On data skewness, stragglers, and MapReduce progress indicators

We tackle the problem of predicting the performance of MapReduce applications, designing accurate progress indicators that keep programmers informed on the percentage of completed computation time during the execution of a job. Through extensive experiments, we show that state-of-the-art progress indicators (including the one provided by Hadoop) can be seriously harmed by data skewness, load unbalancing, and straggling tasks. This is mainly due to their implicit assumption that the running time depends linearly on the input size. We thus design a novel profile-guided progress indicator, called NearestFit, that operates without the linear hypothesis assumption and exploits a careful combination of nearest neighbor regression and statistical curve fitting techniques. Our theoretical progress model requires fine-grained profile data, that can be very difficult to manage in practice. To overcome this issue, we resort to computing accurate approximations for some of the quantities used in our model through space- and time-efficient data streaming algorithms. We implemented NearestFit on top of Hadoop 2.6.0. An extensive empirical assessment over the Amazon EC2 platform on a variety of real-world benchmarks shows that NearestFit is practical w.r.t. space and time overheads and that its accuracy is generally very good, even in scenarios where competitors incur non-negligible errors and wide prediction fluctuations. Overall, NearestFit significantly improves the current state-of-art on progress analysis for MapReduce

Seroprevalence, clinical incidence, and molecular and epidemiological characterisation of small ruminant lentivirus in the indigenous Passirian goat in northern Italy

Eight dairy flocks, comprising a total of 323 indigenous Passirian goats from northern Italy, were examined to determine the seroprevalence and clinical incidence of small ruminant lentivirus (SRLV) infections and to identify the SRLV subtypes. The seroprevalence was 81.5% (55-95%). The clinical incidence was 2.5% (0-8.3%) and was apparently low due to the practice of culling clinically affected animals. Phylogenetic analysis of eight PCR fragments (one sample from each flock) revealed that all proviruses belonged to the SRLV subtype B1, which suggests a common source of infection. Subtype B1 being the only circulating SRLV, coupled with the fact that mixed herd systems are very rare in South Tyrol, gives hope that an eradication programme in goats can be successful even without including sheep as long as sheep are kept strictly and permanently isolated

CAEV : Vorlaufige Ergebnisse eines alternativen Protokolls zur Kontrolle der CAE in einem Ziegenbetrieb der Rasse "Passeirer Gebirgsziege"

Objective: Considering the specific conditions (high sero-prevalence, high genetic merit, rare breed, and commune pasture) in the described herd, an alternative method to control the disease was chosen. The aim of this control program was to reduce clinical signs and to preserve the high genetic merit. Material and methods: The newborns were seggregated immediately after birth and fed with bovine colostrum/milk. At the age of five to six months direct contact with the adults at pasture was possible. Goats tested positive were not killed immediatelly: Animals with low breed value and without signs were slaugthered or sold, goats with high value were kept in the herd as long as possible. Results and conclusions: Infection could not be prevented, but the clinical symptoms almost disappeared. Thus the high genetic potential of this goat herd could be utilized longer. The sexual and aerogenic transmission seemed to be an important factor for spread of infection in this herd. Clinical relevance: Aim, voluntary and perseverance of the breeder and the serological status of neighbouring goat flocks are important factors which have to be considered before the establishment of a control program. The described method seems to be suitable in flocks with high seroprevalence, high genetic merit, and open status. A further evaluation after some years is certainly necessary. Virus persistance and the annually intensive work of the goat colostrum deprived rearing method are certainly disavantages of this alternative program