Which NATS JetStream Setup is Better?

[nrapendra-singh]

Which NATS JetStream Setup is Better?

I need a NATS JetStream setup where one stream is consumed by two consumers:

Real-time Consumer (fast processing)
Analytics Consumer (slower processing)

Approach 1: Source + Mirror Stream

Source Stream (WorkQueue Retention) → Messages deleted after real-time consumer acknowledges.
Mirror Stream (Limits Retention) → Keeps a copy for analytics consumer.

✅ Pros: Keeps the source stream lightweight for fast processing.
❌ Cons:
Requires duplicating messages to a mirror stream.
Increases resource usage in the JetStream cluster (storage, replication, processing).

Approach 2: Single Stream with Limits Retention

Both consumers read from the same stream.
Messages persist until storage or message limits are reached.

✅ Pros: Simpler setup, no message duplication.
❌ Cons: Stream can grow large, potentially slowing down real-time processing.

Which approach is more efficient and scalable?

[jnmoyne]

It's not because a stream is larger that delivery of messages to consumers takes longer, therefore approach 2 is simpler, more efficient and doesn't have the Cons you list.

[nrapendra-singh]

@jnmoyne , Thanks for your reply.What are the potential impacts or side effects of having a large stream in NATS JetStream?

[jnmoyne]

Mostly increased memory usage if you have a lot of different subject being used in the stream (the servers maintain per subject indexing).