CAMP: A Cost Adaptive Multi-Queue Eviction Policy for Key-Value Stores

TL;DR

CAMP is an efficient, cost-aware eviction policy for key-value stores that adapts to workload changes, outperforming traditional LRU and manual partitioning methods in speed and utility.

Contribution

CAMP introduces a practical, approximate GDS-based eviction policy that considers size and cost, achieving high effectiveness with low overhead.

Findings

CAMP matches GDS eviction effectiveness with minimal data structure updates.

CAMP outperforms LRU and manual partitioning in speed and utility.

Implementation on Twitter's memcached demonstrates real-world applicability.

Abstract

Cost Adaptive Multi-queue eviction Policy (CAMP) is an algorithm for a general purpose key-value store (KVS) that manages key-value pairs computed by applications with different access patterns, key-value sizes, and varying costs for each key-value pair. CAMP is an approximation of the Greedy Dual Size (GDS) algorithm that can be implemented as efficiently as LRU. In particular, CAMP's eviction policies are as effective as those of GDS but require only a small fraction of the updates to an internal data structure in order to make those decisions. Similar to an implementation of LRU using queues, it adapts to changing workload patterns based on the history of requests for different key-value pairs. It is superior to LRU because it considers both the size and cost of key-value pairs to maximize the utility of the available memory across competing applications. We compare CAMP with both LRU and an alternative that requires human intervention to partition memory into pools and assign grouping of key-value pairs to different pools. The results demonstrate CAMP is as fast as LRU while outperforming both LRU and the pooled alternative. We also present results from an implementation of CAMP using Twitter's version of memcached.