RDB vs AOF comparison in Redis - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the Redis persistence method that saves snapshots of the dataset at intervals.

Redis

redis.conf setting for periodic snapshot saving is [1]

Drag options to blanks, or click blank then click option'

Asave

Bmaxmemory

Cappendonly

Dtimeout

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'appendonly' with snapshot saving

Using 'maxmemory' which controls memory limits

The save directive in Redis config sets intervals for RDB snapshots.

2fill in blank

medium

Complete the code to enable the Redis append-only file persistence.

Redis

To enable AOF, set appendonly to [1] in redis.conf

Drag options to blanks, or click blank then click option'

Ayes

Bno

Cauto

Doff

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'no' or 'off' disables AOF

Using 'auto' is not a valid value

Setting appendonly yes enables AOF persistence in Redis.

3fill in blank

hard

Fix the error in the command to rewrite the AOF file.

Redis

Use the command [1] to rewrite the appendonly.aof file safely.

Drag options to blanks, or click blank then click option'

AFLUSHALL

BBGREWRITEAOF

CBGSAVE

DSAVE

Attempts:

3 left

💡 Hint

Common Mistakes

Using SAVE or BGSAVE which only affect RDB files

Using FLUSHALL which clears all data

BGREWRITEAOF triggers a background rewrite of the AOF file to reduce its size.

4fill in blank

hard

Fill both blanks to complete the Redis config lines for RDB and AOF persistence.

Redis

save [1]
appendonly [2]

Drag options to blanks, or click blank then click option'

A900 1

Byes

Cno

D300 10

Attempts:

3 left

💡 Hint

Common Mistakes

Putting 'no' for appendonly disables AOF

Using invalid save intervals

The save 900 1 means save snapshot if 1 change in 900 seconds.
The appendonly yes enables AOF persistence.

5fill in blank

hard

Fill all three blanks to complete the Redis config for AOF fsync policy and RDB snapshot interval.

Redis

appendonly [1]
appendfsync [2]
save [3]

Drag options to blanks, or click blank then click option'

Ayes

Beverysec

C900 1

Dno

Attempts:

3 left

💡 Hint

Common Mistakes

Setting appendonly to no disables AOF

Using 'always' or 'no' for appendfsync instead of 'everysec'

Enable AOF with appendonly yes, set fsync every second with appendfsync everysec, and save RDB snapshot every 900 seconds if 1 change with save 900 1.

Practice

1. Which Redis persistence method saves the entire dataset at specific time intervals?

easy

A. AOF (Append Only File)

B. RDB (Redis Database snapshot)

C. Both RDB and AOF save snapshots

D. Neither RDB nor AOF save snapshots

Solution

1. Step 1: Understand RDB persistence

   RDB saves the dataset by creating snapshots at set intervals.

2. Step 2: Compare with AOF

   AOF logs every write operation, not snapshots.

3. Final Answer:

   RDB (Redis Database snapshot) -> Option B

4. Quick Check:

   Snapshot saving = RDB [OK]

Hint: RDB = snapshots at intervals, AOF = logs every change [OK]

Common Mistakes:

• Confusing AOF with snapshot saving
• Thinking both save snapshots
• Believing neither saves snapshots

2. Which of the following is the correct Redis command to enable AOF persistence?

easy

A. CONFIG SET appendonly yes

B. CONFIG SET save "900 1 300 10 60 10000"

C. CONFIG SET rdbcompression no

D. CONFIG SET maxmemory-policy allkeys-lru

Solution

1. Step 1: Identify AOF enabling command

   The command to enable AOF is CONFIG SET appendonly yes.

2. Step 2: Check other options

   CONFIG SET save "900 1 300 10 60 10000" sets RDB save intervals, C disables RDB compression, D sets memory eviction policy.

3. Final Answer:

   CONFIG SET appendonly yes -> Option A

4. Quick Check:

   Enable AOF = appendonly yes [OK]

Hint: Enable AOF with 'appendonly yes' command [OK]

Common Mistakes:

• Confusing RDB save command with AOF
• Using unrelated config commands
• Forgetting to set appendonly to yes

3. Given Redis configured with AOF enabled and fsync set to 'everysec', what is the expected data durability behavior?

medium

A. Data is saved only at intervals, risking data loss of last seconds

B. Every write is immediately saved to disk, no data loss

C. Data is never saved to disk automatically

D. Data is saved only when Redis restarts

Solution

1. Step 1: Understand AOF with fsync everysec

   With fsync set to 'everysec', Redis writes AOF data to disk every second.

2. Step 2: Analyze durability implications

   This means data could be lost if Redis crashes within the last second before fsync.

3. Final Answer:

   Data is saved only at intervals, risking data loss of last seconds -> Option A

4. Quick Check:

   AOF everysec fsync = possible 1-second data loss [OK]

Hint: AOF everysec fsync means possible 1-second data loss [OK]

Common Mistakes:

• Assuming every write is immediately saved
• Thinking data is never saved automatically
• Confusing with no persistence

4. You enabled both RDB and AOF persistence in Redis, but after a crash, data is missing. What is the most likely cause?

medium

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

B. Redis was not restarted after enabling persistence

C. RDB snapshot interval is too long, losing recent changes

D. AOF file is corrupted and Redis cannot load it

Solution

1. Step 1: Understand RDB and AOF coexistence

   Redis supports both RDB and AOF, preferring to load AOF first on restart if available.

2. Step 2: Analyze data loss causes

   With both enabled, if data is missing after a crash, the most likely cause is AOF corruption, causing fallback to the older RDB snapshot and loss of recent changes.

3. Final Answer:

   AOF file is corrupted and Redis cannot load it -> Option D

4. Quick Check:

   Data loss with both = AOF corrupted [OK]

Hint: With both enabled, data loss likely from AOF corruption [OK]

Common Mistakes:

• Believing Redis can't use both persistences
• Thinking RDB interval too long is the cause
• Forgetting to restart Redis

5. You want Redis to recover data quickly after a crash but can tolerate losing up to 1 minute of recent writes. Which persistence setup is best?

hard

A. Enable AOF with fsync always, disable RDB

B. Enable both RDB and AOF with fsync everysec

C. Enable RDB snapshots every 60 seconds, disable AOF

D. Disable both RDB and AOF for fastest performance

Solution

1. Step 1: Match recovery speed and data loss tolerance

   RDB snapshots every 60 seconds allow fast recovery but may lose up to 1 minute of data.

2. Step 2: Compare with AOF options

   AOF with fsync always is slower but safer; both enabled adds overhead; disabling persistence risks total data loss.

3. Final Answer:

   Enable RDB snapshots every 60 seconds, disable AOF -> Option C

4. Quick Check:

   Fast recovery + 1 min loss = RDB every 60s [OK]

Hint: RDB snapshots match fast recovery with some data loss [OK]

Common Mistakes:

• Choosing AOF for fast recovery despite slower startup
• Enabling both causing unnecessary overhead
• Disabling persistence risking total data loss