问题 单项选择题

在并发控制的技术中,最常用的是封锁方法。对于共享锁(S)和排他锁(X)来说,下面列出的相容关系中,哪一个是不正确的

A.X/X:TRUE

B.S/S:TRUE

C.S/X:FALSE

D.X/S:FALSE

答案

参考答案:A

解析: 为了避免发生并发操作引起的数据不一致性问题,则采用数据封锁技术实现并发控制。封锁是防止存取同一资源的用户之间相互干扰的机制,即当一个用户对数据库某个数据对象执行修改操作时,对该部分数据加锁,拒绝其他用户对该部分的并发访问要求,直至该事务执行完毕才释放数据对象。所以X/X:TRUE是不对的。

阅读理解

A Smashing tradition: MIT Students Drop Piano

One of the highlights of the school year at the Massachusetts Institute of Technology only lasts a few seconds but has a big influence. Residents of an MIT dormitory dropped an upright piano from their roof on 26th April to celebrate the last day students can drop classes without having them appear on their college report.

About 200 onlookers watched as the piano crashed into a second piano, a baby grand, positioned on the ground six stories below for a better smash. People scrambled (争先恐后) for souvenir pieces-keys, hammers, strings and splinters. The tradition began in 1972 at the Baker House dormitory and has been observed irregularly until 2006 when it became an annual event.

Crafton Family Comes Back Home after 7 Years at Sea

While most of us will love to go on a vacation for a week or two on a small private sailboat, without doubt, spending seven precious years on sea is something most of us will never imagine or dare to do. However, that is what an American family has done. Tom Crafton and Kathy Crafton along with their three children have traveled across the world on their 43-foot sailboat named Nueva Vida. Over the past seven years the family had sailed 30,000 miles and visited more than 20 different countries. The family has recently come back to their homeland.

_____________________________________________

Living in the limelight(聚光灯)can be difficult but as these splendid pictures show for one bear the tourist train never stops. This arctic animal loves nothing more than an audience and will even climb out of his snowy bed to give the crowd a wave. The funny poses(姿态) of the friendly polar bear were caught on camera by Swedish photographer, Hams Strand.

小题1:Which of the following is true about the first incident?

A.The typical style of celebration has been kept alive every year since1972.

B.Another small piano on the ground is meant to hold the falling one.

C.The students dropped the piano in celebration of their graduation.

D.The tradition became an annual event for MIT students several years ago.小题2:The writer thinks Crafton family’s seven-year sailing is ______.

A.unusual

B.strange

C.common

D.doubtful小题3:What would be the best subtitle for the third incident?

A.The Limelight Makes Polar Bear Live Hard

B.Splendid Pictures of Polar Bear Attract Tourists

C.The Tourist Train Would Stop without Polar Bear

D.Polar Bear Says Hello to Tourists with a Friendly Wave小题4:The passage is probably taken out of ______.

A.a novel

B.a magazine

C.a diary

D.a report

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