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哪种DML操作产生undo多

原创 Linux操作系统 作者:keeptrying 时间:2012-04-09 20:14:01 0 删除 编辑
The number of bytes required to store information that is needed in case of rollback depends
on the type of transaction being performed:

Deletes are expensive for rollback segments; they need to store the actual row itself. If you can use TRUNCATE instead, performance is improved.

Inserts use little rollback space; only the rowid is kept.

The amount used for updates depends on how many columns are being updated.

Indexed values generate more rollback, because the server process must change values
in the index as well as in the table. For updates on indexed columns, the Oracle server
records in the rollback segment the old data value, the old index value, and the new
index value. Updating rows that change partitions will also generate more rollback.

Direct path inserts / appends / loads are not likely to use much rollback.

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