Evaluation Overview of the Replication Methods for High Availability Databases

摘要

In this paper we describe the properties of the 2-safe, 1-safe, 0-safe and 1/0-safe replication methods. The 2-safe and 1-safe replication methods have been analyzed for many years and the problems of these replication methods are well known. The properties of the 0-safe and 1/0-safe designs have not yet been analyzed. All the replication designs use at least two copies of the database. Under normal operation both/all the database copies of the 2-safe replication design are up to date. The 1-safe replication design only use one up to date copy of the database. In the 0-safe replication design none of the databases are up to date. Therefore, we call this replication design 0-safe. The inconsistency between the 0-safe database copies must be managed by using countermeasures, which reduce the problems of the missing distributed isolation property.