Request-aware Cooperative I/O Scheduling for Scale-out Database Applications


Hyungil Jo and Sung-hun Kim, Sungkyunkwan University; Sangwook Kim, Apposha; Jinkyu Jeong and Joonwon Lee, Sungkyunkwan University


Interactive data center applications suffer from the tail latency problem. Since most modern data center applications take the sharded architecture to serve scale-out services, a request comprises multiple sub-requests handled in individual back-end nodes. Depending on the state of each back-end node, a node may issue multiple I/Os for a single sub-request. Since traditional I/O scheduling operates in an application-agnostic manner, it sometimes causes a long latency gap between the responses of sub-requests, thereby delaying the response to endusers. In this paper, we propose a request-aware cooperative I/O scheduling scheme to reduce the tail latency of a database application. Our proposed scheme captures request arrival order at the front-end of an application and exploits it to make a decision for I/O scheduling in individual back-end nodes. We implemented a prototype based on MongoDB and the Linux kernel and evaluated it with a read-intensive scan workload. Experimental results show that our proposed scheme effectively reduces the latency gap between sub-requests, thereby reducing the tail latency.

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@inproceedings {203382,
author = {Hyungil Jo and Sung-hun Kim and Sangwook Kim and Jinkyu Jeong and Joonwon Lee},
title = {Request-aware Cooperative I/O Scheduling for Scale-out Database Applications},
booktitle = {9th {USENIX} Workshop on Hot Topics in Storage and File Systems (HotStorage 17)},
year = {2017},
address = {Santa Clara, CA},
url = {},
publisher = {{USENIX} Association},