Pub/Sub when system memory is maxed out

[ilshm]

Hello,

I'm currently using Redis for pub/sub messaging in a project where system memory is often near its limit. I've noticed that while Redis handles key-value operations and evictions smoothly under memory pressure, I'm concerned about how it manages memory for pub/sub messages under similar conditions.

Could you clarify how Redis handles memory allocation for transient pub/sub messages, especially when the system is at its memory capacity? Specifically, I'm interested in understanding:

1. How Redis allocates and manages memory for processing large pub/sub messages.
2. What happens if a pub/sub message is received when Redis is operating at or near the maxmemory limit? Does this situation affect the triggering of the LRU eviction mechanism?
3. Are there any best practices for configuring Redis in environments where frequent large pub/sub messages are common and memory is a constraint

Thank you!

[sundb]

1. How Redis allocates and manages memory for processing large pub/sub messages.

Redis will send a pub message to every connection.

2. What happens if a pub/sub message is received when Redis is operating at or near the maxmemory limit? Does this situation affect the triggering of the LRU eviction mechanism?

since pubscribe/subscribe are non-writable, they aren't limited by maxmemory.
LRU is for keyspace, but pub/sub doesn't generate any dataset, so pub/sub is not affected by eviction.

3. Are there any best practices for configuring Redis in environments where frequent large pub/sub messages are common and memory is a constraint

what version are you using? if > 7.0, you can use client eviction to evict the connection that read the traffic too slow.