File Allocation Research Articles

Multiple copy file allocation and placement in a distributed information network

The problem of minimizing query, update and storage costs in a distributed information network in which one or more m sites may receive a copy of one or more of m different files is studied in this work. The problem is known to be NP complete. Cost efficiency considerations further dictate that for each query emanating site there be exactly one designated responder site. A model to solve the problem is formulated. Two heuristics based on the problem structure are proposed and their performance relative to each other and to an optimal procedure is reported for problems with up to four files and up to eight sites.

Data allocation in distributed database systems

The problem of allocating the data of a database to the sites of a communication network is investigated. This problem deviates from the well-known file allocation problem in several aspects. First, the objects to be allocated are not known a priori; second, these objects are accessed by schedules that contain transmissions between objects to produce the result. A model that makes it possible to compare the cost of allocations is presented; the cost can be computed for different cost functions and for processing schedules produced by arbitrary query processing algorithms. For minimizing the total transmission cost, a method is proposed to determine the fragments to be allocated from the relations in the conceptual schema and the queries and updates executed by the users. For the same cost function, the complexity of the data allocation problem is investigated. Methods for obtaining optimal and heuristic solutions under various ways of computing the cost of an allocation are presented and compared. Two different approaches to the allocation management problem are presented and their merits are discussed.

Computational complexity of the file allocation problem in distributed database systems

AbstractIn most studies of the optimum allocation problem of the data file in the distributed database system, access to individual files is considered independent, ignoring the relation among files. This assumption may not be appropriate in actual cases. In this paper, the expression for the query cost is simplified as long as the essential aspect of the problem is maintained. A formulation is made based on a clear distinction between the part of the file which can be considered as independent in the individual access, and the part which is not. Then for each formulation, the computational complexity in the optimum file allocation is discussed. It is shown that the problem for the former can be answered in a polynomial time, while the latter is NP‐hard.

Reliability of disk file organisation for microcomputers

The problem of organisation of directories and file allocation data in disk storage is discussed. Two types of data structures are analysed: the linear directory with an embedded disk map and the tree directory with a separate disk map. To compare reliability of different directory structures some criteria are introduced which address the problem of expected data loss due to a single disk surface fault. The analysis is illustrated by the example of the directory structures in two commonly used microcomputer operating systems: CP/M and PC-DOS.

Disk file allocation based on the buddy system

The buddy system is known for its speed and simplicity. However, high internal and external fragmentation have made it unattractive for use in operating system file layout. A variant of the binary buddy system that reduces fragmentation is described. Files are allocated on up to t extents, and inoptimally allocated files are periodically reallocated. The Dartmouth Time-Sharing System (DTSS) uses this method. Several installations of DTSS, representing different classes of workload, are studied to measure the method's performance. Internal fragmentation varies from 2-6 percent, and external fragmentation varies from 0-10 percent for expected request sizes. Less than 0.1 percent of the CPU is spent executing the algorithm. In addition, most files are stored contiguously on disk. The mean number of extents per file is less than 1.5, and the upper bound is t . Compared to the tile layout method used by UNIX, the buddy system results in more efficient access but less efficient utilization of disk space. As disks become larger and less expensive per byte, strategies that achieve efficient I/O throughput at the expense of some storage loss become increasingly attractive.

Optimizing the Structure of Distributed Process Control Systems

The number of stations of local area network of the distributed process control system, being determined at the stage of design, influences greatly on the execution time of the system application functions. It is shown, that increasing the number of stations not always improves this time. This time depends also on allocation of processing operations, application programs for operations and files at the stations. The problem of optimizing the structure of the distributed process control system is formulated as obtaining the number of stations and the allocation of operations, programs and files tit the stations, pursuing the goal to minimize the execution time of system application functions. The problem formulation takes into account the constraint on station memory size. The problem is formulated as a nonlinear zero-one programming problem. The presented heuristic algorithm for solving this problem is based on a directed search of suboptimal solution.

Linked hashing: An improvement of open addressing techniques for large secondary storage files

An improvement of open addressing resolution schemes for hash-based files on secondary storage is defined in this paper. Linked hashing exploits the increase in compressibility of a hash file when buckets are larger, given a fixed file allocation. Both average access times and the number of records stored can significantly improve, for large files where the ratio between the key length and the record length is much less than 1.

Optimal file allocation in a loop topology local area network

The optimal file allocation in a loop topology local area network is investigated. The model, formulated as a 0–1 programming problem, takes into consideration several constraints that the objective function is subjected to. The model is initially a non-linear program which is reduced to linear form by a heuristic simplification. Results are presented for three typical situations.

The file allocation problem—A queueing network optimization approach

A set of customers use a connected network of computer installations, each accessing the network from a particular node. These customers share information contained in a set of data files. A typical customer's need is characterized by a request requiring a subset of these files being accessed in a Markovian sequence. The cycle time for this customer is the total time taken on the average to complete his request sequence. The objective is to locate a single copy of each of the files in such a way that a weighted sum of these response times is minimized. The problem is modelled as a Closed Queueing Network optimization problem. Models are developed for both single and multiple chain cases. An incremental analysis approach is used to solve the single chain case. For the multiple chain case, it is shown how this model approximates to a set partitioning problem under certain conditions. Efficient heuristics are developed to solve this partitioning problem. With certain simplifying assumptions, the associated communication problem is then included in the model.

Reliability analysis of a non-redundant repairable multiplexing unit : A. Pattavina, A. Roveri and A. Leccese. IEEE Trans. Reliab.R-34(3), 275 (1985)

In this paper, the problem of determining an optimal file allocation in a distributed database is considered. The solution method is based on the isomorphism between the non-redundant file allocation problem and the “multiple choice constraints” knapsack problem, which is a well-known, classical problem of operations research. An ‘ad hoc’ branch and bound algorithm is then introduced for the redundant file allocation problem. Computational results showing the efficiency of the proposed technique are included.

Distributed computer system design: An interactive procedure

This paper presents an overview of an interactive system for the design of a distributed computer system. The system helps the designer in finding the optimal combination of processors of varying power to be located at various nodes of the system. It also helps in finding the optimal allocation of data files or databases. The system allows the designer to trade-off between the conflicting objectives: low investment and operating cost and high availability of data. Reasonable relative weights are assigned to each data file, and design objectives can be assigned priorities. A value added network such as TELENET is assumed for data communication. Also, multiple copies of the data file or database may exist in the system to achieve higher data availability and better response time.

Adaptive File Allocation in Star Computer Network

In this paper, we study the allocation of files in a star network. Unlike previous algorithms which assume that files are independently accessed and independently assigned, the interaction of files during the processing of queries is directly incorporated into our cost model. We present an adaptive algorithm, which is much faster than existing algorithms on file allocation, obtains solutions which are on the average only 0.1 percent away from the optimal solutions, and possesses many desirable properties such as the satisfaction of some necessary and sufficient conditions for file allocation.

A note on redundant Disk Modulo allocation

Preliminary consideration of redundant Disk Modulo file allocations to multiple disks finds that strict optimal performance can be obtained for 2 p disks via (⌈ p p 2 ⌉) -fold replication.

Modeling of multiple copy update costs for file allocation in distributed databases

The file allocation problem for distributed databases has been extensively studied in the literature and the objective is to minimize total costs consisting of storage, query and update communication costs. Current modeling of update communication costs is simplistic and does not capture the working of most of the protocols that have been proposed. This paper shows that more accurate modeling of update costs can be achieved fairly easily without an undue increase in the complexity of the formulation. In particular, formulations for two classes of update protocols are shown. Existing heuristics can be used on these formulations to obtain good solutions.

Evaluation of the File Redundancy in Distributed Database Systems

This paper treats the file redundancy issue in distributed database systems, asking what is the optimal number of file copies, given the ratio r of the frequency of update requests to the frequency of all file access requests (i.e., queries and updates). Formulations of this type of problem, including optimal file allocation, have been attempted by a number of authors, and some algorithms have been proposed. Although such algorithms can be used to solve particular problems, it seems difficult to draw general conclusions applicable to a wide variety of practical distributed database systems. To probe into this hard to formulate but interesting problem, our paper constructs simplified network models of distributed database systems, and computes the optimal number of file copies, as well as their locations, to minimize the communication cost. For several network types, we plot the optimal number of file copies as a function of the ratio r.

A heuristic approximation for reducing problem size in network file allocation models

The design of distributed processing systems has increasingly drawn the attention of systems designers as more and more organizations recognize the advantages of decentralizing operations. However, determination of an optimal or preferred distributed data base configuration is a nontrivial task. A viable model for allocating files to nodes in a distributed system must consider the tradeoffs between costs and service and the unique characteristics of the system, including the planned redundancy inherent in the file organization. It also must be solvable within the current state of the art. This paper presents a mixed-integer linear programming model which allows assignment of replicated and/or partitioned files to the nodes of a distributed network while considering query, update and storage costs associated with the file assignments. The resulting model, though large, is solvable even for networks with a substantial number of nodes and links. Because the model relies on an average communication cost for determining file location, results are presented comparing the model performance to that of a model utilizing exact communication costs.

The Isomorphism of Simple File Allocation

In this paper, we show that the simple file allocation problem in computer science is isomorphic to the single commodity warehouse location problem in operations research. In simple file allocation, costs due to query and update accesses and storage are considered. Design requirements such as reliability, availability, and delay are not taken into account. Due to this isomorphism, many techniques which have been developed for the warehouse location problem can be applied to solve the simple file allocation problem. Furthermore, there are techniques and conditions developed for one problem which match closely with techniques and conditions developed for the other problem. Based on a combined set of conditions developed in computer science and operations research, a heuristic for file allocation is presented.

File Allocation in a Distributed Computer Communication Network

An algorithm is presented to determine locations for the storage of copies of files in store-and-forward computer communications networks. The algorithm determines storage locations which minimize the sum of network file storage costs and message transmission costs. Networks that use adaptive routing techniques are the primary focus. Feasible file locations must satisfy network performance requirements for file availability and delay by message class. An effective method of evaluating delay constraints for networks using adaptive routing techniques is introduced. The algorithm uses the solution to a p-median problem to identify initial candidate file placements. Interaction between a set of file movement rules and a network simulator is employed to modify initial placements to fmd near-optimal locations which satisfy the network performance constraints.

Use of tree structures for processing files

In data processing problems, files are frequently used which must both be searched and altered. Binary search techniques are efficient for searching large files, but the associated file organization is not readily adapted to the file alterations. Conversely, a chained file allocation permits elcient alteration but cannot be searched efficiently. A file organized into a tree-like structure is discussed, and it is shown that such a file may both be searched and altered with times proportional to s log, N , where N is the number of file items and s is a parameter of the tree. It is also shown that optimizing the value of s leads to a search time which is only 25 per cent slower than the binary search. The tree organization employs two data chains and may be considered to be a compromise between the organizations for the binary search and the chained file. The relation of the tree organization to multidimensional indexing and to the trie structure is also discussed.

Optimal file allocation in a computer network: a solution method based on the knapsack problem

In this paper, the problem of determining an optimal file allocation in a distributed database is considered. The solution method is based on the isomorphism between the non-redundant file allocation problem and the “multiple choice constraints” knapsack problem, which is a well-known, classical problem of operations research. An ‘ad hoc’ branch and bound algorithm is then introduced for the redundant file allocation problem. Computational results showing the efficiency of the proposed technique are included.