LTRIM for list capping in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command LTRIM do?

The LTRIM command trims a list to only keep the specified range of elements, removing all others outside that range.

beginner

How can LTRIM be used to keep only the latest 100 items in a Redis list?

Use LTRIM key 0 99 to keep only the first 100 elements (index 0 to 99) and remove older elements beyond that.

beginner

What happens if you use LTRIM key 0 -1 on a Redis list?

It keeps the entire list unchanged because -1 means the last element, so the range covers the whole list.

intermediate

Why is LTRIM useful for list capping in Redis?

It helps limit the size of a list to a fixed number of recent items, saving memory and keeping data manageable.

intermediate

If you want to keep the last 50 elements of a list, which LTRIM command should you use?

Use LTRIM key -50 -1 to keep the last 50 elements, where -50 is the 50th element from the end.

What does LTRIM mylist 0 9 do?

A Keeps the first 10 elements of 'mylist' and removes the rest

B Removes the first 10 elements of 'mylist'

C Keeps the last 10 elements of 'mylist'

D Deletes the entire 'mylist'

LTRIM with 0 9 keeps elements from index 0 to 9, which is the first 10 elements.

How do you keep only the last 20 elements of a Redis list named 'events'?

A LTRIM events 0 19

B LTRIM events -20 -1

C LTRIM events 20 -1

D LTRIM events -1 -20

Using negative indexes, -20 is the 20th element from the end, so LTRIM events -20 -1 keeps the last 20 elements.

What happens if LTRIM is called with a start index greater than the end index?

A The list remains unchanged

B An error is returned

C The list is cleared (emptied)

D The list is reversed

If start > end, LTRIM removes all elements, resulting in an empty list.

Which Redis command is commonly used together with LTRIM to implement a capped list?

A LPUSH

B GET

C DEL

D SET

LPUSH adds new elements to the head of the list, and LTRIM trims it to a fixed size, together implementing a capped list.

If you want to keep the entire list unchanged, which LTRIM command would you use?

A LTRIM key 0 0

B LTRIM key -1 0

C LTRIM key 1 0

D LTRIM key 0 -1

LTRIM key 0 -1 keeps the whole list because -1 means the last element.

Explain how the Redis command LTRIM helps in managing the size of a list.

Think about keeping only a fixed number of recent entries.

Describe the difference between using positive and negative indexes in the LTRIM command.

Consider how you count positions from the front or back of the list.