Program Transformations for Asynchronous and Batched Query Submission

The performance of database/Web-service backed applications can be significantly improved by asynchronous submission of queries/requests well ahead of the point where the results are needed, so that results are likely to have been fetched already when they are actually needed. However, manually writing applications to exploit asynchronous query submission is tedious and error-prone. In this paper we address the issue of automatically transforming a program written assuming synchronous query submission, to one that exploits asynchronous query submission. Our program transformation method is based on data flow analysis and is framed as a set of transformation rules. Our rules can handle query executions within loops, unlike some of the earlier work in this area. We also present a novel approach that, at runtime, can combine multiple asynchronous requests into batches, thereby achieving the benefits of batching in addition to that of asynchronous submission. We have built a tool that implements our transformation techniques on Java programs that use JDBC calls; our tool can be extended to handle Web service calls. We have carried out a detailed experimental study on several real-life applications, which shows the effectiveness of the proposed rewrite techniques, both in terms of their applicability and the performance gains achieved.Comment: 14 page

Tight Probability Bounds with Pairwise Independence

Probability bounds on the sum of $n$ pairwise independent Bernoulli random variables exceeding an integer $k$ have been proposed in the literature. However, these bounds are not tight in general. In this paper, we provide three results towards finding tight probability bounds on the sum of pairwise independent Bernoulli random variables. Firstly, for $k = 1$, the tightest upper bound on the probability of the union of $n$ pairwise independent events is provided. Secondly, for $k \geq 2$, the tightest upper bound with identical marginals is provided. Lastly, for general pairwise independent Bernoulli random variables, new upper bounds are derived for $k \geq 2$, by ordering the probabilities. These bounds improve on existing bounds and are tight under certain conditions. The proofs of tightness are developed using techniques of linear optimization. Numerical examples are provided to quantify the improvement of the bounds over existing bounds.Comment: 33 pages, 4 figure

Probability bounds for nn random events under (n−1)(n-1)-wise independence

A collection of $n$ random events is said to be $(n - 1)$-wise independent if any $n - 1$ events among them are mutually independent. We characterise all probability measures with respect to which $n$ random events are $(n - 1)$-wise independent. We provide sharp upper and lower bounds on the probability that at least $k$ out of $n$ events with given marginal probabilities occur over these probability measures. The bounds are shown to be computable in polynomial time.Comment: 18 pages, 2 table

calcifying odontogenic cyst- a three - dimensional radiological evaluation by cone beam computed tomography

Calcifying odontogenic cysts is an odontogenic cyst that gives rise to painless swelling which expand and occasionally perforate bone. Most of them are between 2 to 4 cm in diameter. Approximately 75% occur in anterior canine-incisor region. The highest incidence of occurence is between 10 and 29 years. Radiographically they appear as well-circumscribed, unilocular cyst-like areas with scattered radioacities which range from mere flecks to large masses. The related tooth usually gets displaced. Radiopaque flecks occur in radiographic features of some lesions which undergo osteolysis during their development. The radiopaque flecks occur as a result of dystrophic calcifications in long standing chronic mature lesions. The location of such radiopaque flecks whether pericoronal or periapical is also crucial in narrowing the diagnosis. Radiopaque flecks in pericoronal region occurs in calcifying epithelial odontogenic tumour, ameloblastic fibro-odontoma, whereas in calcifying odontogenic cyst , such radiopaque flecks appears small, discrete, pebble-like with a smooth outline in periapical region. Such pebbles of radiopaque specks were incidentally seen in cone beam computed tomography in a 20-year-old male evaluated radiographically in orthogonal planes in coronal, axial, sagittal slices and three-dimensional reconstructed view and treated by surgical enucleation was described here

DBridge: A program rewrite tool for set-oriented query execution

We present DBridge, a novel static analysis and program transformation tool to optimize database access. Traditionally, rewrite of queries and programs are done independently, by the database query optimzier and the language compiler respectively, leaving out many optimization opportunities. Our tool aims to bridge this gap by performing holistic transformations, which include both program and query rewrite. Many applications invoke database queries multiple times with different parameter values. Such query invocations made using imperative loops are often the cause of poor performance due to random I/O and round trip delays. In practice, such performance issues are addressed by manually rewriting the application to make it set oriented. Such manual rewriting of programs is often time consuming and error prone. Guravannavar et. al. propose program analysis and transformation techniques for automatically rewriting an application to make it set oriented. DBridge implements these program transformation techniques for Java programs that use JDBC to access database. In this demonstration, we showcase the holistic program/query transformations that DBridge can perform, over a variety of scenarios taken from real-world applications. We then walk through the design of DBridge, which uses the SOOT optimization framework for static analysis. Finally, we demonstrate the performance gains achieved through the transformations

Extremal probability bounds in combinatorial optimization

In this paper, we compute the tightest possible bounds on the probability that the optimal value of a combinatorial optimization problem in maximization form with a random objective exceeds a given number, assuming only knowledge of the marginal distributions of the objective coefficient vector. The bounds are 'extremal' since they are valid across all joint distributions with the given marginals. We analyze the complexity of computing the bounds, assuming discrete marginals, and identify instances when the bounds are computable in polynomial time. For compact 0/1 V-polytopes, we show that the tightest upper bound is weakly NP-hard to compute by providing a pseudopolynomial time algorithm. On the other hand, the tightest lower bound is shown to be strongly NP-hard to compute for compact 0/1 V-polytopes by restricting our attention to Bernoulli random variables. For compact 0/1 H-polytopes, for the special case of PERT networks arising in project management, we show that the tightest upper bound is weakly NP-hard to compute by providing a pseudopolynomial time algorithm. The results in the paper complement existing results in the literature for computing the probability with independent random variables.</p