RDB snapshots (point-in-time) in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Understanding RDB Snapshot Timing

If a Redis server is configured to save an RDB snapshot every 60 seconds, what will be the state of the data in the snapshot file if the server crashes after 45 seconds of the last snapshot?

A The snapshot contains all data up to the last 60-second save point, missing changes made in the last 45 seconds.

B The snapshot contains all data including the last 45 seconds before the crash.

C The snapshot file will be empty because the server crashed before the next save.

D The snapshot contains only the data from the last 10 seconds before the crash.

💡 Hint

Think about when Redis saves snapshots and what happens if it crashes before the next save.

Redis saves snapshots at configured intervals. If it crashes before the next scheduled save, the snapshot file only contains data up to the last successful save point, so recent changes are lost.

🧠 Conceptual

intermediate

RDB Snapshot Configuration Impact

Which Redis configuration setting controls how often RDB snapshots are saved to disk?

A timeout

B appendonly

C maxmemory-policy

D save

💡 Hint

Look for the setting related to snapshot intervals.

The 'save' configuration defines the frequency of RDB snapshots by specifying time and number of changes.

🔧 Debug

advanced

Diagnosing Missing Data After Crash

A Redis server is configured to save snapshots every 30 seconds. After a crash, the RDB file is loaded but recent data is missing. Which of the following is the most likely cause?

A The append-only file (AOF) was corrupted and Redis ignored it.

B The server crashed before the next snapshot was saved, so recent changes were lost.

C The snapshot file was overwritten with an empty file during the crash.

D The Redis server was configured to never save snapshots.

💡 Hint

Consider how RDB snapshots work and when data is persisted.

RDB snapshots only save data at intervals. If the server crashes before the next save, recent changes are lost because they were not persisted.

📝 Syntax

advanced

Correct Redis CLI Command to Trigger Manual RDB Save

Which Redis CLI command triggers an immediate RDB snapshot save to disk?

A SAVEALL

B BGSAVE

C SAVE

D SNAPSHOT

💡 Hint

One command saves synchronously, the other asynchronously.

BGSAVE triggers an asynchronous background save of the RDB snapshot, allowing the server to continue processing commands. SAVE triggers a synchronous save, blocking the server until complete.

❓ optimization

expert

Optimizing RDB Snapshot Frequency for Data Safety and Performance

You want to configure Redis to balance data safety and server performance by saving RDB snapshots only when at least 100 changes have occurred within 60 seconds. Which 'save' configuration line achieves this?

A save 60 100

B save 100 60

C save 60 1

D save 100 60 1

💡 Hint

The 'save' directive format is: save

The 'save 60 100' means Redis saves a snapshot if 100 changes happen within 60 seconds.