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Hashing in Databases

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Questions and Answers

What is the term for the field used to access a group of records in a hash table?

Index field

Hash key

Hash field (correct)

Hash value

What is the primary purpose of a hash function in a hash table?

To retrieve records from a disk block

To map a data item of arbitrary size to a fixed value (correct)

To map a fixed value to a data item of arbitrary size

To store records in a specific order

What is the advantage of using a 2-stage structure with a directory and buckets in hash tables?

It increases the number of available slots

It reduces the number of available slots

It takes advantage of the fact that the result of applying a hash function is always a non-negative integer (correct)

It allows for faster retrieval of records

What is the term for the array of 2d bucket addresses maintained in extendible hashing?

Directory Signup and view all the answers

What is the purpose of choosing a hashing function in internal hashing?

To transform the hash field value into an integer Signup and view all the answers

What is the characteristic of the result of applying a hash function in extendible hashing?

It is always a non-negative integer Signup and view all the answers

What is the role of the first d bits of the hash value in extendible hashing?

Determining the directory entry address Signup and view all the answers

What happens when a bucket with d’ = d overflows in extendible hashing?

Doubling is needed Signup and view all the answers

What is the advantage of extendible hashing in terms of performance?

Performance does not degrade as the file grows Signup and view all the answers

What is the maximum directory size in extendible hashing?

2^b, where b is the number of bits in the hash value Signup and view all the answers

What is the drawback of extendible hashing when the directory needs to be doubled or halved?

Reorganisation is expensive Signup and view all the answers

What is the consequence of splitting a bucket in extendible hashing?

Only records in one bucket are redistributed to two new buckets Signup and view all the answers