06121 Abstracts Collection -- Atomicity: A Unifying Concept in Computer Science

From 19.03.06 to 24.03.06, the Dagstuhl Seminar 06121 ``Atomicity: A Unifying Concept in Computer Science\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Log-based middleware server recovery with transaction support

Abstract Providing enterprises with reliable and available Web-based application programs is a challenge. Applications are traditionally spread over multiple nodes, from user (client), to middle tier servers, to back end transaction systems, e.g. databases. It has proven very difficult to ensure that these applications persist across system crashes so that "exactly once" execution is produced, always important and sometimes essential, e.g., in the financial area. Our system provides a framework for exactly once execution of multitier Web applications, built on a commercially available Web infrastructure. Its capabilities include low logging overhead, recovery isolation (independence), and consistency between mid-tier and transactional back end. Good application performance is enabled via persistent shared state in the middle tier while providing for private session state as well. Our extensive experiments confirm both the desired properties and the good performance

The Case for Log Structuring in Database Systems

Introduction and Background The notion of a log structured file system (LFS) [6, 9] evolved from earlier efforts using similar techniques [8, 2] as a means to improve write performance of file systems. Other benefits include faster metadata operations, e.g. file create and delete. But there is controversy about the the utility of LFS for database systems, especially in light of the critique in [10]. This position paper argues that LFS has wonderful potential as the underpinning of a database system, solving a number of problems that are known to be quite vexing, and providing some additional important benefits. These include atomic writes, system management and scalability, storage efficiency, and recovery system performance. There are three inter-related ideas in LFS. LFS virtualizes the placement of files on disk. Every write to a file dynamically relocates the data being written. Thus, a write must also update the data structures involved in this relocation mapping. Becaus

MLR: A Recovery Method for Multi-level Systems

To achieve high concurrency in a database system has meant building a system that copes well with important special cases. Recent work on multilevel systems suggests a systematic way of providing high concurrency. A multi-level system using locks permits restrictive low level locks of a subtransaction to be replaced with less restrictive high level locks when a subtransaction commits, hence enhancing concurrency. This is possible because sub-transactions can be undone by executing high level compensation actions rather than by restoring a prior lower level state. We describe a recovery scheme, called Multi-Level Recovery (MLR) that logs this high level undo operation with the commit record for the subtransaction that it compensates, posting log records to only a single log. A variant of the method copes with nested transactions, and both nested and multi-level transactions can be treated in a unified fashion

Recovery for Shared Disk Systems Using Multiple Redo Logs

A new method for redo logging and recovery is described. It is designed to work in a data sharing system where multiple nodes can access common data. Particularly important is that each node can have its own log. Crash recovery is possible based on the contents of just one of these logs. Media recovery is supported via a form of merging of the logs. The method requires no time synchronization between nodes, and does not use timestamps to order the log records during the merge. The method should work with many undo recovery methods. Conventional checkpointing schemes can be adapted to the scheme, enabling the redo scan point to be advanced and the log to be truncated. Finally, the method makes possible a new paradigm for distributed DBMSs which has the potential to exploit inexpensive desktop processing and improve availability and responsiveness. Keywords: logging, database recovery, data sharing systems c flDigital Equipment Corporation 1990. All rights reserved. 1 Introduction 1.1..