Geo-proximity with sorted sets in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Find nearby locations within 5 km

Given a Redis sorted set storing locations with their longitude and latitude, which command returns all locations within 5 kilometers of the point (13.361389, 38.115556) sorted by distance?

Redis

GEOADD Sicily 13.361389 38.115556 Palermo 15.087269 37.502669 Catania
GEOSEARCH Sicily FROMLONLAT 13.361389 38.115556 BYRADIUS 5 km ASC WITHDIST

A GEOSEARCH Sicily FROMLONLAT 13.361389 38.115556 BYRADIUS 5 km

B GEORADIUS Sicily 13.361389 38.115556 5 km WITHDIST ASC

C GEOSEARCH Sicily FROMLONLAT 13.361389 38.115556 BYRADIUS 5 km ASC WITHDIST

D GEORADIUS Sicily 13.361389 38.115556 5 km

💡 Hint

Use the modern GEOSEARCH command with BYRADIUS and WITHDIST to get sorted results.

GEOSEARCH with BYRADIUS and WITHDIST returns members within the radius sorted by distance ascending. GEORADIUS is deprecated and may not guarantee sorting.

🧠 Conceptual

intermediate

Understanding GEOADD and member storage

What does the GEOADD command do in Redis when used with a sorted set?

A Adds a member with longitude and latitude coordinates to a sorted set, using the geohash score internally.

B Adds a member with a numeric score to a sorted set without any coordinate information.

C Removes a member from a sorted set based on its longitude and latitude.

D Returns the distance between two members in a sorted set.

💡 Hint

GEOADD stores geographic data as scores in a sorted set.

GEOADD adds members with longitude and latitude, encoding them as geohash scores internally in the sorted set.

📝 Syntax

advanced

Identify the syntax error in GEOSEARCH usage

Which option contains a syntax error when trying to find locations within 10 km of (15, 37)?

A GEOSEARCH Sicily FROMLONLAT 15 37 BYRADIUS 10 km WITHCOORD

B GEOSEARCH Sicily FROMLONLAT 15 37 BYRADIUS 10 km WITHDIST

C GEOSEARCH Sicily FROMLONLAT 15 37 BYRADIUS 10 km ASC WITHDIST

D GEOSEARCH Sicily FROMLONLAT 15 37 BYRADIUS 10 km WITHDIST ASC

💡 Hint

Check the order of options WITHDIST and ASC in the command.

The ASC keyword must come immediately after BYRADIUS and before any WITH* options. Option D places ASC after WITHDIST, causing a syntax error.

❓ optimization

advanced

Optimizing geo queries for large datasets

You have a Redis sorted set with 1 million geo locations. Which approach optimizes querying locations within 1 km radius efficiently?

A Use GEOSEARCH with BYRADIUS 1 km and LIMIT 100 to reduce returned results.

B Store locations in multiple sorted sets by region and query only relevant sets.

C Use GEORADIUS with a large radius and filter results client-side.

D Use GEOADD with higher precision coordinates to improve query speed.

💡 Hint

Think about partitioning data to reduce search space.

Partitioning locations into multiple sorted sets by region reduces the number of items searched, improving query speed.

🔧 Debug

expert

Debugging unexpected empty results from GEOSEARCH

You run the command: GEOSEARCH places FROMLONLAT 40.7128 -74.0060 BYRADIUS 10 km WITHDIST But it returns an empty list, even though you know members exist nearby. What is the most likely cause?

A The longitude and latitude values are swapped; longitude should be -74.0060 and latitude 40.7128.

B BYRADIUS requires the radius unit to be specified as 'meters' instead of 'km'.

C The sorted set 'places' does not contain any members added with GEOADD.

D WITHDIST option is not supported with GEOSEARCH and causes no results.

💡 Hint

Remember the order of longitude and latitude in GEO commands.

Redis GEO commands expect longitude first, then latitude. Swapping them causes the search to look in the wrong area, returning empty results.