052-1

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

这个错误原因应该是高峰时期数据脏块产生，然后undo空间不够要清除延时的缓存，无法读到查询发起时的数据
关于一致性读 http://blog.itpub.net/26736162/viewspace-2080746/