Predictive caching and prefetching of query results in search engines

Abstract

We study the caching of query result pages in Web search engines. Popular search engines receive millions of queries per day, and e cient policies for caching query results may enable them to lower their response time and reduce their hardware requirements. We present PDC (probability driven cache), a novel scheme tailored for caching search results, that is based on a probabilistic model of search engine users. We then use a trace of over seven million queries submitted to the search engine AltaVista to evaluate PDC, as well as traditional LRU and SLRU based caching schemes. The trace driven simulations show that PDC outperforms the other policies. We also examine the prefetching of search results, and demonstrate that prefetching can increase cache hit ratios by 50% for large caches, and can double the hit ratios of small caches. When integrating prefetching into PDC, we attain hit ratios of over 0:53.

Second Chance: A Hybrid Approach for Dynamic Result Caching in Search Engines

“…Earlier works show that prefetching significantly improves the cache hit rate [Fagni et al 2006;Lempel and Moran 2003]. However, this technique incurs additional load on the backend servers due to the overhead of preparing the result pages that are not yet requested.…”

“…However, this technique incurs additional load on the backend servers due to the overhead of preparing the result pages that are not yet requested. Moreover, in order to make space for the prefetched pages, the result cache may be forced to evict some entries that would potentially lead to a cache hit [Lempel and Moran 2003]. Therefore, prefetching must be handled by taking into account both the additional load on the backend servers and the eviction of entries in the result cache.…”

“…The probability driven cache (PDC) policy proposed by Lempel and Moran [2003] exploits the result page browsing behavior of the search engine users while deciding on the cache content. This work does not propose another prefetching strategy but applies the aforementioned basic prefetching strategy on top of PDC.…”

“…In the literature on result caching, the issues of eviction [Gan and Suel 2009], prefetching [Fagni et al 2006;Lempel and Moran 2003], and admission [Baeza-Yates et al 2007] are well investigated. In cache eviction, upon a cache miss, a selected entry is deleted from the cache.…”

A Last-Resort Semantic Cache for Web Queries

“…In this sense, dynamic caching techniques based on replacement policies like LRU or LFU achieved a better performance. Along the same lines, Lempel and Moran [11] calculate a score for the queries that allows for an estimation of how probable it is that a query will be made in the future, a technique called Probability Driven Caching (PDC). Lately, Fagni et al [6] have proposed a structure for caching where they maintain a static collection and a dynamic one, achieving good results, called Static-Dynamic Caching (SDC).…”