An efficient transient versioning method

Abstract

Transient versioning methods, where prior versions are maintained temporarily, are proposed to execute long-running queries without affecting concurrent transactions. However, transactions in these methods do not exploit the prior versions. This paper presents a transientversioning method, called Dynamic Versioning, which uses the transient versions to not only support queries but also increase concurrency among transactions. Data conflicts due to incompatible requests are resolved by dynamically creating dependence orders among the requesting transactions and queries. These orders help precisely identify the prior versions that have to be kept for the queries. Since only the required versions are stored, the storage overhead for the transient versions is reduced to the minimum possible. We present the results of simulation experiments that show that our method provides high transaction concurrency and supports queries almost as efficiently as the other transient-versioning methods, while incurring only a fraction of the storage overhead.