On-line data migration approaches and their performance comparisons

The rapid development of hardware technology suggests that database machines should be upgraded from time to time so that database servers can provide satisfactory performance all the time. In order to perform such an upgrade, the database server is required to be taken offline for a long time so that databases in the old machine can be moved to the new one. Current applications, however, require that databases should be continually available 24 hours a day and 7 days a week, and they cannot afford an offline database for any significant amount of time. Such a contradiction is affecting negatively the business activity of companies, hospitals, polices, etc., and has become a serious problem. In this paper we address a very practical and important subject: upgrading a database machine on line, i.e., moving a database from the old machine to the new one concurrently with users´ reading and writing of the database. Four approaches are examined, and performance study is conducted