behavior. In particular, each algorithm in our library has identified strengths related to specific reference pattern characteristics, which are matched, at run-time, with measured characteristics of the actual reference pattern. The matching of algorithm to reference pattern is performed using a decision-tree based selection scheme. The contribution of this work consists in new optimizations for reduction parallelization and in the introduction of a new approach to the optimization of irregular applications: Characteristic based customization.