Consistency in a Partitioned Network: A Survey

Recently, several strategies for transaction processing in partitioned distributed database systems with replicated data have been proposed. We survey these strategies in light of the competing goals of maintaining correctness and achieving high availability. Extensions and combinations are then discussed, and guidelines for the selection of a strategy for a particular application are presented

Could cash and good parenting affect child cognitive development? A cross-sectional study in South Africa and Malawi

BACKGROUND: Social protection interventions, including cash grants and care provision have been shown to effectively reduce some negative impacts of the HIV epidemic on adolescents and families. Less is known about the role of social protection on younger HIV affected populations. This study explored the impact of cash grants on children's cognitive development. Additionally, we examined whether combined cash and care (operationalised as good parenting) was associated with improved cognitive outcomes. METHODS: The sample included 854 children, aged 5 - 15, participating in community-based organisation (CBO) programmes for children affected by HIV in South Africa and Malawi. Data on child cognitive functioning were gathered by a combination of caregiver report and observer administered tests. Primary caregivers also reported on the economic situation of the family, cash receipt into the home, child and household HIV status. Parenting was measured on a 10 item scale with good parenting defined as a score of 8 or above. RESULTS: About half of families received cash (55%, n = 473), only 6% (n = 51) reported good parenting above the cut-off point but no cash, 18% (n = 151) received combined cash support and reported good parenting, and 21% (n = 179) had neither. Findings show that cash receipt was associated with enhanced child cognitive outcomes in a number of domains including verbal working memory, general cognitive functioning, and learning. Furthermore, cash plus good parenting provided an additive effect. Child HIV status had a moderating effect on the association between cash or/plus good parenting and cognitive outcomes. The association between cash and good parenting and child cognitive outcomes remained significant among both HIV positive and negative children, but overall the HIV negative group benefited more. CONCLUSIONS: This study shows the importance of cash transfers and good parenting on cognitive development of young children living in HIV affected environments. Our data clearly indicate that combined provision (cash plus good parenting) have added value

Nonblocking Commit Protocols

"From a certain point onward there is no longer any turning back. That is the point that must be reached." Kafka Protocols that allow operational sites to continue transac-tion processing even though site failures have occurred are called nonblocking. Many applications require nonblocking Qrotocols. This paper investigates the properties of non-blocking protocols. Necessary and sufficient conditions for a protocol to be nonblocking are presented and from these conditions a method for designing them is derived. Both a central site nonblocking protocol and a decentralized non-blocking protocol are presented

Determining the Last Process to Fail

A total failure occurs whenever all processes cooperatively executing a distributed task fail before the task's completion. A frequent prerequisite for recovery from a total failure is the identification of the last group (LAST) of processes concurrently failing. Herein, we derive necessary and sufficient conditions for computing LAST from the local failure data of recovered processes. These conditions are easily translated into decision procedures for LAST membership using either complete or incomplete failure data. The choice of failure data itself is dictated by two requirements: (1) it can be cheaply maintained, and (2) maximum fault-tolerance is afforded in the sense that the expected number of recoveries required for identifying LAST is minimized

A Quorum-Based Commit Protocol

Herein, we propose a commit protocol and an associated recovery protocol that is resilient to site failures, lost messages, and network partitioning. The protocols do not require that a failure be correctly identified or even detected. The only potential effect of undetected failures is a degradation in performance. The protocols use a weighted voting scheme that supports an arbitrary degree of data replication (including none) and allows unilaterally aborts by any site. This last property facilitates the integration of these protocols with concurrency control protocols. Both protocols are centralized protocols with low message overhead

The Inherent Cost of Nonblocking Commitment

A commitment protocol orchestrates the execution of a distributed transaction, allowing each participant to "vote" on the transaction and then applying a pre-specified rule to decide the outcome (commit or abort). A nonblocking is able to correctly terminate a transaction at all operational participants in the presence of any number of benign processor failures. Herein, we derive strong lower bounds for both non-blocking protocols and their less fault-tolerant blocking counterparts. Results on message complexity are both surprising and encouraging: the message complexities of the two classes of protocols are identical. Results on time complexity were less encouraging: nonblocking protocols are approximately 50% more expensive. However, we show how to overlap non-blocking executions of interfering transactions and thereby reduce their extra cost

Extensions of the Reduction Process in the Wong-Youssefi Strategy for Query Processing

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Patterns of Communication in Consensus Protocols

This paper presents a taxonomy of consensus problems, based on their safeness and liveness properties, and then explores the relationships among the different problems in the taxonomy. Each problem is characterized by the communication patterns of protocols solving it. This then becomes the basis for a new notion of reducibility between problems. Formally, problem $P_{1}$ reduces to problem $P_{2}$ whenever each set of communication patterns of a protocol for $P_{2}$ is the set of comunication patterns of a protocol for $P_{1}$. This means intuitively that any protocol for $P_{2}$ can solve $P_{1}$ by relabeling local states and padding messages. Consequently, the message complexity (measured in number of messages) of $P_{1}$ is not greater than the message complexity of $P_{2}$. Our method of characterizing and comparing problems is the principal contribution of this paper