Dynamic finite versioning: An effective versioning approach to concurrent transaction and query processing

Severe data contention may exist between short update transactions and long read-only queries if both are to access the same database through a conventional concurrency control method. In this paper, we present dynamic finite versioning (DFV) schemes to effectively support concurrent processing of transactions and queries. Without acquiring locks, queries read from a small, fixed number of dynamically derived, transaction-consistent, but maybe slightly obsolete, logical snapshots of the database. On the other hand, transactions access the most up-to-date data in the database without data contention from queries. Intermediate versions created between snapshots are automatically discarded. Furthermore, dirty pages updated by active transactions are allowed to be written back into the database before commitment (i.e., the STEAL policy), and at the same time, consistent logical snapshots can be advanced automatically without quiescing the ongoing transactions or queries.