由 macro 发布于: 2001-03-04 14:05

Number of online redo log files

To determine the appropriate number of online redo log files for a database instance,you have to test different configurations.

In some cases,a database instance may require only two groups ,In other situations , a database instance may require additional groups to guarantee that the groups are always available to LGWR.For example,if messages in the LGWR trace file or in the ALTER file indicate that LGWR frequently has to wait for a group because a checkpoint has not completed or a group has not been archived,you need to add groups.


Although the oracle server allows multiplexed groups to contain different numbers of members,try to build up a symmetric configuration. An symmetric configuration should only be the temporary result of an unusual situation such as a disk failure.


Location of online redo log files

on different disks

Sizing Online Redo Log Files

The minimum size of an online redo log file is 50 KB and the maximum size is specific to the operation system.Members of different groups can have different sizes; however , there is no benefit to having different-sized groups.

Different-sized groups should only be required as a temproary result if you want to change the size of the members of the online redo log groups,In this case,you have to create new online redo log groups with different sizes,and then remove the old groups.
The following situations might influence the configuration of the online redo log files:
1.Number of log switches and checkpoints
2.Number and amount of redo entries
3.Amount of space on the storage medium;for example ,on a tape if archiving is enabled

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Macro Zeng

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