In this paper we address the performance issues that arise as a result of the two level scheduling in a database/operating system. At the upper (database) level transactions are logically scheduled so as to maintain the database integrity. At the lower (operating system) level physical disk requests are scheduled. We consider the performance problems that result from the interplay between these two levels of scheduling. Our model assumes the existence of a dictionary that must be consulted prior to the execution of a transaction. We derive the optimal disk placement of this dictionary and our results show that the waiting time for dictionary look-up is the critical component in the transaction response-time for a wide range of transaction sizes. To alleviate this problem we suggest alternative approaches to dictionary placement in such systems.

--Authors’ Abstract

The authors model the transaction execution on a detailed level. The model is then analyzed using basic probabilistic methods. The analysis is done carefully, the derivations are presented in detail, and they are easy to follow. Some numerical results and their interpretation are also included. The main conclusions are that the dictionary placement has a critical influence on the performance, particularly with heavy transaction traffic, and that the use of dictionary carries a significant overhead compared with systems that can function without it.