Notes on ‘Expert Oracle’ — No.9.2: Redo&Undo — How Redo works?

1. Redo log is made for

   a. Data Blocks

   b. Indexes

   c. Undo (That’s intersting)

2. The Redo info is first made in Cache, and it will be flushed into disk when

   a. 3 seconds passed

   b. The Redo Cache is 1/3 full or is over 1MB

   c. Commit happens

3. How Redo log helps with restoring?

  a. We use redo log to redo all commited transactions (Roll-Forward)

  b. After doing last step, we’ve already got the undo info for uncommited transactions, since it is also recorded in Redo Log

  c. The we do "Undo", to rollback uncommited transactions.


4.Again, Redo log is only for restore.

  a. The log is never read online.

  b. When online, the log is only being written, not being read.

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