一些问题
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suzhiyang
Jun 5, 2010, 10:38:10 AM6/5/10
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闫老师：
您好！
第八章习题（P374）：
1.这里所指的a high degree of
security是不是safety?就是说一个可靠的系统应该长时间运行而不DOWN掉？
3.这里的failure如果是的话，应该是response failure吧。
btw,书上P324中讲到的几种failure，response failure和arbitrary
failure分不太清楚，区别是不是在于前者是返回一个错误的结果（对于某一个输入/REQUEST）；而后者是不管你有没有REQUEST，它都把不知道什么样的结果/消息乱发一气？
4.Q: Can the model of triple modular redundancy described in the text
handle Byzantine failures?
这个TMR和后面的Byzantine failures有什么关系？
20. Q: Does a stateless server need to take checkpoints?
However, there is no need to take checkpoints for the sake of the state of the distributed system.
Checkpointing is done only for local recovery.
这里，stateless server是什么意思？解释的这句是什么意思？
谢谢！
2010-06-05
suzhiyang
Hongfei Yan
Jun 5, 2010, 11:34:57 AM6/5/10
to cs501pku
2010/6/5 suzhiyang <suzh...@gmail.com>
闫老师：您好！第八章习题（P374）：1.这里所指的a high degree of security是不是safety?就是说一个可靠的系统应该长时间运行而不DOWN掉？
不是safety.
Page 323 Often, dependable systems are also required to provide a high degree of security,
especially when it comes to issues such as integrity. We will discuss security in the next chapter.
especially when it comes to issues such as integrity. We will discuss security in the next chapter.
3.这里的failure如果是的话，应该是response failure吧。btw,书上P324中讲到的几种failure，response failure和arbitrary failure分不太清楚，区别是不是在于前者是返回一个错误的结果（对于某一个输入/REQUEST）；而后者是不管你有没有REQUEST，它都把不知道什么样的结果/消息乱发一气？
是response failure
response failure产生错误，但是发request的可以容易的检测到。
arbitrary failure产生错误，but which cannot be detected as being incorrect
response failure产生错误，但是发request的可以容易的检测到。
arbitrary failure产生错误，but which cannot be detected as being incorrect
4.Q: Can the model of triple modular redundancy described in the text handle Byzantine failures?这个TMR和后面的Byzantine failures有什么关系？
TMR is able to tolerate the loss or malfunctioning of some components.
Byzantine failures are intended to model any arbitrary type of processor malfunction.
Byzantine failures are intended to model any arbitrary type of processor malfunction.
20. Q: Does a stateless server need to take checkpoints?However, there is no need to take checkpoints for the sake of the state of the distributed system.Checkpointing is done only for local recovery.这里，stateless server是什么意思？解释的这句是什么意思？
Page 90, A stateless server does not keep information on the state of its clients, and can
change its own state without having to inform any client (Birman, 2005).
page 91, Note that in many stateless designs, the server actually does maintain information
on its clients, but crucial is the fact that if this information is lost, it will
not lead to a disruption of the service offered by the server. For example, a Web
server generally logs all client requests. This information is useful, for example, to
decide whether certain documents should be replicated, and where they should be
replicated to. Clearly, there is no penalty other than perhaps in the form of suboptimal
performance if the log is lost.
翻译：没有必要为了保证分布式系统的状态而作恢复点（因为是stateless server）。恢复点只为本地恢复用。
change its own state without having to inform any client (Birman, 2005).
page 91, Note that in many stateless designs, the server actually does maintain information
on its clients, but crucial is the fact that if this information is lost, it will
not lead to a disruption of the service offered by the server. For example, a Web
server generally logs all client requests. This information is useful, for example, to
decide whether certain documents should be replicated, and where they should be
replicated to. Clearly, there is no penalty other than perhaps in the form of suboptimal
performance if the log is lost.
翻译：没有必要为了保证分布式系统的状态而作恢复点（因为是stateless server）。恢复点只为本地恢复用。
谢谢！2010-06-05
suzhiyang
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