GreedyDual-Join: Locality-Aware Buffer Management for Approximate Join Processing Over Data Streams

We investigate adaptive buffer management techniques for approximate evaluation of sliding window joins over multiple data streams. In many applications, data stream processing systems have limited memory or have to deal with very high speed data streams. In both cases, computing the exact results of joins between these streams may not be feasible, mainly because the buffers used to compute the joins contain much smaller number of tuples than the tuples contained in the sliding windows. Therefore, a stream buffer management policy is needed in that case. We show that the buffer replacement policy is an important determinant of the quality of the produced results. To that end, we propose GreedyDual-Join (GDJ) an adaptive and locality-aware buffering technique for managing these buffers. GDJ exploits the temporal correlations (at both long and short time scales), which we found to be prevalent in many real data streams. We note that our algorithm is readily applicable to multiple data streams and multiple joins and requires almost no additional system resources. We report results of an experimental study using both synthetic and real-world data sets. Our results demonstrate the superiority and flexibility of our approach when contrasted to other recently proposed techniques

Efficiency of cache-replacement algorithms while retrieving data from a relational database and XML files in a web based system

Caching has been applied in Web based information systems in order toreduce the transmission of redundant network traffic and response latency by savingcopies of the content obtained from the Web closer to the end user. The efficiencyof caching is influenced to a significant extent by the cache replacement algorithmswhich are triggered when the cache becomes full and old objects must be evicted tomake space for the new ones.This paper presents a framework that can be used in future work to tunecache-replacement algorithms while data is simultaneously retrieved from arelational database and XML files in a web based environment, by a large numberof end-users. Three replacement policies are considered: Least Recently Used(LRU), Least Frequently Used (LFU) and Lowest Latency First (LLF). Theexperimental results obtained from the framework show that data caching greatlyimproves the overall performance of web based systems, and the type of the appliedcache replacement policy also plays an important role in the performance. In thescenarios considered in this paper, the LLF algorithm produced the bestperformance when retrieving data from a relational database, while the LFUalgorithm was the most efficient algorithm when data was retrieved from an XMLfile

Incremental Discovery of Process Maps

Protsessikaeve on meetodite kogu, analüüsimaks protsesside teostuse jooksul loodud sündmuste logisid, et saada teavet nende parandamiseks. Protsessikaeve meetodite kogu, mida nimetatakse automatiseeritud protsessi avastuseks, lubab analüütikutel leida informatsiooni äriprotsesside mudelite kohta sündmuste logidest. Automatiseeritud protsessi avastusmeetodeid kasutatakse tavaliselt ühenduseta keskkonnas, mis tähendab, et protsessi mudel avastatakse hetketõmmisena tervest sündmuste logist. Samas on olukordi, kus uued juhtumid tulevad peale sellise suure kiirusega, et ei ole mõtet salvestada tervet sündmuste logi ja pidevalt nullist taasavastada mudelit. Selliste olukordade jaoks oleks vaja võrgus olevaid protsessi avastusmeetmeid. Andes sisendiks protsessi teostuse käigus loodud sündmuste voo, võrgus oleva protsessi avastusmeetodi eesmärk on järjepidevalt uuendada protsessi mudelit, tehes seda piiratud hulga mäluga ja säilitades sama täpsust, mida suudavad meetodid ühenduseta keskkondades. Olemasolevad meetodid vajavad palju mälu, et saavutada tulemusi, mis oleks võrreldavad ühenduseta keskkonnas saadud tulemustega. Käesolev lõputöö pakub välja võrgus oleva protsessi avastusraamistiku, ühtlustades protsessi avastus probleemi vähemälu haldusega ja kasutades vähemälu asenduspoliitikaid lahendamaks antud probleemi. Loodud raamistik on kirjutatud kasutades .NET-i, integreeritud Minit protsessikaeve tööriistaga ja analüüsitud kasutades elulisi ärijuhte.Process mining is a body of methods to analyze event logs produced during the execution of business processes in order to extract insights for their improvement. A family of process mining methods, known as automated process discovery, allows analysts to extract business process models from event logs. Traditional automated process discovery methods are intended to be used in an offline setting, meaning that the process model is extracted from a snapshot of an event log stored in its entirety. In some scenarios however, events keep coming with a high arrival rate to the extent that it is impractical to store the entire event log and to continuously re-discover a process model from scratch. Such scenarios require online automated process discovery approaches. Given an event stream produced by the execution of a business process, the goal of an online automated process discovery method is to maintain a continuously updated model of the process with a bounded amount of memory while at the same time achieving similar accuracy as offline methods. Existing automated discovery approaches require relatively large amounts of memory to achieve levels of accuracy comparable to that of offline methods. This thesis proposes a online process discovery framework that addresses this limitation by mapping the problem of online process discovery to that of cache memory management, and applying well-known cache replacement policies to the problem of online process discovery. The proposed framework has been implemented in .NET, integrated with the Minit process mining tool and comparatively evaluated against an existing baseline, using real-life datasets

Cooperative announcement-based caching for video-on-demand streaming

Recently, video-on-demand (VoD) streaming services like Netflix and Hulu have gained a lot of popularity. This has led to a strong increase in bandwidth capacity requirements in the network. To reduce this network load, the design of appropriate caching strategies is of utmost importance. Based on the fact that, typically, a video stream is temporally segmented into smaller chunks that can be accessed and decoded independently, cache replacement strategies have been developed that take advantage of this temporal structure in the video. In this paper, two caching strategies are proposed that additionally take advantage of the phenomenon of binge watching, where users stream multiple consecutive episodes of the same series, reported by recent user behavior studies to become the everyday behavior. Taking into account this information allows us to predict future segment requests, even before the video playout has started. Two strategies are proposed, both with a different level of coordination between the caches in the network. Using a VoD request trace based on binge watching user characteristics, the presented algorithms have been thoroughly evaluated in multiple network topologies with different characteristics, showing their general applicability. It was shown that in a realistic scenario, the proposed election-based caching strategy can outperform the state-of-the-art by 20% in terms of cache hit ratio while using 4% less network bandwidth

Optimizing the Performance of Data Warehouse by Query Cache Mechanism

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