Methods and apparatus for optimizing undo log usage

Claim 1

In a data processing system including a plurality of nodes and a non-volatile storage medium divided into sections, the plurality of nodes making changes to the sections by way of transactions, each transaction comprising a series of changes made to at least one section by at least one node, and each transaction being committed if a record of the changes effected by that transaction as well as an indication of the completion of that transaction are reliably stored on the storage medium, and otherwise being uncommitted, a first one of the plurality of nodes comprising: a memory for holding a copy of at least one section; processing means, coupled to the memory, for making changes to the copy of the at least one section in the memory; at least one undo buffer containing a sequential list of the changes made by the processing means to the copy of the at least one section in the memory, each undo buffer corresponding to changes made by the first node to a different uncommitted transaction for which , and each buffer; a redo buffer containing a sequential list of changes made by the processing means in the corresponding node to the copy of the at least one section in memory; storing means, coupled to the memory, for storing the copy of the at least one section back into the storage medium; and log management means, coupled to the undo buffers and to the redo buffer, for selectively storing the portions of the undo buffers and redo buffer to the storage medium to ensure that the effects of all changes of uncommitted transactions can be removed and the effects of all changes of committed transactions can be recreated.