A Study on Update Propagation of Cached Spatial Data in Client-Server Environment

Youngsang Shin

Abstract

In a client-server spatial database, it is desirable to maintain the cached data in a client side to minimize the communication overhead over a network. This thesis deals with the issues of concurrency and consistency of map updates in this environment. A client transaction to update map data is an interactive work and takes a long time to complete it. The map update in a client site may affect the other sites' updates because of dependencies between spatial data stored at different sites. The concurrent updates should be propagated to the other clients as well as the server to keep the consistency of map replication in a client cache, and also the communication overhead of the update propagation should be minimized not to lose the benefit of caching.

The existing locking-based approaches cannot effectively control the concurrency of long transactions, and the optimistic approaches have the rollback problem due to update conflict. In addition, spatial objects may have the additional consistency constraint, with which the existing approaches cannot satisfy. This thesis defines the dependencies between spatial objects located in different sites as global spatial relationships. A new consistency control method with the minimum communication overhead should be introduced to support the concurrent updates of cached client spatial data.

The newly proposed cache region locking with CR lock and CX lock controls the update dependency due to global spatial relationships. CS lock and COD lock are suggested to use optimistic detection-based approaches for guaranteeing the consistency of cached client data. The cooperative update protocol uses these extended locking primitives and Spatial Relationship-based 2PC. This thesis argues that the concurrent updates of cached client spatial data can be achieved by deciding on collaborative updates or independent updates based on global spatial relationships.