Sleepers and workaholics

TLDR

Future mobile wireless computing will involve many low‑powered palm‑top users that frequently disconnect and move between cells, making cache invalidation strategies difficult to design. The study proposes a taxonomy of cache invalidation strategies and examines how client disconnection times affect their performance. The authors evaluate the performance of different cache invalidation strategies under varying client disconnection times. For frequently disconnected units (sleepers), signature‑based invalidation performs best, while for continuously connected units (workaholics), periodic broadcast of changed data items is optimal.

Abstract

In the mobile wireless computing environment of the future a large number of users equipped with low powered palm-top machines will query databases over the wireless communication channels. Palmtop based units will often be disconnected for prolonged periods of time due to the battery power saving measures; palmtops will also frequencly relocate between different cells and connect to different data servers at different times. Caching of frequently accessed data items will be an important technique that will reduce contention on the narrow bandwidth wireless channel. However, cache invalidation strategies will be severely affected by the disconnection and mobility of the clients. The server may no longer know which clients are currently residing under its cell and which of them are currently on. We propose a taxonomy of different cache invalidation strategies and study the impact of client's disconnection times on their performance. We determine that for the units which are often disconnected (sleepers) the best cache invalidation strategy is based on signatures previously used for efficient file comparison. On the other hand, for units which are connected most of the time (workaholics), the best cache invalidation strategy is based on the periodic broadcast of changed data items.