How many block accesses average saved on using secondryindex, Database Management System

Assignment Help:

An un- ordered student file has 20,000 records stored on a disk having the Block size as 1 K. Suppose that each student record is of 100 bytes, the secondary index field is of 8 bytes, and block pointer is also of 8 bytes, find how many block accesses on average may be saved on using secondary index on enrolment number.

Answer:

Number of accesses without using Secondary Index:

Number of records in the file = 20000

Block size = 1024 bytes

Record size = 100 bytes

Number of records per block = integer value of [1024 / 100] = 10

Number of disk blocks acquired by the file = [Number of records / records per block]

= [20000/10] = 2000

 

As the file is un-ordered any search on an average will require about half of the above blocks to be accessed. Thus, average number of block accesses = 1000

Number of accesses with Secondary Index:

Size of an index entry = 8+8 = 16 bytes

Number of index entries that can be stored per block

= integer value of [1024 / 16] = 64

Number of index entries = number of records = 20000

Number of index blocks = ceiling of [20000/ 64] = 320

Number of index block transfers to find the value in index blocks = ceiling of [log2320] = 9

One block move will be needed to get the data records using the index pointer after the needed index value has been located. So total number of block transmits with secondary index = 9 + 1 = 10

Therefore,, the Secondary index would save about 1990 block transmit for the given case. This is a huge saving compared to primary index. Please also compare the size of secondary index to primary index.

Let us now see an illustration of a secondary index that is on an attribute that is not an alternate key.

 

 

 

 

                                269_how many block accesses average saved on using Secondryindex.png


Related Discussions:- How many block accesses average saved on using secondryindex

RDBMS, what is RDBMS? how it works? good example.

what is RDBMS? how it works? good example.

List the set operations of sql, List the set operations of SQL? 1) Unio...

List the set operations of SQL? 1) Union 2) Intersect operation 3) The except operation

What is an index, What is an Index? An index is a small table having on...

What is an Index? An index is a small table having only two columns. The first column has a copy of the primary or candidate key of a table and the second column having a set o

Client server databases, Client Server Databases- The concept behind the C...

Client Server Databases- The concept behind the Client/Server systems is simultaneous, cooperative processing. It is an approach that presents a one systems view from a user's vie

Data aggregation, Q.   Explain  data aggregatio n and discuss differen...

Q.   Explain  data aggregatio n and discuss different design constraints. Sol. Aggregation   One limitation of the E-R model is that it cannot express relationships amon

Which types of data supported by mysql, Which types of data supported by My...

Which types of data supported by MySQL for Time and Date formats?  MySQL supports a number of time and date column formats: Some of them are 1) DATE 2) DATETIME 3) TIM

Discuss the different layers of ansi sparc architecture, Q.1 Briefly discus...

Q.1 Briefly discuss the different layers of ANSI SPARC architecture. Ans: The three layers of ANSI SPARC architecture are like this: 1. Internal view is at the lowest leve

What is data mining?, Question 1 Define OLTP? Explain the Differences betw...

Question 1 Define OLTP? Explain the Differences between OLTP and Data Warehouse Question 2 What is Architecture? Explain various components involved in it Question

Explain er model, Question 1 Explain ER model Question 2 What are the...

Question 1 Explain ER model Question 2 What are the characteristics of a computer provided information? Question 3 What are facts and guidelines to be considered when se

Sql, find the name of supplier who supply some red part

find the name of supplier who supply some red part

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd