AOF (Append Only File) in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of Redis AOF?

Redis uses AOF (Append Only File) for a specific reason related to data persistence. What is the main goal of using AOF in Redis?

A To compress the database files to save disk space

B To log every write operation received by the server for data recovery

C To replicate data to other Redis servers in real-time

D To store only the latest snapshot of the database

💡 Hint

Think about how Redis can recover data after a restart.

AOF logs every write operation so Redis can replay these commands to rebuild the dataset after a restart, ensuring data durability.

❓ query_result

intermediate

What happens if Redis AOF file is corrupted?

Consider Redis configured to use AOF persistence. If the AOF file becomes corrupted, what will Redis do when it tries to load the data on startup?

A Redis will refuse to start and show an error about AOF corruption

B Redis will automatically fix the corrupted AOF file and start normally

C Redis will ignore the AOF file and start with an empty dataset

D Redis will load the last RDB snapshot instead of the AOF file

💡 Hint

Think about Redis's safety checks when loading persistence files.

If the AOF file is corrupted, Redis will detect this and refuse to start to avoid loading inconsistent data. Manual repair or recovery is needed.

📝 Syntax

advanced

Which Redis configuration line correctly enables AOF with fsync every second?

Choose the correct Redis configuration line to enable AOF persistence and set fsync policy to sync every second.

A appendonly yes\naof-fsync everysec

B appendonly yes\naof-fsync no

C appendonly no\naof-fsync everysec

D appendonly yes\naof-fsync always

💡 Hint

Check the exact spelling and values for enabling AOF and fsync policy.

To enable AOF, 'appendonly yes' is required. To fsync every second, the correct setting is 'appendfsync everysec'.

❓ optimization

advanced

How to reduce AOF file size without losing data?

You notice your Redis AOF file is growing very large. Which method safely reduces the AOF file size while preserving all data?

A Disable AOF and rely only on RDB snapshots

B Delete the AOF file and restart Redis to create a new one

C Run the BGREWRITEAOF command to rewrite the AOF file compactly

D Manually edit the AOF file to remove old commands

💡 Hint

Think about a Redis command designed to optimize AOF files safely.

BGREWRITEAOF rewrites the AOF file in a compact form by removing redundant commands, preserving all data safely.

🔧 Debug

expert

Why does Redis AOF rewrite sometimes fail to reduce file size?

After running BGREWRITEAOF, you notice the AOF file size did not decrease as expected. What is the most likely reason?

A The AOF file was corrupted before rewriting

B Redis was not restarted after the rewrite command

C BGREWRITEAOF only works if appendonly is set to no

D The dataset has many keys with large values that cannot be further compressed

💡 Hint

Consider what affects the size of the rewritten AOF file.

If the dataset contains many large keys or complex data, the rewritten AOF file may not be much smaller because all data must be saved.