Multiple version database concurrency control system

Abstract

An improved concurrency control system for application to a distributed concurrent transaction and query processing system using multi-version database records to overcome delays arising from lock conflicts. Read-only queries are afforded a consistent 'stable state' of the database during the life of the query. Updating transactions requiring locks can proceed without waiting for the termination of long queries. At least two database versions are necessary, although availability of more versions permits long read-only queries to phase-out over time without forcing new queries to use aged 'stable-state' data and without roll-back. Read-only queries can be terminated and converted to locking transactions to permit an update of the 'stable state' database version before the queries would normally terminate. A novel record key structure having a plurality of substructures corresponding to the several database versions is used to access database records. Rapid selection of proper record version and efficient version tracking and updating is effected using several bit-mapped transaction index tables.