Structure of the Online Redo Log

Online redo log files contain redo records. A redo record is made up of a group of change vectors, each of which describes a change to a data block. For example, an update to a salary in the employees table generates a redo record that describes changes to the data segment block for the table, the undo segment data block, and the transaction table of the undo segments.

The redo records have all relevant metadata for the change, including the following:

• SCN and time stamp of the change

• Transaction ID of the transaction that generated the change

• SCN and time stamp when the transaction committed (if it committed)

• Type of operation that made the change

• Name and type of the modified data segment

  联机重做日志结构

  
  

  联机重做日志文件中包含的重做记录。重做记录由一组变化矢量，每一个都描述了一种改变一个数据块。例如，在员工的工资表的更新产生重做记录，描述变化的数据段块表，回滚段的数据块，undo段的事务表。

  
  

  重做记录所有相关的元数据的变化，包括以下内容：

  SCN和时间戳的变化

  Transaction ID 的交易产生的变化

  SCN和时间戳的事务提交时（如果它提交）

  类型操作，而改变

  修改后的数据段的名称和类型