Explain the use of leases in a discovery service to cope with the problem of service volatility.
What will be an ideal response?
The problem is that services may fail or become disconnected at any time, leaving stale entries in the service directory.
Assume a lease expiry time of t seconds. The list of services in a directory is fresh to within t seconds because any server that is still alive will renew its lease before its expiry time. If a server leaves, crashes, or becomes disconnected from a lookup service, the latter will delete its entry as soon as the lease expires. Therefore an unavailable server is registered only for a maximum of t seconds after it becomes unavailable. A client that, nonetheless, obtains a stale server entry, will discover this when it tries to connect.
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To select the account from which to send an email message when there are multiple accounts, click the ____________________ button in the Untitled - Message window, and then click the desired email account.
Fill in the blank(s) with the appropriate word(s).
Which of the following is not a relational operator?
A. = B. < C. >= D. >
?When a website is using SSL, the site's URL in the Location or Address bar begins with ____.
A. ?http:// B. ?https:// C. ?ftp:// D. ?SSLtp://
Answer the following statements true (T) or false (F)
1. Symmetric multiprocessors (SMPs) are one of the earliest, and still the most common, example of parallel organization. 2. The term SMP refers to a computer hardware architecture and also to the operating system behavior that reflects that architecture. 3. An attractive feature of an SMP is that the existence of multiple processors is transparent to the user. 4. The main drawback of the bus organization is reliability. 5. An SMP operating system manages processor and other computer resources so that the user perceives a single operating system controlling system resources.