Redis persistence overview (RDB, AOF) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Redis RDB persistence?

RDB persistence saves a snapshot of your Redis data to disk at specific intervals. It creates a compact file representing the database state at a point in time.

beginner

What does AOF stand for in Redis persistence?

AOF stands for Append Only File. It logs every write operation received by the server, allowing Redis to rebuild the dataset by replaying these commands.

intermediate

How does RDB differ from AOF in Redis?

RDB saves snapshots at intervals, so data between saves can be lost on crash. AOF logs every write, so it can recover more recent data but the file is larger and slower to write.

intermediate

When might you prefer RDB persistence over AOF?

Use RDB when you want faster restarts and smaller files, and can tolerate some data loss between snapshots, like for caching scenarios.

advanced

What is a common strategy to combine RDB and AOF in Redis?

Many use both: RDB for fast snapshots and AOF for durability. Redis can load RDB first, then replay AOF to recover the latest data.

What does Redis RDB persistence do?

A Encrypts data in memory

B Logs every write operation to a file

C Saves periodic snapshots of the database to disk

D Deletes old data automatically

RDB persistence saves snapshots of the database at intervals to disk.

Which Redis persistence method logs every write command?

A RDB

B AOF

C Snapshotting

D Eviction

AOF (Append Only File) logs every write command to rebuild data.

What is a downside of using only RDB persistence?

A Logs grow too large quickly

B Very slow data recovery

C Cannot restart Redis

D Data loss between snapshots if Redis crashes

RDB snapshots happen at intervals, so data written after the last snapshot can be lost on crash.

Why might AOF files be larger than RDB files?

A Because AOF logs every write operation

B Because AOF compresses data

C Because AOF deletes old data

D Because AOF stores data in memory only

AOF logs every write command, so the file grows with every operation.

What is a common Redis persistence setup for durability and speed?

A Use both RDB and AOF together

B Use only AOF logging

C Use only RDB snapshots

D Disable persistence

Combining RDB and AOF gives fast restarts and better durability.

Explain the main differences between Redis RDB and AOF persistence methods.

Think about how often data is saved and how Redis recovers data.

Describe a scenario where using both RDB and AOF persistence together is beneficial.

Consider what happens during Redis restart and crash recovery.

Practice

1. What is the main purpose of Redis persistence?

easy

A. To speed up data retrieval during queries

B. To save data so it is not lost after a restart

C. To compress data for less storage use

D. To encrypt data for security

Solution

1. Step 1: Understand Redis persistence goal

   Redis persistence is designed to keep data safe even if Redis restarts or crashes.

2. Step 2: Match purpose with options

   Only To save data so it is not lost after a restart talks about saving data across restarts, which matches the goal.

3. Final Answer:

   To save data so it is not lost after a restart -> Option B

4. Quick Check:

   Persistence means saving data = A [OK]

Hint: Persistence means data stays after restart [OK]

Common Mistakes:

• Confusing persistence with speed optimization
• Thinking persistence compresses data
• Assuming persistence encrypts data

2. Which Redis persistence method saves snapshots of the dataset at intervals?

easy

A. None of the above

B. AOF (Append Only File)

C. Both AOF and RDB

D. RDB (Redis Database)

Solution

1. Step 1: Recall persistence methods

   RDB saves snapshots of the dataset at set intervals, while AOF logs every write operation.

2. Step 2: Identify correct method for snapshots

   Only RDB matches the description of saving snapshots periodically.

3. Final Answer:

   RDB (Redis Database) -> Option D

4. Quick Check:

   Snapshots = RDB [OK]

Hint: Snapshots = RDB saves whole data periodically [OK]

Common Mistakes:

• Mixing AOF with snapshot saving
• Choosing both methods as snapshot savers
• Thinking AOF saves snapshots

3. Given Redis configured with both RDB and AOF enabled, which statement is true about data recovery after a crash?

medium

A. Redis will use the AOF log if available, otherwise the RDB snapshot

B. Redis will use only the RDB snapshot for recovery

C. Redis will use only the AOF log for recovery

D. Redis cannot recover data if both are enabled

Solution

1. Step 1: Understand recovery priority

   When both RDB and AOF are enabled, Redis prefers AOF for recovery because it has more recent data.

2. Step 2: Analyze options

   Redis will use the AOF log if available, otherwise the RDB snapshot correctly states Redis uses AOF if available, else falls back to RDB.

3. Final Answer:

   Redis will use the AOF log if available, otherwise the RDB snapshot -> Option A

4. Quick Check:

   AOF if available else RDB = B [OK]

Hint: AOF has latest data, used first for recovery [OK]

Common Mistakes:

• Assuming Redis uses only RDB always
• Thinking Redis cannot recover with both enabled
• Believing AOF is ignored if RDB exists

4. You configured Redis with AOF persistence but notice the AOF file is not growing after writes. What is the most likely cause?

medium

A. AOF rewrite is stuck and blocking writes

B. Redis is only using RDB snapshots

C. AOF persistence is disabled in the config

D. Redis does not support AOF persistence

Solution

1. Step 1: Check AOF file behavior

   If AOF file size does not increase after writes, it suggests AOF is not active or enabled.

2. Step 2: Identify cause from options

   AOF persistence is disabled in the config states AOF persistence is disabled, which explains no file growth.

3. Final Answer:

   AOF persistence is disabled in the config -> Option C

4. Quick Check:

   No AOF growth means AOF disabled = C [OK]

Hint: No AOF file growth? Check if AOF is enabled [OK]

Common Mistakes:

• Assuming Redis does not support AOF
• Thinking AOF rewrite blocks all writes
• Confusing RDB usage with AOF file size

5. You want to minimize data loss in Redis but keep fast restart times. Which persistence setup is best?

hard

A. Enable both RDB snapshots and AOF with fsync every second

B. Enable only AOF with every write logged

C. Disable persistence and rely on backups

D. Enable only RDB snapshots every hour

Solution

1. Step 1: Understand trade-offs

   RDB snapshots are fast but risk losing data between snapshots. AOF logs every write but can slow restarts.

2. Step 2: Analyze combined setup

   Enabling both with AOF fsync every second balances minimal data loss and reasonable restart speed.

3. Step 3: Evaluate other options

   Only RDB risks data loss; only AOF can slow restarts; disabling persistence risks total data loss.

4. Final Answer:

   Enable both RDB snapshots and AOF with fsync every second -> Option A

5. Quick Check:

   Best mix for safety and speed = D [OK]

Hint: Combine RDB + AOF for safety and speed [OK]

Common Mistakes:

• Choosing only RDB and ignoring data loss risk
• Choosing only AOF and ignoring restart speed
• Disabling persistence entirely