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

Media Recovery with Time-Split

The Cambridge laboratory became operational in 1988 and is located at One Kendall Square, near MIT. CRL engages in computing research to extend the state of the computing art in areas likely to be important to Digital and its customers in future years. CRL’s main focus is applications technology; that is, the creation of knowledge and tools useful for the preparation of important classes of applications. CRL Technical Reports can be ordered by electronic mail. To receive instructions, send a message to one of the following addresses, with the word help in the Subject line

Concurrency and Recovery for Index Trees

Providing high concurrency in B + -trees has been studied extensively. But few efforts have been documented for combining concurrency methods with a recovery scheme that preserves well-formed trees across system crashes. We describe an approach for this that works for a class of index trees that is a generalization of the B link -tree. A major feature of our method is that it works with a range of different recovery methods. It achieves this by decomposing structure changes in an index tree into a sequence of atomic actions, each one leaving the tree well-formed and each working on a separate level of the tree. All atomic actions on levels of the tree above the leaf level are independent of database transactions, and so are of short duration. Keywords: concurrency, recovery, indexing, access methods, B-trees c flDigital Equipment Corporation and Betty Salzberg 1991. All rights reserved. 1 College of Computer Science, Northeastern University, Boston, MA. This work was partially s..

Groups Generated By Groups Of Root Type 1 In Omega(v).

PhDMathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/187073/2/7215000.pd

On-line Reorganization of Sparsely-populated B+-trees

In this paper, we present an efficient method to do on-line reorganization of sparsely-populated B+-trees. Our method locks a minimum number of pages to do reorganization. It reorganizes the leaves first, compacting in short operations groups of leaves with the same parent. These groups form small reorganization units. During compacting, only the leaves of one reorganization unit are locked and then for a shorter time their common parent is also locked. After compacting, optionally, the new leaves may swap locations or be moved into empty pages so that they are in key order on the disk. We also propose heuristics for minimizing the number of leaf swaps (as opposed to leaf moves) to be done at the end of leaf reorganization. This further increases concurrency. After the leaves are reorganized, the method shrinks the tree by making a copy of the upper part of the tree while leaving the leaves in place. At most one index page is share locked until the copy is complete. Thus, most of t..