IMU疑惑

eof007

我只是对IMU事务回滚处理有些奇怪。
对于正常的系统，回滚都很少，可能oracle认为怎么处理都影响不大。
按照IMU原理，是可以把IMU回滚事务完全丢掉，在redo file中不做任何记录的，当做这个事务不存在。

[ 本帖最后由 eof007 于 2010-8-16 10:42 编辑 ]

Yong Huang

> 按照IMU原理，是可以把IMU回滚事务完全丢掉，在redo file中不做任何记录的，当做这个事务不存在。

I guess it's a matter of how much code change Oracle wants to make. What you say sounds like simplifying Oracle code. But in fact, it may actually be adding more complexity, because there's so much detail to take care of in this risky code change. (For example, you still need to deal with the changes already made to the datafile blocks even if you throw away redo.) So Oracle chooses the easier way, i.e. making the least change.

Yong Huang

[ 本帖最后由 Yong Huang 于 2010-8-16 09:39 编辑 ]

sundog315

原帖由 Yong Huang 于 2010-8-16 23:32 发表
> 按照IMU原理，是可以把IMU回滚事务完全丢掉，在redo file中不做任何记录的，当做这个事务不存在。

I guess it's a matter of how much code change Oracle wants to make. What you say sounds like simplifying Oracle code. But in fact, it may actually be adding more complexity, because there's so much detail to take care of in this risky code change. (For example, you still need to deal with the changes already made to the datafile blocks even if you throw away redo.) So Oracle chooses the easier way, i.e. making the least change.

Yong Huang

从程序开发角度，确实有可能是这样。猜想一下，IMU可能在rollback\commit前增加将imu打包为undo segment的操作。但是，去修改rollback\commit相关的代码，加入相关IMU内容，可能风险很大。