Browsing by Author "Verma, Rakesh M."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Efficient Archivable Time Index: A Dynamic Indexing Scheme for Temporal Data(McGraw Hill, 1994) Verma, Rakesh M.; Varman, Peter J.We present a practical and asymptotically optimal indexing structure for a versioned timestamped database with step-wise constant data. Three version operations, insertions, updates, and deletes are allowed for the present version, whereas query operations are allowed for any version, present or past. Snapshot and time-range queries can be answered optimally with this structure. As a two-level index, attribute-search and attribute-history queries can be solved in time proportional to the output size plus an additive logarithmic term. The time index uses linear storage; this improves upon previous work which either had logarithmic query overhead time and quadratic space, or linear space and linear query overhead time. The tradeoff is a small increase in the time for version operations from constant to logarithmic. All measures are worst-case. The index has a natural structure for archiving in write-once storage media like optical disks.Item An Efficient Multiversion Access Structure(2007-05) Varman, Peter J.; Verma, Rakesh M.An efficient multiversion access structure for a transaction-time database is presented. Our method requires optimal storage and query times for several important queries and logarithmic update times. Three version operations}inserts, updates, and deletes}are allowed on the current database, while queries are allowed on any version, present or past. The following query operations are performed in optimal query time: key range search, key history search, and time range view. The key-range query retrieves all records having keys in a specified key range at a specified time; the key history query retrieves all records with a given key in a specified time range; and the time range view query retrieves all records that were current during a specified time interval. Special cases of these queries include the key search query, which retrieves a particular version of a record, and the snapshot query which reconstructs the database at some past time. To the best of our knowledge no previous multiversion access structure simultaneously supports all these query and version operations within these time and space bounds. The bounds on query operations are worst case per operation, while those for storage space and version operations are (worst-case) amortized over a sequence of version operations. Simulation results show that good storage utilization and query performance is obtained.Item Tight Bounds for Prefetching and Buffer Management Algorithms for Parallel I/O Systems(Rice University, 1999-12) Varman, Peter J.; Verma, Rakesh M.; Electrical and Computer Engineering; Varman LaboratoryThe I/O performance of applications in multiple-disk systems can be improved by overlapping disk accesses. This requires the use of appropriate prefetching and buffer management algorithms that ensure the most useful blocks are accessed and retained in the buffer. In this paper, we answer several fundamental questions on prefetching and buffer management for distributed-buffer parallel I/O systems. First, we derive and prove the optimality of an algorithm, P-min, that minimizes the number of parallel I/Os. Second, we analyze P-con, an algorithm that always matches its replacement decisions with those of the well-known demand-paged MIN algorithm. We show that P-con can become fully sequential in the worst case. Third, we investigate the behavior of on-line algorithms for multiple-disk prefetching and buffer management. We define and analyze P-lru, a parallel version of the traditional LRU buffer management algorithm. Unexpectedly, we find that the competitive ratio of P-lru is independent of the number of disks. Finally, we present the practical performance of these algorithms on randomly generated reference strings. These results confirm the conclusions derived from the analysis on worst case inputs.