Kevin R. Rose

Managing the Performance Impact of Administrative Utilities

Administrative utilities (e.g., filesystem and database backups, garbage collection in the Java Virtual Machines) are an essential part of the operation of production systems. Since production work can be severely degraded by the execution of such utilities, it is desirable to have policies of the form “There should be no more than an x% degradation of production work due to utility execution.” Two challenges arise in providing such policies: (1) providing an effective mechanism for throttling the resource consumption of utilities and (2) continuously translating from policy expressions of “degradation units” into the appropriate settings for the throttling mechanism. We address (1) by using self-imposed sleep, a technique that forces utilities to slow down their processing by a configurable amount. We address (2) by employing an online estimation scheme in combination with a feedback loop. This throttling system is autonomous and adaptive and allows the system to self-manage its utilities to limit their performance impact, with only high-level policy input from the administrator. We demonstrate the effectiveness of these approaches in a prototype system that incorporates these capabilities into IBM’s DB2 Universal Database server.

Control Theory: a Foundational Technique for Self Managing Databases

Control theory is a well established discipline that has emerged from aeronautical, electrical, and mechanical engineering to provide a formal approach to building robust systems. While similar robustness concerns exist in database management systems, control theory is rarely used due to the lack of canonical control models and a dearth of control theory expertise among database researchers. We discuss our experience with using control theory to build self managing databases, showing experimental results, discussing pitfalls and limitations, and contrasting formal models against with feedback loops. While our experience indicates that control theory is a good paradigm for database self management, control theory should be used Judiciously since its techniques are not suited to all problems in database administration.