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043-013

原创 Linux操作系统 作者:jbymy2000 时间:2012-03-04 11:33:43 0 删除 编辑
13. You executed the following query:
SELECT operation, undo_sql, table_name FROM flashback_transaction_que
ry;
Which statement is correct regarding the query output?
A. It would return information regarding only the last committed tran
saction.
B. It would return only the active transactions in all the undo segme
nts in the database.
C. It would return only the committed transactions in all the undo se
gments in the database.
D. It would return both active and committed transactions in all the
undo segments in the database.
E. It would return information regarding the transactions that began
and were committed in the last 30 minutes.
Answer: D
flashback_transaction_query 中的数据来自undo datafile,只要事务
对应的before image 在undo datafile 中存在,flashback_transaction_query 里面就可
以查询到数据...目前没发现受那个参数的制约。
undo中除了active的数据还有expired和unexpired的数据。C不全面。
插一句。select的时候会对比数据中的scn,如果小于当前值,那么就会去undo中找。

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