Caching A technical approach to the same problem is to use caching techniques to bring the data to the user. An extreme case is complete replication of all data as used in many Lotus Notes databases, but this may not be possible on a small portable system. In traditional RAM or disk caches the algorithms must be fast and automatic, but some cache misses are acceptable. For mobile systems, a cache miss during a period of disconnection stops work completely. This implies that more complex algorithms are necessary including user involvement.
Wireless networks allow synchronous activity during periods of connection.
However, during periods of disconnection only asynchronous activity is possible. Where systems allow for both modes, the transition between the two is assumed to be planned and infrequent. Why conflicts arise Where shared data is held in local caches there is a danger of conflicts due to simultaneous updates. Locking strategies are not acceptable in most asynchronous applications as they may freeze data for unbounded amounts of time. Measurements by the CODA group indicate that for UNIX file usage conflicts are rare at most a few per cent of files may be affected.