1Z0-052-001

View the Exhibit and examine the attributes of an undo tablespace.

1、In an OLTP system, the user SCOTT has started a query on a large table in the peak transactional hour that performs bulk inserts. The query runs for more than 15 minutes and then SCOTT receives the following error: 
ORA-01555: snapshot too old  
What could be the reason for this error? 
A.The query is unable to get a read-consistent image. 
B.There is not enough space in Flash Recovery Area. 
C.There is not enough free space in the flashback  archive. 

D.The query is unable to place data blocks in undo tablespace 
Answer: A   

看下图，检查undo tablespace 的属性

图中undo保留时间15min ；绝对保留：否

tablespace：115m 自动扩展：否

在OLTP系统中，用户SCOTT在交易高峰时段对一个大表进行批量插入操作，该操作执行了超过15min并且报错如下：ORA-01555: snapshot too old （快照过旧）

ORA-01555: snapshot too old: rollback segment number string with name "string" too small

Cause: rollback records needed by a reader for consistent read are overwritten by other writers

Action: If in Automatic Undo Management mode, increase undo_retention setting. Otherwise, use larger rollback segments

造成该错误的原因是：A、The query is unable to get a read-consistent image.（没有足够的还原数据来实现读取一致性）

错误答案：B、闪回日志空间不足。          原因是超过15min undo被删除，并非空间不足。

 C、闪回存档无足够空间   

                 D、无法定位undo表空间的数据块