Media recovery with time-split B-trees
AssigneeDigital Equipment Corporation
InventorsDavid Lomet, Betty Salzberg
Life of this patent
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Abstract
Modern database systems provide media recovery by taking periodic backups and applying a transaction log to the backup to bring the data up-to-date. A multi-versioned database is one that retains and provides access to historical versions of data. The present invention shows how a history database, supported by the Time-Split B-tree, can be used to also provide the backup function of media recovery. Thus, the same versions used for database history are used for database backup. The cost of taking a backup is comparable to the cost of a good differential backup method, whereby only changed data is backed up. The media recovery cost, especially when the media failure is only partial, e.g., a single disk page, will frequently be lower.
Claims10
For use in a database system, a method of media recovery, comprising the steps of:
- providing a two-dimensional search structure at least partly defined by nodes and key and time dimensions, such that certain data in the database system is located by traversing the nodes using respective ones of the key and time dimensions, said nodes including history nodes which are periodically written to a secure medium and including current nodes and index nodes;
- time-splitting into current nodes and history nodes, current nodes having data that has changed and has not been written to the secure medium;
- and
- using only the history nodes to recover from an undesired and abnormal system interruption.
Dependencies are inferred from the claim text.