Combined RDB + AOF in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use both RDB and AOF in Redis?

Redis supports two persistence methods: RDB snapshots and AOF logs. What is the main advantage of combining both methods for data durability?

A It provides faster recovery by loading a snapshot and then replaying recent commands from the AOF log.

B It reduces memory usage by storing data only in RDB files and ignoring AOF logs.

C It disables data persistence to improve performance during peak loads.

D It automatically compresses data to save disk space without any data loss.

💡 Hint

Think about how snapshots and logs complement each other in restoring data.

Using both RDB and AOF allows Redis to quickly load a snapshot (RDB) and then replay recent write commands from the AOF log. This combination ensures faster recovery and better durability.

❓ query_result

intermediate

Result of Redis persistence config

Given this Redis configuration snippet:

save 900 1
save 300 10
save 60 10000
appendonly yes
aof-use-rdb-preamble yes

What does enabling aof-use-rdb-preamble yes do when Redis restarts?

A Redis ignores the RDB snapshot and loads only the AOF file.

B Redis loads the RDB snapshot first, then replays the AOF commands recorded after the snapshot.

C Redis disables AOF and uses only RDB snapshots for persistence.

D Redis merges RDB and AOF files into a single file for faster loading.

💡 Hint

Consider how the RDB preamble affects the AOF loading process.

When aof-use-rdb-preamble is enabled, Redis writes an RDB snapshot at the start of the AOF file. On restart, Redis loads this snapshot first, then replays the commands after it, speeding up recovery.

📝 Syntax

advanced

Identify the invalid Redis config line

Which of the following Redis configuration lines is invalid when combining RDB and AOF persistence?

A save 900 1

B appendonly yes

C aof-use-rdb-preamble maybe

D appendfsync everysec

💡 Hint

Check the allowed values for aof-use-rdb-preamble.

The aof-use-rdb-preamble option only accepts yes or no. The value maybe is invalid and causes a syntax error.

❓ optimization

advanced

Optimizing Redis restart time with combined persistence

You want to minimize Redis restart time while ensuring no data loss. Which configuration change best achieves this when using both RDB and AOF?

A Enable <code>aof-use-rdb-preamble yes</code> and set <code>appendfsync everysec</code>.

B Enable RDB snapshots only and disable AOF.

C Disable RDB snapshots and rely only on AOF with <code>appendfsync always</code>.

D Set <code>appendfsync no</code> and rely on RDB snapshots every 60 seconds.

💡 Hint

Think about how the RDB preamble and AOF sync frequency affect restart and durability.

Using aof-use-rdb-preamble yes speeds up restart by loading a snapshot first. appendfsync everysec balances durability and performance by syncing AOF every second.

🔧 Debug

expert

Why does Redis fail to load combined persistence?

A Redis server is configured with:

appendonly yes
aof-use-rdb-preamble yes
save 900 1

On restart, Redis fails with an error about AOF file corruption. Which is the most likely cause?

A Redis does not support using RDB snapshots and AOF together.

B The <code>aof-use-rdb-preamble</code> option must be set to <code>no</code> when <code>appendonly yes</code> is enabled.

C The <code>save</code> directive conflicts with <code>appendonly yes</code> causing a syntax error.

D The AOF file was manually edited and the RDB preamble is corrupted.

💡 Hint

Consider what happens if the AOF file is manually changed.

Manually editing the AOF file can corrupt the RDB preamble at the start, causing Redis to fail loading the combined persistence file.