Redis: More than a Cache

Everyone uses Redis for caching. But did you know it can do spatial queries?

Geospatial Indexing

Redis has a GEO API. You can store coordinates.

GEOADD cities 13.361389 38.115556 "Palermo"
GEOADD cities 15.087269 37.502669 "Catania"

Now, find everything within 100km of Palermo:

GEORADIUS cities 13.36 38.11 100 km
# 1) "Palermo"
# 2) "Catania"

HyperLogLog

Count unique visitors (cardinality) with 99% accuracy using only 12KB of memory, whether you have 100 or 100 million users.

Conclusion

Redis is a Swiss Army Knife. Don't just use it for set and get. Explore the structures.