XTRIM for stream capping in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the effect of this XTRIM command?

Given a Redis stream named mystream with 1000 entries, what will be the number of entries after running this command?

XTRIM mystream MAXLEN 100

Redis

XTRIM mystream MAXLEN 100

A The stream will have 1000 entries, no change occurs.

B The stream will have exactly 900 entries, the newest entries removed.

C The stream will have exactly 100 entries, the oldest entries removed.

D The command will cause an error because MAXLEN requires a minimum of 1000.

💡 Hint

MAXLEN trims the stream to keep only the newest entries up to the specified count.

XTRIM with MAXLEN 100 keeps only the latest 100 entries by removing older ones.

🧠 Conceptual

intermediate

What does the ~ (approximate) flag do in XTRIM?

Consider the command:
XTRIM mystream MAXLEN ~ 100
What is the purpose of the ~ flag in this context?

Redis

XTRIM mystream MAXLEN ~ 100

A It forces Redis to trim exactly 100 entries, no approximation allowed.

B It allows Redis to trim the stream approximately to 100 entries for better performance.

C It disables trimming and only returns the current length of the stream.

D It causes an error because ~ is not a valid flag for XTRIM.

💡 Hint

The ~ flag is used to improve performance by allowing approximate trimming.

Using ~ lets Redis trim close to the specified length but not exactly, improving speed.

📝 Syntax

advanced

Which XTRIM command syntax is correct to cap a stream to 500 entries approximately?

Choose the syntactically correct Redis command to trim mystream to approximately 500 entries.

A XTRIM mystream MAXLEN ~ 500

B XTRIM mystream MAXLEN 500 ~

C XTRIM mystream MAXLEN ~500

D XTRIM mystream MAXLEN=~ 500

💡 Hint

The approximate flag ~ must come immediately after MAXLEN.

The correct syntax places ~ right after MAXLEN followed by the number.

❓ optimization

advanced

Why use approximate trimming (~) instead of exact trimming in XTRIM?

What is the main advantage of using XTRIM mystream MAXLEN ~ 1000 over XTRIM mystream MAXLEN 1000?

A Approximate trimming disables trimming and only returns the stream length.

B Approximate trimming guarantees the stream length is exactly 1000 entries.

C Approximate trimming causes Redis to trim entries randomly.

D Approximate trimming reduces CPU usage by allowing Redis to trim in batches.

💡 Hint

Think about performance and resource usage when trimming large streams.

Approximate trimming lets Redis trim less frequently and in batches, saving CPU.

🔧 Debug

expert

What error occurs with this XTRIM command?

Given the command:
XTRIM mystream MAXLEN -100
What will Redis respond?

Redis

XTRIM mystream MAXLEN -100

A An error: 'ERR The MAXLEN argument must be a positive integer'

B The stream is trimmed to 100 entries ignoring the negative sign.

C The stream is cleared completely because negative length means zero entries.

D No error, Redis treats -100 as a large positive number.

💡 Hint

MAXLEN must be a positive number; negative values are invalid.

Redis rejects negative MAXLEN values with an error message.