RDB configuration (save intervals) in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the effect of this Redis configuration snippet?

Given the Redis configuration line:
save 900 1
What does this setting do?

Redis

save 900 1

A Redis saves the DB every 900 seconds regardless of changes.

B Redis disables saving the DB automatically.

C Redis saves the DB if at least 1 key changed within 900 seconds.

D Redis saves the DB if at least 900 keys changed within 1 second.

💡 Hint

Think about the meaning of the two numbers in the 'save' directive.

The 'save' directive syntax is 'save '. It triggers a DB save if at least keys changed within seconds.

🧠 Conceptual

intermediate

Why might you configure multiple 'save' intervals in Redis?

Redis allows multiple 'save' directives like:
save 900 1
save 300 10
save 60 10000
Why would an administrator set multiple save intervals?

A To save the DB more frequently when many keys change and less frequently when fewer keys change.

B To save the DB only once at the shortest interval specified.

C To disable saving when the number of changes is below the smallest threshold.

D To save the DB only if all conditions are met simultaneously.

💡 Hint

Think about how different thresholds affect save frequency.

Multiple 'save' directives allow Redis to save more often when many keys change quickly, and less often when changes are rare, balancing performance and durability.

📝 Syntax

advanced

Identify the syntax error in this Redis save configuration line

Which option contains a syntax error in Redis 'save' configuration?

A save 900 1

B save 60

C save 300 5

D save 120 100

💡 Hint

The 'save' directive requires two arguments.

The 'save' directive must have two arguments: seconds and number of changes. Option B only has one argument, causing a syntax error.

❓ optimization

advanced

Which Redis save interval configuration best balances performance and durability for a busy server?

Consider a Redis server with frequent writes. Which save configuration is best to reduce performance impact but keep data safe?

A

save 900 1
save 300 10
save 60 10000

B

save 60 1
save 30 5
save 10 10

C save 3600 10000

D save 1 100000

💡 Hint

Think about how often saves happen and how many changes trigger them.

Option A sets multiple intervals that save more often when many keys change and less often when few keys change, balancing durability and performance.

🔧 Debug

expert

Why does this Redis server never save snapshots despite 'save' directives present?

A Redis server has these lines in redis.conf:
save 900 1
save 300 10
But it never creates RDB snapshots. What is the most likely cause?

A The server is running in cluster mode which disables RDB saving.

B The server has no keys, so no changes trigger saving.

C The server is configured with 'appendonly yes' which disables RDB snapshots.

D The 'save' directives are overridden by a 'save ""' directive disabling snapshots.

💡 Hint

Check if any configuration disables saving explicitly.

A 'save ""' directive disables all RDB snapshotting, overriding other 'save' lines. This is a common cause of no snapshots despite save directives.