问题 填空题

在并发控制中,事务是数据库的逻辑工作单位,是用户定义的一组操作序列,一个程序可以包含多个事务,事务是并发控制的 【15】

答案

参考答案:改前值

解析:[评析] 由于系统在正常事务处理时登记日志,对数据库中的更新活动进行了必要的记录,这样当发生故障时就可以利用日志文件中的信息进行故障恢复,即反向扫描日志文件,查找该事务的更新操作,恢复到操作前的状态——“改前值”。

阅读理解

根据短文判断正(T)误(F)。

     Young people can have problems with their minds. Some students become worried because they

have to study very hard. Others have trouble getting on well with people like their parents and classmates.

      Jiu, a second year junior student from Fujian, could not understand his teacher and was doing badly

in class. He became so worried about it that he started to cut his fingers (手指)with a knife.

     Another student, 14-year-old Lan from Guangzhou, was afraid of exams. She got very worried, and

when she looked at the exam paper, she couldn't think of anything to write.

     A recent (最近的) report says about 18 percent of teens have mental (精神上) problems. Their

troubles include (包括) being worried and very unhappy, and having problems in learning and getting on

with people.

     Many students who have problems won't go for advice or help. Some think they will look stupid if

they go to see a doctor. Others don't want to talk about their secrets.

     An expert on teenagers has the following advice for teens:

     ●Talk to your parents or teachers often.

     ●Take part in group activities and play sports.

     ●Go to see a doctor if you feel unhappy or unwell.

( )1. Young people don't have problems with their minds.                    

( )2. It is important to get on well with others.                          

( )3. Lan was not worried about her exam.                                  

( )4. If we have some problems, we should use alcohol drinks to stop them.

( )5. Jiu could understand his teacher.                                    

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