Session State: Beyond Soft State

The cost and complexity of adminstration of large systems has come to dominate their total cost of ownership. Stateless and soft-state components, e.g. Web servers or network routers, are easy to manage: capacity can be scaled incrementally by adding more nodes, rebalancing of load after failover is easy, and reactive or proactive ("rolling") reboots can be used to handle transient failures. We show that it is possible to achieve the same ease of management for the state-storage subsystem by subdividing persistent state according to the specific guarantees needed by each type. While other systems have addressed persistent-until deleted state, we describe SSM, a store for a previously unaddressed class of state--user-session state--that exhibits the same manageability properties as stateless nodes while providing firm storage guarantees. ANy node can be proactively or reactively rebooted at any time to recover from transient faults, without impacting online performance or losing data. We exploit this simplified manageability by pairig SSM with an application-generic, statistical-anomaly-based framework that detects crashes, hangs, and performance failures, and automatically attempts to recover from them by rebooting faulty nodes. ALthough the detection techniques generate some false positives, the cost of recovery is so low that the false positives have low impact. We provide microbenchmarks to demonstrate SSM's built-in overload protection, failure management and self-tuning. We benchmark SSM integrated into a production enterprise-scale interactive service to demonstrate that these benefits need not come at the cost of significantly decreased throughput or response time.

ssm-nsdi.pdf
PDF file

In  the 1st USENIX/ACM Symposium on Networked Systems Design and Implementation (NSDI '04)

Publisher  Association for Computing Machinery, Inc.
Copyright © 2007 by the Association for Computing Machinery, Inc. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Publications Dept, ACM Inc., fax +1 (212) 869-0481, or permissions@acm.org. The definitive version of this paper can be found at ACM’s Digital Library --http://www.acm.org/dl/.

Details

TypeInproceedings
> Publications > Session State: Beyond Soft State