On the Benefit of Virtualization: Strategies for Flexible Server Allocation

Virtualization technology facilitates a dynamic, demand-driven allocation and migration of servers. This paper studies how the flexibility offered by network virtualization can be used to improve Quality-of-Service parameters such as latency, while taking into account allocation costs. A generic use case is considered where both the overall demand issued for a certain service (for example, an SAP application in the cloud, or a gaming application) as well as the origins of the requests change over time (e.g., due to time zone effects or due to user mobility), and we present online and optimal offline strategies to compute the number and location of the servers implementing this service. These algorithms also allow us to study the fundamental benefits of dynamic resource allocation compared to static systems. Our simulation results confirm our expectations that the gain of flexible server allocation is particularly high in scenarios with moderate dynamics

Functorial Data Migration

In this paper we present a simple database definition language: that of categories and functors. A database schema is a small category and an instance is a set-valued functor on it. We show that morphisms of schemas induce three "data migration functors", which translate instances from one schema to the other in canonical ways. These functors parameterize projections, unions, and joins over all tables simultaneously and can be used in place of conjunctive and disjunctive queries. We also show how to connect a database and a functional programming language by introducing a functorial connection between the schema and the category of types for that language. We begin the paper with a multitude of examples to motivate the definitions, and near the end we provide a dictionary whereby one can translate database concepts into category-theoretic concepts and vice-versa.Comment: 30 page

Automated Verification of Virtualized Infrastructures

Virtualized infrastructures and clouds present new challenges for security analysis and formal verification: they are complex environments that continuously change their shape, and that give rise to non-trivial security goals such as isolation and failure resilience requirements. We present a platform that connects declarative and expressive description languages with state-of-the art verification methods. The languages integrate homogeneously descriptions of virtualized infras-tructures, their transformations, their desired goals, and evaluation strategies. The different verification tools range from model checking to theorem proving; this allows us to exploit the complementary strengths of methods, and also to understand how to best represent the analysis problems in different contexts. We consider first the static case where the topology of the virtual infrastructure is fixed and demonstrate that our platform allows for the declarative specification of a large class of properties. Even though tools that are special-ized to checking particular properties perform better than our generic approach, we show with a real-world case study that our approach is practically feasible. We finally consider also the dynamic case where the intruder can actively change the topology (by migrating machines). The combination of a complex topology and changes to it by an intruder is a problem that lies beyond the scope of previous analysis tools and to which we can give first positive verification results

Poverty reduction in a refugee-hosting economy: A natural experiment

The role of migration in reducing poverty in developing countries has been investigated mainly from the perspective of migrants and their relatives. This paper exploits the time and spatial variations in the way households in the region of Kagera (Tanzania) traced between 1991 and 2004 have been affected by massive refugee inflows to assess how migration may affect poverty in the hosting communities. Large population inflows from Burundi and Rwanda have improved the welfare of the hosting population, particularly for the poor. Despite the process of structural transformation observed in the refugee-hosting economy, such pro-poor development is mainly explained by improved agricultural labor productivity and income diversification among the poor.Migration, Poverty, Refugees, Structural transformation,

Evolving NoSQL Databases Without Downtime

NoSQL databases like Redis, Cassandra, and MongoDB are increasingly popular because they are flexible, lightweight, and easy to work with. Applications that use these databases will evolve over time, sometimes necessitating (or preferring) a change to the format or organization of the data. The problem we address in this paper is: How can we support the evolution of high-availability applications and their NoSQL data online, without excessive delays or interruptions, even in the presence of backward-incompatible data format changes? We present KVolve, an extension to the popular Redis NoSQL database, as a solution to this problem. KVolve permits a developer to submit an upgrade specification that defines how to transform existing data to the newest version. This transformation is applied lazily as applications interact with the database, thus avoiding long pause times. We demonstrate that KVolve is expressive enough to support substantial practical updates, including format changes to RedisFS, a Redis-backed file system, while imposing essentially no overhead in general use and minimal pause times during updates.Comment: Update to writing/structur

Runtime protection via dataflow flattening

Software running on an open architecture, such as the PC, is vulnerable to inspection and modification. Since software may process valuable or sensitive information, many defenses against data analysis and modification have been proposed. This paper complements existing work and focuses on hiding data location throughout program execution. To achieve this, we combine three techniques: (i) periodic reordering of the heap, (ii) migrating local variables from the stack to the heap and (iii) pointer scrambling. By essentialy flattening the dataflow graph of the program, the techniques serve to complicate static dataflow analysis and dynamic data tracking. Our methodology can be viewed as a data-oriented analogue of control-flow flattening techniques. Dataflow flattening is useful in practical scenarios like DRM, information-flow protection, and exploit resistance. Our prototype implementation compiles C programs into a binary for which every access to the heap is redirected through a memory management unit. Stack-based variables may be migrated to the heap, while pointer accesses and arithmetic may be scrambled and redirected. We evaluate our approach experimentally on the SPEC CPU2006 benchmark suit

Migration and Economic Mobility in Tanzania: Evidence from a Tracking Survey

This study explores the extent to which migration has contributed to improved living standards of individuals in Tanzania. Using longitudinal data on individuals, the authors estimate the impact of migration on consumption growth between 1991 and 2004. The analysis addresses concerns about heterogeneity and unobservable factors correlated with both income changes and the decision to migrate. The findings show that migration adds 36 percentage points to consumption growth, during a period of considerable growth in consumption. These results are robust to numerous tests and alternative specifications. Unpacking the findings, the analysis finds that moving out of agriculture is correlated with much higher growth than staying in agriculture, although growth is always higher in any sector if one physically moves. Economic mobility is strongly linked to geographic mobility. The puzzle is why more people do not move if returns to geographic mobility are high. The evidence is consistent with models in which exit barriers are set by home communities (through social and family norms) that prevent migration of certain categories of people.adult mortality; agricultural activities; agricultural produce; AIDS epidemic; basic needs; Business Ownership; Change in Consumption; consumption aggregate; consumption data; consumption expenditure

The Pathways out of Poverty in Rural Indonesia: an empirical assessment

Since most poor live in rural areas, primarily engaged in low productivity farm activity, the pathway out of poverty must be strongly connected to productivity increases, whether they are realised in farming, rural non-farm enterprises or via urban migration. By utilizing the IFLS panel dataset for 1993 and 2000 from Indonesia, this paper shows, using empirical techniques, which pathways out of poverty were most successful in Indonesia?s past. Our findings suggest that the increased engagement of rural farmers in rural non-farm enterprises is a key way to alleviate rural poverty.

Pathways out of poverty during an economic crisis : an empirical assessment of rural Indonesia

Most poor people in developing countries still live in rural areas and are primarily engaged in low productivity farming activities. Thus pathways out of poverty are likely to be strongly connected to productivity increases in the rural economy, whether they are realized in farming, in rural nonfarm enterprises, or by way of rural-urban migration. The authors use cross-sectional data from the Central Statistical Board for 1993 and 2002, as well as a panel data set from the Indonesia Family Life Survey for 1993 and 2000, to show which pathways out of poverty were most successful over this period. The findings suggest that increased engagement of farmers in rural nonfarm enterprises is an important route out of rural poverty, but that most of the rural agricultural poor that exit poverty still do so while remaining rural and agricultural. So changes in agricultural prices, wages, and productivity still play a critical role in moving people out of poverty.Rural Poverty Reduction,Population Policies,Achieving Shared Growth,Economic Theory&Research