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Oracle Database Administration for Microsoft SQL Server DBAs by Michelle Malcher

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Undo, Redo, and Logs

Undo versus redo—this almost sounds like the start of a bad joke. Undo and redo were in a boat. Undo jumps out. Who is left on the boat? Redo! In all seriousness, understanding the purpose of the redo logs and undo tablespace will also help explain read consistency and why SELECT statements do not block writers and writers do not block readers in Oracle databases.

Transaction Logs Versus Redo Logs

In SQL Server, transactions and changes are written out to the transaction log, which is used by SQL Server to either commit the changes or roll back changes. There is also a save point that can be used for larger transactions, to basically commit the changes up to this point and continue with the transaction. The logs can either ...

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