Oracle Undo

When data is changed in the oracle database, the information needed to undo the changes is recorded so that the change can be undone (Rolled back). The record is basically just theĀ originalĀ information. Information is recorded in rollback segments and the undo tablespaces. This informationĀ is also used to provide read consistency which allows long running transactions …

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The Oracle Redo Log

One of the most important ideas in Oracle is that your data is safe. It is protected from corruption and also from system crashes. One of the most important ways that it does this is through the Redo logs. A Redo log record is written to describe the changes every time some data is changed …

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Oracle Read Consistency

Oracle is a multi user system and as such, multiple processes need to access the database at the same time to perform both reads and writes. Each one needs to get a consistent view of the data – one that does not change during a tranaction. Oracle ensures that the data that a process gets …

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Row Level Locking in Oracle

In Oracle, the Undo records allow data that is being modified to be accessed. Oracle uses row level locking to prevent two processes from trying to update the same data at the same time. Only the rows being modified are locked. This means that the rest of the table can still be modified while a …

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