Timestamp-based result cache invalidation for web search engines

The result cache is a vital component for efficiency of large-scale web search engines, and maintaining the freshness of cached query results is the current research challenge. As a remedy to this problem, our work proposes a new mechanism to identify queries whose cached results are stale. The basic idea behind our mechanism is to maintain and compare generation time of query results with update times of posting lists and documents to decide on staleness of query results. The proposed technique is evaluated using a Wikipedia document collection with real update information and a real-life query log. We show that our technique has good prediction accuracy, relative to a baseline based on the time-to-live mechanism. Moreover, it is easy to implement and incurs less processing overhead on the system relative to a recently proposed, more sophisticated invalidation mechanism

A result cache invalidation scheme for web search engines

Ankara : The Department of Computer Engineering and the Graduate School of Engineering and Science of Bilkent University, 2011.Thesis (Master's) -- Bilkent University, 2011.Includes bibliographical references leaves 51-55.The result cache is a vital component for the efficiency of large-scale web search engines, and maintaining the freshness of cached query results is a current research challenge. As a remedy to this problem, our work proposes a new mechanism to identify queries whose cached results are stale. The basic idea behind our mechanism is to maintain and compare the generation time of query results with the update times of posting lists and documents to decide on staleness of query results. The proposed technique is evaluated using a Wikipedia document collection with real update information and a real-life query log. Throughout the experiments, we compare our approach with two baseline strategies from literature together with a detailed evaluation. We show that our technique has good prediction accuracy, relative to the baseline based on the time-to-live (TTL) mechanism. Moreover, it is easy to implement and it incurs less processing overhead on the system relative to a recently proposed, more sophisticated invalidation mechanism.Alıcı, ŞadiyeM.S

DotSlash: Providing Dynamic Scalability to Web Applications with On-demand Distributed Query Result Caching

Scalability poses a significant challenge for today's web applications, mainly due to the large population of potential users. To effectively address the problem of short-term dramatic load spikes caused by web hotspots, we developed a self-configuring and scalable rescue system called DotSlash. The primary goal of our system is to provide dynamic scalability to web applications by enabling a web site to obtain resources dynamically, and use them autonomically without any administrative intervention. To address the database server bottleneck, DotSlash allows a web site to set up on-demand distributed query result caching, which greatly reduces the database workload for read mostly databases, and thus increases the request rate supported at a DotSlash-enabled web site. The novelty of our work is that our query result caching is on demand, and operated based on load conditions. The caching remains inactive as long as the load is normal, but is activated once the load is heavy. This approach offers good data consistency during normal load situations, and good scalability with relaxed data consistency for heavy load periods. We have built a prototype system for the widely used LAMP configuration, and evaluated our system using the RUBBoS bulletin board benchmark. Experiments show that a DotSlash-enhanced web site can improve the maximum request rate supported by a factor of 5 using 8 rescue servers for the RUBBoS submission mix, and by a factor of 10 using 15 rescue servers for the RUBBoS read-only mix

Timestamp-based cache invalidation for search engines

We propose a new mechanism to predict stale queries in the result cache of a search engine. The novelty of our approach is in the use of timestamps in staleness predictions. We show that our approach incurs very little overhead on the system while its prediction accuracy is comparable to earlier works. © 2011 Authors

Efficient result caching mechanisms in search engines

Ankara : The Department of Computer Engineering and the Graduate School of Engineering and Science of Bilkent University, 2014.Thesis (Master's) -- Bilkent University, 2014.Includes bibliographical references leaves 60-63.The performance of a search engine depends on its components such as crawler, indexer and processor. The query latency, accuracy and recency of the results play crucial role in determining the performance. High performance can be provided with powerful hardware in the data center, but keeping the operational costs restrained is mandatory for search engines for commercial durability. This thesis focuses on techniques to boost the performance of search engines by means of reducing both the number of queries issued to the backend and the cost to process a query stream. This can be accomplished by taking advantage of the temporal locality of the queries. Caching the result for a recently issued query removes the need to reprocess this query when it is issued again by the same or different user. Therefore, deploying query result cache decreases the load on the resources of the search engine which increases the processing power. The main objective of this thesis is to improve search engine performance by enhancing productivity of result cache. This is done by endeavoring to maximize the cache hit rate and minimizing the processing cost by using the per query statistics such as frequency, timestamp and cost. While providing high hit rates and low processing costs improves performance, the freshness of the queries in the cache has to be considered as well for user satisfaction. Therefore, a variety of techniques are examined in this thesis to bound the staleness of cache results without blasting the backend with refresh queries. The offered techniques are demonstrated to be efficient by using real query log data from a commercial search engine.Sazoğlu, Fethi BurakM.S

Strategies for setting time-to-live values in result caches

In web query result caching, staleness of queries are often bounded via a time-to-live (TTL) mechanism, which expires the validity of cached query results at some point in time. In this work, we evaluate the performance of three alternative TTL mechanisms: time-based TTL, frequency-based TTL, and click-based TTL. Moreover, we propose hybrid approaches obtained by pair-wise combination of these mechanisms. Our results indicate that combining time-based TTL with frequency-based TTL yields superior performance (i.e., lower stale query traffic and less redundant computation) than using a particular mechanism in isolation. Copyright is held by the owner/author(s)

Quaestor: Query web caching for database-as-a-service providers

Today, web performance is primarily governed by round-trip latencies between end devices and cloud services. To improve performance, services need to minimize the delay of accessing data. In this paper, we propose a novel approach to low latency that relies on existing content delivery and web caching infrastructure. The main idea is to enable application-independent caching of query results and records with tunable consistency guarantees, in particular bounded staleness. Q uaestor (Query Store) employs two key concepts to incorporate both expiration-based and invalidation-based web caches: (1) an Expiring Bloom Filter data structure to indicate potentially stale data, and (2) statistically derived cache expiration times to maximize cache hit rates. Through a distributed query invalidation pipeline, changes to cached query results are detected in real-time. The proposed caching algorithms offer a new means for data-centric cloud services to trade latency against staleness bounds, e.g. in a database-as-a-service. Q uaestor is the core technology of the backend-as-a-service platform Baqend, a cloud service for low-latency websites. We provide empirical evidence for Q uaestor 's scalability and performance through both simulation and experiments. The results indicate that for read-heavy workloads, up to tenfold speed-ups can be achieved through Q uaestor 's caching. </jats:p

Adaptive time-to-live strategies for query result caching in web search engines

An important research problem that has recently started to receive attention is the freshness issue in search engine result caches. In the current techniques in literature, the cached search result pages are associated with a fixed time-to-live (TTL) value in order to bound the staleness of search results presented to the users, potentially as part of a more complex cache refresh or invalidation mechanism. In this paper, we propose techniques where the TTL values are set in an adaptive manner, on a per-query basis. Our results show that the proposed techniques reduce the fraction of stale results served by the cache and also decrease the fraction of redundant query evaluations on the search engine backend compared to a strategy using a fixed TTL value for all queries. © 2012 Springer-Verlag Berlin Heidelberg

Second chance: A hybrid approach for dynamic result caching and prefetching in search engines

Cataloged from PDF version of article.Web search engines are known to cache the results of previously issued queries. The stored results typically contain the document summaries and some data that is used to construct the final search result page returned to the user. An alternative strategy is to store in the cache only the result document IDs, which take much less space, allowing results of more queries to be cached. These two strategies lead to an interesting trade-off between the hit rate and the average query response latency. In this work, in order to exploit this trade-off, we propose a hybrid result caching strategy where a dynamic result cache is split into two sections: an HTML cache and a docID cache. Moreover, using a realistic cost model, we evaluate the performance of different result prefetching strategies for the proposed hybrid cache and the baseline HTML-only cache. Finally, we propose a machine learning approach to predict singleton queries, which occur only once in the query stream. We show that when the proposed hybrid result caching strategy is coupled with the singleton query predictor, the hit rate is further improved. © 2013 ACM