Streams

Redis Streams

Streams are an append-only log data structure, introduced in Redis 5.0. They are similar to Apache Kafka topics but built into Redis. Each entry in a stream has a unique ID and consists of field-value pairs.

Why Streams?

• Event sourcing: Record every event (order placed, user clicked, sensor reading)
• Message queues: Producers add messages, consumers read them
• Activity feeds: Append events and read recent history
• Audit logs: Immutable, ordered record of changes

XADD — Append an Entry

XADD mystream * name "Alice" action "login"
XADD mystream * name "Bob" action "purchase" item "book"

The * tells Redis to auto-generate a unique ID (timestamp-based). Each entry has field-value pairs, like a mini hash.

XLEN — Count Entries

XLEN mystream    -- (integer) 2

XRANGE — Read Entries (Oldest First)

XRANGE mystream - +

Use - for the minimum ID and + for the maximum. This returns all entries in chronological order.

XREVRANGE — Read Entries (Newest First)

XREVRANGE mystream + -

XREAD — Read From One or More Streams

XREAD COUNT 2 STREAMS mystream 0

XREAD reads entries after the given ID. Use 0 to start from the beginning. The COUNT option limits how many entries are returned.

Stream Entry IDs

Every stream entry has an ID in the format <millisecondsTime>-<sequenceNumber>, e.g. 1526919030474-0. When you use *, Redis generates this automatically. You can also specify your own IDs if they are greater than the last entry.

XTRIM — Limit Stream Length

XTRIM mystream MAXLEN 1000

Trims the stream to the most recent 1000 entries, removing the oldest.

Real-World: Event Log

# Log user events
XADD events:user:42 * type "page_view" url "/products"
XADD events:user:42 * type "add_to_cart" product "laptop"
XADD events:user:42 * type "checkout" total "999"

# Read all events for this user
XRANGE events:user:42 - +
XLEN events:user:42

Pub/Sub vs Streams

Redis also has a Pub/Sub system (PUBLISH/SUBSCRIBE) for real-time messaging. The key differences:

Pub/Sub is ideal for real-time notifications where missing a message is acceptable. Streams are better when you need reliability, persistence, and the ability to replay history.

Your Task

Build an event log for a web application:

1. XADD three events to events:
   • type "signup" user "alice"
   • type "login" user "bob"
   • type "purchase" user "alice" amount "50"
2. Use XLEN to count the entries
3. Use XRANGE to read all entries