draft optional author:staab
Relays may support the verb COUNT, which provides a mechanism for obtaining event counts.
Some queries a client may want to execute against connected relays are prohibitively expensive, for example, in order to retrieve follower counts for a given pubkey, a client must query all kind-3 events referring to a given pubkey only to count them. The result may be cached, either by a client or by a separate indexing server as an alternative, but both options erode the decentralization of the network by creating a second-layer protocol on top of Nostr.
This NIP defines the verb COUNT, which accepts a subscription id and filters as specified in NIP 01 for the verb REQ. Multiple filters are OR'd together and aggregated into a single count result.
["COUNT", <subscription_id>, <filters JSON>...]
Counts are returned using a COUNT response in the form {"count": <integer>}. Relays may use probabilistic counts to reduce compute requirements.
["COUNT", <subscription_id>, {"count": <integer>}]
Examples:
# Followers count
["COUNT", <subscription_id>, {"kinds": [3], "#p": [<pubkey>]}]
["COUNT", <subscription_id>, {"count": 238}]
# Count posts and reactions
["COUNT", <subscription_id>, {"kinds": [1, 7], "authors": [<pubkey>]}]
["COUNT", <subscription_id>, {"count": 5}]