Performance aspects of distributed caches using TTL-based consistency

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Scopus citations


Web objects are stored and can be requested from numerous servers, including authoritative origin servers and caches. Objects can be modified only by their origin servers and weak consistency with cached copies is maintained by limiting their lifetime durations. Copies fetched from origin servers are received with maximum time-to-live (TTL) that equals their lifetime duration whereas copies obtained through a cache have shorter TTLs since their age (elapsed time since fetched from the origin) is deducted from their lifetime duration. A request served by a cache constitutes a hit if the cache has a fresh copy of the object. Otherwise, the request is considered a miss and is propagated to another server. Performance is measured by the number of requests constituting cache misses. It is evident that the number of cache misses depends on the age of the copies the cache receives. Thus, a cache that sends requests to another cache would suffer more misses than a cache that sends requests directly to an authoritative server. More subtly, the number of misses depends on the particular configuration of higher-level caches, e.g., whether one or more higher-level caches are used. Guided by practices for Web caching, we model and compare different configurations. We also analyze the effect of pre-term refreshes at high-level caches and extended lifetimes at low-level caches and reveal patterns that may seem counter-intuitive at first. Even though TTLbased consistency is very widely used, our work seems to be the first to formally analyze it. Our analysis yields insights and guidelines for improving the performance of Web caches.

Original languageEnglish
Title of host publicationAutomata, Languages and Programming - 28th International Colloquium, ICALP 2001, Proceedings
EditorsFernando Orejas, Paul G. Spirakis, Jan van Leeuwen
PublisherSpringer Verlag
Number of pages13
ISBN (Print)3540422870, 9783540422877
StatePublished - 2001
Event28th International Colloquium on Automata, Languages and Programming, ICALP 2001 - Crete, Greece
Duration: 8 Jul 200112 Jul 2001

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume2076 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference28th International Colloquium on Automata, Languages and Programming, ICALP 2001


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