Component replication in application servers

Three-tier middleware architecture is commonly used for hosting large-scale distributed applications. Typically the application is decomposed into three layers: front-end, middle tier and back-end. Front-end ("Web server") is responsible for handling user interactions and acts as a client of the middle tier, while back-end provides storage facilities for applications. Middle tier (' Application server') is usually the place where all computations are performed, so this layer provides middleware services for transactions, security and so forth. The benefit of this architecture is that it allows flexible configuration such as partitioning and clustering for improved performance and scalability. On this architecture, availability measures, such as replication, can be introduced in each tier in an application specific manner. Among the three tier described above, the availability of the middle tier and the back-end tier are the most important, as these tiers provide the computation and the data for the applications. This thesis investigates how replication for availability can be incorporated within the middle and back-end tiers. The replication mechanisms must guarantee exactly once execution of user request despite failures of application and database servers. The thesis develops an approach that requires enhancements to the middle tier only for supporting replication of both the tiers. The design, implementation and performance evaluation of such a middle tier based replication scheme for multi-database transactions on a widely deployed open source application server (1Boss) are presented.EThOS - Electronic Theses Online ServiceQUE Project, Department of Informatics, ITB, Bandung, IndonesiaGBUnited Kingdo

Middleware-based Database Replication: The Gaps between Theory and Practice

The need for high availability and performance in data management systems has been fueling a long running interest in database replication from both academia and industry. However, academic groups often attack replication problems in isolation, overlooking the need for completeness in their solutions, while commercial teams take a holistic approach that often misses opportunities for fundamental innovation. This has created over time a gap between academic research and industrial practice. This paper aims to characterize the gap along three axes: performance, availability, and administration. We build on our own experience developing and deploying replication systems in commercial and academic settings, as well as on a large body of prior related work. We sift through representative examples from the last decade of open-source, academic, and commercial database replication systems and combine this material with case studies from real systems deployed at Fortune 500 customers. We propose two agendas, one for academic research and one for industrial R&D, which we believe can bridge the gap within 5-10 years. This way, we hope to both motivate and help researchers in making the theory and practice of middleware-based database replication more relevant to each other.Comment: 14 pages. Appears in Proc. ACM SIGMOD International Conference on Management of Data, Vancouver, Canada, June 200

Adaptive Caching of Distributed Components

Die Zugriffslokalität referenzierter Daten ist eine wichtige Eigenschaft verteilter Anwendungen. Lokales Zwischenspeichern abgefragter entfernter Daten (Caching) wird vielfach bei der Entwicklung solcher Anwendungen eingesetzt, um diese Eigenschaft auszunutzen. Anschliessende Zugriffe auf diese Daten können so beschleunigt werden, indem sie aus dem lokalen Zwischenspeicher bedient werden. Gegenwärtige Middleware-Architekturen bieten dem Anwendungsprogrammierer jedoch kaum Unterstützung für diesen nicht-funktionalen Aspekt. Die vorliegende Arbeit versucht deshalb, Caching als separaten, konfigurierbaren Middleware-Dienst auszulagern. Durch die Einbindung in den Softwareentwicklungsprozess wird die frühzeitige Modellierung und spätere Wiederverwendung caching-spezifischer Metadaten gewährleistet. Zur Laufzeit kann sich das entwickelte System außerdem bezüglich der Cachebarkeit von Daten adaptiv an geändertes Nutzungsverhalten anpassen.Locality of reference is an important property of distributed applications. Caching is typically employed during the development of such applications to exploit this property by locally storing queried data: Subsequent accesses can be accelerated by serving their results immediately form the local store. Current middleware architectures however hardly support this non-functional aspect. The thesis at hand thus tries outsource caching as a separate, configurable middleware service. Integration into the software development lifecycle provides for early capturing, modeling, and later reuse of cachingrelated metadata. At runtime, the implemented system can adapt to caching access characteristics with respect to data cacheability properties, thus healing misconfigurations and optimizing itself to an appropriate configuration. Speculative prefetching of data probably queried in the immediate future complements the presented approach

Sandboxed, Online Debugging of Production Bugs for SOA Systems

Short time-to-bug localization is extremely important for any 24x7 service-oriented application. To this end, we introduce a new debugging paradigm called live debugging. There are two goals that any live debugging infrastructure must meet: Firstly, it must offer real-time insight for bug diagnosis and localization, which is paramount when errors happen in user-facing applications. Secondly, live debugging should not impact user-facing performance for normal events. In large distributed applications, bugs which impact only a small percentage of users are common. In such scenarios, debugging a small part of the application should not impact the entire system. With the above-stated goals in mind, this thesis presents a framework called Parikshan, which leverages user-space containers (OpenVZ) to launch application instances for the express purpose of live debugging. Parikshan is driven by a live-cloning process, which generates a replica (called debug container) of production services, cloned from a production container which continues to provide the real output to the user. The debug container provides a sandbox environment, for safe execution of monitoring/debugging done by the users without any perturbation to the execution environment. As a part of this framework, we have designed customized-network proxies, which replicate inputs from clients to both the production and test-container, as well safely discard all outputs. Together the network duplicator, and the debug container ensure both compute and network isolation of the debugging environment. We believe that this piece of work provides the first of its kind practical real-time debugging of large multi-tier and cloud applications, without requiring any application downtime, and minimal performance impact

Design and implementation of a programmable middleware

This thesis presents a languagebased, safely programmable middleware for the simple, highlevel, and expressive construction of composable open systems. The middleware provides services for pickling, components, and distribution. All are based on a minimal set of primitives and syntax extensions, such that they otherwise can be completely implemented and customized in a highlevel language with automatic memory management, exception handling, higherorder functions, futures, and dynamic types. Using this approach, it becomes possible to describe the complete architecture of the middleware system, and to leverage the language\u27;s safety features in the middleware itself.Die vorliegende Arbeit beschreibt eine Programmiersprachenbasierte programmierbare Middleware, die eine einfache Konstruktion offener Systeme auf hoher Ebene ermöglicht. Die Middleware bietet Dienste für Pickling, Komponenten und Verteilung an, die allesamt auf einem minimalen Satz an Primitiven und Syntaxerweiterungen beruhen. Der Hauptteil der Dienste kann so in einer höheren Programmiersprache mit automatischer Speicherverwaltung, Ausnahmebehandlung, Prozeduren höherer Ordnung, Futures und dynamischen Typen realisiert werden. Dies ermöglicht es, die Architektur der Middleware vollständig zu beschreiben, sowie die Sicherheitsgarantien der höheren Programmiersprache in der Implementierung der Middleware selbst zu nutzen

Systemunterstützung für den Abgleich von Geschäftsobjekten zwischen Anwendungsservern über WebServices: Systemunterstützung für den Abgleich von Geschäftsobjekten zwischen Anwendungsservern über WebServices

Geschäftsanwendungen wie Supply Chain Management (SCM) oder Customer Relationship Management (CRM) werden repliziert, um eine hohe Skalierbarkeit und schnellen lokalen Zugriff zu erreichen. Die Geschäftsobjekte als Datencontainer der Anwendungen müssen infolge von Änderungen synchronisiert werden. Diese Arbeit leistet einen Beitrag zur Effizienzsteigerung des Synchronisationsprozesses durch die Reduzierung der Anzahl der Synchronisationsnachrichten sowie der zu übertragenden Datenmenge - auch unter Berücksichtigung des entstehenden Mehraufwands durch zusätzliche Verarbeitungsprozesse.Business applications such as supply chain management (SCM) or customer relationship management (CRM) are replicated in order to reach high scalability and fast local access. The business objects representing the data containers have to be synchronized to stay consistent across the application servers. This thesis provides a contribution to reach more efficiency during the synchronization process by reducing the amount of synchronization messages and the amount of data to be transmitted. The additional effort due to further processing steps is taken into account via a proper cost model