A Concurrency Control Algorithm for an Open and Safe Nested Transaction Model

We present a concurrency control algorithm for an open and safe nested transaction model. We use prewrite operations in our model to increase the concurrency. Prewrite operations are modeled as subtransactions in the nested transaction tree. The subtransaction which initiates prewrite subtransactions are modelled as recovery point subtransaction. The recovery point subtransaction can release their locks before its ancestors commit. Thus, our model increases the concurrency in comparison to other nested transaction models. Our model is useful an environment of long-running transactions common in object oriented databases, computer aided design and in the software development proces

Design and evaluation of a new transaction execution model for multidatabase systems

Cataloged from PDF version of article.In this paper, we present a new transaction execution model that captures the formalism and semantics of various extended transaction models and adopts them to a multidatabase system (MDBS) environment. The proposed model covers nested transactions, various dependency types among transactions, and commit independent transactions. The formulation of complex MDBS transaction types can be accomplished easily with the extended semantics captured in the model. A detailed performance model of an MDBS is employed in investigating the performance implications of the proposed transaction model. © Elsevier Science Inc. 1997

Maintaining consistency in distributed systems

In systems designed as assemblies of independently developed components, concurrent access to data or data structures normally arises within individual programs, and is controlled using mutual exclusion constructs, such as semaphores and monitors. Where data is persistent and/or sets of operation are related to one another, transactions or linearizability may be more appropriate. Systems that incorporate cooperative styles of distributed execution often replicate or distribute data within groups of components. In these cases, group oriented consistency properties must be maintained, and tools based on the virtual synchrony execution model greatly simplify the task confronting an application developer. All three styles of distributed computing are likely to be seen in future systems - often, within the same application. This leads us to propose an integrated approach that permits applications that use virtual synchrony with concurrent objects that respect a linearizability constraint, and vice versa. Transactional subsystems are treated as a special case of linearizability

An EVACS simulation with nested transactions

Documented here is the recent effort of the MISSION Kernel Team on an Extra-Vehicular Activity Control System (EVACS) simulation with nested transactions. The team has implemented the EVACS simulation along with a design for nested transactions. The EVACS simulation is a project wide aid to exploring Mission and Safety Critical (MASC) applications and their support software. For this effort it served as a trial scenario for demonstrating nested transactions and exercising the transaction support design. The EVACS simulation is a simulation of some aspects of the Extra-Vehicular Activity Control System, in particular, just the selection of communication frequencies. Its current definition is quite narrow, serving only as a starting point for prototyping purposes. (EVACS itself may be supplanted in a larger scenario of a lunar outpost with astronauts and a lunar rover.) Initially the simulation of frequency selection was written without consideration of nested transactions. This scenario was then modified to embed its processing in nested transactions. To simplify the prototyping effort, only two aspects of the general design for transaction support have been implemented: the basic architecture and state recovery. The simulation has been implemented in the programming language Smalltalk. It consists of three components: (1) a simulation support code which provides the framework for initiating, interacting and tracing the system; (2) the EVACS application code itself, including its calls upon nested transaction support; and (3) a transaction support code which implements the logic necessary for nested transactions. Each of these components deserves further description, but for now only the transaction support is discussed

S-Store: Streaming Meets Transaction Processing

Stream processing addresses the needs of real-time applications. Transaction processing addresses the coordination and safety of short atomic computations. Heretofore, these two modes of operation existed in separate, stove-piped systems. In this work, we attempt to fuse the two computational paradigms in a single system called S-Store. In this way, S-Store can simultaneously accommodate OLTP and streaming applications. We present a simple transaction model for streams that integrates seamlessly with a traditional OLTP system. We chose to build S-Store as an extension of H-Store, an open-source, in-memory, distributed OLTP database system. By implementing S-Store in this way, we can make use of the transaction processing facilities that H-Store already supports, and we can concentrate on the additional implementation features that are needed to support streaming. Similar implementations could be done using other main-memory OLTP platforms. We show that we can actually achieve higher throughput for streaming workloads in S-Store than an equivalent deployment in H-Store alone. We also show how this can be achieved within H-Store with the addition of a modest amount of new functionality. Furthermore, we compare S-Store to two state-of-the-art streaming systems, Spark Streaming and Storm, and show how S-Store matches and sometimes exceeds their performance while providing stronger transactional guarantees

Mission and Safety Critical (MASC): An EVACS simulation with nested transactions

The Extra-Vehicular Activity Control System (EVACS) Simulation with Nested Transactions, a recent effort of the MISSION Kernel Team, is documented. The EVACS simulation is a simulation of some aspects of the Extra-Vehicular Activity Control System, in particular, just the selection of communication frequencies. The simulation is a tool to explore mission and safety critical (MASC) applications. For the purpose of this effort, its current definition is quite narrow serving only as a starting point for prototyping purposes. (Note that EVACS itself has been supplanted in a larger scenario of a lunar outpost with astronauts and a lunar rover). The frequency selection scenario was modified to embed its processing in nested transactions. Again as a first step, only two aspects of transaction support were implemented in this prototype: architecture and state recovery. Issues of concurrency and distribution are yet to be addressed

Impact of Public Market Information System (PMIS) on Farmers Food Marketing Decisions: Case of Benin

To sell their surpluses of maize, the main staple in Benin, farmers may choose among three modes of transaction: they may sell under a contract with itinerant traders, or they may sell without a contract at the farmgate or on distant markets. It has been postulated that farmers may choose a profitable mode of transaction if they have good access to information on the prevailing market conditions. Using detailed farm household survey data from Benin, this paper applies the Nested Logit model to test this hypothesis. The results show that farmers are likely to opt for selling at the farmgate without a contract if they have good access to information. However, such a decision may not be related to access to information through the government supported 'Public Market Information System' but rather it is likely to be induced by access to information through farmers' own social networks.Public Market Information System, farmers, modes of transaction, liberalization, Agribusiness, Agricultural and Food Policy,

Packet Transactions: High-level Programming for Line-Rate Switches

Many algorithms for congestion control, scheduling, network measurement, active queue management, security, and load balancing require custom processing of packets as they traverse the data plane of a network switch. To run at line rate, these data-plane algorithms must be in hardware. With today's switch hardware, algorithms cannot be changed, nor new algorithms installed, after a switch has been built. This paper shows how to program data-plane algorithms in a high-level language and compile those programs into low-level microcode that can run on emerging programmable line-rate switching chipsets. The key challenge is that these algorithms create and modify algorithmic state. The key idea to achieve line-rate programmability for stateful algorithms is the notion of a packet transaction : a sequential code block that is atomic and isolated from other such code blocks. We have developed this idea in Domino, a C-like imperative language to express data-plane algorithms. We show with many examples that Domino provides a convenient and natural way to express sophisticated data-plane algorithms, and show that these algorithms can be run at line rate with modest estimated die-area overhead.Comment: 16 page

The Dividend and Share Repurchase Policies of Canadian Firms

We empirically investigate dividend and share repurchase policies of Canadian firms. We have sent aquestionnaire to the 500 largest non-financial Canadian companies listed on the Toronto StockExchange, of which 191 usable responses were returned. These data are used to measure firmcharacteristics. We use several logit regression analyses to test the structure and determinants of thedividend and share repurchase choice. Our results are consistent with a structure in which thecompany first decides whether it wants to pay out cash to its shareholders or not. In the second stagethe firm decides on the form of the payout: dividends, share repurchases or both. Payout is determinedby free cash flow. The choice for dividends and repurchases depends on behavioral and taxpreferences. Furthermore, the payout is less likely to be dividends if the company has executive stockoption plans. Finally, we find evidence for the Brennan and Thakor (1990) model. According to thismodel the existence of asymmetric information amongst outsiders is associated with a preference fordividend payments over share repurchases.dividends;nested logit models;payout decisions;share repurchases;strategic financial decisions

The Dividend and Share Repurchase Policies of Canadian Firms: Empirical Evidence based on New Research Design

We empirically investigate dividend and share repurchase policies of Canadian firms. We use several logit regression analyses to test the structure and determinants of the dividend and share repurchase choice. We have sent a questionnaire to the 500 largest non-financial Canadian companies listed on the Toronto Stock Exchange, of which 191 usable responses were returned. These data are used to measure firm characteristics. Our results are consistent with a structure in which the company first decides whether it wants to pay out cash to its shareholders or not. In the second stage the firm decides on the form of the payout: dividends, share repurchases or both. Payout is determined by free cash flow. The type of payout depends on behavioral and tax preferences. Furthermore, the payout is less likely to be dividends if the company has executive stock option plans. Finally, we find evidence for the Brennan and Thakor (1990) model. According to this model the existence of asymmetric information amongst outsiders is associated with a preference for dividend payments over share repurchases.dividend policy;shares