Dynamic, finite versioning for concurrent transaction and query processing

A data processing system supporting concurrent transaction and query processing of a database comprising:

• direct access storage means for storing physical copies of said database;
• plurality of terminal means for concurrently accessing said database for transactions and queries;
• and
• processor means connected to said plurality of terminal means and said direct access storage means for managing said transactions and queries using a dynamic, finite versioning scheme for accessing said database in which there is no interference between transactions and queries and no quiescence of either transactions or queries for allowing queries to access a more up-to-date version of said database wherein the logical versions that a physical page represents change implicitly over time, said processor means including one or more central processor units and memory means for storing information;
• said processor means dynamically maintaining a plurality of finite logical versions of each page in said database and allowing for a physical page copy to represent simultaneously a plurality of logical versions of a page;
• said direct access storage means recording time-invariant information, including a time-stamp and a transaction identifier, with each physical page copy when it is created, said time stamp recording a time at which a physical page is updated by a transaction and said transaction identifier recording an identifier of a transaction last updating the physical page;
• said memory means maintaining time-varying information which represents a system state, including a time-stamp of a current query snapshot time, a transaction list recording active transactions at a time when said current query snapshot was taken, and a transaction list recording active transactions currently still in progress;
• said processor means using said time-varying information to generate a transaction-consistent query snapshot of said database for accesses by queries without quiescing either transaction or query processing, a query snapshot being identified by a time-stamp and an active transaction list at a time when the snapshot was taken;
• said processor means further using said time-invariant information kept with each physical page copy and said time-varying information in memory to dynamically identify appropriate version pages of said database for transaction and query accesses to avoid transaction and query interference.