ShortTail: taming tail latency for erasure-code-based in-memory systems

Abstract

In-memory systems with erasure coding (EC) enabled are widely used to achieve high performance and data availability. However, as the scale of clusters grows, the server-level fail-slow problem is becoming increasingly frequent, which can create long tail latency. The influence of long tail latency is further amplified in EC-based systems due to the synchronous nature of multiple EC sub-operations. In this paper, we propose an EC-enabled in-memory storage system called ShortTail, which can achieve consistent performance and low latency for both reads and writes. First, ShortTail uses a lightweight request monitor to track the performance of each memory node and identify any fail-slow node. Second, ShortTail selectively performs degraded reads and redirected writes to avoid accessing fail-slow nodes. Finally, ShortTail posts an adaptive write strategy to reduce write amplification of small writes. We implement ShortTail on top of Memcached and compare it with two baseline systems. The experimental results show that ShortTail can reduce the P99 tail latency by up to 63.77%; it also brings significant improvements in the median latency and average latency.

Keywords

Erasure code / In-memory system / Node fail-slow / Small write / Tail latency

RIGHTS & PERMISSIONS

Zhejiang University Press