MOS上关于RBA的介绍

Question About RBA (Redo Block Address) [ID 759966.1]
  修改时间08-JAN-2009     类型HOWTO     状态MODERATED  

In this Document
  Goal
  Solution

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Applies to:

Oracle Server – Enterprise Edition – Version: 10.2.0.3
Information in this document applies to any platform.

Goal

1. What is RBA? Can you explain it in relation to a transaction and commit scn?How can I find out
which RBAs exist in a archive log/redo log? 3. For example:
Completed checkpoint up to RBA [0x19.2.10], SCN: 5586949

Solution

A "Redo Block Address" (RBA) describes a physical location within a redo log file. An RBA consists
of the following:

Log sequence number
Block number within log file
Byte offset within block

The structure of the redo block address is given below :
1 – The number of the redo log.
[4 bytes]

2 – The block offset from the beginning of the redo log file.
[4 bytes]

3 – The byte offset within the block.
[2 bytes]

So in this case, RBA [0x19.2.10] maps to Log squence 25, Block number 2 with byte offset 16.

As for the relation between RBA and SCN, you can see that RBA is actually a physical location inside the redo log file while SCN is the system change number that is in fact a unit of time (a timestamp) maintained by the database kernel which is used to order events.

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RBA：重做记录的物理地址。由4部分组成，分别是日志线程号、日志序列号、日志文件块编号好日志文件块字节偏移量，长度为10字节。修改操作的SCN、SUBSCN和该操作的RBA都会被写入在重做记录中。
RBA经常以“Thread:n RBA: 0xffffff.ffffffff.ffff”的形式出现在转储文件中，比如“Thread:1 RBA: 0x000015.00000005.0010”，其含义就是在1号线程21号序列号重做日志文件的第5个块中的第16字节处。