Throttling Utilities in the IBM DB2 Universal Database Server

This paper describes a control system that provides the “utilities throttling” feature in the IBM DB2 Universal DatabaseTM v8.1.

Administrative utilities (e.g., filesystem and database backups, antivirus scan) are essential to the operation of production systems. Unfortunately, production work can be severely degraded by the concurrent execution of such utilities. Hence, it is desirable for the system to self-manage its utilities to limit their performance impact, with only high-level policy input from the administrator. We focus on policies of the form “There should be no more than an x% degradation of production work due to utility execution.”

We have designed a throttling mechanism called selfimposed sleep (SIS) which forces utilities to slow down their processing by a configurable amount. We design a feedback control system based on online measurements of an internal database metric that correlates with system performance. A novel aspect of this problem is estimating the baseline, defined as the performance that the system would provide if the utility was not executing. The final control system combines an online state estimator with a PI controller that achieves good performance and adapts to changing workloads.