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14
View Serializable Updates of Concurrent Index Structures
 DBPL 2001 : 247262, LNCS 2397
, 2001
"... Abstract. We present new algorithms for concurrent reading and updating of B *trees and binary search trees. Our algorithms are based on the wellknown link technique, and improve previously proposed solutions in several respects. We prove formally that our algorithms are correct. We show that they ..."
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Cited by 1 (0 self)
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Abstract. We present new algorithms for concurrent reading and updating of B *trees and binary search trees. Our algorithms are based on the wellknown link technique, and improve previously proposed solutions in several respects. We prove formally that our algorithms are correct. We show that they satisfy a view serializability criterion, which fails for previous solutions. This stronger serializability criterion is central to the proof that several subtle (but essential) optimizations incorporated in our algorithms are correct. 1
Brief Announcement: Solvability of Geocasting in Mobile AdHoc Networks
"... We present a model of a mobile adhoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem despite connectivity and no matter how slowly the nodes move. Even ..."
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We present a model of a mobile adhoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem despite connectivity and no matter how slowly the nodes move. Even if each node maintains a stable connection with each of its neighbours for some period of time, it is impossible to solve geocast if nodes move too fast. Additionally, we give a tradeoff lower bound which shows that the faster the nodes can move, the more costly it would be to solve the geocast problem. Finally, for the onedimensional case of the mobile adhoc network, we provide an algorithm for geocasting and we prove its correctness given exact bounds on the speed of movement.
SciHadoop: Arraybased Query Processing in Hadoop
"... Hadoop has become the de facto platform for largescale data analysis in commercial applications, and increasingly so in scientific applications. However, Hadoop’s byte stream data model causes inefficiencies when used to process scientific data that is commonly stored in highlystructured, arrayba ..."
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Cited by 14 (2 self)
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Hadoop has become the de facto platform for largescale data analysis in commercial applications, and increasingly so in scientific applications. However, Hadoop’s byte stream data model causes inefficiencies when used to process scientific data that is commonly stored in highlystructured, arraybased binary file formats resulting in limited scalability of Hadoop applications in science. We introduce SciHadoop, a Hadoop plugin allowing scientists to specify logical queries over arraybased data models. SciHadoop executes queries as map/reduce programs defined over the logical data model. We describe the implementation of a SciHadoop prototype for NetCDF data sets and quantify the performance of five separate optimizations that address the following goals for several representative aggregate queries: reduce total data transfers, reduce remote reads, and reduce unnecessary reads. Two optimizations allow holistic aggregate queries to be evaluated opportunistically during the map phase; two additional optimizations intelligently partition input data to increase read locality, and one optimization avoids block scans by examining the data dependencies of an executing query to prune input partitions. Experiments involving a holistic function show runtime improvements of up to 8x, with drastic reductions of IO, both locally and over the network.
Relating the PSPACE reasoning power of Boolean Programs and Quantified Boolean Formulas
, 2000
"... We present a new propositional proof system based on a recent new characterization of
polynomial space (PSPACE) called Boolean Programs, due to Cook and Soltys. We show
that this new system, BPLK, is polynomially equivalent to the system G, which is based
on the familiar and very different quantifie ..."
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Cited by 13 (9 self)
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We present a new propositional proof system based on a recent new characterization of
polynomial space (PSPACE) called Boolean Programs, due to Cook and Soltys. We show
that this new system, BPLK, is polynomially equivalent to the system G, which is based
on the familiar and very different quantified Boolean formula (QBF) characterization of
PSPACE due to Stockmeyer and Meyer. We conclude with a discussion of some closely
related open problems and their implications.
Mobility versus the cost of geocasting in mobile adhoc networks
, 2007
"... Abstract. We present a model of a mobile adhoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem despite connectivity and no matter how slowly the nodes m ..."
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Cited by 2 (2 self)
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Abstract. We present a model of a mobile adhoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem despite connectivity and no matter how slowly the nodes move. Even if each node maintains a stable connection with each of its neighbours for some period of time, it is impossible to solve geocast if nodes move too fast. Additionally, we give a tradeoff lower bound which shows that the faster the nodes can move, the more costly it would be to solve the geocast problem. Finally, for the onedimensional case of the mobile adhoc network, we provide an algorithm for geocasting and we prove its correctness given exact bounds on the speed of movement.
SIDR: StructureAware Intelligent Data Routing in Hadoop
"... The MapReduce framework is being extended for domains quite different from the web applications for which it was designed, including the processing of big structured data, e.g., scientific and financial data. Previous work using MapReduce to process scientific data ignores existing structure when as ..."
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Cited by 1 (0 self)
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The MapReduce framework is being extended for domains quite different from the web applications for which it was designed, including the processing of big structured data, e.g., scientific and financial data. Previous work using MapReduce to process scientific data ignores existing structure when assigning intermediate data and scheduling tasks. In this paper, we present a method for incorporating knowledge of the structure of scientific data and executing query into the MapReduce communication model. Built in SciHadoop, a version of the Hadoop MapReduce framework for scientific data, SIDR intelligently partitions and routes intermediate data, allowing it to: remove Hadoop’s global barrier and execute Reduce tasks prior to all Map tasks completing; minimize intermediate key skew; and produce early, correct results. SIDR executes queries up to 2.5 times faster than Hadoop and 37 % faster than SciHadoop; produces initial results with only 6 % of the query completed; and produces dense, contiguous output.
Divergent Physical Design Tuning for Replicated Databases
"... We introduce divergent designs as a novel tuning paradigm for database systems that employ replication. A divergent design installs a different physical configuration (e.g., indexes and materialized views) with each database replica, specializing replicas for different subsets of the workload. At ru ..."
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Cited by 2 (1 self)
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We introduce divergent designs as a novel tuning paradigm for database systems that employ replication. A divergent design installs a different physical configuration (e.g., indexes and materialized views) with each database replica, specializing replicas for different subsets of the workload. At runtime, queries are routed to the subset of the replicas configured to yield the most efficient execution plans. When compared to uniformly designed replicas, divergent replicas can potentially execute their subset of the queries significantly faster, and their physical configurations could be initialized and maintained (updated) in less time. However, the specialization of divergent replicas limits the ability to loadbalance the workload at runtime. We formalize the divergent design problem, characterize the properties of good designs, and analyze the complexity of identifying the optimal divergent design. Our paradigm captures the tradeoff between load balancing among all n replicas vs. load balancing among m ≤ n specialized replicas. We develop an effective algorithm (leveraging singlenodetuning functionality) to compute good divergent designs for all the points of this tradeoff. Experimental results validate the effectiveness of the algorithm and demonstrate that divergent designs can substantially improve workload performance.
Distributed Aerial Scanning in Mobile AdHoc Networks ∗
"... We formally define the aerial scanning problem. A set of unmanned aerial vehicles (UAVs) cooperate to frequently scan a given geographic area. Each UAV can only photograph a small portion of it at a time. Each UAV maintains the necessary information to create a global picture of the geographic area. ..."
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We formally define the aerial scanning problem. A set of unmanned aerial vehicles (UAVs) cooperate to frequently scan a given geographic area. Each UAV can only photograph a small portion of it at a time. Each UAV maintains the necessary information to create a global picture of the geographic area. This global picture consists of smaller pictures that are taken within small time of each other and also none is taken too far in the past. UAVs exchange information over a synchronous mobile adhoc network. For this network, we propose efficient solutions to the aerial scanning problem that tolerate a bounded number of UAV failures.
Toronto, Ontario,
, 2004
"... In this paper, we are interested in transformations of selfstabilizing algorithms from one model to another that preserve stabilization. We propose an easy technique for proving correctness of a natural class of transformations of selfstabilizing algorithms from any model to any other. We present ..."
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In this paper, we are interested in transformations of selfstabilizing algorithms from one model to another that preserve stabilization. We propose an easy technique for proving correctness of a natural class of transformations of selfstabilizing algorithms from any model to any other. We present a new transformation of selfstabilizing algorithms from a message passing model to a shared memory model with a finite number of registers of bounded size and processors of bounded memory and prove it correct using our technique. This transformation is not waitfree, but we prove that no such transformation can be waitfree. For our transformation, we use a new selfstabilizing tokenpassing algorithm for the shared memory model. This algorithm stabilizes in O(n log 2 n) rounds, which improves existing algorithms. 1
Abstract
"... We present a model of a mobile adhoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem despite connectivity and no matter how slowly the nodes move. Even ..."
Abstract
 Add to MetaCart
We present a model of a mobile adhoc network in which nodes can move arbitrarily on the plane with some bounded speed. We show that without any assumption on some topological stability, it is impossible to solve the geocast problem despite connectivity and no matter how slowly the nodes move. Even if each node maintains a stable connection with each of its neighbours for some period of time, it is impossible to solve geocast if nodes move too fast. Additionally, we give a tradeoff lower bound which shows that the faster the nodes can move, the more costly it would be to solve the geocast problem. Finally, for the onedimensional case of the mobile adhoc network, we provide an algorithm for geocasting and we prove its correctness given exact bounds on the speed of movement.
Results 1  10
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