XRANGE and XREVRANGE in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of XRANGE with specific ID range

Given a Redis stream named mystream with entries:

1) ID: 1609459200000-0, fields: {"name": "Alice", "age": "30"}
2) ID: 1609459201000-0, fields: {"name": "Bob", "age": "25"}
3) ID: 1609459202000-0, fields: {"name": "Charlie", "age": "35"}

What is the output of the command:

XRANGE mystream 1609459200000-0 1609459201000-0

Redis

XRANGE mystream 1609459200000-0 1609459201000-0

A [["1609459200000-0", {"name": "Alice", "age": "30"}], ["1609459201000-0", {"name": "Bob", "age": "25"}]]

B [["1609459201000-0", {"name": "Bob", "age": "25"}], ["1609459202000-0", {"name": "Charlie", "age": "35"}]]

C [["1609459200000-0", {"name": "Alice", "age": "30"}], ["1609459202000-0", {"name": "Charlie", "age": "35"}]]

D []

💡 Hint

XRANGE returns entries in the given ID range inclusive, in ascending order.

XRANGE returns all entries with IDs between the start and end IDs inclusive, ordered from smallest to largest ID.

❓ query_result

intermediate

Output of XREVRANGE with specific ID range

Using the same Redis stream mystream as before, what is the output of:

XREVRANGE mystream 1609459202000-0 1609459200000-0

Redis

XREVRANGE mystream 1609459202000-0 1609459200000-0

A [["1609459202000-0", {"name": "Charlie", "age": "35"}], ["1609459201000-0", {"name": "Bob", "age": "25"}], ["1609459200000-0", {"name": "Alice", "age": "30"}]]

B [["1609459200000-0", {"name": "Alice", "age": "30"}], ["1609459201000-0", {"name": "Bob", "age": "25"}]]

C [["1609459201000-0", {"name": "Bob", "age": "25"}], ["1609459202000-0", {"name": "Charlie", "age": "35"}]]

D []

💡 Hint

XREVRANGE returns entries in the given ID range inclusive, in descending order.

XREVRANGE returns all entries with IDs between the start and end IDs inclusive, ordered from largest to smallest ID.

📝 Syntax

advanced

Identify the syntax error in XRANGE usage

Which of the following XRANGE commands will cause a syntax error in Redis?

A XRANGE mystream 1609459200000-0 1609459201000-0

B XRANGE mystream 1609459200000-0

C XRANGE mystream 1609459200000-0 1609459201000-0 COUNT 2

D XRANGE mystream - +

💡 Hint

XRANGE requires both start and end IDs to be specified.

Option B is missing the end ID argument, causing a syntax error.

❓ optimization

advanced

Optimizing XRANGE with COUNT

You want to fetch only the latest 3 entries from a Redis stream mystream. Which command is the most efficient?

A XRANGE mystream - + COUNT 3

B XREVRANGE mystream - + COUNT 3

C XRANGE mystream + - COUNT 3

D XREVRANGE mystream + - COUNT 3

💡 Hint

To get latest entries, use XREVRANGE with descending order and COUNT.

XREVRANGE with + to - and COUNT 3 returns the latest 3 entries efficiently.

🧠 Conceptual

expert

Understanding XRANGE and XREVRANGE ID boundaries

Consider a Redis stream mystream with entries having IDs:
1000-0, 1000-1, 1001-0, 1002-0.

What will be the output of:

XRANGE mystream 1000-1 1002-0

and

XREVRANGE mystream 1002-0 1000-1

respectively?

A XRANGE returns entries with IDs 1000-1, 1001-0; XREVRANGE returns entries 1002-0, 1001-0

B XRANGE returns entries with IDs 1000-0, 1000-1, 1001-0; XREVRANGE returns entries 1002-0, 1001-0, 1000-0

C XRANGE returns entries with IDs 1000-1, 1001-0, 1002-0; XREVRANGE returns entries 1002-0, 1001-0, 1000-1

D Both commands return empty lists because the ranges are invalid

💡 Hint

XRANGE and XREVRANGE include the boundary IDs specified.

Both commands include entries with IDs equal to the start and end IDs. The order differs: XRANGE ascending, XREVRANGE descending.