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A fundamental challenge in database replication is to maintain a low cost of updates while assuring global system consistency. The difficulty of the problem is magnified for wide-area network settings due to the high latency and the increased likelihood of network partitions. As a consequence, most of the research in the area has focused either on improving the performance of local transaction execution or on replication models with weaker semantics, which rely on application knowledge to resolve potential conflicts.

In this work we identify the performance bottleneck of the existing synchronous replication schemes as residing in the update synchronization algorithm. We compare the performance of several such synchronization algorithms and highlight the large performance gap between various methods. We design a generic, synchronous replication scheme that uses an enhanced synchronization algorithm and demonstrate its practicality by building a prototype that replicates a PostgreSQL database system. We claim that the use of an optimized synchronization engine is the key to building a practical synhronous replication system for wide-area network settings.