cachesack · research

CacheSack

CacheSack is a flash-cache admission optimizer that assigns workload categories policy mixtures using estimated disk-read cost, flash writes and cache occupancy.

Related Observatory article: CacheSack on hesela.com

Its four choices are NeverAdmit, AdmitOnSecondMiss, AdmitOnMiss and AdmitOnWrite; the last also admits read misses. Policy mixtures are optimized under a capacity bound using an approximate retention-time model. [1]

A lower-tier RAM buffer can serve a flash miss. Counting flash hits alone therefore misses the disk-read objective. [1]

Policy fractions describe fractions of blocks in a category, not per-request admission probabilities. The reported five-minute training windows can use older access history retained by the ghost cache. The paper gives a sufficient condition: ghost-cache TTL exceeds the optimal modeled retention time, rather than every candidate horizon. Relative cost weights are not disclosed, limiting independent reconstruction of the production cost objective. [1]

Relations

related

Cache admission, Flashield, Request hit ratio, Ghost cache entry

Citations

1. Yang et al. CacheSack: Admission Optimization for Google Datacenter Flash Caches. ATC 2022, pp. 1021-1036; sections 3.4, 5, 6.3-6.5, 7.1 and Appendix A. (accessed 2026-11-12)

Further reading

2. Hesela. Layered-cache read accounting. (accessed 2026-11-12)

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