Modeling TTL-based Internet caches
Modeling TTL-based Internet caches
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DOI：
10.1109/infcom.2003.1208693
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发表时间：
2003-07
期刊：
影响因子：
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通讯作者：
Jaeyeon Jung;A. Berger;H. Balakrishnan
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文献类型：
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作者：
Jaeyeon Jung;A. Berger;H. Balakrishnan
本文提出了一种使用基于生存时间（TTL）的一致性策略的缓存命中率建模的方法。基于TTL的一致性，如DNS和Web缓存所示，是一种策略，其中数据项一旦被检索，就在称为“生存时间”的时期内保持有效。使用大TTL周期的高速缓存系统已知具有高命中率和良好的可扩展性，但是使用较短TTL周期的效果还没有很好地理解。我们将命中率建模为请求到达时间和TTL选择的函数，使我们能够更好地理解TTL周期较短的缓存行为。我们的命中率公式是封闭的形式，并依赖于一个简化的假设的间隔时间的请求的数据项的问题：这些请求可以建模为一个序列的独立和相同分布的随机变量。分析大量的DNS跟踪，我们发现公式的结果与观察到的统计数据惊人地匹配;特别是，该分析能够充分解释Jung等人的有些违反直觉的经验发现，即DNS访问的该高速缓存命中率作为TTL的函数迅速增加，对于15分钟的TTL超过80%。
This paper presents a way of modeling the hit rates of caches that use a time-to-live (TTL)-based consistency policy. TTL-based consistency, as exemplified by DNS and Web caches, is a policy in which a data item, once retrieved, remains valid for a period known as the "time-to-live". Cache systems using large TTL periods are known to have high hit rates and scale well, but the effects of using shorter TTL periods are not well understood. We model hit rate as a function of request arrival times and the choice of TTL, enabling us to better understand cache behavior for shorter TTL periods. Our formula for the hit rate is closed form and relies upon a simplifying assumption about the interarrival times of requests for the data item in question: that these requests can be modeled as a sequence of independent and identically distributed random variables. Analyzing extensive DNS traces, we find that the results of the formula match observed statistics surprisingly well; in particular, the analysis is able to adequately explain the somewhat counterintuitive empirical finding of Jung et al. that the cache hit rate for DNS accesses rapidly increases as a function of TTL, exceeding 80% for a TTL of 15 minutes.