Improve media recovery performance
看11g的backup and recovery文档，oracle鼓吹11g媒体恢复更快。不过现在找不到11g的VLDB看实际效果。
Improved media recovery performance for databases on SMP systems
Media recovery of databases on symmetric multiprocessing (SMP) computers is now faster. The performance improvements include the following:
*More parallelism
*More efficient asynchronous redo read, parse, and apply
*Fewer synchronization points in the parallel apply algorithm
*The media recovery checkpoint at a redo log boundary no longer blocks the apply of the next logNo configuration is necessary, although you can use new parallel recovery wait events for tuning if the default apply rate is not satisfactory.
不过10g中数据库归档日志恢复在同等配置下比9i要快很多。9i中需要5分钟恢复一个归档日志,10g中直需要2分钟就可以了。
提高归档日志恢复的速度无非以下几个方法:
增大db_cache_size
使用并行恢复recover standby database parallel N
增加db_writer 进程
Disable db_block_checsum（不推荐）
当然了，更高的硬件和存储
参考几个文档:
Oracle9i Media Recovery Best Practices
Data Guard Redo Apply and Media Recovery
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“增加db_writer 进程”?
归档日志不是由arch来写的
media recovery会触发checkpoint让dbwr写dirty block到磁盘。因此一定的并行(包括db writter)可以增加吞吐量从而减少恢复的时间。