無線網路資料存取之快取無效策略探討

在無線網路的環境中，大致上可分為伺服器(Server)、及用戶端(Mobile Client)。伺服器的資料庫有全部資料，而用戶端的快取僅儲存部份資料。當用戶端要求資料時，用戶端上傳要求的訊息給伺服器，伺服器收到後將被要求的資料回傳給用戶端。為了要減少頻寬及能源的浪費，於是在用戶端建立快取，便成了普遍的解決方法。然而快取與資料庫間必須達到同步，才不致於誤用過期的資料。故如何讓用戶端快取資料與伺服器資料保持一致性，即為本論文的研究重點。本論文提出了兩個方法，一個是先將資料分類之後，給與熱門資料較短廣播週期，冷門資料較長廣播週期的ABI+HCQU(Adaptive Broadcast Interval + Hot/ Cold/ Query/ Update)；另一個則是用低功率向鄰近節點要求自己快取內沒有或無效的資料，並採用電腦內快取資料的同步方式MESI修改成適合Client-Server環境的同步方式，此方法即為SWRCC+MUVI(SleepWakeup/ Recovery/ Check/ Confirm + Modified/ Uncertain/ Valid/ Invalid)。模擬結果顯示出ABI+HCQU的平均存取時間及快取失誤比率，皆能達到不錯的效能。而SWRCC+MUVI透過向鄰近節點取得快取失誤資料的方式，成功的減少頻寬消耗量，而且其所消耗的頻寬也相當少。另外，本論文也將提出的方法應用在XML資料庫之上，同樣也獲得相當不錯的成效，因此也驗證了本論文所提出方法之實用性。

關鍵字

無線網路資料存取；快取無效策略；無線網路環境；資料庫；用戶端；無效驗證報告；用戶端快取；資料同步；斷線；模擬評估；效能分析

並列摘要

Cache invalidation is an effective approach to maintain data consistency between the server and mobile clients in a mobile environment. This paper presents two new cache invalidation schemes, ABI+HCQU and SWRCC+MUVI, which are designed according to the real situations in a mobile environment, like MANET. ABI+HCQU divides data into different groups based on their utilization ratios (Hot/ Cold/ Query/ Update) and adapts their broadcasting intervals (ABI) accordingly to suit the actual needs. SWRCC+MUVI (SleepWakeup/ Recovery/ Check/ Confirm + Modified/ Uncertain/ Valid/ Invalid) aims to solve the validity problem of cached data after a client is disconnected from the server. The two schemes are shown through experimental evaluation and performance analyses to outperform most existing schemes in terms of data access time, cache miss ratios, query uplink ratios and bandwidth consumption. We also implement our two schemes – with slight modifications – on the XML database and prove that both schemes can achieve the same goal (as TS) with more favorable results. This further confirms that our cache invalidation schemes are not only theoretically but practically feasible.

並列關鍵字

mobile data accesses ； cache invalidation ； mobile environments ； database servers ； mobile clients ； invalidation reports ； client caches ； data consistency ； disconnection ； experimental evaluation ； performance analyses ； MANET

參考文獻

[1] N. Chand, R.C. Joshi, and M. Misra, “Energy Efficient Cache Invalidation in Wireless Mobile Environment,” Proc. 2005 IEEE Int’l Conf. on Personal Wireless Communications, Jan. 2005, pp. 244-248.

[2] A. Madhukar and R. Alhajj, “An Adaptive Energy Efficient Cache Invalidation Scheme for Mobile Databases,” Proc. 2006 ACM Symp. on Applied Computing, Apr. 2006, pp. 1122-1126.

[3] D. Barbara and T. Imielinski, “Sleepers and Workaholics: Caching Strategies in Mobile Environments, ” Proc. 1994 ACM Int’l Conf. on Management of Data, vol. 23, no. 2, pp. 1-12, May 1994.

[6] G. Cao, “A Scalable Low-Latency Cache Invalidation Strategy for Mobile Environments,” IEEE Trans. on Knowledge and Data Engineering, vol. 15, no. 5, pp. 1251-1265, Sept./Oct. 2003.

[7] C.C. Wu, J.F. Fang, and P.C. Hung, “A Counter-Based Cache Invalidation Scheme for Mobile Environments with Stateless Servers,” Proc. 2003 IEEE Pacific Rim Conf. On Communications, Computers and Signal Processing, Aug. 2003, pp. 623-626.

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無線網路資料存取之快取無效策略探討

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