Memory usage analysis (INFO memory) in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Understanding used_memory in INFO memory

You run the command INFO memory on a Redis server and see the field used_memory:1048576. What does this number represent?

A The total number of bytes allocated by Redis for all data and overhead.

B The amount of free memory available on the server.

C The maximum memory Redis is allowed to use.

D The memory used only by keys stored in Redis, excluding overhead.

💡 Hint

Think about what 'used_memory' means in terms of Redis's memory allocation.

The used_memory field shows the total bytes Redis has allocated from the operating system, including data and internal overhead.

❓ query_result

intermediate

Interpreting memory fragmentation ratio

In the output of INFO memory, you see mem_fragmentation_ratio:1.25. What does this value indicate?

A Redis is using 25% more memory than the data size due to fragmentation and overhead.

B Redis has 25% free memory available for new data.

C Redis is using 75% of the maximum allowed memory.

D Redis has fragmented 25% of its keys.

💡 Hint

Fragmentation ratio compares allocated memory to actual data size.

The mem_fragmentation_ratio shows how much extra memory Redis uses compared to the raw data size, due to fragmentation and allocator overhead.

📝 Syntax

advanced

Correct command to check memory usage

Which of the following Redis commands correctly returns memory usage information?

A GET MEMORY

B MEMORY USAGE keyname

C INFO memory

D SHOW MEMORY

💡 Hint

The command to get server info including memory is a single word.

INFO memory returns detailed memory stats. MEMORY USAGE keyname returns memory used by a specific key, not overall info.

🧠 Conceptual

advanced

Effect of maxmemory on INFO memory output

If you set a maxmemory limit in Redis configuration, which field in INFO memory output will reflect this limit?

A used_memory_rss

B maxmemory

C mem_fragmentation_ratio

D used_memory_peak

💡 Hint

Look for a field that directly relates to a configured memory limit.

The maxmemory field shows the configured maximum memory Redis can use.

🔧 Debug

expert

Diagnosing unexpected high used_memory_rss

You notice used_memory_rss is much higher than used_memory in INFO memory. What is the most likely cause?

A The Redis server is using swap space heavily.

B Redis is leaking memory due to a bug in key eviction.

C The <code>used_memory</code> value is incorrectly calculated.

D Memory fragmentation or allocator overhead causing Redis to hold more memory from OS than used internally.

💡 Hint

Consider how operating system memory allocation differs from Redis internal usage.

used_memory_rss shows memory allocated from OS, which can be higher due to fragmentation and allocator behavior.