Token transactions

摘要

Executing a transaction in a conventional distributed database system involves the execution of several subtransactions, each at a remote site where the data reside and running a two-phase commit protocol at the end of the transaction. With the advent of fast communication networks, we consider an alternative paradigm where the remote data being accessed are dynamically migrated to the initiation site of the transaction. One example of such a system is a distributed shared virtual memory system.

In this paper, we examine the problem of recovery from system failure in data migration systems. Most data migration systems use the notion of tokens for the access rights a site has on the data elements it caches. Our goal is to recover the site's knowledge of the set of tokens it owned when a system failure occurred. Our approach is to consider the token knowledge at each site as a fragment of a global token database and the data migration activities as token transactions that update this distributed database. We have developed a unique commit protocol for token transactions, called unilateral commit (UCP), that efficiently achieves consistency and recoverability of the token state. The correctness of UCP with respect to the two-phase commit protocol is also presented.