Redis data model (key-value) - Time & Space Complexity

Time complexity data not available for this pattern.

Practice

1. What is the main purpose of the key in a Redis key-value data model?

easy

A. To store multiple values together

B. To uniquely identify the stored data

C. To perform calculations on data

D. To format the data for display

Solution

1. Step 1: Understand the role of keys in Redis

   Keys in Redis act as unique names that identify each piece of data stored.

2. Step 2: Differentiate keys from values

   Values hold the actual data, while keys are used to find or access that data quickly.

3. Final Answer:

   To uniquely identify the stored data -> Option B

4. Quick Check:

   Key = Unique identifier [OK]

Hint: Keys uniquely name data for fast access [OK]

Common Mistakes:

• Thinking keys store multiple values
• Confusing keys with data formatting
• Assuming keys perform calculations

2. Which of the following is the correct Redis command syntax to set a key named user:1 with value John?

easy

A. STORE user:1 John

B. GET user:1 John

C. SET user:1 John

D. SET user:1 = John

Solution

1. Step 1: Recall the Redis command to store a key-value pair

   The command to set a key with a value is SET key value.

2. Step 2: Check each option's syntax

   SET user:1 John matches the correct syntax. Options A, B, and C use incorrect commands or syntax.

3. Final Answer:

   SET user:1 John -> Option C

4. Quick Check:

   SET key value = correct syntax [OK]

Hint: Use SET key value to store data [OK]

Common Mistakes:

• Using GET instead of SET to store data
• Adding '=' sign in command
• Using STORE command which doesn't exist

3. Given the following Redis commands executed in order:

SET counter 10
INCR counter
GET counter

What will be the output of the last command?

medium

A. 11

B. 10

C. counter

D. Error

Solution

1. Step 1: Analyze the commands executed

   First, SET counter 10 sets the key counter to string "10". Then, INCR counter increments the numeric value by 1.

2. Step 2: Understand the effect of INCR and GET

   INCR converts the string "10" to number 10, adds 1 to make 11, and stores it back. GET returns the current value, which is now "11".

3. Final Answer:

   11 -> Option A

4. Quick Check:

   10 + 1 = 11 [OK]

Hint: INCR adds 1 to numeric string values [OK]

Common Mistakes:

• Assuming GET returns the key name
• Thinking INCR works on non-numeric strings
• Expecting no change after INCR

4. You run the command INCR mykey but get an error. Which of the following is the most likely cause?

medium

A. The command syntax is incorrect

B. The key mykey does not exist

C. The Redis server is down

D. The value of mykey is not an integer

Solution

1. Step 1: Understand INCR command requirements

   INCR requires the key's value to be an integer or not exist (which initializes it to 0).

2. Step 2: Identify error cause

   If the key exists but holds a non-integer value (like a string), INCR will cause an error.

3. Final Answer:

   The value of mykey is not an integer -> Option D

4. Quick Check:

   INCR needs integer value [OK]

Hint: INCR fails if value is non-integer [OK]

Common Mistakes:

• Assuming missing key causes error
• Blaming server status without checking value
• Thinking syntax is wrong when command is correct

5. You want to store user session data in Redis using the key-value model. Which approach best ensures each session is uniquely stored and easily retrieved?

hard

A. Use a key pattern like session:{session_id} with the session data as the value

B. Store all sessions in a single key as a JSON string

C. Use the same key session for all users and overwrite values

D. Store session data as keys and user IDs as values

Solution

1. Step 1: Understand unique key requirements for sessions

   Each user session must have a unique key to avoid overwriting and allow quick access.

2. Step 2: Evaluate options for storing sessions

   Use a key pattern like session:{session_id} with the session data as the value uses a unique key pattern with session IDs, which is best practice. Store all sessions in a single key as a JSON string stores all sessions in one key, making access slow and complex. Use the same key session for all users and overwrite values overwrites data. Store session data as keys and user IDs as values reverses key-value roles, which is inefficient.

3. Final Answer:

   Use a key pattern like session:{session_id} with the session data as the value -> Option A

4. Quick Check:

   Unique keys per session = best practice [OK]

Hint: Use unique keys with session IDs for each session [OK]

Common Mistakes:

• Storing all sessions in one key
• Overwriting session data with same key
• Confusing keys and values roles