Hash indexes in DBMS Theory - Mini Project: Build & Apply

Understanding Hash Indexes in Databases

📖 Scenario: You are working with a simple database system that uses hash indexes to speed up data retrieval. Hash indexes help find data quickly by using a hash function to map keys to specific locations.Imagine a library where each book has a unique ID number. Instead of searching every shelf, the library uses a hash index to know exactly which shelf to check.

🎯 Goal: Build a basic hash index structure step-by-step to understand how keys map to buckets and how to retrieve data efficiently.

📋 What You'll Learn

Create a dictionary representing data records with unique keys

Define a hash function to map keys to bucket numbers

Use the hash function to create a hash index mapping buckets to keys

Add a final step to retrieve keys from a specific bucket

💡 Why This Matters

🌍 Real World

Hash indexes are used in databases to quickly locate data without scanning the entire dataset, improving search speed.

💼 Career

Understanding hash indexes is important for database administrators and developers to optimize data retrieval and design efficient database systems.

1

Create the data records dictionary

Create a dictionary called records with these exact entries: 101: 'Book A', 102: 'Book B', 203: 'Book C', 304: 'Book D', and 405: 'Book E'.

DBMS Theory

# Create the records dictionary with the given keys and values
# Your code here

Need a hint?

Use curly braces {} to create a dictionary with the given key-value pairs.

2

Define the hash function

Define a function called hash_function that takes a key and returns the remainder when the key is divided by 3 using the modulus operator %.

DBMS Theory

records = {101: 'Book A', 102: 'Book B', 203: 'Book C', 304: 'Book D', 405: 'Book E'}
# Define the hash_function that returns key % 3
# Your code here

Need a hint?

The modulus operator % gives the remainder of division. Use it to map keys to buckets 0, 1, or 2.

3

Create the hash index mapping buckets to keys

Create an empty dictionary called hash_index. Use a for loop with variables key and value to iterate over records.items(). Inside the loop, use hash_function(key) to get the bucket number. Add the key to the list of keys in hash_index for that bucket. If the bucket does not exist, create a new list.

DBMS Theory

records = {101: 'Book A', 102: 'Book B', 203: 'Book C', 304: 'Book D', 405: 'Book E'}
def hash_function(key):
    return key % 3

# Create hash_index dictionary and fill it using a for loop
# Your code here

Need a hint?

Check if the bucket exists in hash_index. If not, create an empty list before adding keys.

4

Retrieve keys from a specific bucket

Create a variable called bucket_to_check and set it to 2. Then create a variable called keys_in_bucket that gets the list of keys from hash_index for bucket_to_check. Use the get() method with an empty list as the default value.

DBMS Theory

records = {101: 'Book A', 102: 'Book B', 203: 'Book C', 304: 'Book D', 405: 'Book E'}
def hash_function(key):
    return key % 3

hash_index = {}
for key, value in records.items():
    bucket = hash_function(key)
    if bucket not in hash_index:
        hash_index[bucket] = []
    hash_index[bucket].append(key)

# Set bucket_to_check to 2 and get keys_in_bucket from hash_index
# Your code here

Need a hint?

Use the get() method on hash_index to safely retrieve keys for the bucket.