Multidimensional indexing is crucial for enabling a fast search over large-scale data. Owing to the unprecedented scale of data, extending such indexing technology has recently gained attention in distributed environments. The goal of existing efforts in distributed indexing has been the localization of queries to data residing at a small number of nodes (i.e., locality-preserving indexing) to minimize communication cost. However, considering that workloads often correlate with data locality, such indexing often generates hotspots. Location-based queries are typically skewed to disaster areas during certain periods of time, e.g., during Hurricane Irene, search traffic increased by more than 2000%. To alleviate such hotspots, we propose workload-balancing as an optimization goal. A cost model analytically supporting the need for load balancing is first developed, then a distributed index that evenly distributes the workload is presented. Our empirical study suggests that hotspots degrading search performance can be effectively alleviated. Specifically, when deployed to Amazon EC2, our proposed scheme showed maximum speed-up of 127.7%. Even in hostile settings where workload is not at all correlated with the search criteria, the proposed scheme's performance is comparable to existing approaches optimized for such settings.

"Who can fix this bug?" is an important question in bug triage to "accurately" assign developers to bug reports. To address this question, recent research treats it as a optimizing recommendation accuracy problem and proposes a solution that is essentially an instance of content-based recommendation (CBR). However, CBR is well-known to cause over-specialization, recommending only the types of bugs that each developer has solved before. This problem is critical in practice, as some experienced developers could be overloaded, and this would slow the bug fixing process. In this paper, we take two directions to address this problem: First,we reformulate the problem as an optimization problem of both accuracy and cost. Second, we adopt a content-boosted collaborative filtering (CBCF), combining an existing CBR with a collaborative filtering recommender (CF), which enhances the recommendationquality of either approach alone. However, unlike general recommendation scenarios, bug fix history is extremely sparse. Due to the nature of bug fixes, one bug is fixed by only one developer, which makes it challenging to pursue the above two directions. To address this challenge, we develop a topic-model to reduce the sparseness and enhance the quality of CBCF. Our experimental evaluation shows that our solution reduces the cost efficiently by 30% without seriously compromising accuracy.

To support rapid and efficient software development, we propose to demonstrate our tool, integrating code search into software development process. For example, a developer, right during writing a module, can find a code piece sharing the same syntactic structure from a large code corpus representing the wisdom of other developers in the same team (or in the universe of open-source code). While there exist commercial code search engines on the code universe, they treat software as text (thus oblivious of syntactic structure), and fail at finding semantically related code. Meanwhile, existing tools, searching for syntactic clones, do not focus on efficiency, focusing on “post-mortem” usage scenario of detecting clones “after” the code development is completed. In clear contrast, we focus on optimizing efficiency for syntactic code search and making this search “interactive” for large-scale corpus, to complement the existing two lines of research. From our demonstration, we will show how such interactive search supports rapid software development, as similarly claimed lately in SE and HCI communities. As an enabling technology, we design efficient index building and traversal techniques, optimized for code corpus and code search workload. Our tool can identify relevant code in the corpus of 1.7 million code pieces in a sub-second response time, without compromising any accuracy obtained by a state-of-the-art tool, as we report our extensive evaluation results in.

In this paper, we propose a scalable instant code clone search engine for large-scale software repositories. While there are commercial code search engines available, they treat software as text and often fail to find semantically related code. Meanwhile, existing tools for semantic code clone searches take a "post-mortem" approach involving the detection of clones "after" the code development is completed, and hence, fail to return the results instantly. In clear contrast, we combine the strength of these two lines of existing research, by supporting instant code clone detection. To achieve this goal, we propose scalable indexing structures on vector abstractions of code. Our proposed algorithms allow developers to detect clones of a given code segment among the 1.7 million code segments from 492 open source projects in sub-second response times, without compromising the accuracy obtained by a state-of-the-art tool.

A dynamic skyline query retrieves the moving data objects that are not spatially dominated by any other object with respect to a given query point. Existing efforts on supporting such queries, however, supports location as a single dynamic attribute and one or more static dimensions. In a clear contrast, this paper focuses on the continuous skyline computation on moving data with an arbitrary number of dynamic queriable dimensions, e.g., to model both location and its volatility, with and without static dimension. Toward the goal, we investigate the relative positions and velocities of the initial skyline points with respect to the query, to derive a search region for skyline candidates. After retrieving these candidates, we further prune out some candidates and examine their spatial relations to monitor the changes in the skyline.