Matthias Rohr

Generating Probabilistic and Intensity-Varying Workload for Web-Based Software Systems

This paper presents an approach and a corresponding tool for generating probabilistic and intensity-varying workload for Web-based software systems. The workload to be generated is specified in two types of models. An application model specifies the possible interactions with the Web-based software system, as well as all required low-level protocol details by means of a hierarchical finite state machine. Based on the application model, the probabilistic usage is specified in corresponding user behavior models by means of Markov chains. Our tool Markov4JMeter implements our approach to probabilistic workload generation by extending the popular workload generation tool JMeter. A case study demonstrates how probabilistic workload for a sample Web application can be modeled and executed using Markov4JMeter.

Automatic Failure Diagnosis Support in Distributed Large-Scale Software Systems Based on Timing Behavior Anomaly Correlation

Manual failure diagnosis in large-scale software systems is time-consuming and error-prone. Automatic failure diagnosis support mechanisms can potentially narrow down, or even localize faults within a very short time which both helps to preserve system availability. A large class of automatic failure diagnosis approaches consists of two steps: 1) computation of component anomaly scores; 2) global correlation of the anomaly scores for fault localization. In this paper, we present an architecture-centric approach for the second step. In our approach, component anomaly scores are correlated based on architectural dependency graphs of the software system and a rule set to address error propagation. Moreover, the results are graphically visualized in order to support fault localization and to enhance maintainability. The visualization combines architectural diagrams automatically derived from monitoring data with failure diagnosis results. In a case study, the approach is applied to a distributed sample Web application which is subject to fault injection.

Trustworthy software systems: a discussion of basic concepts and terminology

Basic concepts and terminology for trustworthy software systems are discussed. Our discussion of definitions for terms in the domain of trustworthy software systems is based on former achievements in dependable, trustworthy and survivable systems. We base our discussion on the established literature and on approved standards. These concepts are discussed in the context of our graduate school TrustSoft on trustworthy software systems. In TrustSoft, we consider trustworthiness of software systems as determined by correctness, safety, quality of service (performance, reliability, availability), security, and privacy. Particular means to achieve trustworthiness of component-based software systems - as investigated in TrustSoft - are formal verification, quality prediction and certification; complemented by fault diagnosis and fault tolerance for increased robustness.

An adaptation framework enabling resource-efficient operation of software systems

This paper gives an overview about our current work on a framework which aims at operating component-based software systems more efficiently. Efficiency, in terms of the number of allocated data center resources, is improved by executing architecture-level runtime adaptations based on current workload situations. The proposed framework, called SLAstic, is described and open questions to be answered in future work are raised.

Research issues in software fault categorization

Software faults are a major threat for the dependability of software systems. When we intend to study the impact of software faults on software behavior, examine the quality of fault tolerance mechanisms, or evaluate diagnostic techniques, the issue of distinguishing fault categories and their frequency distribution arises immediately. This article surveys the literature that provides quantitative data on categories of software faults and discusses the applicability of these software fault category distributions to fault injection case studies.

Workload-intensity-sensitive timing behavior analysis for distributed multi-user software systems

In many multi-user software systems, such as online shopping systems, varying workload intensity causes high statistical variance in timing behavior distributions. However, this major impact on timing behavior is often ignored. This paper introduces our approach WITiBA (Workload-Intensity-Sensitive Timing Behavior Analysis) to consider inter-dependencies between concurrent executions of software operations within a distributed system to reduce the standard deviation for succeeding analysis steps. This can be beneficial for analysis methods or simulation methods in terms of tighter confidence intervals, or shorter simulations.

Trace-Context Sensitive Performance Profiling for Enterprise Software Applications

Software response time distributions can be of high variance and multi-modal. Such characteristics reduce confidence or applicability in various statistical evaluations. We contribute an approach to correlating response times to their corresponding operation execution sequence. This provides calling-context sensitive timing behavior models. The approach is based on three equivalence relations: caller-context, stack-context, and trace-context equivalence. To prevent model size explosion, a tree-based hierarchy provides timing behavior models that provide a trade-off between timing behavior model size and the amount of calling-context information considered. In the case study, our approach provides response time distributions with significantly lower standard deviation, compared to using less or no calling-context information. An example from a performance analysis of an industry system demonstrates that multi-modal distributions can be replaced by multiple unimodal distributions using trace-context analysis.

The 5 % Approach as Building Block of an Energy System Dominated by Renewables

We describe an approach for doubling distribution grid capacity for connecting renewable generators based on curtailing a maximum of 5 % of the yearly energy fed into the grid on a per-generator basis. The paper contains information about the control unit needed for automatic minimum curtailment and the field test that has been set up to validate the approach. Furthermore, topics concerning the operationalization of the 5 % approach using both operational technology and information technology are discussed.

Towards a modular and scalable architecture for high-level smart grid applications

Sensor and actor population within future smart distribution grids is much denser than within transmission grids. Thereby, future grid management systems have to cope with larger amounts of data than todays grid management systems. Also, future high-level applications for network management must be suited for use within automatic control loops. This results in new challenges for designing high-level application components for power grid management. This paper addresses related software engineering challenges and presents solutions for designing software within the context of grid management.

Evaluation of control flow traces in software applications for intrusion detection

Software security has become an important requirement, particularly for systems that are publicly accessible through the Internet. Such systems can be equipped with intrusion detection systems to uncover security breaches. In this paper, we present a novel application-level intrusion detection approach. A normal behavior profile is created from application-internal control flow in terms of operation execution traces. Anomalous control flows indicative for intrusion attempts are detected by continuously monitoring and analyzing the software system. A case study demonstrates the intrusion detection approachs applicability in the context of a multi-user Java Web application.