[zt] 10gR2 rman对Unused Block Compression-优快云博客

本文介绍Oracle 10gR2中RMAN对未分配块进行压缩的功能，在特定条件下能显著减少备份占用的空间。适用于兼容参数设置为10.2、无保证还原点、本地管理的数据文件等场景。

在10gR2中,rman最显著的一个特征就是对未分配的块进行压缩,但它必须满足一些必要的条件,在满足该条件下做了测试,效果非常理想,创建一个2g的数据文件,备份集只增加了8m,而且数据文件总的容量在2g,备份集才588m.

备份的脚本:

rman>backup full database format = 'd:test.bak';

必须满足的条件如下:

Unused Block Compression Of Datafile Backups to Backup Sets
When backing up datafiles into backup sets, RMAN does not back up the contents of data blocks that have never been allocated. (In previous releases, this behavior. was referred to as NULL compression.)
RMAN also skips other datafile blocks that do not currently contain data, if all of the following conditions apply:
■ The COMPATIBLE initialization parameter is set to 10.2
■ There are currently no guaranteed restore points defined for the database
■ The datafile is locally managed
■ The datafile is being backed up to a backup set as part of a full backup or a level 0 incremental backup
■ The backup set is being created on disk.
Skipping unused data blocks where possible enables RMAN to back up datafiles using less space, and can make I/O more efficient.

出处： http://xzh2000.itpub.net/post/96/64549

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