How is reliable message delivery ensured in Redis Pub/Sub system?

In Redis Pub/Sub, the message delivery mechanism does not guarantee reliability: if the subscriber is not connected or cannot process the message in time, it will be lost. Redis Pub/Sub is a "fire-and-forget" delivery system.

To ensure reliable message delivery, other mechanisms are usually used, such as:

• Redis Streams — support message storage and guarantee that subscribers can receive all messages even during temporary disconnections.
• External message brokers (RabbitMQ, Kafka), which provide delivery acknowledgment and retries.

If Pub/Sub is used, reliability can be increased at the application level, for example:

• The subscriber confirms message receipt (ACK) via a separate channel.
• If no acknowledgment is received, the message is resent.

However, this requires additional logic and is not implemented by Redis Pub/Sub itself.

Example of using Redis Streams for reliable delivery in Python:

import redis

r = redis.Redis()

# Adding a message to the stream
r.xadd('mystream', {'message': 'hello'})

# Reading messages with acknowledgment
messages = r.xread({'mystream': '0-0'}, count=1, block=0)
# Processing and acknowledgment of messages are implemented at the application level