List vs sorted set for sequences in Redis - Practice Questions

Challenge - 5 Problems

❓ query_result

intermediate

Output of adding elements to a Redis List

What will be the output of the following Redis commands?

Commands:
LPUSH mylist 10
LPUSH mylist 20
LRANGE mylist 0 -1

Redis

LPUSH mylist 10
LPUSH mylist 20
LRANGE mylist 0 -1

A ["20", "10"]

B ["10", "20"]

C ["10"]

D []

💡 Hint

Remember LPUSH adds elements to the head of the list.

LPUSH adds elements to the start of the list, so the last pushed element appears first when reading from 0 to -1.

❓ query_result

intermediate

Output of adding elements to a Redis Sorted Set

What will be the output of the following Redis commands?

Commands:
ZADD myzset 5 "apple"
ZADD myzset 1 "banana"
ZADD myzset 3 "cherry"
ZRANGE myzset 0 -1 WITHSCORES

Redis

ZADD myzset 5 "apple"
ZADD myzset 1 "banana"
ZADD myzset 3 "cherry"
ZRANGE myzset 0 -1 WITHSCORES

A ["cherry", "3", "banana", "1", "apple", "5"]

B ["apple", "5", "banana", "1", "cherry", "3"]

C ["apple", "banana", "cherry"]

D ["banana", "1", "cherry", "3", "apple", "5"]

💡 Hint

Sorted sets order elements by score ascending.

ZRANGE returns elements ordered by score from lowest to highest. Scores are included with WITHSCORES.

🧠 Conceptual

advanced

Choosing between Redis List and Sorted Set for sequence with duplicates

You want to store a sequence of events that can have duplicate timestamps and need to preserve insertion order. Which Redis data structure is best suited?

A Redis Sorted Set, because it automatically orders by score and allows duplicates.

B Redis List, because it preserves insertion order and allows duplicates.

C Redis Hash, because it stores key-value pairs efficiently.

D Redis Set, because it stores unique elements without order.

💡 Hint

Consider if duplicates and order matter.

Redis Lists preserve insertion order and allow duplicates. Sorted Sets do not allow duplicate members and order by score.

📝 Syntax

advanced

Identify the invalid Redis command for adding to a Sorted Set

Which of the following commands will cause a syntax error when adding elements to a Redis Sorted Set?

A ZADD myzset "orange" 10

B ZADD myzset 10 "orange"

C ZADD myzset 5 "grape"

D ZADD myzset 3 "melon"

💡 Hint

Check the order of arguments for ZADD command.

ZADD syntax requires the score first, then the member. Option A reverses them causing syntax error.

❓ optimization

expert

Optimizing retrieval of top N recent events with timestamps in Redis

You store events with timestamps as scores in a Redis Sorted Set. You want to efficiently retrieve the 10 most recent events. Which command is best?

A ZRANGE myzset -10 -1 WITHSCORES

B ZRANGEBYSCORE myzset +inf -inf LIMIT 0 10

C ZREVRANGE myzset 0 9 WITHSCORES

D ZREM myzset 0 9

💡 Hint

Think about ordering and direction of retrieval.

ZREVRANGE returns elements from highest to lowest score, so it efficiently gets the most recent events.