Monitoring with INFO command in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of INFO command for memory stats

What is the output of the following Redis command snippet when querying memory stats?

INFO memory

Assume Redis server is running normally with some keys stored.

Redis

INFO memory

A Shows a JSON object with memory usage details

B Returns only the total number of keys stored in Redis

C Contains lines like 'used_memory:', 'used_memory_rss:', and 'mem_fragmentation_ratio:' with numeric values

D Outputs an error saying 'unknown command INFO memory'

💡 Hint

INFO command sections are divided by categories like memory, server, clients, etc.

The INFO memory command returns memory-related statistics as plain text lines with key:value pairs, including used_memory and fragmentation ratio. It does not return JSON or errors if Redis is running.

🧠 Conceptual

intermediate

Understanding INFO command sections

Which of the following is NOT a valid section you can query with the Redis INFO command?

A server

B network

C persistence

D clients

💡 Hint

Check Redis documentation for INFO command sections.

Redis INFO command supports sections like server, clients, memory, persistence, stats, replication, cpu, commandstats, cluster, and keyspace. 'network' is not a valid section.

❓ Troubleshoot

advanced

Diagnosing missing INFO command output

You run INFO on your Redis server but get an empty response. What is the most likely cause?

Redis

INFO

A You connected to the wrong port where no Redis server is running

B Redis server is running in protected mode and INFO command is disabled

C The Redis server is running but has no data stored yet

D The INFO command requires authentication and you did not authenticate

💡 Hint

Check your connection and server status.

If INFO returns empty, it usually means no Redis server is responding on that port. Protected mode or authentication issues cause errors, not empty output. Having no data still returns INFO output.

✅ Best Practice

advanced

Using INFO command for monitoring in production

Which practice is best when using the Redis INFO command for monitoring in a production environment?

A Avoid using INFO command and rely only on Redis logs

B Run INFO command frequently (every second) to get real-time stats

C Run INFO command only once after server restart

D Run INFO command periodically (e.g., every minute) and parse output for key metrics

💡 Hint

Consider performance impact and usefulness of data.

Running INFO too frequently can add load. Periodic checks balance data freshness and performance. Logs alone do not provide detailed metrics.

🔀 Workflow

expert

Interpreting INFO command output for memory troubleshooting

Given this snippet of Redis INFO memory output:

used_memory:10485760
used_memory_rss:20971520
mem_fragmentation_ratio:2.0

What does this indicate about Redis memory usage?

Redis

INFO memory

A Redis is using twice as much memory from the OS than it actually needs, indicating possible memory fragmentation

B Redis memory usage is normal and fragmentation ratio below 1.0

C Redis is using less memory than allocated, so no fragmentation is present

D Redis has a memory leak causing used_memory to be zero

💡 Hint

Compare used_memory and used_memory_rss values and fragmentation ratio.

used_memory_rss is the actual memory allocated by OS. A fragmentation ratio of 2.0 means Redis is using twice the memory it needs, indicating fragmentation or overhead.

Practice

1. What does the Redis INFO command primarily provide?

easy

A. A snapshot of the Redis server status and statistics

B. A list of all keys stored in Redis

C. The configuration file contents

D. A backup of the Redis database

Solution

1. Step 1: Understand the purpose of INFO command

   The INFO command is designed to give a snapshot of the Redis server's current status and statistics.

2. Step 2: Compare with other options

   Listing keys, showing config files, or backups are done by other commands, not INFO.

3. Final Answer:

   A snapshot of the Redis server status and statistics -> Option A

4. Quick Check:

   INFO = Server status snapshot [OK]

Hint: INFO shows server stats, not keys or configs [OK]

Common Mistakes:

• Confusing INFO with commands like KEYS or CONFIG
• Thinking INFO returns data backups
• Assuming INFO lists all stored keys

2. Which of the following is the correct syntax to get only the memory section info from Redis?

easy

A. INFO --section=memory

B. INFO -memory

C. GET INFO memory

D. INFO memory

Solution

1. Step 1: Recall Redis INFO command syntax

   The correct syntax to get a specific section is INFO section_name, for example, INFO memory.

2. Step 2: Eliminate incorrect options

   Options with dashes or GET keyword are invalid Redis command syntax.

3. Final Answer:

   INFO memory -> Option D

4. Quick Check:

   INFO section_name = INFO memory [OK]

Hint: Use INFO followed by section name without dashes [OK]

Common Mistakes:

• Adding dashes before section name
• Using GET keyword with INFO
• Using double dashes or equal signs

3. Given the Redis INFO output snippet:

used_memory:1024000
connected_clients:5
uptime_in_seconds:3600

What does connected_clients indicate?

medium

A. Number of clients currently connected to Redis

B. Number of keys stored in Redis

C. Total memory used by Redis in bytes

D. Redis server uptime in seconds

Solution

1. Step 1: Identify the meaning of connected_clients

   The connected_clients field shows how many clients are currently connected to the Redis server.

2. Step 2: Differentiate from other fields

   used_memory is memory usage, uptime_in_seconds is server uptime, and keys count is not shown here.

3. Final Answer:

   Number of clients currently connected to Redis -> Option A

4. Quick Check:

   connected_clients = active connections [OK]

Hint: connected_clients means active users connected now [OK]

Common Mistakes:

• Confusing connected_clients with key count
• Mixing memory usage with client count
• Assuming uptime is client count

4. You run INFO client but get an error. What is the most likely cause?

medium

A. Redis server is down

B. You need to run INFO without any arguments

C. The section name 'client' is misspelled or unsupported

D. You must use GET instead of INFO

Solution

1. Step 1: Check valid section names for INFO

   Redis INFO supports specific section names like 'clients' (plural), not 'client' (singular).

2. Step 2: Understand error cause

   Using an invalid or misspelled section name causes an error, not server down or wrong command usage.

3. Final Answer:

   The section name 'client' is misspelled or unsupported -> Option C

4. Quick Check:

   INFO section names must be exact [OK]

Hint: Use exact section names; 'clients' not 'client' [OK]

Common Mistakes:

• Using singular instead of plural section names
• Assuming server is down without checking
• Trying GET command instead of INFO

5. You want to monitor Redis memory usage and client connections continuously. Which approach using the INFO command is best?

hard

A. Run INFO once and save output to a file

B. Run INFO memory and INFO clients repeatedly in a script with a delay

C. Use INFO all once and check manually later

D. Run CONFIG GET memory and CONFIG GET clients repeatedly

Solution

1. Step 1: Identify continuous monitoring needs

   To monitor memory and clients continuously, you need repeated INFO queries with a delay to track changes over time.

2. Step 2: Evaluate options

   Running INFO memory and INFO clients repeatedly in a script fits this need. Running once or using CONFIG GET won't provide continuous updates.

3. Final Answer:

   Run INFO memory and INFO clients repeatedly in a script with a delay -> Option B

4. Quick Check:

   Repeated INFO calls = continuous monitoring [OK]

Hint: Use repeated INFO calls in script for live monitoring [OK]

Common Mistakes:

• Running INFO only once for monitoring
• Using CONFIG GET which is for config, not stats
• Running INFO all once expecting continuous data