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Abstract-Synchronous execution of queries or Web service requests forces the calling application to block until the query/request is satisfied. The performance of applications can be significantly improved by asynchronous submission of queries, which allows the application to perform other processing instead of blocking while the query is executed, and to concurrently issue multiple queries. Concurrent submission of multiple queries can allow the query execution engine to better utilize multiple processors and disks, and to reorder disk IO requests to minimize seeks. Concurrent submission also reduces the impact of network round-trip latency and delays at the database, when processing multiple queries. However, manually writing applications to exploit asynchronous query submission is tedious.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 dataflow 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 have built a tool that implements our transformation techniques on Java code that uses 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 rewritten using our transformation techniques. The experimental study shows the effectiveness of the proposed rewrite techniques, both in terms of their applicability and performance gains achieved.

In this paper we address the problem of optimizing performance of database/web-service backed applications by means of automatically prefetching query results. Prefetching has been performed in earlier work based on predicting query access patterns; however such prediction is often of limited value, and can perform unnecessary prefetches. There has been some earlier work on program analysis and rewriting to automatically insert prefetch requests; however, such work has been restricted to rewriting of single procedures. In many cases, the query is in a procedure which does not offer much scope for prefetching within the procedure; in contrast, our approach can perform prefetching in a calling procedure, even when the actual query is in a called procedure, thereby greatly improving the benefits due to prefetching. Our approach does not perform any intrusive changes to the source code, and places prefetch instructions at the earliest possible points while avoiding wasteful prefetches. We have incorporated our techniques into a tool for holistic optimization called DBridge, to prefetch query results in Java programs that use JDBC. Our tool can be easily extended to handle Hibernate API calls as well as Web service requests. Our experiments on several real world applications demonstrate the applicability and significant performance gains due to our techniques.

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Abstract-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.