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Question About RBA (Redo Block Address) [ID 759966.1]

原创 Linux操作系统 作者:spider0283 时间:2012-04-24 15:53:57 0 删除 编辑

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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


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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