Abstract
It can be said that developers do not need to understand the detail of redo and undo as much as DBAs, but developers do need to know the role they play in the database. After first defining redo, we examine what exactly a COMMIT does. We discuss how to find out how much redo is being generated and how to significantly reduce the amount of redo generated by certain operations using the NOLOGGING clause. We also investigate redo generation in relation to issues such as block cleanout and log contention. In the undo section of the chapter, we examine the role of undo data and the operations that generate the most/least undo. Finally, we investigate the infamous ORA-01555: snapshot too old error, its possible causes, and how to avoid it.
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© 2022 The Author(s), under exclusive license to APress Media, LLC, part of Springer Nature
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Kuhn, D., Kyte, T. (2022). Redo and Undo. In: Expert Oracle Database Architecture. Apress, Berkeley, CA. https://doi.org/10.1007/978-1-4842-7499-6_9
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DOI: https://doi.org/10.1007/978-1-4842-7499-6_9
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Publisher Name: Apress, Berkeley, CA
Print ISBN: 978-1-4842-7498-9
Online ISBN: 978-1-4842-7499-6
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