Support for RESP3 and Sharded Pub/Sub in Redis 7

[Rakeshya-Kore]

Redis 7 introduces significant enhancements to the Pub/Sub mechanism. Unlike Redis 6, where Pub/Sub messages were limited to a single shard, Redis 7 employs a sharded Pub/Sub mechanism. This improvement allows Redis to automatically determine which shard should handle the Pub/Sub traffic for a specific channel.

The sharded Pub/Sub mechanism provides the following benefits:

1. Load Distribution: It reduces the concentration of connections on a single shard by distributing Pub/Sub traffic across the cluster.
2. Scalability: This makes the Pub/Sub system more scalable by evenly balancing the workload among available shards.

To leverage the Sharded Pub/Sub feature in Redis 7, the RESP3 protocol is required. However, we have observed that the currently ioredis library does not support RESP3.

We would like to understand:

1. Are there any plans to add RESP3 protocol support in ioredis to enable Redis 7's advanced features like Sharded Pub/Sub?
2. If so, could you share any timelines or progress updates?

[Rakeshya-Kore]

Requesting Someone to update on this ASAP.

[mortensi]

Hello @Rakeshya-Kore, sharded Pub/Sub does not require RESP3. I wonder if you have found some obsolete documents or threads. If this is the case, please let me know. Support for both RESP2 and RESP3 is documented:

• https://redis.io/docs/latest/commands/spublish/
• https://redis.io/docs/latest/commands/ssubscribe/

We are considering supporting Sharded Pub/Sub soon enough; we'll share progress updates later this month.

[Rakeshya-Kore]

Hello @mortensi ,

Thanks for the response! I came across this page: https://redis.io/docs/latest/operate/rs/references/compatibility/resp/#deactivate-resp3, where it says, You cannot use sharded pub/sub if you deactivate RESP3 support.

What I understand from this is that the client must support RESP3 for sharded Pub/Sub to work(If RESP3 is deactivated i.e., the server is using RESP2, then sharded Pub/Sub won't work at all because the protocol does not have the necessary features to support it). Please correct me if I'm wrong and provide further clarity.

Secondly, could you please confirm the last point you mentioned? You mentioned that ioredis is considering supporting Sharded Pub/Sub soon. Does this mean that ioredis does not currently support sharded Pub/Sub?

[mortensi]

For Redis CE, there is no issue with configuring either RESP2 or RESP3 to use sharded pub/sub.

The note refers to Redis Enterprise Software, which means you must enable RESP3 to use sharded pub/sub on RESP2 or RESP3. We are considering improving the note because it seems misleading. Thanks for sharing it!