Abstract: Each node in a data processing system contains at least one undo buffer and one least one redo buffer for insuring that any changes made to a section of a non-volatile storage medium, such as a disk, can be removed, if a transaction has not been committed, or can be recreated if the transaction has not been committed. The undo buffers each correspond to a different uncommitted transaction. The redo buffer contains the changes made to a copy of the section which is maintained in the memory.

Abstract: In a transaction processing system, snapshot records are stored in volatile memory along with volatile state memory records, and modifications to the volatile state memory records by the transactions are logged to an after-image log in non-volatile memory for recovery of the volatile state memory records. For recovery of the snapshot records in volatile memory, when any one of the records of volatile state memory are to be written from volatile memory to non-volatile state memory, the volatile snapshots records of the volatile state memory record are first written from volatile snapshot memory to non-volatile snapshot memory. This ordering of buffer pool flushing permits recovery of the volatile snapshot records from non-volatile state memory or from modifications in the after-image log. Moreover, recovery can be performed without writing modifications to the volatile snapshot records in an after-image log or flushing the snapshot records using an atomic operation.