Computer program product for conducting a lock free read

Abstract

The present invention expounds upon the ANSI “read committed” isolation level by allowing readers to read committed data without waiting for a concurrent writer to the data to finish. The method returns a last committed version of the data as it existed prior to changes made by the concurrent writer. Only two versions of any data record are required to be stored in the record data store, the last committed version and the current version. The last committed version may be generated from an undo log record. Locating the appropriate undo log record may be accomplished by storing a log sequence number in a lock data structure associated with the requested data record. A transaction flag may also stored in the lock data structure to facilitate generating the last committed version. The method may also utilize one or more locks to detect a concurrent writer to the requested data.

Dependencies are inferred from the claim text.