Object relationships in modem software systems are becoming increasingly numerous and complex. Programmers who try to find violations of. such ' relationships need new tools that allow them to explore objects in a large system more efficiently. Many existing debuggers present only a low-level, one-object-at-a-time view of objects and their relationships. We propose a new solution to overcome these problems: query-based debugging. The implementation' of the query-based debugger described here offers programmers an effective query tool that allows efficient searching of large object spaces and quick verification of complex relationships. Even for programs that have large numbers of objects, the debugger achieves interactive response times for common queries by using a combination of fast searching primitives, query optimization, and incremental result delivery.

Abstract. Program errors are hard to find because of the cause-effect gap between the time when an error occurs and the time when the error becomes apparent to the programmer. Although debugging techniques such as conditional and data breakpoints help to find error causes in simple cases, they fail to effectively bridge the cause-effect gap in many situations. Dynamic query-based debuggers offer programmers an effective tool that provides instant error alert by continuously checking inter-object relationships while the debugged program is running. To speed up dynamic query evaluation, our debugger (implemented in portable Java) uses a combination of program instrumentation, load-time code generation, query optimization, and incremental reevaluation. Experiments and a query cost model show that selection queries are efficient in most cases, while more costly join queries are practical when query evaluations are infrequent or query domains are small.

Performance profiling consists of monitoring a software system during execution and then analyzing the obtained data. There are two ways to collect profiling data: event tracing through code instrumentation and statistical sampling. These two approaches have different advantages and drawbacks. This paper proposes a hybrid approach to data collection that combines the completeness of event tracing with the low cost of statistical sampling. We propose to maximize the weighted amount of information obtained during data collection, show that such maximization can be performed in linear time or is NPhard depending on the data collected and the collection implementation. We propose an approximation algorithm for NP-hard case. Our paper also presents an application of the formal approach to an example use case.

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Object relationships in modem software systems are becoming increasingly numerous and complex. Programmers who try to find violations of. such ' relationships need new tools that allow them to explore objects in a large system more efficiently. Many existing debuggers present only a low-level, one-object-at-a-time view of objects and their relationships. We propose a new solution to overcome these problems: query-based debugging. The implementation' of the query-based debugger described here offers programmers an effective query tool that allows efficient searching of large object spaces and quick verification of complex relationships. Even for programs that have large numbers of objects, the debugger achieves interactive response times for common queries by using a combination of fast searching primitives, query optimization, and incremental result delivery.