START_UBAFIL的意义

Kramer wrote:
I thought UBAFIL shows the file number where the first undo block located.

That would be START_UBAFIL, UBAFIL is the file where the most recent undo record has been created.

So the UBAFIL should always be files in the undo tablespace, right?

Not quite - if you haven't yet created any undo records then the various UBAxxx columns will hold zeros. One case you can use to demonstrate this is to engineer an incoming distributed query.

Regards

Jonathan Lewis

START_UBAFIL shows the file number where the first undo block located

UBAFIL is the file where the most recent undo record has been created.

如果还没有undo rescords生成的时候 UBAxxx columns will hold zeros

比如：

SQL> set transaction read only;


Transaction set

会开始一个transcation但是没有生成undo records

所以UBAFIL 为0