Decision function in hybrid self-adaptive WWW cache coherence protocol (hSATTL)

To improve the performance of the multiprocessor, distributed and Internet-based systems, data replication is being introduced. Existence of multiple copies of the same object in the system causes the cache coherence problem. There are two basic mechanisms for maintaining cache coherence: write-invalidate and write-update mechanisms. Various protocols for multiprocessor and distributed systems have been developed that use both coherence mechanisms in order to maintain cache coherence with minimal overhead costs. These protocols are based on a decision function that dynamically switches between write-update and write-invalidate mechanisms. As a part of the hSATTL cache coherence protocol we designed a new decision function adapted for Internet-based systems that dynamically switches between basic coherence mechanisms. In order to prove the efficiency of the designed decision function we compared the performance of the hSATTL protocol with the performance of the ATTL and SATTL protocols, which do not implement decision functions. As the performance measure, we use the server load and the amount of data that is transferred between the server and the proxy in order to maintain cache coherence.