SSD7全部QUIZ答案

Multiple-Choice Quiz 8

1. Which of the following are properties of a good hash function? (c)

It should be computed efficiently.

It should minimize the number of collisions by spreading keys as evenly and uniformly as possible.

It should always use the Modulo (MOD) function.

(a) I only

(b) III only

(c) I and II only

(d) II only

2. Where do heap files add new records? (c)

(a) at random locations in the heap file

(b) in the middle of the heap file

(c) at the end of the heap file

(d) at the beginning of the heap file

3. Hashing exhibits the best performance for

(a) range queries

(b) ordering query results based on the key used for hashing

(c) equality searches involving the key, provided the key is used for hashing

(d) sequential scan of the entire table

4. A sparse index contains entries for (a)

(a) some records of a table

(b) some fields of a table

(c) all fields of a table

(d) all records of a table

5. A primary index _____ defined on a key field, and a secondary index _____ defined on a key field. (d)

(a) need not be, should not be

(b) should be, should not be

(c) need not be, need not be

(d) should be, need not be

6. Each index entry in an index file contains (c)

an indexing value

a pointer to the page where the record with the value appears

an indexing function

(a) I only

(b) I, II, and III

(c) I and II only

(d) III only

7. A cylinder of a multi-platter hard disk consists of (b)

(a) the outermost track

(b) tracks with the same diameter

(c) the innermost track

(d) tracks with different diameters

8. To improve the performance of a database, (d)

(a) never use buffering when transferring data between secondary storage and main memory

(b) never use hash files when deciding on an appropriate indexing structure

(c) always use hash files when deciding on an appropriate indexing structure

(d) minimize the amount of data transferred between secondary storage and main memory

9. The term block transfer time refers to the amount of time it takes to (c)

(a) load the address of a disk block from an index

(b) move the read/write head to the appropriate track on the disk

(c) read data from a disk

(d) position the appropriate disk block under the read/write head

10. The term blocking factor refers to the number of (c)

(a) disk blocks that form a track

(b) disk blocks that are on a hard disk drive platter

(c) database records that can be stored on a disk block

(d) cylinders on a hard disk drive

11. How does chained overflow solve the problem of collisions in hashing? (d)

(a) The first available empty bucket in a chained list of buckets is used.

(b) The first available slot in the overflow area where slots are chained using a hash function is used.

(c) The first available slot in a linked list of slots that is connected to the collision slot is used.

(d) The first available slot in a linked list of overflow buckets that is connected to the hashed bucket is used.

12. A secondary index is an index defined on a(n) _____ field. (a)

(a) non-ordering

(b) ordering

(c) primary key

(d) alternate key

13. Which of the following can be used to measure hard disk drive performance? (b)

Seek time

Rotational latency