EMC题2

易安信笔试题分享：
1 protected成员函数能被肿么调用
2 “has-a” relationship是指的啥，答案有instance, reference, pointer等。。。
3 int, char, short, long的字节数
4 在C++中，变量用时声明是为啥
5 命名空间的作用
6 int a[10][10];
int *b[10];
以下哪个正确
a[3][4] = 91;
b[3][4] = 91;
a[1] =NULL;
b[1] = a[2];
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 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