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.