Redis Extended Data Types: Stream, Geospatial, Bitmap, Bitfield, and HyperLogLog

In the previous article we introduced Redis's five basic data types; this article covers the five extended data types that are useful for specific scenarios.

1. Stream – an append‑only log structure used for message queues, event logging, and notifications. Each entry gets a unique, time‑ordered ID. Common commands include XADD , XREAD , XRANGE , and XLEN . Example:

127.0.0.1:6379> XADD mystream * name Tom age 23 height 178
"1709386483610-0"
127.0.0.1:6379> XREAD COUNT 1 STREAMS mystream 0
...
127.0.0.1:6379> XLEN mystream
(integer) 1

2. Geospatial – stores longitude/latitude pairs and enables radius queries. The main command is GEOADD key longitude latitude member .

3. Bitmap – bit‑level operations on string values, useful for counting, flags, and activity tracking. Commands include SETBIT , GETBIT , and BITCOUNT . Example:

# record login days
127.0.0.1:6379> SETBIT user-login 1 1
(integer) 0
127.0.0.1:6379> SETBIT user-login 3 1
(integer) 0
127.0.0.1:6379> BITCOUNT user-login
(integer) 2

4. Bitfield – treats a string as an array of bits, allowing arbitrary‑width integer reads, writes, and increments. It is ideal for counters and compact numeric storage.

5. HyperLogLog – provides approximate cardinality estimation with low memory usage. Commands include PFADD , PFCOUNT , and PFMERGE . Example:

127.0.0.1:6379> PFADD web-view "Tom" "John" "Tony"
(integer) 1
127.0.0.1:6379> PFCOUNT web-view
(integer) 3

These extended types can simplify implementation of common internet‑scale use cases compared with relational databases. A mind‑map image summarizing all ten Redis data types is provided for quick reference.