Notes on ‘Expert Oracle’ — No.9.4: Redo&Undo — More about Redo Log

1. The large your Redo log is, the more time-consuming your SQL operation is.

2. Can we turn off Redo Log?

   a. Not Recommeded

   b. You can use "NOLOGGING" in SQLs to reduce much of the log.

   c. You can also use "NOLOGGING" for INDEX. This is actually acceptable.

3. How to avoid Log Contention?


   a. Redo Log的存储设备应该支持顺序写,而不是随机写

   b. 准备两组文件组,当一组用于LGWR写在线日志时,另一组则用于ARCH进行日志归档。这样就不会有写竞争。

4. Temporary Table

   There’s no redo log for temp table’s data blocks.  But there will be redo log for undo.

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