易安信笔试题和面试题答案(二)

　　13 There is a huge relation R(A,B,C) of size M and A is the primary key. The tuples in R are sorted by using A and no index is built for R. Each disk block size of b, and each block read takes N seconds. To find a tuple in R with A =17954 the estimated optimized cost is

　　A M*N/b

　　B N*log(M/b)

　　C M*N/(2b)

　　D (M+N)/b

　　E log(M*N)/b

　　14 Which of the following descriptions of reader/writer locks are/is wrong?

　　A caller cannot upgrade its read lock(already obtained) to write lock

　　B caller can downgrade its write lock(already obtained) to read lock

　　C caller can get read lock if there is no write lock held by others

　　D multiple callers can hold a read lock at the same time

　　E only one caller can hold a write lock at a time

　　15 两页的内存，四页的文件，读取顺序为 1 2 1 3 1 2 4 2 1 3 1 2 4 2 1 2 3 4 3 1，FIFO，问cache hit ratio为多少

　　16 线程

　　选项 contained with a process

　　share an address space

　　share signals

　　share errno

　　swith的速度比process快

　　17 which one is not above IP

　　DNS, SNMP, HTTP, ARP, NTP

　　18 Map-Reduce Framework

　　19 Buffer overflow

　　20 system virtualization

　　VM, VMM, IO, memory space

　　21

　　#include

　　using namespace

　　void main()

　　{

　　cout << “hello world” << endl;

　　}

　　修改程序，不能修改主程序，使其输出为

　　initiate

　　hello world

　　destroy

　　22 process & thread

　　virtual memory space

　　kernel register, stack

　　fork

　　copy-on-write