proceeding
LitStream Collection
Home
Berenson, Hal; Bernstein, Phil; Gray, Jim; Melton, Jim; O'Neil, Elizabeth; O'Neil, Patrick
doi: 10.1145/568271.223785pmid: N/A
ANSI SQL-92 MS, ANSI defines Isolation Levels in terms of phenomena: Dirty Reads, Non-Repeatable Reads, and Phantoms. This paper shows that these phenomena and the ANSI SQL definitions fail to properly characterize several popular isolation levels, including the standard locking implementations of the levels covered. Ambiguity in the statement of the phenomena is investigated and a more formal statement is arrived at; in addition new phenomena that better characterize isolation types are introduced. Finally, an important multiversion isolation type, called Snapshot Isolation, is defined.
Molesky, Lory D.; Ramamritham, Krithi
doi: 10.1145/568271.223786pmid: N/A
Significant performance advantages can be gained by implementing a database system on a cache-coherent shared memory multiprocessor. However, problems arise when failures occur. A single node (where a node refers to a processor/memory pair) crash may require a reboot of the entire shared memory system. Fortunately, shared memory multiprocessors that isolate individual node failures are currently being developed. Even with these, because of the side effects of the cache coherency protocol, a transaction executing strictly on a single node may become dependent on the validity of the memory of many nodes thereby inducing unnecessary transaction aborts. This happens when database objects, such as records, and database support structures, such as index structures and shared lock tables, are stored in shared memory.In this paper, we propose crash recovery protocols for shared memory database systems which avoid the unnecessary transaction aborts induced by the effects of using shared physical memory. Our recovery protocols guarantee that if one or more nodes crash, all the effects of active transactions running on the crashed nodes will be undone, and no effects of transactions running on nodes which did not crash will be undone. In order to show the practicality of our protocols, we discuss how existing features of cache-coherent multiprocessors can be utilized to implement these recovery protocols. Specifically, we demonstrate that (1) for many types of database objects and support structures, volatile (in-memory) logging is sufficient to avoid unnecessary transaction aborts, and (2) a very low overhead implementation of this strategy can be achieved with existing multiprocessor features.
Brodsky, Alexander; Kornatzky, Yoram
doi: 10.1145/568271.223788pmid: N/A
We propose a novel data model and its language for querying object-oriented databases where objects may hold spatial, temporal or constraint data, conceptually represented by linear equality and inequality constraints. The proposed LyriC language is designed to provide a uniform and flexible framework for diverse application realms such as (1) constraint-based design in two-, three-, or higher-dimensional space, (2) large-scale optimization and analysis, based mostly on linear programming techniques, and (3) spatial and geographic databases. LyriC extends flat constraint query languages, especially those for linear constraint databases, to structurally complex objects. The extension is based on the object-oriented paradigm, where constraints are treated as first-class objects that are organized in classes. The query language is an extension of the language XSQL, and is built around the idea of extended path expressions. Path expressions in a query traverse nested structures in one sweep. Constraints are used in a query to filter stored constraints and to create new constraint objects.
Fegaras, Leonidas; Maier, David
doi: 10.1145/568271.223789pmid: N/A
We define a standard of effectiveness for a database calculus relative to a query language. Effectiveness judges suitability to serve as a processing framework for the query language, and comprises aspects of coverage, manipulability and efficient evaluation. We present the monoid calculus, and argue its effectiveness for object-oriented query languages, exemplified by OQL of ODMG-93. The monoid calculus readily captures such features as multiple collection types, aggregations, arbitrary composition of type constructors and nested query expressions. We also show how to extend the monoid calculus to deal with vectors and arrays in more expressive ways than current query languages do, and illustrate how it can handle identity and updates.
Gardarin, Georges; Machuca, Fernando; Pucheral, Philippe
doi: 10.1145/568271.223791pmid: N/A
We present a functional paradigm for querying efficiently abstract collections of complex objects. Abstract collections are used to model class extents, multivalued attributes as well as indexes or hashing tables. Our paradigm includes a functional language called OFL (Object Functional Language) and a supporting execution model based on graph traversals. OFL is able to support any complex object algebra with recursion as macros. It is an appropriate target language for OQL-like query compilers. The execution model provides various strategies including set-oriented and pipelined traversals. OFL has been implemented on top of an object manager. Measures of a typical query extracted from a geographical benchmark show the value of hybrid strategies integrating pipelined and set-oriented evaluations. They also show the potential of function result memorization, a typical optimization approach known as "Memoization" 2 in functional languages.
Roussopoulos, Nick; Kelley, Stephen; Vincent, Frédéric
doi: 10.1145/568271.223794pmid: N/A
A frequently encountered type of query in Geographic Information Systems is to find the k nearest neighbor objects to a given point in space. Processing such queries requires substantially different search algorithms than those for location or range queries. In this paper we present an efficient branch-and-bound R-tree traversal algorithm to find the nearest neighbor object to a point, and then generalize it to finding the k nearest neighbors. We also discuss metrics for an optimistic and a pessimistic search ordering strategy as well as for pruning. Finally, we present the results of several experiments obtained using the implementation of our algorithm and examine the behavior of the metrics and the scalability of the algorithm.
doi: 10.1145/568271.223796pmid: N/A
We present a generic solution to a problem which lies at the heart of the unpredictable worst-case performance characteristics of a wide class of multi-dimensional index designs: those which employ a recursive partitioning of the data space. We then show how this solution can produce modified designs with fully predictable and controllable worst-case characteristics. In particular, we show how the recursive partitioning of an n-dimensional dataspace can be represented in such a way that the characteristics of the one-dimensional B-tree are preserved in n dimensions, as far as is topologically possible i.e. a representation guaranteeing logarithmic access and update time, while also guaranteeing a one-third minimum occupancy of both data and index nodes.
Showing 1 to 10 of 85 Articles