Cached Data Items Research Articles

Prefetching and caching for minimizing service costs: Optimal and approximation strategies

Strategically prefetching data has been utilized in practice to improve caching performance. Apart from caching data items upon requests, they can be prefetched into the cache before requests actually occur. The caching and prefetching operations compete for the limited cache space, whose size is typically much smaller than the number of data items. A key question is how to design an optimal prefetching and caching policy, assuming that the future requests can be predicted to certain extend. This question is non-trivial even under an idealized assumption that the future requests are precisely known.To investigate this problem, we propose a cost-based service model. The objective is to find the optimal offline prefetching and caching policy that minimizes the accumulated cost for a given request sequence. By casting it as a min-cost flow problem, we are able to find the optimal policy for a data trace of length N in expected time O(N3∕2) via flow-based algorithms. However, this requires the entire trace for each request and cannot be applied in real time. To this end, we analytically characterize the optimal policy by obtaining an optimal cache eviction mechanism. We derive conditions under which proactive prefetching is a better choice than passive caching. Based on these insights, we propose a lightweight approximation policy that only exploits predictions in the near future. Moreover, the approximation policy can be applied in real time and processes the entire trace in O(N) expected time. We prove that the competitive ratio of the approximation policy is less than 2. Extensive simulations verify its near-optimal performance, for both heavy and light-tailed popularity distributions.

RSU-Assisted Adaptive Scheduling for Vehicle-to-Vehicle Data Sharing in Bidirectional Road Scenarios

This study investigates the synergy between centralized and decentralized (i.e., ad hoc) data scheduling in vehicular ad hoc networks (VANETs) for offloading and balancing the workloads of roadside units (RSU) in bidirectional road scenarios. In the centralized scheduling, an RSU schedules data dissemination using a hybrid of infrastructure-to-vehicle (I2V) and vehicle-to-vehicle (V2V) communications. Specifically, RSUs cooperate with each other by transferring unserved requests, and each RSU schedules the data services based on its locally received requests and the transferred requests. In the decentralized scheduling, vehicles driving in opposite directions share the cached data items via V2V communication when out of the coverage of RSU. The ad hoc scheduling can be benefited from the cooperation among RSUs since the chance for V2V data sharing could be enhanced when considering transferred requests into scheduling at each RSU. We formulate a hybrid of centralized and ad hoc data scheduling (HCA) problem, aiming at best exploiting the synergistic effects of I2V and V2V communication based on centralized data broadcast and ad hoc data sharing. On this basis, we propose an RSU Cooperation-based Adaptive Scheduling (RCAS) algorithm that consists of three mechanisms, including a centralized scheduling mechanism at each RSU, an ad hoc scheduling mechanism for vehicles, and a cluster management mechanism. Finally, we build the simulation model and give a comprehensive performance evaluation, which demonstrates the superiority of the proposed solution under a variety of circumstances.

Performance Analysis of On-Demand Scheduling with and without Network Coding in Wireless Broadcast

On-demand broadcast is a scalable approach to disseminating information to a large population of clients while satisfying dynamic needs of clients, such as in vehicular networks. However, in conventional broadcast approaches, only one data item can be retrieved by clients in one broadcast tick. To further improve the efficiency of wireless bandwidth, in this work, we conduct a comprehensive study on incorporating network coding with representative on-demand scheduling algorithms while preserving their original scheduling criteria. In particular, a graph model is derived to maximize the coding benefit based on the clients’ requested and cached data items. Furthermore, we propose a heuristic coding-based approach, which is applicable for all the on-demand scheduling algorithms with low computational complexity. In addition, based on various application requirements, we classify the existing on-demand scheduling algorithms into three groups—real-time, non-real-time and stretch optimal. In view of different application-specific objectives, we implement the coding versions of representative algorithms in each group. Extensive simulation results conclusively demonstrate the superiority of coding versions of algorithms against their non-coding versions on achieving their respective scheduling objectives.

A Detailed Survey and Comparative Study of Cooperative Caching Methods for Mobile Ad Hoc Networks

:Mobile Ad Hoc Networks (MANETs) are networks that enable server and clients to impart without any settled foundation. MANET is a quickly developing region of research as it discovers use in different applications. In MANETs, network parceling and the fizzling of a mobile node because of weariness of their battery power can significantly diminish data accessibility. Data caching on the client is generally observed as a successful answer for enhancing data availability. Specifically, cooperative caching based on information sharing and coordination of cached data item among numerous clients is much time-consuming. Various cooperative caching plans have been proposed in the ongoing years. This paper examines the highlights for outlining a good cooperative cache management, and it overviews the current cooperative caching scheme. The paper likewise gives a correlation of the cooperative caching scheme and examines open doors for future research work.

Coding-based cooperative caching in on-demand data broadcast environments

Data broadcasting has been commonly deployed in many emerging mobile applications such as intelligent transportation systems and location-based services, because it is a scalable approach to disseminating information from a mobile support station (MSS) to a large population of mobile hosts (MHs). To provide timely data access and better data availability, MHs can store data items broadcast by the MSS in their local caches and share cached data items cooperatively among neighboring peers via peer-to-peer (P2P) communication. However, if MHs are not neighbors, they cannot cooperate even if they have each other’s requested data items in their own caches. Network coding is a technique, by which multiple MHs can decode out different requested data items from an encoded packet broadcast by the MSS in one broadcast time unit. In this work, we propose a network coding based solution to enable MHs which are not neighbors to cooperate indirectly. We formulate the Maximum Channel Efficiency Encoding (MCEE) problem by introducing network coding and cooperative caching techniques in on-demand data broadcast environments. We prove that MCEE is NP-hard by constructing a polynomial-time reduction from the Minimum Clique Cover (MCC) problem. Further, we propose two schemes (NCM and NCB) for on-demand data broadcasting using network coding. In each scheme, we propose two algorithms running at the MSS and MHs for making encoding decisions and decoding requested data items, respectively. We build the simulation model for performance evaluation and the simulation results demonstrate that the proposed schemes not only increase the bandwidth efficiency of the limited downlink communication channel, but also enhance the system performance by reducing the data access latency.

Invalidation Method for Wireless Mobile Network to Maintain Consistency

This paper is proposed for the distributed cache invalidation mechanism (DCIM), it is a client-based cache consistency scheme which is implemented on the top of a previously proposed architecture for the caching data items in mobile ad hoc networks (MANETs), namely COACS, where special nodes cache the queries and the addresses of the nodes that store the responses to these queries. Caching frequently accessed data items on the client side is an effective technique for improving performance in a mobile environment. The classical cache invalidation strategies are not suitable for the mobile environments due to frequent disconnections and mobility of the clients. The huge amount of demand has been created due to trend toward wireless communications and advances in mobile technologies are which increasing the consumer demands for ubiquitous access to Internet-based information and services. DCIM can be implemented using ns2, and compared against the client-based and server-based schemes to assess its performance experimentally. Hear introduce DCIM that is totally client-based. DCIM is a pull- based algorithm that implements adaptive time to live (TTL), piggybacking, and pre-fetching, and provides near strong consistency capabilities. Keywordsdata caching, pull-based, TTL, shared data.

An Administrative Cluster-based Cooperative Caching (ACCC) strategy for Mobile Ad Hoc Networks

Recent explosive growth in computing and wireless communication technologies has led to an increasing interest in mobile ad hoc networks (MANET). Among the many challenges for MANET designers and users, data availability is a critical issue. Caching is considered as an effective solution for the availability problem. Although cooperative caching improves the data access by reducing access latency and bandwidth usage in MANETs, it still suffers from several hurdles and technical problems. This paper introduces a new cooperative caching strategy for MANETs, which is called Administrative Cluster-Based Cooperative Caching (ACCC). ACCC keeps at most two copies of the cached data items in each cluster. Moreover, it develops a new administrative module, which perfectly controls the caching process. ACCC is a cluster-based caching strategy, hence, it divides the network into a set of overlapping clusters. Each cluster is managed by a Cluster Manager (CM) as well as a Cluster Backup (CB). ACCC has several salient features that other techniques do not have such as: (i) the integration between CM and CB besides the integration among all the caching modules improves the data availability within the cluster, (ii) ACCC; maximizes the caching hit ratio, reduces access delay, and saves the battery power of network nodes. ACCC is simulated using Java Caching System JCS2 with the efficient platform Java Enterprise Edition EE8 using a client/server model. Experimental results have shown that ACCC outperforms recent cluster-based caching strategies as it introduces higher cache hit ratio as well as better data availability.

Client Based System on Wireless Sensor Network for Efficient Packet Transmission

Wireless sensor networks are vulnerable to the node distributor dividend, and several distributed protocols has been transfer the data in secure .Where MD5 algorithm that implements adaptive TTL, piggybacking, and perfecting, and provides near strong consistency guarantees. Cached data items are assigned adaptive TTL values that correspond to their update rates at the data source. Expired items as well as non expired ones but meet certain criteria are grouped in validation requests to the data source, which in turn sends the cache devices the actual items that have changed, or invalidates them, based on their request rates. In DHTbased protocol can detect node distributor dividend with high security level to transfer the data. Protocol of this type initial nodes send claiming messages containing a neighbor-list along with a maximum hop limit to randomly selected neighbors then, the subsequent message transmission is regulated by a probabilistic directed technique to approximately maintain a line property through the network as well as to incur sufficient randomness for better performance on communication.

Client Based Cache Consistency Scheme in Wireless Mobile Networks

This paper proposes a client based cache consistency scheme for maintaining cache consistency in wireless mobile networks using a distributed cache invalidation method. This is implemented on top of a previously proposed architecture for caching data items in mobile ad hoc networks (MANETs), namely COCAS. We have also previously proposed a client and server based consistency scheme, named SSUM and DCIM. Client based cache consistency scheme is a pull-based algorithm that implements adaptive time to live (TTL), piggybacking, and prefetching, and provides strong consistency capabilities. We assign an adaptive TTL value to the cached data items in the data source depending on their update rates, where items with expired TTL values are grouped in validation requests to the data source to refresh them. But the unexpired ones with high request rates are prefetched from the server. Index Terms: Cache consistency, Cache invalidation, Distributed cache invalidation method, time to live, wireless mobile networks.

DCIM: Distributed Cache Invalidation Method for Maintaining Cache Consistency in Wireless Mobile Networks

This paper proposes distributed cache invalidation mechanism (DCIM), a client-based cache consistency scheme that is implemented on top of a previously proposed architecture for caching data items in mobile ad hoc networks (MANETs), namely COACS, where special nodes cache the queries and the addresses of the nodes that store the responses to these queries. We have also previously proposed a server-based consistency scheme, named SSUM, whereas in this paper, we introduce DCIM that is totally client-based. DCIM is a pull-based algorithm that implements adaptive time to live (TTL), piggybacking, and prefetching, and provides near strong consistency capabilities. Cached data items are assigned adaptive TTL values that correspond to their update rates at the data source, where items with expired TTL values are grouped in validation requests to the data source to refresh them, whereas unexpired ones but with high request rates are prefetched from the server. In this paper, DCIM is analyzed to assess the delay and bandwidth gains (or costs) when compared to polling every time and push-based schemes. DCIM was also implemented using ns2, and compared against client-based and server-based schemes to assess its performance experimentally. The consistency ratio, delay, and overhead traffic are reported versus several variables, where DCIM showed to be superior when compared to the other systems.

An Energy Conserving Cooperative Caching Policy for Ad Hoc Networks

Without pre-existing infrastructure, a Mobile Ad Hoc Network (MANET) can be easily deployed in a hostile environment such as a military operation area or an area undergoing disaster recovery. With limited bandwidth, the data caching technique may be useful to enhance the performance of a MANET. The cooperative caching scheme is shown to be suitable for MANETs. With cooperative caching schemes, each node shares its cached data items with other nodes in the network to improve the data availability of the network. Unfortunately, the existing cooperative caching schemes did not consider the energy consumption of a mobile node. A mobile node with limited residual energy may exhaust its power very quickly. As a result, the data availability of the network will be degraded. In this paper, we propose an energy conserving cooperative caching scheme which allows a mobile node with more residual energy to cache more data items for other nodes than a mobile node with less residual energy. Simulation results show that the proposed scheme enhance the data availability by reducing the response time of a query and extending the lifetime of the network.

An update-based step-wise optimal cache replacement for wireless data access

Many network applications requires access to most up-to-date information. An update event makes the corresponding cached data item obsolete, and cache hits due to obsolete data items become simply useless to those applications. Frequently accessed but infrequently updated data items should get higher preference while caching, and infrequently accessed but frequently updated items should have lower preference. Such items may not be cached at all or should be evicted from the cache to accommodate items with higher preference. In wireless networks, remote data access is typically more expensive than in wired networks. Hence, an efficient caching scheme considers both data access and update patterns can better reduce data transmissions in wireless networks. In this paper, we propose a step-wise optimal update-based replacement policy, called the Update-based Step-wise Optimal (USO) policy, for wireless data networks to optimize transmission cost by increasing effective hit ratio. Our cache replacement policy is based on the idea of giving preference to frequently accessed but infrequently updated data, and is supported by an analytical model with quantitative analysis. We also present results from our extensive simulations. We demonstrate that (1) the analytical model is validated by the simulation results and (2) the proposed scheme outperforms the Least Frequently Used (LFU) scheme in terms of effective hit ratio and communication cost.

Flexible Data Dissemination Strategy For Effective Cache Consistency In Mobile Wireless Communication Networks

In mobile wireless communication network, caching data items at the mobile clients is important to reduce the data access delay. However, efficient cache invalidation strategies are used to ensure the consistency between the data in the cache of mobile clients and at the database server. Servers use invalidation reports (IRs) to inform the mobile clients about data item updates. This paper proposes and implements a multicast based strategy to maintain cache consistency in mobile environment using AVI as the cache invalidation scheme. The proposed algorithm is outlined as follows – To resolve a query, the mobile client searches its cache to check if its data is valid. If yes, then query is answered, otherwise the client queries the DTA (Dynamic Transmitting Agent) for latest updates and the query is answered. If DTA doesn’t have the latest updates, it gets it from the server. So, the main idea here is that DTA will be multicasting updates to the clients and hence the clients need not uplink to the server individually, thus preserving the network bandwidth. The scenario of simulation is developed in Java. The results demonstrate that the traffic generated in the proposed multicast model is simplified and it also retains cache consistency when compared to the existing methods that used broadcast strategy.

Efficient cache invalidation schemes for mobile data accesses

This paper presents two cache invalidation schemes to maintain data consistency between the server and clients in a mobile environment. Designed according to real situations like MANET, the Adaptive Data Dividing ( ADD) scheme divides data into groups of different utilization ratios and varies group broadcast intervals to reduce data access time and bandwidth consumption. The Data Validity Defining ( DVD) scheme aims to solve the validity problem of cached data items, which usually happens after clients disconnect from the server. Experimental evaluations and performance analyses exhibit that the two schemes outperform most existing cache invalidation schemes in terms of data access time, cache miss ratios, query uplink ratios and bandwidth consumption.

An energy efficient re-access scheme for data caching in data broadcast of a mobile computing environment

Data caching is used to improve the response time and the power consumption of a mobile client in a mobile computing environment. To enhance the performance of data caching, one needs to improve the hit ratio and to reduce the cost in processing a cache miss. In a mobile computing environment, a cached data item of a mobile client needs to remain up-to-date with respect to its corresponding data item in the server. A cached data item which is out of date is called a cached invalidated data item. Accessing a cached invalidated data item can be regarded as processing a cache miss. To access a cached invalidated data item, a mobile client needs to download the new content of the data item from the broadcast channel. This operation is called a re-access operation in this paper. Re-accessing a cached invalidated data item incurs large tuning time overhead. In this paper, we propose a re-access scheme that reduces this overhead by allowing a mobile client to access a cached invalidated data item from the broadcast channel without accessing indices. We analyze the performance of the proposed scheme and validate the analysis through experiments. The experiments showed that the proposed scheme significantly reduces the tuning time of a mobile client. Furthermore, the proposed scheme is robust in the sense that it allows changes on the broadcast structure in data broadcasting.

Energy efficient cache invalidation in a disconnected wireless mobile environment

Caching of frequently accessed data on the mobile clients can reduce the number of uplink requests, server load and query latency and can increase data availability. As cached data items eventually become invalid due to updates at the server, an invalidation strategy is employed to maintain cache consistency so that no obsolete data would be used to serve queries. The basic cache invalidation strategies make use of periodic invalidation reports (IRs) and updated invalidation reports (UIRs) broadcast by the server. This paper presents a synchronous stateful caching strategy called update report (UR). UR strategy preserves the advantages of IR/UIR strategies and improves on their disadvantages. It reduces the size of IR by filtering out noncached items, handles long disconnection, reduces query latency by broadcasting recently requested items immediately after every UIR, conserves client energy and supports mobility. Simulation results prove that UR yields better performance than IR and UIR strategies.

Research in Mobile Database Query Optimization and Processing

The emergence of mobile computing provides the ability to access information at any time and place. However, as mobile computing environments have inherent factors like power, storage, asymmetric communication cost, and bandwidth limitations, efficient query processing and minimum query response time are definitely of great interest. This survey groups a variety of query optimization and processing mechanisms in mobile databases into two main categories, namely: (i) query processing strategy, and (ii) caching management strategy. Query processing includes both pull and push operations (broadcast mechanisms). We further classify push operation into on‐demand broadcast and periodic broadcast. Push operation (on‐demand broadcast) relates to designing techniques that enable the server to accommodate multiple requests so that the request can be processed efficiently. Push operation (periodic broadcast) corresponds to data dissemination strategies. In this scheme, several techniques to improve the query performance by broadcasting data to a population of mobile users are described. A caching management strategy defines a number of methods for maintaining cached data items in clients′ local storage. This strategy considers critical caching issues such as caching granularity, caching coherence strategy and caching replacement policy. Finally, this survey concludes with several open issues relating to mobile query optimization and processing strategy.

Scalable cache invalidation algorithms for mobile data access

In this paper, we address the problem of cache invalidation in mobile and wireless client/server environments. We present cache invalidation techniques that can scale not only to a large number of mobile clients, but also to a large number of data items that can be cached in the mobile clients. We propose two scalable algorithms: the Multidimensional Bit-Sequence (MD-BS) algorithm and the Multilevel Bit-Sequence (ML-BS) algorithm. Both algorithms are based on our prior work on the Basic Bit-Sequences (BS) algorithm. Our study shows that the proposed algorithms are effective for a large number of cached data items with low update rates. The study also illustrates that the algorithms ran be used with other complementary techniques to address the problem of cache invalidation for data items with varied update and access rates.

Concurrency control strategies for ordered data broadcast in mobile computing systems

Although data broadcast has been shown to be an efficient method for disseminating data items in mobile computing systems, the issue on how to ensure consistency and currency of data items provided to mobile transactions (MT), which are generated by mobile clients, has not been examined adequately. While data items are being broadcast, update transactions may install new values for them. If the executions of update transactions and the broadcast of data items are interleaved without any control, mobile transactions may observe inconsistent data values. The problem will be more complex if the mobile clients maintain some cached data items for their mobile transactions. In this paper, we propose a concurrency control method, called ordered update first with order ( OUFO) , for the mobile computing systems where a mobile transaction consists of a sequence of read operations and each MT is associated with a time constraint on its completion time. Besides ensuring data consistency and maximizing currency of data to mobile transactions, OUFO also aims at reducing data access delay of mobile transactions using client caches. A hybrid re-broadcast/invalidation report (IR) mechanism is designed in OUFO for checking the validity of cached data items so as to improve cache consistency and minimize the overhead of transaction restarts due to data conflicts. This is highly important to the performance of the mobile computing systems where the mobile transactions are associated with a deadline constraint on their completion times. Extensive simulation experiments have been performed to compare the performance of OUFO with two other efficient schemes, the multi-version broadcast method and the periodic IR method. The performance results show that OUFO offers better performance in most aspects, even when network disconnection is common.