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Showing posts with label query cost. Show all posts
Showing posts with label query cost. Show all posts

# MCQ on various aspects in DBMS including time required to read disk block pages, block access per second,  primary dense index, secondary, b+ tree index, RDBMS Multiple Choice Questions with Answers

## Database management systems - MCQ exam questions

1. You have a table with 1 million records. Each record fits exactly in one disk block in the hard disk, and the blocks for the table are sequential. The hard disk drive has a 10ms seek latency to start a read operation, and after it starts, it can read 10,000 blocks per second. How much time will you spend to read the entire table?

a) 10.01 seconds

b) 51.01 seconds

c) 100.01 seconds

d) 25.01 seconds

 Answer: (c) 100.01 seconds Since the data stored in sequential (contiguous) order, in one seek we can read all data. Hence, the time required to read the entire table can be calculated as follows; Seektime + time to read all the disk blocks = 10ms + (1000000 blocks / 10000 blocks per sec)                                                                                     = 0.01 + 100 = 100.01 seconds.

2. Which of the following statements is wrong / irrelevant?

a) First and second level of secondary index are dense

b) Primary index can be dense

c) Primary index can be sparse

d) Secondary indices are always dense

 Answer: (a) First and second level of secondary index are dense Multiple levels of indices are used to improve the accessibility in case if the index itself is very large. But a dense index includes all the search key values. Hence, building a dense index in second level on top of first level dense index is redundant.

3. The maximum number of levels between the root node and a leaf node in a B+ tree is called as

a) Degree of a tree

b) Order of a tree

c) Depth of a tree

d) None of the above

 Answer: (c) Depth of a tree The depth of a tree is the maximum number of levels between the root node and a leaf node in the tree. The maximum number of children allowed per parent is referred as Degree or Order of a tree.

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