Database Replication Techniques: A Three Parameter Classification

Data replication is an increasingly important topic as databases are more and more deployed over clusters of workstations. One of the challenges in database replication is to introduce replication without severely affecting performance. Because of this difficulty, current database products use lazy replication, which is very efficient but can compromise consistency. As an alternative, eager replication guarantees consistency but most existing protocols have a prohibitive cost. In order to clarify the current state of the art and open up new avenues for research, this paper analyses existing eager techniques using three key parameters. In our analysis, we distinguish eight classes of eager replication protocols and, for each category, discuss its requirements, capabilities, and cost. The contribution lies in showing when eager replication is feasible and in spelling out the different aspects a database replication protocol must account for.