Two Freshness Metrics for Local Cache Refresh

Research output: Chapter in Book/Report/Conference proceedingConference contribution

26 Scopus citations


We consider a cache refresh system where a local server is connected to multiple remote sources and maintains local copies of the data items at the sources. The data at each source is updated randomly and independently without notifying the local server, while the local server refreshes the corresponding cached data periodically. The freshness of the local cache is measured by two different freshness metrics, age of synchronization (AoS) and age of information (AoI). We address the following problem: given a constrained total refresh rate, how does the local server allocate the refresh rate for each source to maintain overall data freshness? We derive the AoI optimal policy which depends only on the square root of the source popularity. For a large refresh rate, we propose an AoS near-optimal rate allocation policy that is proportional to the cube root of both the source update rate and the source popularity. For small refresh rates, we also prove that the square root law with respect to the popularity minimizes both AoS and AoI.

Original languageEnglish (US)
Title of host publication2018 IEEE International Symposium on Information Theory, ISIT 2018
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages5
ISBN (Print)9781538647806
StatePublished - Aug 15 2018
Event2018 IEEE International Symposium on Information Theory, ISIT 2018 - Vail, United States
Duration: Jun 17 2018Jun 22 2018

Publication series

NameIEEE International Symposium on Information Theory - Proceedings
ISSN (Print)2157-8095


Other2018 IEEE International Symposium on Information Theory, ISIT 2018
Country/TerritoryUnited States

All Science Journal Classification (ASJC) codes

  • Theoretical Computer Science
  • Information Systems
  • Modeling and Simulation
  • Applied Mathematics


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