Slow log for performance analysis in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What does the Redis command SLOWLOG GET 3 return?

You run the command SLOWLOG GET 3 in Redis. What is the expected output?

Redis

SLOWLOG GET 3

A Returns an error because the argument '3' is invalid for SLOWLOG GET.

B Returns the total number of slow log entries stored in Redis.

C Clears the last 3 slow log entries from the slow log.

D Returns the last 3 slow log entries with details like ID, timestamp, execution time, and command arguments.

💡 Hint

Think about what 'GET' means in the context of slow logs.

The command SLOWLOG GET 3 fetches the last 3 slow log entries, showing details such as the unique ID, timestamp, execution time in microseconds, and the command that was slow.

🧠 Conceptual

intermediate

Why is the Redis slow log useful for performance analysis?

Choose the best reason why Redis slow log helps in analyzing performance issues.

A It shows the total memory used by Redis at any moment.

B It records commands that took longer than a configured threshold, helping identify slow operations.

C It deletes keys that cause slowdowns to improve performance.

D It automatically fixes slow commands by optimizing them.

💡 Hint

Think about what kind of information helps find slow commands.

The slow log records commands that exceed a set execution time threshold, allowing developers to find and optimize slow commands.

📝 Syntax

advanced

Which Redis command correctly resets the slow log?

You want to clear all entries in the Redis slow log. Which command will do this?

A SLOWLOG CLEAR

B SLOWLOG RESET

C SLOWLOG DELETE ALL

D SLOWLOG FLUSH

💡 Hint

Check the official Redis command for clearing slow logs.

The correct command to clear all slow log entries is SLOWLOG CLEAR. Other options are invalid commands.

❓ optimization

advanced

How can you configure Redis to log only commands slower than 5 milliseconds?

Which command sets the slow log threshold to 5 milliseconds?

A CONFIG SET slowlog-log-slower-than 5

B CONFIG SET slowlog-threshold 5

C CONFIG SET slowlog-log-slower-than 5000

D CONFIG SET slowlog-threshold 5000

💡 Hint

The threshold is in microseconds, so 5 milliseconds equals 5000 microseconds.

The slow log threshold is set in microseconds. 5 milliseconds = 5000 microseconds, so the correct command is CONFIG SET slowlog-log-slower-than 5000.

🔧 Debug

expert

What error occurs when running SLOWLOG GET -1 in Redis?

You run SLOWLOG GET -1 to get slow log entries. What happens?

A Raises an error: ERR invalid argument for SLOWLOG GET.

B Returns an empty list because negative count is invalid.

C Returns all slow log entries without error.

D Returns the last slow log entry only.

💡 Hint

Check if negative numbers are valid arguments for SLOWLOG GET.

The argument to SLOWLOG GET must be a non-negative integer. Negative values cause an error.