Toward Distributed Write-Back Caching in Programmable Switches

Skewed write-intensive key-value storage workloads are increasingly observed in modern data centers, yet they also incur server overloads due to load imbalance. Programmable switches provide viable solutions for realizing load-balanced caching on the I/O path, and hence implementing write-back caching in programmable switches is a natural approach to absorb frequent writes and improve write performance. However, enabling in-switch write-back caching is challenged by not only the strict programming rules and limited stateful memory of programmable switches, but also the need for reliable protection against data loss due to switch failures. We first propose FarReach, a new caching framework that supports fast, available, and reliable in-switch write-back caching. FarReach carefully co-designs both the control and data planes for cache management in programmable switches, so as to achieve high data-plane performance with lightweight control-plane management. We further extend FarReach into DistReach, which reduces the reliability maintenance overhead via distributed switch deployment. Our experimental results on a Tofino-switch testbed show that FarReach achieves a throughput gain of up to $6.6\times $ over a state-of-the-art in-switch caching approach under skewed write-intensive workloads. Also, DistReach reduces the crash recovery time of FarReach by 77.4%.