Notes on ‘Expert Oracle’ — No.9.3: Redo&Undo — Commit & Rollback

1. What happens if a transaction is commited?

  a. The Redo Log is flushed

  b. Is the data blocks in SGA flushed also?  No.  We don’t need to do that with Redo Log.


2. Is the time of commitment a function of the volumn of manipulated data?

  No. There is not a lot to do when the transactions reach the point of commit.

    a. Flush the Redo log. The log is not so much, since the LGWR has been flushing logs when the transaction starts.

    b. Put the SCN in the Redo Log. (SCN = Indication of a transaction)

3. So, don’t commit frequently. Commit a long transaction.

    a. You don’t have to commit frequently. The time of a single commitment is not getting larger just because your transaction is long.

    b. Everytime you commit, you have to wait for the LGRW to flush the log file. The more you committed, the longer you have to wait. That’s time consuming.

4. The time of Rollback is a function of the data manipulated.

    a. It is actually running the opposite SQLs.

    b. So,  avoid large-scale Rollbacks.

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