XTRIM for stream capping in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command XTRIM do?

The XTRIM command trims a Redis stream to keep its length under a specified maximum, effectively capping the stream size by removing older entries.

beginner

How do you specify the maximum length of a stream when using XTRIM?

You use the MAXLEN option followed by the maximum number of entries you want to keep in the stream.

intermediate

What is the difference between XTRIM MAXLEN and XTRIM MINID?

MAXLEN trims the stream to a maximum number of entries, while MINID trims entries older than a specific stream ID.

intermediate

Why might you want to use the ~ (approximate) option with XTRIM MAXLEN?

Using ~ allows Redis to trim the stream approximately, which is faster because it doesn't guarantee an exact maximum length but improves performance.

beginner

What happens if you run XTRIM mystream MAXLEN 1000 on a stream with 1500 entries?

Redis will remove the oldest 500 entries so that the stream contains only the most recent 1000 entries.

What does the Redis command XTRIM mystream MAXLEN 500 do?

A Keeps only the latest 500 entries in the stream 'mystream'.

B Deletes the stream 'mystream'.

C Adds 500 new entries to the stream 'mystream'.

D Returns the length of the stream 'mystream'.

XTRIM mystream MAXLEN 500 trims the stream to keep only the latest 500 entries, removing older ones.

Which option makes XTRIM trim approximately for better performance?

A ~

B MINID

C MAXLEN

D EXACT

The ~ option tells Redis to trim approximately, improving speed but not guaranteeing exact length.

What does XTRIM mystream MINID 1609459200000-0 do?

A Deletes the stream 'mystream'.

B Keeps entries with IDs greater than or equal to 1609459200000-0.

C Adds a new entry with ID 1609459200000-0.

D Returns the oldest entry in the stream.

MINID trims entries older than the given ID, so only entries with IDs >= 1609459200000-0 remain.

If you want to keep exactly 1000 entries in a stream, which command is best?

A XLEN mystream 1000

B XTRIM mystream MINID 1000

C XADD mystream MAXLEN 1000

D XTRIM mystream MAXLEN 1000

XTRIM mystream MAXLEN 1000 trims the stream to keep at most 1000 entries.

What is the main purpose of using XTRIM on a Redis stream?

A To read entries from the stream.

B To add new entries to the stream.

C To limit the stream size and save memory.

D To rename the stream.

XTRIM is used to cap the stream size, preventing it from growing indefinitely and using too much memory.

Explain how the XTRIM command helps manage Redis streams and why stream capping is important.

Think about why you wouldn't want a stream to grow forever.

Describe the difference between using MAXLEN and MINID options with XTRIM.

One trims by count, the other by entry age.