Memory usage analysis (INFO memory) in Redis - Mini Project: Build & Apply

Memory Usage Analysis with Redis INFO Memory

📖 Scenario: You are managing a Redis server that stores session data for a web application. To keep the server running smoothly, you need to check how much memory Redis is using and understand the memory details.

🎯 Goal: Learn how to use the Redis INFO memory command to get memory usage details and analyze the output.

📋 What You'll Learn

Use the Redis command INFO memory to get memory statistics

Store the output in a variable called memory_info

Extract the used_memory value from memory_info

Extract the maxmemory value from memory_info

💡 Why This Matters

🌍 Real World

Monitoring Redis memory usage helps prevent crashes and optimize performance in real applications like caching and session storage.

💼 Career

Understanding Redis memory info is important for roles like backend developers, DevOps engineers, and system administrators managing Redis servers.

1

Connect to Redis and get memory info

Write a Redis command to get memory information using INFO memory and store the result in a variable called memory_info.

Redis

# Use the Redis command INFO memory and store it in memory_info
# Your code here

Hint

Use execute_command('INFO', 'memory') on your Redis client to get memory info.

2

Extract used_memory from memory_info

Add code to extract the used_memory value from the memory_info string and store it in a variable called used_memory. The value is after the line starting with used_memory:.

Redis

memory_info = redis_client.execute_command('INFO', 'memory')
# Extract used_memory value from memory_info
# Your code here

Hint

Split memory_info by lines and find the line starting with used_memory:. Then split by ':' and convert the second part to an integer.

3

Extract maxmemory from memory_info

Add code to extract the maxmemory value from the memory_info string and store it in a variable called maxmemory. The value is after the line starting with maxmemory:.

Redis

memory_info = redis_client.execute_command('INFO', 'memory')
used_memory = None
for line in memory_info.splitlines():
    if line.startswith('used_memory:'):
        used_memory = int(line.split(':')[1])
        break
# Extract maxmemory value from memory_info
# Your code here

Hint

Use a similar approach as for used_memory to find and convert maxmemory.

4

Check if maxmemory is set and finalize

Add code to check if maxmemory is zero, which means no max memory limit is set. Store the result as a boolean in a variable called is_maxmemory_set. It should be False if maxmemory is 0, otherwise True.

Redis

memory_info = redis_client.execute_command('INFO', 'memory')
used_memory = None
maxmemory = None
for line in memory_info.splitlines():
    if line.startswith('used_memory:'):
        used_memory = int(line.split(':')[1])
    elif line.startswith('maxmemory:'):
        maxmemory = int(line.split(':')[1])
    if used_memory is not None and maxmemory is not None:
        break
# Check if maxmemory is set and store in is_maxmemory_set
# Your code here

Hint

Compare maxmemory to zero and assign the boolean result to is_maxmemory_set.

Practice

1. What does the used_memory field in the INFO memory command represent in Redis?

easy

A. The total number of keys stored in Redis

B. The amount of memory Redis is currently using in bytes

C. The peak memory usage recorded since Redis started

D. The fragmentation ratio of Redis memory

Solution

1. Step 1: Understand the INFO memory output

   The INFO memory command shows various memory stats about Redis.

2. Step 2: Identify used_memory meaning

   used_memory specifically shows how many bytes Redis is currently using in RAM.

3. Final Answer:

   The amount of memory Redis is currently using in bytes -> Option B

4. Quick Check:

   used_memory = current memory used [OK]

Hint: Remember: 'used_memory' means current bytes used [OK]

Common Mistakes:

• Confusing 'used_memory' with total keys count
• Mixing 'used_memory' with peak memory
• Thinking it shows fragmentation ratio

2. Which of the following is the correct Redis CLI command to check memory usage details?

easy

A. GET MEMORY INFO

B. MEMORY USAGE

C. SHOW MEMORY

D. INFO memory

Solution

1. Step 1: Recall Redis commands for memory info

   The Redis command to get detailed memory info is INFO memory.

2. Step 2: Check other options

   MEMORY USAGE exists but returns usage for a single key, not overall memory info. The others are invalid commands.

3. Final Answer:

   INFO memory -> Option D

4. Quick Check:

   Use INFO memory to get memory stats [OK]

Hint: Use 'INFO memory' to get full memory stats [OK]

Common Mistakes:

• Using MEMORY USAGE to get overall memory info
• Typing invalid commands like SHOW MEMORY
• Confusing command names

3. Given this Redis INFO memory output snippet:

used_memory:1048576
used_memory_peak:2097152
mem_fragmentation_ratio:1.5

What does the mem_fragmentation_ratio value of 1.5 indicate?

medium

A. Redis memory is fragmented, using 1.5 times more memory than needed

B. Redis is using 50% more memory than allocated

C. Redis has 1.5 million keys stored

D. Redis memory usage is optimal

Solution

1. Step 1: Understand mem_fragmentation_ratio

   This ratio shows how much extra memory Redis uses due to fragmentation.

2. Step 2: Interpret value 1.5

   A value of 1.5 means Redis uses 1.5 times the memory it actually needs, indicating fragmentation.

3. Final Answer:

   Redis memory is fragmented, using 1.5 times more memory than needed -> Option A

4. Quick Check:

   Fragmentation ratio > 1 means extra memory used [OK]

Hint: Fragmentation ratio >1 means extra memory used [OK]

Common Mistakes:

• Thinking ratio shows number of keys
• Assuming ratio below 1 means fragmentation
• Confusing fragmentation with peak memory

4. You run INFO memory and see used_memory_peak is lower than expected despite high used_memory. What is the likely cause?

medium

A. The command syntax is incorrect

B. Redis is leaking memory and reporting wrong values

C. Redis memory peak resets after restart, but current usage is higher

D. Redis has no keys stored

Solution

1. Step 1: Understand used_memory_peak

   This shows the highest memory Redis used since last restart.

2. Step 2: Compare with used_memory

   If current used_memory is higher, it means memory usage increased after peak was reset (likely after restart).

3. Final Answer:

   Redis memory peak resets after restart, but current usage is higher -> Option C

4. Quick Check:

   Peak resets on restart, current usage can be higher [OK]

Hint: Peak resets on restart; current can exceed peak after restart [OK]

Common Mistakes:

• Assuming memory leak without evidence
• Thinking command syntax is wrong
• Believing no keys means memory usage

5. You notice your Redis server's mem_fragmentation_ratio is consistently above 2.0. What is the best action to reduce memory fragmentation?

hard

A. Run MEMORY PURGE command to defragment memory

B. Increase the number of keys stored

C. Restart Redis to reset memory fragmentation

D. Delete all keys to free memory

Solution

1. Step 1: Understand high fragmentation impact

   A ratio above 2 means Redis uses twice the memory needed, hurting performance.

2. Step 2: Identify Redis command to reduce fragmentation

   MEMORY PURGE triggers allocator to release unused memory and reduce fragmentation.

3. Step 3: Evaluate other options

   Restarting helps temporarily but is disruptive. Increasing keys worsens memory. Deleting all keys is drastic and unnecessary.

4. Final Answer:

   Run MEMORY PURGE command to defragment memory -> Option A

5. Quick Check:

   Use MEMORY PURGE to reduce fragmentation [OK]

Hint: Use MEMORY PURGE to reduce fragmentation without restart [OK]

Common Mistakes:

• Restarting Redis as first fix
• Adding more keys to fix memory
• Deleting all keys unnecessarily