易安信(EMC)笔试题和面试题答案

　　不定向选择

　　1 在C++中，变量用时声明是为啥

　　2 命名空间的作用

　　3 protected成员函数能被肿么调用

　　4 “has-a” relationship是指的啥，答案有instance, reference, pointer等。。。

　　5 int, char, short, long的字节数

　　6 int a[10][10];

　　int b[10];

　　以下哪个正确

　　a[3][4] = 91;

　　b[3][4] = 91;

　　a =NULL;

　　b = a;

　　7 12&&10, 12||10, 12&10, 3>>1, 3>1的结果

　　8 x86_64系统下

　　struct

　　{

　　int i;

　　char c;

　　double d;

　　};

　　union

　　{

　　int i;

　　char c;

　　double d;

　　};

　　char s[100];

　　long c;

　　sizeof的值

　　10. An employee has one or two managers, and one manager manages one or more employees. In database conceptual design, the relationship between entity sets employee and manager is

　　A one to one

　　B one to many

　　C many to one

　　D many to many

　　E none of the above

　　11 There are two relations R1(A, B, C) and R2(B, D, E). Which of following techniques CANNOT be used to improve the performance of the natural join of the two relations?

　　A make use of multiple parallel processes on a multi-core machine to implement the join algorithm

　　B increase the CPU L2 cache hit ratio of the join algorithm implementation

　　C partition the relations to different machines by using join attributes and execute the join on many machines in parallel

　　D when the number of tuples in R2 is large and the number of tuples in R1 is small, build and index on R1 and use index join method

　　E none of the above

　　12 Which of the following statements about checkpoints(with log-based recovery schemes) in databases are/is NOT correct?

　　A checkpoints are used to decrease the time used for failure recovery

　　B checkpoints are done periodically in database to assure ACID properties of transactions

　　C periodic checkpoints decreased the number of log entries that need to be redone during recovery

　　D during checkpointing, updated disk blocks are written to disk

　　E none of the above

　　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 MN/b

　　B Nlog(M/b)

　　C MN/(2b)

　　D (M+N)/b

　　E log(MN)/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 process & thread

　　virtual memory space

　　kernel register, stack

　　fork

　　copy-on-write

　　大题

　　22

　　#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

　　23spinlock 与mutex

　　1. explain

　　2. write the struct definition of spinlock and mutex

　　3. write the release function of mutex

　　4. implement the reader/writer locks

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