SSUBSCRIBE

SSUBSCRIBE subscribes the connection to shard channels. A shard channel is hashed to a cluster slot like a key, and its messages, sent with SPUBLISH, stay within the shard (primary and replicas) that serves that slot instead of going to every node. This keeps Pub/Sub traffic from growing with the size of the cluster. Outside cluster mode, shard channels behave like separate ordinary channels.

In a cluster, all channels in one call must hash to the same slot, and the command is redirected with MOVED to the node that serves it. If the slot moves to another shard later, the subscribers are unsubscribed (they receive an sunsubscribe message) and should subscribe again on the new owner.

The connection enters subscribed mode, as with SUBSCRIBE.

Return value

For each shard channel, a confirmation:

Element	Value
1	Bulk string ssubscribe
2	Bulk string: the shard channel
3	Integer: the number of shard channels this connection is now subscribed to

Each message then arrives as smessage, the shard channel, and the payload. On RESP3 these are push messages.

Examples

127.0.0.1:6379> SSUBSCRIBE orders:{eu}
1) "ssubscribe"
2) "orders:{eu}"
3) (integer) 1
1) "smessage"
2) "orders:{eu}"
3) "order 1001 placed"

Compatibility

Same as Redis 7 and Valkey 8.

See also

SUNSUBSCRIBE, SPUBLISH, PUBSUB SHARDCHANNELS, SUBSCRIBE

In a cluster: Keys, slots and commands in a cluster