Pub/Sub and StreamsLesson 4.2

Redis Streams introduction: durable append-only event logs

XADD command, stream entry ID, XLEN, XRANGE, XREAD, auto-generated IDs, stream as event log, difference from Pub/Sub

Streams: persistent messaging

A Redis Stream is an append-only log of entries. Unlike Pub/Sub, entries persist until explicitly deleted. Consumers can read from any position in history.

Writing to a stream

# '*' auto-generates a timestamp-based ID
XADD events * action "login" userId "42"
# → "1700000000000-0"  (millisecond timestamp + sequence)

XADD events * action "purchase" userId "42" productId "99"

XLEN events   # → 2

Reading entries

# Read all entries from the beginning
XRANGE events - +
# → [[1700...-0, [action, login, userId, 42]], ...]

# Read newest entries (blocking, wait 0ms = forever)
XREAD COUNT 10 BLOCK 0 STREAMS events $

Streams vs Pub/Sub

Pub/Sub delivers only to currently connected subscribers and discards the message immediately. Streams persist every entry. A consumer that goes offline and reconnects can replay missed messages from its last-seen ID. This makes Streams the right choice for audit logs, event sourcing, and reliable task pipelines where message loss is unacceptable.