Cache Consistency Research Articles

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.

Rule-Based Data Mining Cache Replacement Strategy

Caching in mobile environments is used for improving bandwidth usage and reducing query delays among resource constrained devices. It is used in multitudes of approaches. Some rely on the server occasionally broadcasting reports to inform clients of updated data while others permit clients to access data whenever they need it. Caching can be constrained by size and bandwidth; thus, coming up with a good invalidation scheme is critical in improving cache consistency solutions. In this work, the authors propose a new hybrid cache invalidation scheme that makes use of data mining concepts. They also compare their scheme with other related strategies.

Energy-aware optimal cache consistency level for mobile devices

Power consumption in a mobile device is an important performance metric. It is strongly required for the mobile device to access wireless links efficiently because wireless communication expends a significant amount of energy per second. By using cache schemes, we can reduce communication costs and enhance performance by storing and reusing recently used data. However, the cached data on the mobile device should be updated in sync with the original data on the server as they are being modified. With a δ consistency policy, we can provide the energy-efficient cache consistency level by setting δ in accordance with various environmental parameters. This paper proposes a method to determine the optimal δ that minimizes the overhead energy expenditure for mobile devices in wireless web environments. We derive the optimal δ from a mathematical model and conduct a simulation for validation. We also implement a test application for the proposed optimal δ method on a test-bed and assess its performance.

Cluster Based Data Consistency for Cooperative Caching over Partitionable Mobile Adhoc Network

Problem statement: Data availability and consistency are foremost issues in Mobile Ad hoc Networks due to the absence of permanent infrastructure. Cooperative caching addresses the data availability issue through coordinating the mobile nodes and sharing the cache copies among them. In the meantime, the mobile node must ensure the staleness of cache copies. The consistency maintenance resolves the staleness of the data among the source and caching node. Due to addition of more mobile nodes the network size is increased and it leads to increase the caching nodes. The mobility and disconnections causes additional overhead, latency and reduces the data delivery success ratio while updating the cache copy from the source. Approach: This study proposed Adaptive Push and Pull Algorithm for Clusters (APPC) and Cluster Based Data Consistency (CBDC) approach to address the consistency requirements and maintenance in mobile ad hoc network. Results: The CBDC satisfy the consistency requirements in partitioned clusters. The source node transmits the updated data through the cluster heads to the caching nodes. The APPC ensures the validity of cache copy by threshold Time-to-Live (TTL). Thus it provides efficient valid data accessibility in mobile ad hoc network. Conclusion: The simulation results shown that this proposed approach increases packet success ratio and reduces the delay and overhead when compared with the existing approaches Flexible Cache Consistency (FCPP) maintenance and Cluster Based Cooperative Caching Technique (CBCCT) for increasing number of nodes and speed respectively.

A Multi-Level Cache Approach for Realtime Visualization of Massive 3D GIS Data

The real-time visualization of 3D GIS at a whole city scale always faces the challenge of dynamic data loading with high-efficiency. Based on the multi-tier distributed 3D GIS framework, this paper presents a multi-level cache approach for dynamic data loading. It aims to establish in 3D GIS spatial database engine (3DGIS-SDE) the unified management mechanism of caches on three levels, including: the client memory cache (CMC) oriented to sharing application, the client file cache (CFC) organized by index, as well as the application server memory cache (ASMC) of structural consistency. With the help of the proposed optimized cache replacement policy, multi-level cache consistency maintenance as well as multithread loading model designed in the paper, the engine is able to adaptively make full use of each-level caches according to their own application properties and achieve effective coordination between them. Finally, a practical 3D GIS database based on Oracle 11g is employed for test. The experimental results prove this approach could satisfy multi-user concurrent applications of 3D visual exploration.

Knowledge and Cache based Adaptive Query Searching in Unstructured P2P Networks

fficient search is a challenging task in unstructured peer-to- peer networks. In this paper, Knowledge and Cache based Adaptive Query Searching (KCAQS) is proposed that adaptively performs a query searching through either directed flooding or biased random walk based on the number of hop counts in query message. In addition, knowledge intended forwarding is deployed for forwarding a query to the high quality peers through probabilistic knowledge predicted from the previously requested queries. Searched results are properly cached in the peers along the returning path. Synchronized caching is performed to properly update the responses of each peer to its connected corresponding high degree connectivity peer in the overlay network. Due to caching of the same files in many peers, most of the cached responses may become redundant. In order to avoid redundant data, cache consistency is sustained through the flexible polling mechanism where a proper cache update is performed through Additive Decrease Multiplicative Increase (ADMI) algorithm based on file utility. Our experimental study shows that the proposed searching scheme significantly reduces the network search traffic and communication overhead. Performance metrics such as success rate, access latency, network traffic response time and cache hit ratio are evaluated for the proposed scheme.

Performance analysis of cache consistency strategies for multi-hop wireless networks

Data caching is widely used to facilitate information access in wireless mobile networks. Caching frequently used content on mobile clients brings benefits by reducing bandwidth usage, saving energy, and leveraging server workload. Maintaining cache consistency is an important issue in mobile caching and has received much attention by researchers. However, most existing studies on cache consistency strategies are limited to cellular wireless networks in which the mobile terminals can communicate with the base stations directly. In multi-hop wireless network environment, mobile terminals communicate with data server through multiple unreliable links with a high probability of disconnection from the network, which makes it more challenging for the maintenance of cache data consistency. In this paper, we investigate three cache consistency strategies for multi-hop wireless networks: the pull-based strategy POD (pull on demand), the push-based strategy MAT (modified amnesic terminals) and the store and forward strategy PIR (pull-based invalidation report). Extensive theoretical analysis is provided to compare the cache hit ratio, query delay and communication overhead of these methods, and the impact of system parameters on performance is studied as well. Simulation experiments are used to examine the performance of these three schemes, and it is shown that PIR provides the best overall performance.

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.

MashCache: Taming Flash Crowds by Using Their Good Features

This paper presents MashCache, a scalable client-side architecture for taming harsh effects of flash crowds. Like previous systems, MashCache extensively makes use of client resources to cache and share frequently accessed contents. To design MashCache, we carefully investigated the quantitative analysis of flash crowds in the wild and found out that flash crowds have three good features that can be used to simplify the overall design of MashCache. First, flash crowds start up very slowly. MashCache has enough time to prepare for the coming flash crowds. Second, flash crowds last for a short period. Since the accessed content is rarely updated in this short period, MashCache can employ a simple mechanism for cache consistency. Finally, the clients issue the same requests on the target web sites. This feature simplifies the cache management of MashCache because the cache explosion can be avoided. By using these good features of flash crowds, MashCache advances the state-of-the-art of P2P based caching systems for flash crowds; MashCache is a pure P2P system that combines 1) aggressive caching, 2) query-origin key, 3) two-phase delta consistency, and 4) carefully designed cache meta data. MashCache has another advantage. Since it works completely on client-side, MashCache can tolerate flash crowds even if the external services the mashup depends on are not equipped with flash-crowd-resistant mechanisms. In the experiments with up to 2,500 emulated clients, a prototype of MashCache reduces the number of requests to the original web servers by 98.2% with moderate overheads.

Performance-Enhanced Caching Scheme for Web Clusters for Dynamic Content

In order to improve the QoS of applications, clusters of web servers are increasingly used in web services. Caching helps improve performance in web servers, but is largely exploited only for static web content. With more web applications using backend databases today, caching of dynamic content has a crucial role in web performance. This paper presents a set of cache management schemes for handling dynamic data in web clusters by sharing cached contents. These schemes use either automatic or expiry-based cache validation, and work with any type of request distribution. The techniques improve response by utilizing the caches efficiently and reducing redundant database accesses by web servers while ensuring cache consistency. The authors present caching schemes for both horizontal and vertical cluster architectures. Simulations show an appreciable performance rise in response times of queries in clustered web servers.

Adaptive per-user per-object cache consistency management for mobile data access in wireless mesh networks

We propose and analyze an adaptive per-user per-object cache consistency management (APPCCM) scheme for mobile data access in wireless mesh networks. APPCCM supports strong data consistency semantics through integrated cache consistency and mobility management. The objective of APPCCM is to minimize the overall network cost incurred due to data query/update processing, cache consistency management, and mobility management. In APPCCM, data objects can be adaptively cached at the mesh clients directly or at mesh routers dynamically selected by APPCCM. APPCCM is adaptive, per-user and per-object as the decision regarding where to cache a data object accessed by a mesh client is made dynamically, depending on the mesh client’s mobility and data query/update characteristics, and the network’s conditions. We develop analytical models for evaluating the performance of APPCCM and devise a computational procedure for dynamically calculating the overall network cost incurred. We demonstrate via both model-based analysis and simulation validation that APPCCM outperforms non-adaptive cache consistency management schemes that always cache data objects at the mesh client, or at the mesh client’s current serving mesh router for mobile data access in wireless mesh networks.

Fast and correct performance recovery of operating systems using a virtual machine monitor

Rebooting an operating system is a final but effective recovery technique. However, the system performance largely degrades just after the reboot due to the page cache being lost in the main memory. For fast performance recovery, we propose a new reboot mechanism called the warm-cache reboot. The warm-cache reboot preserves the page cache during the reboot and enables an operating system to restore it after the reboot, with the help of a virtual machine monitor (VMM). To perform correct recovery, the VMM guarantees that the reused page cache is consistent with the corresponding files on disks. We have implemented the warm-cache reboot mechanism in the Xen VMM and the Linux operating system. Our experimental results showed that the warm-cache reboot decreased performance degradation just after the reboot. In addition, we confirmed that the file cache corrupted by faults was not reused. The overheads for maintaining cache consistency were not usually large.

Mitigating channel usage in cooperative caching for Mobile Ad hoc Networks

Cooperative caching supports efficient data dissemination and sharing in Mobile Ad hoc Networks (MANETs). Existing cache consistency maintenance algorithms are stateless, where the data source node is unaware of the cache node status. The stateless algorithm is cost-effective as it does not maintain status and suffers from paying to broadcasting. Stateful algorithms can significantly reduce the consistency maintenance cost by maintaining status of the cached data and selectively propagating the data updates. In this paper, a stateful cache consistency maintenance algorithm, Selective Push and Pull (SPP) is proposed which improves the performance of the MANET by saving the bandwidth and reducing the query delay. Omega Consistency Model is designed to satisfy the user specified consistency.

Contention-aware data caching in wireless multi-hop ad hoc networks

This paper studies a challenging problem of cache placement in wireless multi-hop ad hoc networks. More specifically, we study how to achieve an optimal tradeoff between total access delay and caching overheads, by properly selecting a subset of wireless nodes as cache nodes when the network topology changes. We assume a data source updates a data item to be accessed by other client nodes. Most of the existing cache placement algorithms use hop counts to measure the total cost of a caching system, but hop delay in wireless networks varies much due to the contentions among these nodes and the traffic load on each link. Therefore, we evaluate the per-hop delay for each link according to the contentions detected by a wireless node from the MAC layer. We propose two heuristic cache placement algorithms, named Centralized Contention-aware Caching Algorithm (CCCA) and Distributed Contention-aware Caching Algorithm (DCCA), both of which detect the variation of contentions and the change of the traffic flows, in order to evaluate the benefit of selecting a node as a cache node. We also apply a TTL-based cache consistency strategy to maintain the delta consistency among all the cache nodes. Simulation results show that the proposed algorithms achieve better performance than other alternative ones in terms of average query delay, caching overheads, and query success ratio.

Flexible Cache Consistency Maintenance over Wireless Ad Hoc Networks

One of the major applications of wireless ad hoc networks is to extend the Internet coverage and support pervasive and efficient data dissemination and sharing. To reduce data access cost and delay, caching has been widely used as an important technique. The efficiency of data access in caching systems largely depends on the cost for maintaining cache consistency, which can be high in wireless ad hoc networks due to network dynamism. Therefore, to make better trade-off between cache consistency and the cost incurred, it would be highly desirable to provide users the flexibility in specifying consistency requirements for their applications. In this paper, we propose a general consistency model called Probabilistic Delta Consistency (PDC), which integrates the flexibility granted by existing consistency models, covering them as special cases. We also propose the Flexible Combination of Push and Pull (FCPP) algorithm which satisfies user-specified consistency requirements under the PDC model. The analytical model of FCPP is used to derive the balance of minimizing the consistency maintenance cost and ensuring the specified consistency requirement. Extensive simulations are conducted to evaluate whether FCPP can satisfy arbitrarily specified consistency requirements, and whether FCPP works cost-effectively in dynamic wireless ad hoc networks. The evaluation results show that FCPP can adaptively tune itself to satisfy various user-specified consistency requirements. Moreover, it can save the traffic cost by up to 50 percent and reduce the query delay by up to 40 percent, compared with the widely used Pull with TTR algorithm.

SSUM: Smart Server Update Mechanism for Maintaining Cache Consistency in Mobile Environments

This paper proposes a cache consistency scheme based on a previously proposed architecture for caching database data in MANETs. The original scheme for data caching stores the queries that are submitted by requesting nodes in special nodes, called query directories (QDs), and uses these queries to locate the data (responses) that are stored in the nodes that requested them, called caching nodes (CNs). The consistency scheme is server-based in which control mechanisms are implemented to adapt the process of caching a data item and updating it by the server to its popularity and its data update rate at the server. The system implements methods to handle disconnections of QD and CN nodes from the network and to control how the cache of each node is updated or discarded when it returns to the network. Estimates for the average response time of node requests and the average node bandwidth utilization are derived in order to determine the gains (or costs) of employing our scheme in the MANET. Moreover, ns2 simulations were performed to measure several parameters, like the average data request response time, cache update delay, hit ratio, and bandwidth utilization. The results demonstrate the advantage of the proposed scheme over existing systems.

A cache invalidation strategy for mobile networks

The diversity of services delivered over wireless channels has increased people's desire in ubiquitously accessing these services from their mobile devices. However, a ubiquitous mobile computing environment faces several challenges such as scarce bandwidth, limited energy resources, and frequent disconnection of the server and mobile devices. Caching frequently accessed data is an effective technique to improve the network performance because it reduces the network congestion, the query delay, and the power consumption. When caching is used, maintaining cache consistency becomes a major challenge since data items that are updated on the server should be also updated in the cache of the mobile devices. In this paper we propose a new cache invalidation scheme called Selective Adaptive Sorted ( SAS) cache invalidation strategy that overcomes the false invalidation problem that exists in most of the invalidation strategies found in the literature. The performance of the proposed strategy is evaluated and compared with the selective cache invalidation strategy and the updated invalidation report startegy found in the literature. Results showed that a significant cost reduction can be obtained with the proposed strategy when measuring performance metrics such as delay, bandwidth, and energy.

Cache consistency in Wireless Multimedia Sensor Networks

The production of cheap CMOS cameras, which are able to capture rich multimedia content, combined with the creation of low-power circuits, gave birth to what is called Wireless Multimedia Sensor Networks (WMSNs). WMSNs introduce several new research challenges, mainly related to mechanisms to deliver application-level Quality-of-Service (e.g., latency minimization). Such issues have almost completely been ignored in traditional WSNs, where the research focused on energy consumption minimization. Towards achieving this goal, the technique of cooperative caching multimedia content in sensor nodes can efficiently address the resource constraints, the variable channel capacity and the in-network processing challenges associated with WMSNs. The technological advances in gigabyte-storage flash memories make sensor caching to be the ideal solution for latency minimization. Though, with caching comes the issue of maintaining the freshness of cached contents. This article proposes a new cache consistency and replacement policy, called NICC, to address the cache consistency issues in a WMSN. The proposed policies recognize and exploit the mediator nodes that relay on the most “central” points in the sensor network so that they can forward messages with small latency. With the utilization of mediator nodes that lie between the source node and cache nodes, both push-based and pull-based strategies can be applied in order to minimize the query latency and the communication overhead. Simulation results attest that NICC outperforms the state-of-the-art cache consistency policy for MANETs.

Cooperative cache consistency maintenance for pervasive internet access

AbstractCooperative caching is an important technique to support pervasive Internet access. In order to ensure valid data access, the cache consistency must be maintained properly. However, this problem has not been sufficiently studied in mobile computing environments, especially those with ad hoc networks. There are two essential issues in cache consistency maintenance: consistency control initiation and data update propagation. Consistency control initiation not only decides the cache consistency provided to the users, but also impacts the consistency maintenance cost. This issue becomes more challenging in asynchronous and fully distributed ad hoc networks. To this end, we propose the predictive consistency control initiation (PCCI) algorithm, which adaptively initiates consistency control based on its online predictions of forthcoming data updates and cache queries. In order to efficiently propagate data updates through multi‐hop wireless connections, the hierarchical data update propagation (HDUP) algorithm is proposed. Theoretical analysis shows that cooperation among the caching nodes facilitates data update propagation. Extensive simulations are conducted to evaluate performance of both PCCI and HDUP. Evaluation results show that PCCI cost‐effectively initiates consistency control even when faced with dynamic changes in data update rate, cache query rate, node speed, and number of caching nodes. The evaluation results also show that HDUP saves cost for data update propagation by up to 66%. Copyright © 2009 John Wiley & Sons, Ltd.

A proxy-based integrated cache consistency and mobility management scheme for client–server applications in Mobile IP systems

In this paper, we investigate a proxy-based integrated cache consistency and mobility management scheme for supporting client–server applications in Mobile IP systems with the objective to minimize the overall network traffic generated. Our cache consistency management scheme is based on a stateful strategy by which cache invalidation messages are asynchronously sent by the server to a mobile host (MH) whenever data objects cached at the MH have been updated. We use a per-user proxy to buffer invalidation messages to allow the MH to disconnect arbitrarily and to reduce the number of uplink requests when the MH is reconnected. Moreover, the user proxy takes the responsibility of mobility management to further reduce the network traffic. We investigate a design by which the MH’s proxy serves as a gateway foreign agent (GFA) as in the MIP Regional Registration protocol to keep track of the address of the MH in a region, with the proxy migrating with the MH when the MH crosses a regional area. We identify the optimal regional area size under which the overall network traffic cost, due to cache consistency management, mobility management, and query requests/replies, is minimized. The integrated cache consistency and mobility management scheme is demonstrated to outperform MIPv6, no-proxy and/or no-cache schemes, as well as a decoupled scheme that optimally but separately manages mobility and service activities in Mobile IPv6 environments.