Redis Stream: introduced in Redis 5, it is a persistent, append-only log of entries each with an auto-generated ID. Unlike pub/sub, messages are stored and can be re-read, enabling reliable event processing.
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What does a consumer group add to a Redis Stream?
Consumer group: lets several consumers split the work of a stream. Redis records which messages each consumer received and which are acknowledged, supporting reliable, scalable processing.
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What is the role of XACK in Redis Streams?
XACK: after a consumer finishes a message it calls XACK. Until then the message sits in the Pending Entries List (PEL), so a crash mid-processing means the message can be reclaimed and retried.
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What is the Pending Entries List (PEL)?
PEL: tracks messages handed to consumers but not yet acknowledged. If a consumer dies, its pending messages can be claimed (via XCLAIM/XAUTOCLAIM) by another consumer, ensuring no event is lost.
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How can you cap a stream's memory growth?
Stream trimming: passing MAXLEN ~ N to XADD keeps roughly the most recent N entries, evicting older ones. This bounds memory use while retaining a recent history for late consumers.