Persistence and performance trade-off in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Redis Persistence Options

Which Redis persistence method offers the best balance between data durability and write performance?

A RDB snapshots taken at intervals

B AOF with every write fsync

C AOF with fsync every second

D No persistence enabled

💡 Hint

Consider how often data is saved and the impact on write speed.

AOF with fsync every second provides a good trade-off by saving data frequently enough to avoid large data loss, while not slowing down writes as much as fsync on every write.

❓ query_result

intermediate

Result of Redis Command with Persistence Disabled

Assuming Redis is running with persistence disabled, what will be the result after a server restart if the following commands were executed before restart?

SET key1 value1
SET key2 value2

What will be the value of GET key1 after restart?

A nil

B "value1"

C Error: key not found

D "value2"

💡 Hint

Think about what happens to data when persistence is off and the server restarts.

With persistence disabled, all data is stored only in memory. After a restart, memory is cleared, so GET key1 returns nil.

📝 Syntax

advanced

Identify the Correct Redis Configuration for Minimal Data Loss

Which Redis configuration snippet ensures minimal data loss while maintaining reasonable performance?

save 900 1
save 300 10
save 60 10000
appendonly yes
appendfsync everysec

Redis

appendonly yes
appendfsync everysec
save 900 1
save 300 10
save 60 10000

A

appendonly yes
appendfsync always
save 900 1
save 300 10
save 60 10000

B

appendonly yes
appendfsync everysec
save 900 1
save 300 10
save 60 10000

C

appendonly yes
appendfsync no
save 900 1
save 300 10
save 60 10000

D

appendonly no
save 900 1
save 300 10
save 60 10000

💡 Hint

Check which appendfsync option balances durability and performance.

Setting appendonly yes with appendfsync everysec enables AOF persistence with fsync every second, minimizing data loss and keeping performance reasonable.

❓ optimization

advanced

Optimizing Redis for High Write Throughput with Persistence

You want to optimize Redis for high write throughput but still keep data safe in case of crashes. Which approach is best?

A Enable RDB snapshots only with frequent saves

B Disable persistence and rely on replication only

C Enable AOF with appendfsync always

D Enable AOF with appendfsync everysec and tune RDB snapshot intervals

💡 Hint

Think about balancing disk writes frequency and snapshot overhead.

Using AOF with fsync every second reduces disk I/O overhead compared to always fsync, while RDB snapshots provide backups. This balances throughput and durability.

🔧 Debug

expert

Diagnosing Data Loss Despite Persistence Enabled

A Redis server has appendonly yes and appendfsync everysec set, but after a crash, some recent writes are lost. What is the most likely cause?

A appendfsync everysec allows up to 1 second of data loss on crash

B The AOF file was corrupted and Redis could not recover it

C RDB snapshots overwrite the AOF file causing data loss

D Redis was running without enough memory causing eviction

💡 Hint

Consider how appendfsync everysec works during crashes.

appendfsync everysec flushes data to disk every second, so up to one second of writes can be lost if a crash happens before the flush.