redo的构成

To illustrate the creation of change vectors and redo records, consider the following transaction:

Ø

SQL> update emp set empno = 22 where empno = 11

Ø

When this update statement is executed , the sequence of operation is as follows:

1. Change vectors of the redo record are generated

2. The redo record is saved in a redo log buffer

3. The change vectors are applied to the data blocks

Ø The redo records stated in step 1 contains three change vectors

- Change to the transaction table of rollback segment

- Change to the rollback segment datablock

- Change to the data segment block belonging to the EMP table

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